base/image/encoding.cpp

/*******************************************************************************
 * encoding.cpp
 *
 * ---------------------------------------------------------------------------
 * Persistence of Vision Ray Tracer ('POV-Ray') version 3.7.
 * Copyright 1991-2013 Persistence of Vision Raytracer Pty. Ltd.
 *
 * POV-Ray is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * POV-Ray 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 * ---------------------------------------------------------------------------
 * POV-Ray is based on the popular DKB raytracer version 2.12.
 * DKBTrace was originally written by David K. Buck.
 * DKBTrace Ver 2.0-2.12 were written by David K. Buck & Aaron A. Collins.
 * ---------------------------------------------------------------------------
 * $File: //depot/public/povray/3.x/source/base/image/encoding.cpp $
 * $Revision: #1 $
 * $Change: 6069 $
 * $DateTime: 2013/11/06 11:59:40 $
 * $Author: chrisc $
 *******************************************************************************/

// configbase.h must always be the first POV file included within base *.cpp files
#include "base/configbase.h"
#include "base/image/encoding.h"
#include "base/image/image.h"
#include "base/povmsgid.h"

// this must be the last file included
#include "base/povdebug.h"

namespace pov_base
{

/*******************************************************************************/

#define ALPHA_EPSILON 1.0e-6

static const unsigned int MaxBayerMatrixSize = 4;
typedef float BayerMatrix[MaxBayerMatrixSize][MaxBayerMatrixSize];

static const BayerMatrix BayerMatrices[MaxBayerMatrixSize+1] =
{
	// dummy for 0x0
	{ { 0 } },
	// 1x1 (of little use, but here it is)
	{ { 1/2.0-0.5 } },
	// 2x2
	{ { 1/4.0-0.5, 3/4.0-0.5 },
	  { 4/4.0-0.5, 2/4.0-0.5 } },
	// 3x3
	{ { 3/9.0-0.5, 7/9.0-0.5, 4/9.0-0.5 },
	  { 6/9.0-0.5, 1/9.0-0.5, 9/9.0-0.5 },
	  { 2/9.0-0.5, 8/9.0-0.5, 5/9.0-0.5 } },
	// 4x4
	{ {  1/16.0-0.5,  9/16.0-0.5,  3/16.0-0.5, 11/16.0-0.5 },
	  { 13/16.0-0.5,  5/16.0-0.5, 15/16.0-0.5,  7/16.0-0.5 },
	  {  4/16.0-0.5, 12/16.0-0.5,  2/16.0-0.5, 10/16.0-0.5 },
	  { 16/16.0-0.5,  8/16.0-0.5, 14/16.0-0.5,  6/16.0-0.5 } }
};

/*******************************************************************************/

/// Class representing "no-op" dithering rules.
class NoDither : public DitherHandler
{
	public:
		virtual void getOffset(unsigned int x, unsigned int y, OffsetInfo& offLin, OffsetInfo& offQnt);
};

/// Class representing bayer dithering rules, generating a regular pattern.
class BayerDither : public DitherHandler
{
	public:
		BayerDither(unsigned int mxSize);
		virtual void getOffset(unsigned int x, unsigned int y, OffsetInfo& offLin, OffsetInfo& offQnt);
		static inline float getOffset(unsigned int x, unsigned int y, unsigned int ms) { return BayerMatrices[ms][x%ms][y%ms]; }
	protected:
		OffsetInfo  lastErr;
		int         matrixSize;
};

/// Class representing simple 1D error diffusion dithering rules, carrying over the error from one pixel to the next.
class DiffusionDither1D : public DitherHandler
{
	public:
		virtual void getOffset(unsigned int x, unsigned int y, OffsetInfo& offLin, OffsetInfo& offQnt);
		virtual void setError(unsigned int x, unsigned int y, const OffsetInfo& err);
	protected:
		OffsetInfo lastErr;
};

/// Class representing simple 2D error diffusion dithering rules, carrying over the error from one pixel to the right, as well as the two pixels below.
/// @note   This implementation uses an additional 1-line pixel buffer to avoid manipulating the original image.
class DiffusionDither2D : public DitherHandler
{
	public:
		DiffusionDither2D(unsigned int width);
		virtual ~DiffusionDither2D();
		virtual void getOffset(unsigned int x, unsigned int y, OffsetInfo& offLin, OffsetInfo& offQnt);
		virtual void setError(unsigned int x, unsigned int y, const OffsetInfo& err);
	protected:
		unsigned int imageWidth;
		OffsetInfo* nextRowOffset;
		OffsetInfo* thisRowOffset;
};

/// Class representing Floyd-Steinberg dithering rules, carrying over the error from one pixel to the right, as well as the three pixels below.
/// @note   This implementation uses an additional 1-line pixel buffer to avoid manipulating the original image.
class FloydSteinbergDither : public DitherHandler
{
	public:
		FloydSteinbergDither(unsigned int width);
		virtual ~FloydSteinbergDither();
		virtual void getOffset(unsigned int x, unsigned int y, OffsetInfo& offLin, OffsetInfo& offQnt);
		virtual void setError(unsigned int x, unsigned int y, const OffsetInfo& err);
	protected:
		unsigned int imageWidth;
		OffsetInfo* nextRowOffset;
		OffsetInfo* thisRowOffset;
};

/*******************************************************************************/

void NoDither::getOffset(unsigned int x, unsigned int y, OffsetInfo& offLin, OffsetInfo& offQnt)
{
	offLin.clear();
	offQnt.clear();
}

/*******************************************************************************/

BayerDither::BayerDither(unsigned int mxSize) :
	matrixSize(min(mxSize,MaxBayerMatrixSize))
{
	;
}

void BayerDither::getOffset(unsigned int x, unsigned int y, OffsetInfo& offLin, OffsetInfo& offQnt)
{
	offLin.clear();
	offQnt.setAll(getOffset(x, y, matrixSize));
}

/*******************************************************************************/

void DiffusionDither1D::getOffset(unsigned int x, unsigned int y, OffsetInfo& offLin, OffsetInfo& offQnt)
{
	offLin = lastErr; lastErr.clear(); offQnt.clear();
}

void DiffusionDither1D::setError(unsigned int x, unsigned int y, const OffsetInfo& err)
{
	lastErr = err;
}

/*******************************************************************************/

DiffusionDither2D::DiffusionDither2D(unsigned int width) :
	imageWidth(width),
	thisRowOffset(new OffsetInfo[width+1]),
	nextRowOffset(new OffsetInfo[width+1])
{
	;
}

DiffusionDither2D::~DiffusionDither2D()
{
	delete[] thisRowOffset;
	delete[] nextRowOffset;
}

void DiffusionDither2D::getOffset(unsigned int x, unsigned int y, OffsetInfo& offLin, OffsetInfo& offQnt)
{
	offLin = thisRowOffset[x];
	offQnt.clear();
}

void DiffusionDither2D::setError(unsigned int x, unsigned int y, const OffsetInfo& err)
{
	if (x == 0)
	{
		OffsetInfo* tmp = nextRowOffset;
		nextRowOffset = thisRowOffset;
		thisRowOffset = tmp;
		for (unsigned int i = 0; i < imageWidth+1; i ++)
			nextRowOffset[i].clear();
	}
	thisRowOffset[x+1] += err * (2/4.0); // pixel to the right
	nextRowOffset[x]   += err * (1/4.0); // pixel below
	nextRowOffset[x+1] += err * (1/4.0); // pixel below right
}

/*******************************************************************************/

FloydSteinbergDither::FloydSteinbergDither(unsigned int width) :
	imageWidth(width),
	thisRowOffset(new OffsetInfo[width+2]),
	nextRowOffset(new OffsetInfo[width+2])
{
	;
}

FloydSteinbergDither::~FloydSteinbergDither()
{
	delete[] thisRowOffset;
	delete[] nextRowOffset;
}

void FloydSteinbergDither::getOffset(unsigned int x, unsigned int y, OffsetInfo& offLin, OffsetInfo& offQnt)
{
	offLin = thisRowOffset[x+1];
	offQnt.clear();
}

void FloydSteinbergDither::setError(unsigned int x, unsigned int y, const OffsetInfo& err)
{
	if (x == 0)
	{
		OffsetInfo* tmp = nextRowOffset;
		nextRowOffset = thisRowOffset;
		thisRowOffset = tmp;
		for (unsigned int i = 0; i < imageWidth+2; i ++)
			nextRowOffset[i].clear();
	}
	thisRowOffset[x+2] += err * (7/16.0); // pixel to the right
	nextRowOffset[x]   += err * (3/16.0); // pixel below left
	nextRowOffset[x+1] += err * (5/16.0); // pixel below
	nextRowOffset[x+2] += err * (1/16.0); // pixel below right
}

/*******************************************************************************/

DitherHandlerPtr GetDitherHandler(int method, unsigned int imageWidth)
{
	switch (method)
	{
		case kPOVList_DitherMethod_None:            return DitherHandlerPtr(new NoDither());
		case kPOVList_DitherMethod_Diffusion1D:     return DitherHandlerPtr(new DiffusionDither1D());
		case kPOVList_DitherMethod_Diffusion2D:     return DitherHandlerPtr(new DiffusionDither2D(imageWidth));
		case kPOVList_DitherMethod_FloydSteinberg:  return DitherHandlerPtr(new FloydSteinbergDither(imageWidth));
		case kPOVList_DitherMethod_Bayer2x2:        return DitherHandlerPtr(new BayerDither(2));
		case kPOVList_DitherMethod_Bayer3x3:        return DitherHandlerPtr(new BayerDither(3));
		case kPOVList_DitherMethod_Bayer4x4:        return DitherHandlerPtr(new BayerDither(4));
		default:                                    throw POV_EXCEPTION_STRING("Invalid dither method for output");
	}
}

DitherHandlerPtr GetNoOpDitherHandler()
{
	return DitherHandlerPtr(new NoDither());
}

/*******************************************************************************/

float GetDitherOffset(unsigned int x, unsigned int y)
{
	return BayerDither::getOffset(x,y,4);
}

/*******************************************************************************/

inline void AlphaPremultiply(float& fGray, float fAlpha)
{
	fGray *= fAlpha;
}
inline void AlphaPremultiply(float& fRed, float& fGreen, float& fBlue, float fAlpha)
{
	fRed   *= fAlpha;
	fGreen *= fAlpha;
	fBlue  *= fAlpha;
}
inline void AlphaUnPremultiply(float& fGray, float fAlpha)
{
	if (fAlpha == 0)
		// This special case has no perfectly sane solution. We'll just pretend that fAlpha is very, very small but non-zero.
		fAlpha = ALPHA_EPSILON;
	fGray /= fAlpha;
}
inline void AlphaUnPremultiply(float& fRed, float& fGreen, float& fBlue, float fAlpha)
{
	if (fAlpha == 0)
		// This special case has no perfectly sane solution. We'll just pretend that fAlpha is very, very small but non-zero.
		fAlpha = ALPHA_EPSILON;
	fRed   /= fAlpha;
	fGreen /= fAlpha;
	fBlue  /= fAlpha;
}

void SetEncodedGrayValue(Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, unsigned int max, unsigned int gray)
{
	if (!img->IsIndexed() && img->GetMaxIntValue() == max && GammaCurve::IsNeutral(g))
		// avoid potential re-quantization in case we have a pretty match between encoded data and container
		img->SetGrayValue(x, y, gray);
	else
		img->SetGrayValue(x, y, IntDecode(g,gray,max));
}
void SetEncodedGrayAValue(Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, unsigned int max, unsigned int gray, unsigned int alpha, bool premul)
{
	bool doPremultiply   = (alpha != max) && !premul && (img->IsPremultiplied() || !img->HasTransparency()); // need to apply premultiplication if encoded data isn't PM'ed but container content should be
	bool doUnPremultiply = (alpha != max) && premul && !img->IsPremultiplied() && img->HasTransparency(); // need to undo premultiplication if other way round
	if (!doPremultiply && !doUnPremultiply && !img->IsIndexed() && img->GetMaxIntValue() == max && GammaCurve::IsNeutral(g))
		// avoid potential re-quantization in case we have a pretty match between encoded data and container
		img->SetGrayAValue(x, y, gray, alpha);
	else
	{
		float fAlpha = IntDecode(alpha,max);
		float fGray  = IntDecode(g,gray,max);
		if (doPremultiply)
			AlphaPremultiply(fGray, fAlpha);
		else if (doUnPremultiply)
			AlphaUnPremultiply(fGray, fAlpha);
		// else no need to worry about premultiplication
		img->SetGrayAValue(x, y, fGray, fAlpha);
	}
}
void SetEncodedRGBValue(Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, unsigned int max, unsigned int red, unsigned int green, unsigned int blue)
{
	if (!img->IsIndexed() && img->GetMaxIntValue() == max && GammaCurve::IsNeutral(g))
		// avoid potential re-quantization in case we have a pretty match between encoded data and container
		img->SetRGBValue(x, y, red, green, blue);
	else
		img->SetRGBValue(x, y, IntDecode(g,red,max), IntDecode(g,green,max), IntDecode(g,blue,max));
}
void SetEncodedRGBAValue(Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, unsigned int max, unsigned int red, unsigned int green, unsigned int blue, unsigned int alpha, bool premul)
{
	bool doPremultiply   = (alpha != max) && !premul && (img->IsPremultiplied() || !img->HasTransparency()); // need to apply premultiplication if encoded data isn't PM'ed but container content should be
	bool doUnPremultiply = (alpha != max) && premul && !img->IsPremultiplied() && img->HasTransparency(); // need to undo premultiplication if other way round
	if (!doPremultiply && !doUnPremultiply && !img->IsIndexed() && img->GetMaxIntValue() == max && GammaCurve::IsNeutral(g))
		// avoid potential re-quantization in case we have a pretty match between encoded data and container
		img->SetRGBAValue(x, y, red, green, blue, alpha);
	else
	{
		float fAlpha = IntDecode(alpha,  max);
		float fRed   = IntDecode(g,red,  max);
		float fGreen = IntDecode(g,green,max);
		float fBlue  = IntDecode(g,blue, max);
		if (doPremultiply)
			AlphaPremultiply(fRed, fGreen, fBlue, fAlpha);
		else if (doUnPremultiply)
			AlphaUnPremultiply(fRed, fGreen, fBlue, fAlpha);
		// else no need to worry about premultiplication
		img->SetRGBAValue(x, y, fRed, fGreen, fBlue, fAlpha);
	}
}
void SetEncodedGrayValue(Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, float fGray)
{
	img->SetGrayValue(x, y, GammaCurve::Decode(g,fGray));
}
void SetEncodedGrayAValue(Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, float fGray, float fAlpha, bool premul)
{
	bool doPremultiply   = !premul && (img->IsPremultiplied() || !img->HasTransparency()); // need to apply premultiplication if encoded data isn't PM'ed but container content should be
	bool doUnPremultiply = premul && !img->IsPremultiplied() && img->HasTransparency(); // need to undo premultiplication if other way round
	fGray = GammaCurve::Decode(g,fGray);
	if (doPremultiply)
		AlphaPremultiply(fGray, fAlpha);
	else if (doUnPremultiply)
		AlphaUnPremultiply(fGray, fAlpha);
	// else no need to worry about premultiplication
	img->SetGrayAValue(x, y, fGray, fAlpha);
}
void SetEncodedRGBValue(Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, float red, float green, float blue)
{
	img->SetRGBValue(x, y, GammaCurve::Decode(g,red), GammaCurve::Decode(g,green), GammaCurve::Decode(g,blue));
}
void SetEncodedRGBAValue(Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, float fRed, float fGreen, float fBlue, float fAlpha, bool premul)
{
	bool doPremultiply   = !premul && (img->IsPremultiplied() || !img->HasTransparency()); // need to apply premultiplication if encoded data isn't PM'ed but container content should be
	bool doUnPremultiply = premul && !img->IsPremultiplied() && img->HasTransparency(); // need to undo premultiplication if other way round
	fRed   = GammaCurve::Decode(g,fRed);
	fGreen = GammaCurve::Decode(g,fGreen);
	fBlue  = GammaCurve::Decode(g,fBlue);
	if (doPremultiply)
		AlphaPremultiply(fRed, fGreen, fBlue, fAlpha);
	else if (doUnPremultiply)
		AlphaUnPremultiply(fRed, fGreen, fBlue, fAlpha);
	// else no need to worry about premultiplication
	img->SetRGBAValue(x, y, fRed, fGreen, fBlue, fAlpha);
}

unsigned int GetEncodedGrayValue(const Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, unsigned int max, DitherHandler& dh)
{
	float fGray;
	if (!img->IsPremultiplied() && img->HasTransparency())
	{
		// data has transparency and is stored non-premultiplied; precompose against a black background
		float fAlpha;
		img->GetGrayAValue(x, y, fGray, fAlpha);
		AlphaPremultiply(fGray, fAlpha);
	}
	else
	{
		// no need to worry about premultiplication
		fGray = img->GetGrayValue(x, y);
	}
	DitherHandler::OffsetInfo linOff, encOff;
	dh.getOffset(x,y,linOff,encOff);
	unsigned int iGray = IntEncode(g,fGray+linOff.gray,max,encOff.gray,linOff.gray);
	dh.setError(x,y,linOff);
	return iGray;
}
void GetEncodedGrayAValue(const Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, unsigned int max, unsigned int& gray, unsigned int& alpha, DitherHandler& dh, bool premul)
{
	bool doPremultiply   = premul && !img->IsPremultiplied() && img->HasTransparency(); // need to apply premultiplication if encoded data should be premul'ed but container content isn't
	bool doUnPremultiply = !premul && img->IsPremultiplied() && img->HasTransparency(); // need to undo premultiplication if other way round
	float fGray, fAlpha;
	img->GetGrayAValue(x, y, fGray, fAlpha);
	if (doPremultiply)
	{
		AlphaPremultiply(fGray, fAlpha);
	}
	else if (doUnPremultiply)
	{
		// Data has been stored premultiplied, but should be encoded non-premultiplied.
		// Clipping will happen /before/ re-multiplying with alpha (because the latter is done in the viewer), which is equivalent to clipping
		// pre-multiplied components to be no greater than alpha, thereby "killing" highlights on transparent objects;
		// compensate for this by boosting opacity of any exceptionally bright pixels.
		if (fGray > fAlpha)
			fAlpha = min(1.0f, fGray);
		// Need to convert from premultiplied to non-premultiplied encoding.
		AlphaUnPremultiply(fGray, fAlpha);
	}
	else if (!premul)
	{
		// Data has been stored un-premultiplied and should be encoded that way.
		// Clipping will happen /before/ multiplying with alpha (because the latter is done in the viewer), which is equivalent to clipping
		// pre-multiplied components to be no greater than alpha, thereby "killing" highlights on transparent objects;
		// compensate for this by boosting opacity of any exceptionally bright pixels.
		if (fGray > 1.0)
		{
			float fFactor = fGray;
			if (fFactor * fAlpha > 1.0)
				fFactor = 1.0/fAlpha;
			// this keeps the product of alpha*color constant
			fAlpha *= fFactor;
			fGray  /= fFactor;
		}
		// No need for converting between premultiplied and un-premultiplied encoding.
	}
	// else no need to worry about premultiplication
	DitherHandler::OffsetInfo linOff, encOff;
	dh.getOffset(x,y,linOff,encOff);
	gray  = IntEncode(g, fGray + linOff.gray,  max, encOff.gray,  linOff.gray);
	alpha = IntEncode(fAlpha   + linOff.alpha, max, encOff.alpha, linOff.alpha);
	dh.setError(x,y,linOff);
}
void GetEncodedRGBValue(const Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, unsigned int max, unsigned int& red, unsigned int& green, unsigned int& blue, DitherHandler& dh)
{
	float fRed, fGreen, fBlue;
	if (!img->IsPremultiplied() && img->HasTransparency())
	{
		float fAlpha;
		// data has transparency and is stored non-premultiplied; precompose against a black background
		img->GetRGBAValue(x, y, fRed, fGreen, fBlue, fAlpha);
		AlphaPremultiply(fRed, fGreen, fBlue, fAlpha);
	}
	else
	{
		// no need to worry about premultiplication
		img->GetRGBValue(x, y, fRed, fGreen, fBlue);
	}
	DitherHandler::OffsetInfo linOff, encOff;
	dh.getOffset(x,y,linOff,encOff);
	red   = IntEncode(g,fRed   + linOff.red,   max, encOff.red,   linOff.red);
	green = IntEncode(g,fGreen + linOff.green, max, encOff.green, linOff.green);
	blue  = IntEncode(g,fBlue  + linOff.blue,  max, encOff.blue,  linOff.blue);
	dh.setError(x,y,linOff);
}
void GetEncodedRGBAValue(const Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, unsigned int max, unsigned int& red, unsigned int& green, unsigned int& blue, unsigned int& alpha, DitherHandler& dh, bool premul)
{
	bool doPremultiply   = premul && !img->IsPremultiplied() && img->HasTransparency(); // need to apply premultiplication if encoded data should be premul'ed but container content isn't
	bool doUnPremultiply = !premul && img->IsPremultiplied() && img->HasTransparency(); // need to undo premultiplication if other way round
	float fRed, fGreen, fBlue, fAlpha;
	img->GetRGBAValue(x, y, fRed, fGreen, fBlue, fAlpha);
	if (doPremultiply)
	{
		// Data has been stored premultiplied, but should be encoded non-premultiplied.
		// No need for special handling of color components greater than alpha.
		// Need to convert from premultiplied to non-premultiplied encoding.
		AlphaPremultiply(fRed, fGreen, fBlue, fAlpha);
	}
	else if (doUnPremultiply)
	{
		// Data has been stored premultiplied, but should be encoded non-premultiplied.
		// Clipping will happen /before/ re-multiplying with alpha (because the latter is done in the viewer), which is equivalent to clipping
		// pre-multiplied components to be no greater than alpha, thereby "killing" highlights on transparent objects;
		// compensate for this by boosting opacity of any exceptionally bright pixels.
		float fBright = RGBColour(fRed, fGreen, fBlue).greyscale();
		if (fBright > fAlpha)
			fAlpha = min(1.0f, fBright);
		// Need to convert from premultiplied to non-premultiplied encoding.
		AlphaUnPremultiply(fRed, fGreen, fBlue, fAlpha);
	}
	else if (!premul)
	{
		// Data has been stored un-premultiplied and should be encoded that way.
		// Clipping will happen /before/ multiplying with alpha (because the latter is done in the viewer), which is equivalent to clipping
		// pre-multiplied components to be no greater than alpha, thereby "killing" highlights on transparent objects;
		// compensate for this by boosting opacity of any exceptionally bright pixels.
		float fBright = RGBColour(fRed, fGreen, fBlue).greyscale();
		if (fBright > 1.0)
		{
			float fFactor = fBright;
			if (fFactor * fAlpha > 1.0)
				fFactor = 1.0/fAlpha;
			// this keeps the product of alpha*color constant
			fAlpha *= fFactor;
			fRed   /= fFactor;
			fGreen /= fFactor;
			fBlue  /= fFactor;
		}
		// No need for converting between premultiplied and un-premultiplied encoding.
	}
	// else no need to worry about premultiplication
	DitherHandler::OffsetInfo linOff, encOff;
	dh.getOffset(x,y,linOff,encOff);
	red   = IntEncode(g,fRed   + linOff.red,   max, encOff.red,   linOff.red);
	green = IntEncode(g,fGreen + linOff.green, max, encOff.green, linOff.green);
	blue  = IntEncode(g,fBlue  + linOff.blue,  max, encOff.blue,  linOff.blue);
	alpha = IntEncode(fAlpha   + linOff.alpha, max, encOff.alpha, linOff.alpha);
	dh.setError(x,y,linOff);
}

float GetEncodedGrayValue(const Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g)
{
	float fGray;
	if (!img->IsPremultiplied() && img->HasTransparency())
	{
		// data has transparency and is stored non-premultiplied; precompose against a black background
		float fAlpha;
		img->GetGrayAValue(x, y, fGray, fAlpha);
		AlphaPremultiply(fGray, fAlpha);
	}
	else
	{
		// no need to worry about premultiplication
		fGray = img->GetGrayValue(x, y);
	}
	return GammaCurve::Encode(g,fGray);
}
void GetEncodedGrayAValue(const Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, float& fGray, float& fAlpha, bool premul)
{
	bool doPremultiply   = premul && !img->IsPremultiplied() && img->HasTransparency(); // need to apply premultiplication if encoded data should be premul'ed but container content isn't
	bool doUnPremultiply = !premul && img->IsPremultiplied() && img->HasTransparency(); // need to undo premultiplication if other way round
	img->GetGrayAValue(x, y, fGray, fAlpha);
	if (doPremultiply)
		AlphaPremultiply(fGray, fAlpha);
	else if (doUnPremultiply)
		AlphaUnPremultiply(fGray, fAlpha);
	// else no need to worry about premultiplication
	fGray = GammaCurve::Encode(g,fGray);
}
void GetEncodedRGBValue(const Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, float& fRed, float& fGreen, float& fBlue)
{
	if (!img->IsPremultiplied() && img->HasTransparency())
	{
		// data has transparency and is stored non-premultiplied; precompose against a black background
		float fAlpha;
		img->GetRGBAValue(x, y, fRed, fGreen, fBlue, fAlpha);
		AlphaPremultiply(fRed, fGreen, fBlue, fAlpha);
	}
	else
	{
		// no need to worry about premultiplication
		img->GetRGBValue(x, y, fRed, fGreen, fBlue);
	}
	fRed   = GammaCurve::Encode(g,fRed);
	fGreen = GammaCurve::Encode(g,fGreen);
	fBlue  = GammaCurve::Encode(g,fBlue);
}
void GetEncodedRGBAValue(const Image* img, unsigned int x, unsigned int y, const GammaCurvePtr& g, float& fRed, float& fGreen, float& fBlue, float& fAlpha, bool premul)
{
	bool doPremultiply   = premul && !img->IsPremultiplied() && img->HasTransparency(); // need to apply premultiplication if encoded data should be premul'ed but container content isn't
	bool doUnPremultiply = !premul && img->IsPremultiplied() && img->HasTransparency(); // need to undo premultiplication if other way round
	img->GetRGBAValue(x, y, fRed, fGreen, fBlue, fAlpha);
	if (doPremultiply)
		AlphaPremultiply(fRed, fGreen, fBlue, fAlpha);
	else if (doUnPremultiply)
		AlphaUnPremultiply(fRed, fGreen, fBlue, fAlpha);
	// else no need to worry about premultiplication
	fRed   = GammaCurve::Encode(g,fRed);
	fGreen = GammaCurve::Encode(g,fGreen);
	fBlue  = GammaCurve::Encode(g,fBlue);
}

}