plugins/png/PNGImageReader.java

/*
 * Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.imageio.plugins.png;

import java.awt.Point;
import java.awt.Rectangle;
import java.awt.color.ColorSpace;
import java.awt.image.BufferedImage;
import java.awt.image.DataBuffer;
import java.awt.image.DataBufferByte;
import java.awt.image.DataBufferUShort;
import java.awt.image.Raster;
import java.awt.image.WritableRaster;
import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.DataInputStream;
import java.io.EOFException;
import java.io.InputStream;
import java.io.IOException;
import java.io.SequenceInputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.zip.Inflater;
import java.util.zip.InflaterInputStream;
import javax.imageio.IIOException;
import javax.imageio.ImageReader;
import javax.imageio.ImageReadParam;
import javax.imageio.ImageTypeSpecifier;
import javax.imageio.metadata.IIOMetadata;
import javax.imageio.spi.ImageReaderSpi;
import javax.imageio.stream.ImageInputStream;
import com.sun.imageio.plugins.common.InputStreamAdapter;
import com.sun.imageio.plugins.common.ReaderUtil;
import com.sun.imageio.plugins.common.SubImageInputStream;
import java.io.ByteArrayOutputStream;
import sun.awt.image.ByteInterleavedRaster;

class PNGImageDataEnumeration implements Enumeration<InputStream> {

    boolean firstTime = true;
    ImageInputStream stream;
    int length;

    public PNGImageDataEnumeration(ImageInputStream stream)
        throws IOException {
        this.stream = stream;
        this.length = stream.readInt();
        int type = stream.readInt(); // skip chunk type
    }

    @Override
    public InputStream nextElement() {
        try {
            firstTime = false;
            ImageInputStream iis = new SubImageInputStream(stream, length);
            return new InputStreamAdapter(iis);
        } catch (IOException e) {
            return null;
        }
    }

    @Override
    public boolean hasMoreElements() {
        if (firstTime) {
            return true;
        }

        try {
            int crc = stream.readInt();
            this.length = stream.readInt();
            int type = stream.readInt();
            if (type == PNGImageReader.IDAT_TYPE) {
                return true;
            } else {
                return false;
            }
        } catch (IOException e) {
            return false;
        }
    }
}

public class PNGImageReader extends ImageReader {

    /*
     * Note: The following chunk type constants are autogenerated.  Each
     * one is derived from the ASCII values of its 4-character name.  For
     * example, IHDR_TYPE is calculated as follows:
     *            ('I' << 24) | ('H' << 16) | ('D' << 8) | 'R'
     */

    // Critical chunks
    static final int IHDR_TYPE = 0x49484452;
    static final int PLTE_TYPE = 0x504c5445;
    static final int IDAT_TYPE = 0x49444154;
    static final int IEND_TYPE = 0x49454e44;

    // Ancillary chunks
    static final int bKGD_TYPE = 0x624b4744;
    static final int cHRM_TYPE = 0x6348524d;
    static final int gAMA_TYPE = 0x67414d41;
    static final int hIST_TYPE = 0x68495354;
    static final int iCCP_TYPE = 0x69434350;
    static final int iTXt_TYPE = 0x69545874;
    static final int pHYs_TYPE = 0x70485973;
    static final int sBIT_TYPE = 0x73424954;
    static final int sPLT_TYPE = 0x73504c54;
    static final int sRGB_TYPE = 0x73524742;
    static final int tEXt_TYPE = 0x74455874;
    static final int tIME_TYPE = 0x74494d45;
    static final int tRNS_TYPE = 0x74524e53;
    static final int zTXt_TYPE = 0x7a545874;

    static final int PNG_COLOR_GRAY = 0;
    static final int PNG_COLOR_RGB = 2;
    static final int PNG_COLOR_PALETTE = 3;
    static final int PNG_COLOR_GRAY_ALPHA = 4;
    static final int PNG_COLOR_RGB_ALPHA = 6;

    // The number of bands by PNG color type
    static final int[] inputBandsForColorType = {
         1, // gray
        -1, // unused
         3, // rgb
         1, // palette
         2, // gray + alpha
        -1, // unused
         4  // rgb + alpha
    };

    static final int PNG_FILTER_NONE = 0;
    static final int PNG_FILTER_SUB = 1;
    static final int PNG_FILTER_UP = 2;
    static final int PNG_FILTER_AVERAGE = 3;
    static final int PNG_FILTER_PAETH = 4;

    static final int[] adam7XOffset = { 0, 4, 0, 2, 0, 1, 0 };
    static final int[] adam7YOffset = { 0, 0, 4, 0, 2, 0, 1 };
    static final int[] adam7XSubsampling = { 8, 8, 4, 4, 2, 2, 1, 1 };
    static final int[] adam7YSubsampling = { 8, 8, 8, 4, 4, 2, 2, 1 };

    private static final boolean debug = true;

    ImageInputStream stream = null;

    boolean gotHeader = false;
    boolean gotMetadata = false;

    ImageReadParam lastParam = null;

    long imageStartPosition = -1L;

    Rectangle sourceRegion = null;
    int sourceXSubsampling = -1;
    int sourceYSubsampling = -1;
    int sourceMinProgressivePass = 0;
    int sourceMaxProgressivePass = 6;
    int[] sourceBands = null;
    int[] destinationBands = null;
    Point destinationOffset = new Point(0, 0);

    PNGMetadata metadata = new PNGMetadata();

    DataInputStream pixelStream = null;

    BufferedImage theImage = null;

    // The number of source pixels processed
    int pixelsDone = 0;

    // The total number of pixels in the source image
    int totalPixels;

    public PNGImageReader(ImageReaderSpi originatingProvider) {
        super(originatingProvider);
    }

    @Override
    public void setInput(Object input,
                         boolean seekForwardOnly,
                         boolean ignoreMetadata) {
        super.setInput(input, seekForwardOnly, ignoreMetadata);
        this.stream = (ImageInputStream)input; // Always works

        // Clear all values based on the previous stream contents
        resetStreamSettings();
    }

    private String readNullTerminatedString(String charset, int maxLen) throws IOException {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        int b = 0;
        int count = 0;
        while ((maxLen > count++) && ((b = stream.read()) != 0)) {
            if (b == -1) throw new EOFException();
            baos.write(b);
        }
        if (b != 0) {
            throw new IIOException("Found non null terminated string");
        }
        return new String(baos.toByteArray(), charset);
    }

    private void readHeader() throws IIOException {
        if (gotHeader) {
            return;
        }
        if (stream == null) {
            throw new IllegalStateException("Input source not set!");
        }

        try {
            byte[] signature = new byte[8];
            stream.readFully(signature);

            if (signature[0] != (byte)137 ||
                signature[1] != (byte)80 ||
                signature[2] != (byte)78 ||
                signature[3] != (byte)71 ||
                signature[4] != (byte)13 ||
                signature[5] != (byte)10 ||
                signature[6] != (byte)26 ||
                signature[7] != (byte)10) {
                throw new IIOException("Bad PNG signature!");
            }

            int IHDR_length = stream.readInt();
            if (IHDR_length != 13) {
                throw new IIOException("Bad length for IHDR chunk!");
            }
            int IHDR_type = stream.readInt();
            if (IHDR_type != IHDR_TYPE) {
                throw new IIOException("Bad type for IHDR chunk!");
            }

            this.metadata = new PNGMetadata();

            int width = stream.readInt();
            int height = stream.readInt();

            // Re-use signature array to bulk-read these unsigned byte values
            stream.readFully(signature, 0, 5);
            int bitDepth          = signature[0] & 0xff;
            int colorType         = signature[1] & 0xff;
            int compressionMethod = signature[2] & 0xff;
            int filterMethod      = signature[3] & 0xff;
            int interlaceMethod   = signature[4] & 0xff;

            // Skip IHDR CRC
            stream.skipBytes(4);

            stream.flushBefore(stream.getStreamPosition());

            if (width <= 0) {
                throw new IIOException("Image width <= 0!");
            }
            if (height <= 0) {
                throw new IIOException("Image height <= 0!");
            }
            if (bitDepth != 1 && bitDepth != 2 && bitDepth != 4 &&
                bitDepth != 8 && bitDepth != 16) {
                throw new IIOException("Bit depth must be 1, 2, 4, 8, or 16!");
            }
            if (colorType != 0 && colorType != 2 && colorType != 3 &&
                colorType != 4 && colorType != 6) {
                throw new IIOException("Color type must be 0, 2, 3, 4, or 6!");
            }
            if (colorType == PNG_COLOR_PALETTE && bitDepth == 16) {
                throw new IIOException("Bad color type/bit depth combination!");
            }
            if ((colorType == PNG_COLOR_RGB ||
                 colorType == PNG_COLOR_RGB_ALPHA ||
                 colorType == PNG_COLOR_GRAY_ALPHA) &&
                (bitDepth != 8 && bitDepth != 16)) {
                throw new IIOException("Bad color type/bit depth combination!");
            }
            if (compressionMethod != 0) {
                throw new IIOException("Unknown compression method (not 0)!");
            }
            if (filterMethod != 0) {
                throw new IIOException("Unknown filter method (not 0)!");
            }
            if (interlaceMethod != 0 && interlaceMethod != 1) {
                throw new IIOException("Unknown interlace method (not 0 or 1)!");
            }

            metadata.IHDR_present = true;
            metadata.IHDR_width = width;
            metadata.IHDR_height = height;
            metadata.IHDR_bitDepth = bitDepth;
            metadata.IHDR_colorType = colorType;
            metadata.IHDR_compressionMethod = compressionMethod;
            metadata.IHDR_filterMethod = filterMethod;
            metadata.IHDR_interlaceMethod = interlaceMethod;
            gotHeader = true;
        } catch (IOException e) {
            throw new IIOException("I/O error reading PNG header!", e);
        }
    }

    private void parse_PLTE_chunk(int chunkLength) throws IOException {
        if (metadata.PLTE_present) {
            processWarningOccurred(
"A PNG image may not contain more than one PLTE chunk.\n" +
"The chunk wil be ignored.");
            return;
        } else if (metadata.IHDR_colorType == PNG_COLOR_GRAY ||
                   metadata.IHDR_colorType == PNG_COLOR_GRAY_ALPHA) {
            processWarningOccurred(
"A PNG gray or gray alpha image cannot have a PLTE chunk.\n" +
"The chunk wil be ignored.");
            return;
        }

        byte[] palette = new byte[chunkLength];
        stream.readFully(palette);

        int numEntries = chunkLength/3;
        if (metadata.IHDR_colorType == PNG_COLOR_PALETTE) {
            int maxEntries = 1 << metadata.IHDR_bitDepth;
            if (numEntries > maxEntries) {
                processWarningOccurred(
"PLTE chunk contains too many entries for bit depth, ignoring extras.");
                numEntries = maxEntries;
            }
            numEntries = Math.min(numEntries, maxEntries);
        }

        // Round array sizes up to 2^2^n
        int paletteEntries;
        if (numEntries > 16) {
            paletteEntries = 256;
        } else if (numEntries > 4) {
            paletteEntries = 16;
        } else if (numEntries > 2) {
            paletteEntries = 4;
        } else {
            paletteEntries = 2;
        }

        metadata.PLTE_present = true;
        metadata.PLTE_red = new byte[paletteEntries];
        metadata.PLTE_green = new byte[paletteEntries];
        metadata.PLTE_blue = new byte[paletteEntries];

        int index = 0;
        for (int i = 0; i < numEntries; i++) {
            metadata.PLTE_red[i] = palette[index++];
            metadata.PLTE_green[i] = palette[index++];
            metadata.PLTE_blue[i] = palette[index++];
        }
    }

    private void parse_bKGD_chunk() throws IOException {
        if (metadata.IHDR_colorType == PNG_COLOR_PALETTE) {
            metadata.bKGD_colorType = PNG_COLOR_PALETTE;
            metadata.bKGD_index = stream.readUnsignedByte();
        } else if (metadata.IHDR_colorType == PNG_COLOR_GRAY ||
                   metadata.IHDR_colorType == PNG_COLOR_GRAY_ALPHA) {
            metadata.bKGD_colorType = PNG_COLOR_GRAY;
            metadata.bKGD_gray = stream.readUnsignedShort();
        } else { // RGB or RGB_ALPHA
            metadata.bKGD_colorType = PNG_COLOR_RGB;
            metadata.bKGD_red = stream.readUnsignedShort();
            metadata.bKGD_green = stream.readUnsignedShort();
            metadata.bKGD_blue = stream.readUnsignedShort();
        }

        metadata.bKGD_present = true;
    }

    private void parse_cHRM_chunk() throws IOException {
        metadata.cHRM_whitePointX = stream.readInt();
        metadata.cHRM_whitePointY = stream.readInt();
        metadata.cHRM_redX = stream.readInt();
        metadata.cHRM_redY = stream.readInt();
        metadata.cHRM_greenX = stream.readInt();
        metadata.cHRM_greenY = stream.readInt();
        metadata.cHRM_blueX = stream.readInt();
        metadata.cHRM_blueY = stream.readInt();

        metadata.cHRM_present = true;
    }

    private void parse_gAMA_chunk() throws IOException {
        int gamma = stream.readInt();
        metadata.gAMA_gamma = gamma;

        metadata.gAMA_present = true;
    }

    private void parse_hIST_chunk(int chunkLength) throws IOException,
        IIOException
    {
        if (!metadata.PLTE_present) {
            throw new IIOException("hIST chunk without prior PLTE chunk!");
        }

        /* According to PNG specification length of
         * hIST chunk is specified in bytes and
         * hIST chunk consists of 2 byte elements
         * (so we expect length is even).
         */
        metadata.hIST_histogram = new char[chunkLength/2];
        stream.readFully(metadata.hIST_histogram,
                         0, metadata.hIST_histogram.length);

        metadata.hIST_present = true;
    }

    private void parse_iCCP_chunk(int chunkLength) throws IOException {
        String keyword = readNullTerminatedString("ISO-8859-1", 80);
        int compressedProfileLength = chunkLength - keyword.length() - 2;
        if (compressedProfileLength <= 0) {
            throw new IIOException("iCCP chunk length is not proper");
        }
        metadata.iCCP_profileName = keyword;

        metadata.iCCP_compressionMethod = stream.readUnsignedByte();

        byte[] compressedProfile =
          new byte[compressedProfileLength];
        stream.readFully(compressedProfile);
        metadata.iCCP_compressedProfile = compressedProfile;

        metadata.iCCP_present = true;
    }

    private void parse_iTXt_chunk(int chunkLength) throws IOException {
        long chunkStart = stream.getStreamPosition();

        String keyword = readNullTerminatedString("ISO-8859-1", 80);
        metadata.iTXt_keyword.add(keyword);

        int compressionFlag = stream.readUnsignedByte();
        metadata.iTXt_compressionFlag.add(Boolean.valueOf(compressionFlag == 1));

        int compressionMethod = stream.readUnsignedByte();
        metadata.iTXt_compressionMethod.add(Integer.valueOf(compressionMethod));

        long pos = stream.getStreamPosition();
        int remainingLen = (int)(chunkStart + chunkLength - pos);
        String languageTag = readNullTerminatedString("UTF8", remainingLen);
        metadata.iTXt_languageTag.add(languageTag);

        pos = stream.getStreamPosition();
        remainingLen = (int)(chunkStart + chunkLength - pos);
        if (remainingLen < 0) {
            throw new IIOException("iTXt chunk length is not proper");
        }
        String translatedKeyword =
            readNullTerminatedString("UTF8", remainingLen);
        metadata.iTXt_translatedKeyword.add(translatedKeyword);

        String text;
        pos = stream.getStreamPosition();
        int textLength = (int)(chunkStart + chunkLength - pos);
        if (textLength < 0) {
            throw new IIOException("iTXt chunk length is not proper");
        }
        byte[] b = new byte[textLength];
        stream.readFully(b);

        if (compressionFlag == 1) { // Decompress the text
            text = new String(inflate(b), "UTF8");
        } else {
            text = new String(b, "UTF8");
        }
        metadata.iTXt_text.add(text);

        // Check if the text chunk contains image creation time
        if (keyword.equals(PNGMetadata.tEXt_creationTimeKey)) {
            // Update Standard/Document/ImageCreationTime from text chunk
            int index = metadata.iTXt_text.size() - 1;
            metadata.decodeImageCreationTimeFromTextChunk(
                    metadata.iTXt_text.listIterator(index));
        }
    }

    private void parse_pHYs_chunk() throws IOException {
        metadata.pHYs_pixelsPerUnitXAxis = stream.readInt();
        metadata.pHYs_pixelsPerUnitYAxis = stream.readInt();
        metadata.pHYs_unitSpecifier = stream.readUnsignedByte();

        metadata.pHYs_present = true;
    }

    private void parse_sBIT_chunk() throws IOException {
        int colorType = metadata.IHDR_colorType;
        if (colorType == PNG_COLOR_GRAY ||
            colorType == PNG_COLOR_GRAY_ALPHA) {
            metadata.sBIT_grayBits = stream.readUnsignedByte();
        } else if (colorType == PNG_COLOR_RGB ||
                   colorType == PNG_COLOR_PALETTE ||
                   colorType == PNG_COLOR_RGB_ALPHA) {
            metadata.sBIT_redBits = stream.readUnsignedByte();
            metadata.sBIT_greenBits = stream.readUnsignedByte();
            metadata.sBIT_blueBits = stream.readUnsignedByte();
        }

        if (colorType == PNG_COLOR_GRAY_ALPHA ||
            colorType == PNG_COLOR_RGB_ALPHA) {
            metadata.sBIT_alphaBits = stream.readUnsignedByte();
        }

        metadata.sBIT_colorType = colorType;
        metadata.sBIT_present = true;
    }

    private void parse_sPLT_chunk(int chunkLength)
        throws IOException, IIOException {
        metadata.sPLT_paletteName = readNullTerminatedString("ISO-8859-1", 80);
        int remainingChunkLength = chunkLength -
                (metadata.sPLT_paletteName.length() + 1);
        if (remainingChunkLength <= 0) {
            throw new IIOException("sPLT chunk length is not proper");
        }

        int sampleDepth = stream.readUnsignedByte();
        metadata.sPLT_sampleDepth = sampleDepth;

        int numEntries = remainingChunkLength/(4*(sampleDepth/8) + 2);
        metadata.sPLT_red = new int[numEntries];
        metadata.sPLT_green = new int[numEntries];
        metadata.sPLT_blue = new int[numEntries];
        metadata.sPLT_alpha = new int[numEntries];
        metadata.sPLT_frequency = new int[numEntries];

        if (sampleDepth == 8) {
            for (int i = 0; i < numEntries; i++) {
                metadata.sPLT_red[i] = stream.readUnsignedByte();
                metadata.sPLT_green[i] = stream.readUnsignedByte();
                metadata.sPLT_blue[i] = stream.readUnsignedByte();
                metadata.sPLT_alpha[i] = stream.readUnsignedByte();
                metadata.sPLT_frequency[i] = stream.readUnsignedShort();
            }
        } else if (sampleDepth == 16) {
            for (int i = 0; i < numEntries; i++) {
                metadata.sPLT_red[i] = stream.readUnsignedShort();
                metadata.sPLT_green[i] = stream.readUnsignedShort();
                metadata.sPLT_blue[i] = stream.readUnsignedShort();
                metadata.sPLT_alpha[i] = stream.readUnsignedShort();
                metadata.sPLT_frequency[i] = stream.readUnsignedShort();
            }
        } else {
            throw new IIOException("sPLT sample depth not 8 or 16!");
        }

        metadata.sPLT_present = true;
    }

    private void parse_sRGB_chunk() throws IOException {
        metadata.sRGB_renderingIntent = stream.readUnsignedByte();

        metadata.sRGB_present = true;
    }

    private void parse_tEXt_chunk(int chunkLength) throws IOException {
        String keyword = readNullTerminatedString("ISO-8859-1", 80);
        int textLength = chunkLength - keyword.length() - 1;
        if (textLength < 0) {
            throw new IIOException("tEXt chunk length is not proper");
        }
        metadata.tEXt_keyword.add(keyword);

        byte[] b = new byte[textLength];
        stream.readFully(b);
        metadata.tEXt_text.add(new String(b, "ISO-8859-1"));

        // Check if the text chunk contains image creation time
        if (keyword.equals(PNGMetadata.tEXt_creationTimeKey)) {
            // Update Standard/Document/ImageCreationTime from text chunk
            int index = metadata.tEXt_text.size() - 1;
            metadata.decodeImageCreationTimeFromTextChunk(
                    metadata.tEXt_text.listIterator(index));
        }
    }

    private void parse_tIME_chunk() throws IOException {
        metadata.tIME_year = stream.readUnsignedShort();
        metadata.tIME_month = stream.readUnsignedByte();
        metadata.tIME_day = stream.readUnsignedByte();
        metadata.tIME_hour = stream.readUnsignedByte();
        metadata.tIME_minute = stream.readUnsignedByte();
        metadata.tIME_second = stream.readUnsignedByte();

        metadata.tIME_present = true;
    }

    private void parse_tRNS_chunk(int chunkLength) throws IOException {
        int colorType = metadata.IHDR_colorType;
        if (colorType == PNG_COLOR_PALETTE) {
            if (!metadata.PLTE_present) {
                processWarningOccurred(
"tRNS chunk without prior PLTE chunk, ignoring it.");
                return;
            }

            // Alpha table may have fewer entries than RGB palette
            int maxEntries = metadata.PLTE_red.length;
            int numEntries = chunkLength;
            if (numEntries > maxEntries && maxEntries > 0) {
                processWarningOccurred(
"tRNS chunk has more entries than prior PLTE chunk, ignoring extras.");
                numEntries = maxEntries;
            }
            metadata.tRNS_alpha = new byte[numEntries];
            metadata.tRNS_colorType = PNG_COLOR_PALETTE;
            stream.read(metadata.tRNS_alpha, 0, numEntries);
            stream.skipBytes(chunkLength - numEntries);
        } else if (colorType == PNG_COLOR_GRAY) {
            if (chunkLength != 2) {
                processWarningOccurred(
"tRNS chunk for gray image must have length 2, ignoring chunk.");
                stream.skipBytes(chunkLength);
                return;
            }
            metadata.tRNS_gray = stream.readUnsignedShort();
            metadata.tRNS_colorType = PNG_COLOR_GRAY;
        } else if (colorType == PNG_COLOR_RGB) {
            if (chunkLength != 6) {
                processWarningOccurred(
"tRNS chunk for RGB image must have length 6, ignoring chunk.");
                stream.skipBytes(chunkLength);
                return;
            }
            metadata.tRNS_red = stream.readUnsignedShort();
            metadata.tRNS_green = stream.readUnsignedShort();
            metadata.tRNS_blue = stream.readUnsignedShort();
            metadata.tRNS_colorType = PNG_COLOR_RGB;
        } else {
            processWarningOccurred(
"Gray+Alpha and RGBS images may not have a tRNS chunk, ignoring it.");
            return;
        }

        metadata.tRNS_present = true;
    }

    private static byte[] inflate(byte[] b) throws IOException {
        InputStream bais = new ByteArrayInputStream(b);
        InputStream iis = new InflaterInputStream(bais);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();

        int c;
        try {
            while ((c = iis.read()) != -1) {
                baos.write(c);
            }
        } finally {
            iis.close();
        }
        return baos.toByteArray();
    }

    private void parse_zTXt_chunk(int chunkLength) throws IOException {
        String keyword = readNullTerminatedString("ISO-8859-1", 80);
        int textLength = chunkLength - keyword.length() - 2;
        if (textLength < 0) {
            throw new IIOException("zTXt chunk length is not proper");
        }
        metadata.zTXt_keyword.add(keyword);

        int method = stream.readUnsignedByte();
        metadata.zTXt_compressionMethod.add(method);

        byte[] b = new byte[textLength];
        stream.readFully(b);
        metadata.zTXt_text.add(new String(inflate(b), "ISO-8859-1"));

        // Check if the text chunk contains image creation time
        if (keyword.equals(PNGMetadata.tEXt_creationTimeKey)) {
            // Update Standard/Document/ImageCreationTime from text chunk
            int index = metadata.zTXt_text.size() - 1;
            metadata.decodeImageCreationTimeFromTextChunk(
                    metadata.zTXt_text.listIterator(index));
        }
    }

    private void readMetadata() throws IIOException {
        if (gotMetadata) {
            return;
        }

        readHeader();

        /*
         * Optimization: We can skip reading metadata if ignoreMetadata
         * flag is set and colorType is not PNG_COLOR_PALETTE. However,
         * we parse tRNS chunk to retrieve the transparent color from the
         * metadata. Doing so, helps PNGImageReader to appropriately
         * identify and set transparent pixels in the decoded image for
         * colorType PNG_COLOR_RGB and PNG_COLOR_GRAY.
         */
        int colorType = metadata.IHDR_colorType;
        if (ignoreMetadata && colorType != PNG_COLOR_PALETTE) {
            try {
                while (true) {
                    int chunkLength = stream.readInt();

                    // verify the chunk length first
                    if (chunkLength < 0 || chunkLength + 4 < 0) {
                        throw new IIOException("Invalid chunk length " + chunkLength);
                    }

                    int chunkType = stream.readInt();

                    if (chunkType == IDAT_TYPE) {
                        // We've reached the first IDAT chunk position
                        stream.skipBytes(-8);
                        imageStartPosition = stream.getStreamPosition();
                        /*
                         * According to PNG specification tRNS chunk must
                         * precede the first IDAT chunk. So we can stop
                         * reading metadata.
                         */
                        break;
                    } else if (chunkType == tRNS_TYPE) {
                        parse_tRNS_chunk(chunkLength);
                        // After parsing tRNS chunk we will skip 4 CRC bytes
                        stream.skipBytes(4);
                    } else {
                        // Skip the chunk plus the 4 CRC bytes that follow
                        stream.skipBytes(chunkLength + 4);
                    }
                }
            } catch (IOException e) {
                throw new IIOException("Error skipping PNG metadata", e);
            }

            gotMetadata = true;
            return;
        }

        try {
            loop: while (true) {
                int chunkLength = stream.readInt();
                int chunkType = stream.readInt();
                // Initialize chunkCRC, value assigned has no significance
                int chunkCRC = -1;

                // verify the chunk length
                if (chunkLength < 0) {
                    throw new IIOException("Invalid chunk length " + chunkLength);
                };

                try {
                    /*
                     * As per PNG specification all chunks should have
                     * 4 byte CRC. But there are some images where
                     * CRC is not present/corrupt for IEND chunk.
                     * And these type of images are supported by other
                     * decoders. So as soon as we hit chunk type
                     * for IEND chunk stop reading metadata.
                     */
                    if (chunkType != IEND_TYPE) {
                        stream.mark();
                        stream.seek(stream.getStreamPosition() + chunkLength);
                        chunkCRC = stream.readInt();
                        stream.reset();
                    }
                } catch (IOException e) {
                    throw new IIOException("Invalid chunk length " + chunkLength);
                }

                switch (chunkType) {
                case IDAT_TYPE:
                    // If chunk type is 'IDAT', we've reached the image data.
                    if (imageStartPosition == -1L) {
                        /*
                         * The PNG specification mandates that if colorType is
                         * PNG_COLOR_PALETTE then the PLTE chunk should appear
                         * before the first IDAT chunk.
                         */
                        if (colorType == PNG_COLOR_PALETTE &&
                            !(metadata.PLTE_present))
                        {
                            throw new IIOException("Required PLTE chunk"
                                    + " missing");
                        }
                        /*
                         * PNGs may contain multiple IDAT chunks containing
                         * a portion of image data. We store the position of
                         * the first IDAT chunk and continue with iteration
                         * of other chunks that follow image data.
                         */
                        imageStartPosition = stream.getStreamPosition() - 8;
                    }
                    // Move to the CRC byte location.
                    stream.skipBytes(chunkLength);
                    break;
                case IEND_TYPE:
                    /*
                     * If the chunk type is 'IEND', we've reached end of image.
                     * Seek to the first IDAT chunk for subsequent decoding.
                     */
                    stream.seek(imageStartPosition);

                    /*
                     * flushBefore discards the portion of the stream before
                     * the indicated position. Hence this should be used after
                     * we complete iteration over available chunks including
                     * those that appear after the IDAT.
                     */
                    stream.flushBefore(stream.getStreamPosition());
                    break loop;
                case PLTE_TYPE:
                    parse_PLTE_chunk(chunkLength);
                    break;
                case bKGD_TYPE:
                    parse_bKGD_chunk();
                    break;
                case cHRM_TYPE:
                    parse_cHRM_chunk();
                    break;
                case gAMA_TYPE:
                    parse_gAMA_chunk();
                    break;
                case hIST_TYPE:
                    parse_hIST_chunk(chunkLength);
                    break;
                case iCCP_TYPE:
                    parse_iCCP_chunk(chunkLength);
                    break;
                case iTXt_TYPE:
                    if (ignoreMetadata) {
                        stream.skipBytes(chunkLength);
                    } else {
                        parse_iTXt_chunk(chunkLength);
                    }
                    break;
                case pHYs_TYPE:
                    parse_pHYs_chunk();
                    break;
                case sBIT_TYPE:
                    parse_sBIT_chunk();
                    break;
                case sPLT_TYPE:
                    parse_sPLT_chunk(chunkLength);
                    break;
                case sRGB_TYPE:
                    parse_sRGB_chunk();
                    break;
                case tEXt_TYPE:
                    parse_tEXt_chunk(chunkLength);
                    break;
                case tIME_TYPE:
                    parse_tIME_chunk();
                    break;
                case tRNS_TYPE:
                    parse_tRNS_chunk(chunkLength);
                    break;
                case zTXt_TYPE:
                    if (ignoreMetadata) {
                        stream.skipBytes(chunkLength);
                    } else {
                        parse_zTXt_chunk(chunkLength);
                    }
                    break;
                default:
                    // Read an unknown chunk
                    byte[] b = new byte[chunkLength];
                    stream.readFully(b);

                    StringBuilder chunkName = new StringBuilder(4);
                    chunkName.append((char)(chunkType >>> 24));
                    chunkName.append((char)((chunkType >> 16) & 0xff));
                    chunkName.append((char)((chunkType >> 8) & 0xff));
                    chunkName.append((char)(chunkType & 0xff));

                    int ancillaryBit = chunkType >>> 28;
                    if (ancillaryBit == 0) {
                        processWarningOccurred(
"Encountered unknown chunk with critical bit set!");
                    }

                    metadata.unknownChunkType.add(chunkName.toString());
                    metadata.unknownChunkData.add(b);
                    break;
                }

                // double check whether all chunk data were consumed
                if (chunkCRC != stream.readInt()) {
                    throw new IIOException("Failed to read a chunk of type " +
                            chunkType);
                }
            }
        } catch (IOException e) {
            throw new IIOException("Error reading PNG metadata", e);
        }

        gotMetadata = true;
    }

    // Data filtering methods

    private static void decodeSubFilter(byte[] curr, int coff, int count,
                                        int bpp) {
        for (int i = bpp; i < count; i++) {
            int val;

            val = curr[i + coff] & 0xff;
            val += curr[i + coff - bpp] & 0xff;

            curr[i + coff] = (byte)val;
        }
    }

    private static void decodeUpFilter(byte[] curr, int coff,
                                       byte[] prev, int poff,
                                       int count) {
        for (int i = 0; i < count; i++) {
            int raw = curr[i + coff] & 0xff;
            int prior = prev[i + poff] & 0xff;

            curr[i + coff] = (byte)(raw + prior);
        }
    }

    private static void decodeAverageFilter(byte[] curr, int coff,
                                            byte[] prev, int poff,
                                            int count, int bpp) {
        int raw, priorPixel, priorRow;

        for (int i = 0; i < bpp; i++) {
            raw = curr[i + coff] & 0xff;
            priorRow = prev[i + poff] & 0xff;

            curr[i + coff] = (byte)(raw + priorRow/2);
        }

        for (int i = bpp; i < count; i++) {
            raw = curr[i + coff] & 0xff;
            priorPixel = curr[i + coff - bpp] & 0xff;
            priorRow = prev[i + poff] & 0xff;

            curr[i + coff] = (byte)(raw + (priorPixel + priorRow)/2);
        }
    }

    private static int paethPredictor(int a, int b, int c) {
        int p = a + b - c;
        int pa = Math.abs(p - a);
        int pb = Math.abs(p - b);
        int pc = Math.abs(p - c);

        if ((pa <= pb) && (pa <= pc)) {
            return a;
        } else if (pb <= pc) {
            return b;
        } else {
            return c;
        }
    }

    private static void decodePaethFilter(byte[] curr, int coff,
                                          byte[] prev, int poff,
                                          int count, int bpp) {
        int raw, priorPixel, priorRow, priorRowPixel;

        for (int i = 0; i < bpp; i++) {
            raw = curr[i + coff] & 0xff;
            priorRow = prev[i + poff] & 0xff;

            curr[i + coff] = (byte)(raw + priorRow);
        }

        for (int i = bpp; i < count; i++) {
            raw = curr[i + coff] & 0xff;
            priorPixel = curr[i + coff - bpp] & 0xff;
            priorRow = prev[i + poff] & 0xff;
            priorRowPixel = prev[i + poff - bpp] & 0xff;

            curr[i + coff] = (byte)(raw + paethPredictor(priorPixel,
                                                         priorRow,
                                                         priorRowPixel));
        }
    }

    private static final int[][] bandOffsets = {
        null,
        { 0 }, // G
        { 0, 1 }, // GA in GA order
        { 0, 1, 2 }, // RGB in RGB order
        { 0, 1, 2, 3 } // RGBA in RGBA order
    };

    private WritableRaster createRaster(int width, int height, int bands,
                                        int scanlineStride,
                                        int bitDepth) {

        DataBuffer dataBuffer;
        WritableRaster ras = null;
        Point origin = new Point(0, 0);
        if ((bitDepth < 8) && (bands == 1)) {
            dataBuffer = new DataBufferByte(height*scanlineStride);
            ras = Raster.createPackedRaster(dataBuffer,
                                            width, height,
                                            bitDepth,
                                            origin);
        } else if (bitDepth <= 8) {
            dataBuffer = new DataBufferByte(height*scanlineStride);
            ras = Raster.createInterleavedRaster(dataBuffer,
                                                 width, height,
                                                 scanlineStride,
                                                 bands,
                                                 bandOffsets[bands],
                                                 origin);
        } else {
            dataBuffer = new DataBufferUShort(height*scanlineStride);
            ras = Raster.createInterleavedRaster(dataBuffer,
                                                 width, height,
                                                 scanlineStride,
                                                 bands,
                                                 bandOffsets[bands],
                                                 origin);
        }

        return ras;
    }

    private void skipPass(int passWidth, int passHeight)
        throws IOException, IIOException  {
        if ((passWidth == 0) || (passHeight == 0)) {
            return;
        }

        int inputBands = inputBandsForColorType[metadata.IHDR_colorType];
        int bitsPerRow = Math.
                multiplyExact((inputBands * metadata.IHDR_bitDepth), passWidth);
        int bytesPerRow = (bitsPerRow + 7) / 8;

        // Read the image row-by-row
        for (int srcY = 0; srcY < passHeight; srcY++) {
            // Skip filter byte and the remaining row bytes
            pixelStream.skipBytes(1 + bytesPerRow);
        }
    }

    private void updateImageProgress(int newPixels) {
        pixelsDone += newPixels;
        processImageProgress(100.0F*pixelsDone/totalPixels);
    }

    private void decodePass(int passNum,
                            int xStart, int yStart,
                            int xStep, int yStep,
                            int passWidth, int passHeight) throws IOException {

        if ((passWidth == 0) || (passHeight == 0)) {
            return;
        }

        WritableRaster imRas = theImage.getWritableTile(0, 0);
        int dstMinX = imRas.getMinX();
        int dstMaxX = dstMinX + imRas.getWidth() - 1;
        int dstMinY = imRas.getMinY();
        int dstMaxY = dstMinY + imRas.getHeight() - 1;

        // Determine which pixels will be updated in this pass
        int[] vals =
          ReaderUtil.computeUpdatedPixels(sourceRegion,
                                          destinationOffset,
                                          dstMinX, dstMinY,
                                          dstMaxX, dstMaxY,
                                          sourceXSubsampling,
                                          sourceYSubsampling,
                                          xStart, yStart,
                                          passWidth, passHeight,
                                          xStep, yStep);
        int updateMinX = vals[0];
        int updateMinY = vals[1];
        int updateWidth = vals[2];
        int updateXStep = vals[4];
        int updateYStep = vals[5];

        int bitDepth = metadata.IHDR_bitDepth;
        int inputBands = inputBandsForColorType[metadata.IHDR_colorType];
        int bytesPerPixel = (bitDepth == 16) ? 2 : 1;
        bytesPerPixel *= inputBands;

        int bitsPerRow = Math.multiplyExact((inputBands * bitDepth), passWidth);
        int bytesPerRow = (bitsPerRow + 7) / 8;
        int eltsPerRow = (bitDepth == 16) ? bytesPerRow/2 : bytesPerRow;

        // If no pixels need updating, just skip the input data
        if (updateWidth == 0) {
            for (int srcY = 0; srcY < passHeight; srcY++) {
                // Update count of pixels read
                updateImageProgress(passWidth);
                /*
                 * If read has been aborted, just return
                 * processReadAborted will be called later
                 */
                if (abortRequested()) {
                    return;
                }
                // Skip filter byte and the remaining row bytes
                pixelStream.skipBytes(1 + bytesPerRow);
            }
            return;
        }

        // Backwards map from destination pixels
        // (dstX = updateMinX + k*updateXStep)
        // to source pixels (sourceX), and then
        // to offset and skip in passRow (srcX and srcXStep)
        int sourceX =
            (updateMinX - destinationOffset.x)*sourceXSubsampling +
            sourceRegion.x;
        int srcX = (sourceX - xStart)/xStep;

        // Compute the step factor in the source
        int srcXStep = updateXStep*sourceXSubsampling/xStep;

        byte[] byteData = null;
        short[] shortData = null;
        byte[] curr = new byte[bytesPerRow];
        byte[] prior = new byte[bytesPerRow];

        // Create a 1-row tall Raster to hold the data
        WritableRaster passRow = createRaster(passWidth, 1, inputBands,
                                              eltsPerRow,
                                              bitDepth);

        // Create an array suitable for holding one pixel
        int[] ps = passRow.getPixel(0, 0, (int[])null);

        DataBuffer dataBuffer = passRow.getDataBuffer();
        int type = dataBuffer.getDataType();
        if (type == DataBuffer.TYPE_BYTE) {
            byteData = ((DataBufferByte)dataBuffer).getData();
        } else {
            shortData = ((DataBufferUShort)dataBuffer).getData();
        }

        processPassStarted(theImage,
                           passNum,
                           sourceMinProgressivePass,
                           sourceMaxProgressivePass,
                           updateMinX, updateMinY,
                           updateXStep, updateYStep,
                           destinationBands);

        // Handle source and destination bands
        if (sourceBands != null) {
            passRow = passRow.createWritableChild(0, 0,
                                                  passRow.getWidth(), 1,
                                                  0, 0,
                                                  sourceBands);
        }
        if (destinationBands != null) {
            imRas = imRas.createWritableChild(0, 0,
                                              imRas.getWidth(),
                                              imRas.getHeight(),
                                              0, 0,
                                              destinationBands);
        }

        // Determine if all of the relevant output bands have the
        // same bit depth as the source data
        boolean adjustBitDepths = false;
        int[] outputSampleSize = imRas.getSampleModel().getSampleSize();
        for (int b = 0; b < inputBands; b++) {
            if (outputSampleSize[b] != bitDepth) {
                adjustBitDepths = true;
                break;
            }
        }

        // If the bit depths differ, create a lookup table per band to perform
        // the conversion
        int[][] scale = null;
        if (adjustBitDepths) {
            int maxInSample = (1 << bitDepth) - 1;
            int halfMaxInSample = maxInSample/2;
            scale = new int[inputBands][];
            for (int b = 0; b < inputBands; b++) {
                int maxOutSample = (1 << outputSampleSize[b]) - 1;
                scale[b] = new int[maxInSample + 1];
                for (int s = 0; s <= maxInSample; s++) {
                    scale[b][s] =
                        (s*maxOutSample + halfMaxInSample)/maxInSample;
                }
            }
        }

        // Limit passRow to relevant area for the case where we
        // will can setRect to copy a contiguous span
        boolean useSetRect = srcXStep == 1 &&
            updateXStep == 1 &&
            !adjustBitDepths &&
            (imRas instanceof ByteInterleavedRaster);

        if (useSetRect) {
            passRow = passRow.createWritableChild(srcX, 0,
                                                  updateWidth, 1,
                                                  0, 0,
                                                  null);
        }

        // Decode the (sub)image row-by-row
        for (int srcY = 0; srcY < passHeight; srcY++) {
            // Update count of pixels read
            updateImageProgress(passWidth);
            /*
             * If read has been aborted, just return
             * processReadAborted will be called later
             */
            if (abortRequested()) {
                return;
            }
            // Read the filter type byte and a row of data
            int filter = pixelStream.read();
            try {
                // Swap curr and prior
                byte[] tmp = prior;
                prior = curr;
                curr = tmp;

                pixelStream.readFully(curr, 0, bytesPerRow);
            } catch (java.util.zip.ZipException ze) {
                // TODO - throw a more meaningful exception
                throw ze;
            }

            switch (filter) {
            case PNG_FILTER_NONE:
                break;
            case PNG_FILTER_SUB:
                decodeSubFilter(curr, 0, bytesPerRow, bytesPerPixel);
                break;
            case PNG_FILTER_UP:
                decodeUpFilter(curr, 0, prior, 0, bytesPerRow);
                break;
            case PNG_FILTER_AVERAGE:
                decodeAverageFilter(curr, 0, prior, 0, bytesPerRow,
                                    bytesPerPixel);
                break;
            case PNG_FILTER_PAETH:
                decodePaethFilter(curr, 0, prior, 0, bytesPerRow,
                                  bytesPerPixel);
                break;
            default:
                throw new IIOException("Unknown row filter type (= " +
                                       filter + ")!");
            }

            // Copy data into passRow byte by byte
            if (bitDepth < 16) {
                System.arraycopy(curr, 0, byteData, 0, bytesPerRow);
            } else {
                int idx = 0;
                for (int j = 0; j < eltsPerRow; j++) {
                    shortData[j] =
                        (short)((curr[idx] << 8) | (curr[idx + 1] & 0xff));
                    idx += 2;
                }
            }

            // True Y position in source
            int sourceY = srcY*yStep + yStart;
            if ((sourceY >= sourceRegion.y) &&
                (sourceY < sourceRegion.y + sourceRegion.height) &&
                (((sourceY - sourceRegion.y) %
                  sourceYSubsampling) == 0)) {

                int dstY = destinationOffset.y +
                    (sourceY - sourceRegion.y)/sourceYSubsampling;
                if (dstY < dstMinY) {
                    continue;
                }
                if (dstY > dstMaxY) {
                    break;
                }

               /*
                * For PNG images of color type PNG_COLOR_RGB or PNG_COLOR_GRAY
                * that contain a specific transparent color (given by tRNS
                * chunk), we compare the decoded pixel color with the color
                * given by tRNS chunk to set the alpha on the destination.
                */
                boolean tRNSTransparentPixelPresent =
                    theImage.getSampleModel().getNumBands() == inputBands + 1 &&
                    metadata.hasTransparentColor();
                if (useSetRect &&
                    !tRNSTransparentPixelPresent) {
                    imRas.setRect(updateMinX, dstY, passRow);
                } else {
                    int newSrcX = srcX;

                    /*
                     * Create intermediate array to fill the extra alpha
                     * channel when tRNSTransparentPixelPresent is true.
                     */
                    final int[] temp = new int[inputBands + 1];
                    final int opaque = (bitDepth < 16) ? 255 : 65535;
                    for (int dstX = updateMinX;
                         dstX < updateMinX + updateWidth;
                         dstX += updateXStep) {

                        passRow.getPixel(newSrcX, 0, ps);
                        if (adjustBitDepths) {
                            for (int b = 0; b < inputBands; b++) {
                                ps[b] = scale[b][ps[b]];
                            }
                        }
                        if (tRNSTransparentPixelPresent) {
                            if (metadata.tRNS_colorType == PNG_COLOR_RGB) {
                                temp[0] = ps[0];
                                temp[1] = ps[1];
                                temp[2] = ps[2];
                                if (ps[0] == metadata.tRNS_red &&
                                    ps[1] == metadata.tRNS_green &&
                                    ps[2] == metadata.tRNS_blue) {
                                    temp[3] = 0;
                                } else {
                                    temp[3] = opaque;
                                }
                            } else {
                                // when tRNS_colorType is PNG_COLOR_GRAY
                                temp[0] = ps[0];
                                if (ps[0] == metadata.tRNS_gray) {
                                    temp[1] = 0;
                                } else {
                                    temp[1] = opaque;
                                }
                            }
                            imRas.setPixel(dstX, dstY, temp);
                        } else {
                            imRas.setPixel(dstX, dstY, ps);
                        }
                        newSrcX += srcXStep;
                    }
                }

                processImageUpdate(theImage,
                                   updateMinX, dstY,
                                   updateWidth, 1,
                                   updateXStep, updateYStep,
                                   destinationBands);
            }
        }

        processPassComplete(theImage);
    }

    private void decodeImage()
        throws IOException, IIOException  {
        int width = metadata.IHDR_width;
        int height = metadata.IHDR_height;

        this.pixelsDone = 0;
        this.totalPixels = width*height;

        if (metadata.IHDR_interlaceMethod == 0) {
            decodePass(0, 0, 0, 1, 1, width, height);
        } else {
            for (int i = 0; i <= sourceMaxProgressivePass; i++) {
                int XOffset = adam7XOffset[i];
                int YOffset = adam7YOffset[i];
                int XSubsampling = adam7XSubsampling[i];
                int YSubsampling = adam7YSubsampling[i];
                int xbump = adam7XSubsampling[i + 1] - 1;
                int ybump = adam7YSubsampling[i + 1] - 1;

                if (i >= sourceMinProgressivePass) {
                    decodePass(i,
                               XOffset,
                               YOffset,
                               XSubsampling,
                               YSubsampling,
                               (width + xbump)/XSubsampling,
                               (height + ybump)/YSubsampling);
                } else {
                    skipPass((width + xbump)/XSubsampling,
                             (height + ybump)/YSubsampling);
                }

                /*
                 * If read has been aborted, just return
                 * processReadAborted will be called later
                 */
                if (abortRequested()) {
                    return;
                }
            }
        }
    }

    private void readImage(ImageReadParam param) throws IIOException {
        readMetadata();

        int width = metadata.IHDR_width;
        int height = metadata.IHDR_height;

        // Init default values
        sourceXSubsampling = 1;
        sourceYSubsampling = 1;
        sourceMinProgressivePass = 0;
        sourceMaxProgressivePass = 6;
        sourceBands = null;
        destinationBands = null;
        destinationOffset = new Point(0, 0);

        // If an ImageReadParam is available, get values from it
        if (param != null) {
            sourceXSubsampling = param.getSourceXSubsampling();
            sourceYSubsampling = param.getSourceYSubsampling();

            sourceMinProgressivePass =
                Math.max(param.getSourceMinProgressivePass(), 0);
            sourceMaxProgressivePass =
                Math.min(param.getSourceMaxProgressivePass(), 6);

            sourceBands = param.getSourceBands();
            destinationBands = param.getDestinationBands();
            destinationOffset = param.getDestinationOffset();
        }
        Inflater inf = null;
        try {
            stream.seek(imageStartPosition);

            Enumeration<InputStream> e = new PNGImageDataEnumeration(stream);
            InputStream is = new SequenceInputStream(e);

           /* InflaterInputStream uses an Inflater instance which consumes
            * native (non-GC visible) resources. This is normally implicitly
            * freed when the stream is closed. However since the
            * InflaterInputStream wraps a client-supplied input stream,
            * we cannot close it.
            * But the app may depend on GC finalization to close the stream.
            * Therefore to ensure timely freeing of native resources we
            * explicitly create the Inflater instance and free its resources
            * when we are done with the InflaterInputStream by calling
            * inf.end();
            */
            inf = new Inflater();
            is = new InflaterInputStream(is, inf);
            is = new BufferedInputStream(is);
            this.pixelStream = new DataInputStream(is);

            /*
             * PNG spec declares that valid range for width
             * and height is [1, 2^31-1], so here we may fail to allocate
             * a buffer for destination image due to memory limitation.
             *
             * If the read operation triggers OutOfMemoryError, the same
             * will be wrapped in an IIOException at PNGImageReader.read
             * method.
             *
             * The recovery strategy for this case should be defined at
             * the level of application, so we will not try to estimate
             * the required amount of the memory and/or handle OOM in
             * any way.
             */
            theImage = getDestination(param,
                                      getImageTypes(0),
                                      width,
                                      height);

            Rectangle destRegion = new Rectangle(0, 0, 0, 0);
            sourceRegion = new Rectangle(0, 0, 0, 0);
            computeRegions(param, width, height,
                           theImage,
                           sourceRegion, destRegion);
            destinationOffset.setLocation(destRegion.getLocation());

            // At this point the header has been read and we know
            // how many bands are in the image, so perform checking
            // of the read param.
            int colorType = metadata.IHDR_colorType;
            if (theImage.getSampleModel().getNumBands()
                == inputBandsForColorType[colorType] + 1
                && metadata.hasTransparentColor()) {
                checkReadParamBandSettings(param,
                    inputBandsForColorType[colorType] + 1,
                    theImage.getSampleModel().getNumBands());
            } else {
                checkReadParamBandSettings(param,
                    inputBandsForColorType[colorType],
                    theImage.getSampleModel().getNumBands());
            }

            clearAbortRequest();
            processImageStarted(0);
            if (abortRequested()) {
                processReadAborted();
            } else {
                decodeImage();
                if (abortRequested()) {
                    processReadAborted();
                } else {
                    processImageComplete();
                }
            }

        } catch (IOException e) {
            throw new IIOException("Error reading PNG image data", e);
        } finally {
            if (inf != null) {
                inf.end();
            }
        }
    }

    @Override
    public int getNumImages(boolean allowSearch) throws IIOException {
        if (stream == null) {
            throw new IllegalStateException("No input source set!");
        }
        if (seekForwardOnly && allowSearch) {
            throw new IllegalStateException
                ("seekForwardOnly and allowSearch can't both be true!");
        }
        return 1;
    }

    @Override
    public int getWidth(int imageIndex) throws IIOException {
        if (imageIndex != 0) {
            throw new IndexOutOfBoundsException("imageIndex != 0!");
        }

        readHeader();

        return metadata.IHDR_width;
    }

    @Override
    public int getHeight(int imageIndex) throws IIOException {
        if (imageIndex != 0) {
            throw new IndexOutOfBoundsException("imageIndex != 0!");
        }

        readHeader();

        return metadata.IHDR_height;
    }

    @Override
    public Iterator<ImageTypeSpecifier> getImageTypes(int imageIndex)
      throws IIOException
    {
        if (imageIndex != 0) {
            throw new IndexOutOfBoundsException("imageIndex != 0!");
        }

        readHeader();

        ArrayList<ImageTypeSpecifier> l =
            new ArrayList<ImageTypeSpecifier>(1);

        ColorSpace rgb;
        ColorSpace gray;
        int[] bandOffsets;

        int bitDepth = metadata.IHDR_bitDepth;
        int colorType = metadata.IHDR_colorType;

        int dataType;
        if (bitDepth <= 8) {
            dataType = DataBuffer.TYPE_BYTE;
        } else {
            dataType = DataBuffer.TYPE_USHORT;
        }

        switch (colorType) {
        /*
         * For PNG images of color type PNG_COLOR_RGB or PNG_COLOR_GRAY that
         * contain a specific transparent color (given by tRNS chunk), we add
         * ImageTypeSpecifier(s) that support transparency to the list of
         * supported image types.
         */
        case PNG_COLOR_GRAY:
            readMetadata(); // Need tRNS chunk

            if (metadata.hasTransparentColor()) {
                gray = ColorSpace.getInstance(ColorSpace.CS_GRAY);
                bandOffsets = new int[2];
                bandOffsets[0] = 0;
                bandOffsets[1] = 1;
                l.add(ImageTypeSpecifier.createInterleaved(gray,
                                                           bandOffsets,
                                                           dataType,
                                                           true,
                                                           false));
            }
            // Packed grayscale
            l.add(ImageTypeSpecifier.createGrayscale(bitDepth,
                                                     dataType,
                                                     false));
            break;

        case PNG_COLOR_RGB:
            readMetadata(); // Need tRNS chunk

            if (bitDepth == 8) {
                if (metadata.hasTransparentColor()) {
                    l.add(ImageTypeSpecifier.createFromBufferedImageType(
                            BufferedImage.TYPE_4BYTE_ABGR));
                }
                // some standard types of buffered images
                // which can be used as destination
                l.add(ImageTypeSpecifier.createFromBufferedImageType(
                          BufferedImage.TYPE_3BYTE_BGR));

                l.add(ImageTypeSpecifier.createFromBufferedImageType(
                          BufferedImage.TYPE_INT_RGB));

                l.add(ImageTypeSpecifier.createFromBufferedImageType(
                          BufferedImage.TYPE_INT_BGR));

            }

            if (metadata.hasTransparentColor()) {
                rgb = ColorSpace.getInstance(ColorSpace.CS_sRGB);
                bandOffsets = new int[4];
                bandOffsets[0] = 0;
                bandOffsets[1] = 1;
                bandOffsets[2] = 2;
                bandOffsets[3] = 3;

                l.add(ImageTypeSpecifier.
                    createInterleaved(rgb, bandOffsets,
                                      dataType, true, false));
            }
            // Component R, G, B
            rgb = ColorSpace.getInstance(ColorSpace.CS_sRGB);
            bandOffsets = new int[3];
            bandOffsets[0] = 0;
            bandOffsets[1] = 1;
            bandOffsets[2] = 2;
            l.add(ImageTypeSpecifier.createInterleaved(rgb,
                                                       bandOffsets,
                                                       dataType,
                                                       false,
                                                       false));
            break;

        case PNG_COLOR_PALETTE:
            readMetadata(); // Need tRNS chunk

            /*
             * The PLTE chunk spec says:
             *
             * The number of palette entries must not exceed the range that
             * can be represented in the image bit depth (for example, 2^4 = 16
             * for a bit depth of 4). It is permissible to have fewer entries
             * than the bit depth would allow. In that case, any out-of-range
             * pixel value found in the image data is an error.
             *
             * http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html#C.PLTE
             *
             * Consequently, the case when the palette length is smaller than
             * 2^bitDepth is legal in the view of PNG spec.
             *
             * However the spec of createIndexed() method demands the exact
             * equality of the palette lengh and number of possible palette
             * entries (2^bitDepth).
             *
             * {@link javax.imageio.ImageTypeSpecifier.html#createIndexed}
             *
             * In order to avoid this contradiction we need to extend the
             * palette arrays to the limit defined by the bitDepth.
             */

            int plength = 1 << bitDepth;

            byte[] red = metadata.PLTE_red;
            byte[] green = metadata.PLTE_green;
            byte[] blue = metadata.PLTE_blue;

            if (metadata.PLTE_red.length < plength) {
                red = Arrays.copyOf(metadata.PLTE_red, plength);
                Arrays.fill(red, metadata.PLTE_red.length, plength,
                            metadata.PLTE_red[metadata.PLTE_red.length - 1]);

                green = Arrays.copyOf(metadata.PLTE_green, plength);
                Arrays.fill(green, metadata.PLTE_green.length, plength,
                            metadata.PLTE_green[metadata.PLTE_green.length - 1]);

                blue = Arrays.copyOf(metadata.PLTE_blue, plength);
                Arrays.fill(blue, metadata.PLTE_blue.length, plength,
                            metadata.PLTE_blue[metadata.PLTE_blue.length - 1]);

            }

            // Alpha from tRNS chunk may have fewer entries than
            // the RGB LUTs from the PLTE chunk; if so, pad with
            // 255.
            byte[] alpha = null;
            if (metadata.tRNS_present && (metadata.tRNS_alpha != null)) {
                if (metadata.tRNS_alpha.length == red.length) {
                    alpha = metadata.tRNS_alpha;
                } else {
                    alpha = Arrays.copyOf(metadata.tRNS_alpha, red.length);
                    Arrays.fill(alpha,
                                metadata.tRNS_alpha.length,
                                red.length, (byte)255);
                }
            }

            l.add(ImageTypeSpecifier.createIndexed(red, green,
                                                   blue, alpha,
                                                   bitDepth,
                                                   DataBuffer.TYPE_BYTE));
            break;

        case PNG_COLOR_GRAY_ALPHA:
            // Component G, A
            gray = ColorSpace.getInstance(ColorSpace.CS_GRAY);
            bandOffsets = new int[2];
            bandOffsets[0] = 0;
            bandOffsets[1] = 1;
            l.add(ImageTypeSpecifier.createInterleaved(gray,
                                                       bandOffsets,
                                                       dataType,
                                                       true,
                                                       false));
            break;

        case PNG_COLOR_RGB_ALPHA:
            if (bitDepth == 8) {
                // some standard types of buffered images
                // wich can be used as destination
                l.add(ImageTypeSpecifier.createFromBufferedImageType(
                          BufferedImage.TYPE_4BYTE_ABGR));

                l.add(ImageTypeSpecifier.createFromBufferedImageType(
                          BufferedImage.TYPE_INT_ARGB));
            }

            // Component R, G, B, A (non-premultiplied)
            rgb = ColorSpace.getInstance(ColorSpace.CS_sRGB);
            bandOffsets = new int[4];
            bandOffsets[0] = 0;
            bandOffsets[1] = 1;
            bandOffsets[2] = 2;
            bandOffsets[3] = 3;

            l.add(ImageTypeSpecifier.createInterleaved(rgb,
                                                       bandOffsets,
                                                       dataType,
                                                       true,
                                                       false));
            break;

        default:
            break;
        }

        return l.iterator();
    }

    /*
     * Super class implementation uses first element
     * of image types list as raw image type.
     *
     * Also, super implementation uses first element of this list
     * as default destination type image read param does not specify
     * anything other.
     *
     * However, in case of RGB and RGBA color types, raw image type
     * produces buffered image of custom type. It causes some
     * performance degradation of subsequent rendering operations.
     *
     * To resolve this contradiction we put standard image types
     * at the first positions of image types list (to produce standard
     * images by default) and put raw image type (which is custom)
     * at the last position of this list.
     *
     * After this changes we should override getRawImageType()
     * to return last element of image types list.
     */
    @Override
    public ImageTypeSpecifier getRawImageType(int imageIndex)
      throws IOException {

        Iterator<ImageTypeSpecifier> types = getImageTypes(imageIndex);
        ImageTypeSpecifier raw = null;
        do {
            raw = types.next();
        } while (types.hasNext());
        return raw;
    }

    @Override
    public ImageReadParam getDefaultReadParam() {
        return new ImageReadParam();
    }

    @Override
    public IIOMetadata getStreamMetadata()
        throws IIOException {
        return null;
    }

    @Override
    public IIOMetadata getImageMetadata(int imageIndex) throws IIOException {
        if (imageIndex != 0) {
            throw new IndexOutOfBoundsException("imageIndex != 0!");
        }
        readMetadata();
        return metadata;
    }

    @Override
    public BufferedImage read(int imageIndex, ImageReadParam param)
        throws IIOException {
        if (imageIndex != 0) {
            throw new IndexOutOfBoundsException("imageIndex != 0!");
        }

        try {
            readImage(param);
        } catch (IOException |
                 IllegalStateException |
                 IllegalArgumentException e)
        {
            throw e;
        } catch (Throwable e) {
            throw new IIOException("Caught exception during read: ", e);
        }
        return theImage;
    }

    @Override
    public void reset() {
        super.reset();
        resetStreamSettings();
    }

    private void resetStreamSettings() {
        gotHeader = false;
        gotMetadata = false;
        metadata = null;
        pixelStream = null;
        imageStartPosition = -1L;
    }
}