1 /*
2  * jcprepct.c
3  *
4  * Copyright (C) 1994-1996, Thomas G. Lane.
5  * This file is part of the Independent JPEG Group's software.
6  * For conditions of distribution and use, see the accompanying README file.
7  *
8  * This file contains the compression preprocessing controller.
9  * This controller manages the color conversion, downsampling,
10  * and edge expansion steps.
11  *
12  * Most of the complexity here is associated with buffering input rows
13  * as required by the downsampler.  See the comments at the head of
14  * jcsample.c for the downsampler's needs.
15  */
16 
17 #define JPEG_INTERNALS
18 #include "jinclude.h"
19 #include "jpeglib.h"
20 
21 
22 /* At present, jcsample.c can request context rows only for smoothing.
23  * In the future, we might also need context rows for CCIR601 sampling
24  * or other more-complex downsampling procedures.  The code to support
25  * context rows should be compiled only if needed.
26  */
27 #ifdef INPUT_SMOOTHING_SUPPORTED
28 #define CONTEXT_ROWS_SUPPORTED
29 #endif
30 
31 
32 /*
33  * For the simple (no-context-row) case, we just need to buffer one
34  * row group's worth of pixels for the downsampling step.  At the bottom of
35  * the image, we pad to a full row group by replicating the last pixel row.
36  * The downsampler's last output row is then replicated if needed to pad
37  * out to a full iMCU row.
38  *
39  * When providing context rows, we must buffer three row groups' worth of
40  * pixels.  Three row groups are physically allocated, but the row pointer
41  * arrays are made five row groups high, with the extra pointers above and
42  * below "wrapping around" to point to the last and first real row groups.
43  * This allows the downsampler to access the proper context rows.
44  * At the top and bottom of the image, we create dummy context rows by
45  * copying the first or last real pixel row.  This copying could be avoided
46  * by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
47  * trouble on the compression side.
48  */
49 
50 
51 /* Private buffer controller object */
52 
53 typedef struct {
54   struct jpeg_c_prep_controller pub; /* public fields */
55 
56   /* Downsampling input buffer.  This buffer holds color-converted data
57    * until we have enough to do a downsample step.
58    */
59   JSAMPARRAY color_buf[MAX_COMPONENTS];
60 
61   JDIMENSION rows_to_go;	/* counts rows remaining in source image */
62   int next_buf_row;		/* index of next row to store in color_buf */
63 
64 #ifdef CONTEXT_ROWS_SUPPORTED	/* only needed for context case */
65   int this_row_group;		/* starting row index of group to process */
66   int next_buf_stop;		/* downsample when we reach this index */
67 #endif
68 } my_prep_controller;
69 
70 typedef my_prep_controller * my_prep_ptr;
71 
72 
73 /*
74  * Initialize for a processing pass.
75  */
76 
77 METHODDEF(void)
start_pass_prep(j_compress_ptr cinfo,J_BUF_MODE pass_mode)78 start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
79 {
80   my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
81 
82   if (pass_mode != JBUF_PASS_THRU)
83     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
84 
85   /* Initialize total-height counter for detecting bottom of image */
86   prep->rows_to_go = cinfo->image_height;
87   /* Mark the conversion buffer empty */
88   prep->next_buf_row = 0;
89 #ifdef CONTEXT_ROWS_SUPPORTED
90   /* Preset additional state variables for context mode.
91    * These aren't used in non-context mode, so we needn't test which mode.
92    */
93   prep->this_row_group = 0;
94   /* Set next_buf_stop to stop after two row groups have been read in. */
95   prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
96 #endif
97 }
98 
99 
100 /*
101  * Expand an image vertically from height input_rows to height output_rows,
102  * by duplicating the bottom row.
103  */
104 
105 LOCAL(void)
expand_bottom_edge(JSAMPARRAY image_data,JDIMENSION num_cols,int input_rows,int output_rows)106 expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols,
107 		    int input_rows, int output_rows)
108 {
109   register int row;
110 
111   for (row = input_rows; row < output_rows; row++) {
112     jcopy_sample_rows(image_data, input_rows-1, image_data, row,
113 		      1, num_cols);
114   }
115 }
116 
117 
118 /*
119  * Process some data in the simple no-context case.
120  *
121  * Preprocessor output data is counted in "row groups".  A row group
122  * is defined to be v_samp_factor sample rows of each component.
123  * Downsampling will produce this much data from each max_v_samp_factor
124  * input rows.
125  */
126 
127 METHODDEF(void)
pre_process_data(j_compress_ptr cinfo,JSAMPARRAY input_buf,JDIMENSION * in_row_ctr,JDIMENSION in_rows_avail,JSAMPIMAGE output_buf,JDIMENSION * out_row_group_ctr,JDIMENSION out_row_groups_avail)128 pre_process_data (j_compress_ptr cinfo,
129 		  JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
130 		  JDIMENSION in_rows_avail,
131 		  JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
132 		  JDIMENSION out_row_groups_avail)
133 {
134   my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
135   int numrows, ci;
136   JDIMENSION inrows;
137   jpeg_component_info * compptr;
138 
139   while (*in_row_ctr < in_rows_avail &&
140 	 *out_row_group_ctr < out_row_groups_avail) {
141     /* Do color conversion to fill the conversion buffer. */
142     inrows = in_rows_avail - *in_row_ctr;
143     numrows = cinfo->max_v_samp_factor - prep->next_buf_row;
144     numrows = (int) MIN((JDIMENSION) numrows, inrows);
145     (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
146 				       prep->color_buf,
147 				       (JDIMENSION) prep->next_buf_row,
148 				       numrows);
149     *in_row_ctr += numrows;
150     prep->next_buf_row += numrows;
151     prep->rows_to_go -= numrows;
152     /* If at bottom of image, pad to fill the conversion buffer. */
153     if (prep->rows_to_go == 0 &&
154 	prep->next_buf_row < cinfo->max_v_samp_factor) {
155       for (ci = 0; ci < cinfo->num_components; ci++) {
156 	expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
157 			   prep->next_buf_row, cinfo->max_v_samp_factor);
158       }
159       prep->next_buf_row = cinfo->max_v_samp_factor;
160     }
161     /* If we've filled the conversion buffer, empty it. */
162     if (prep->next_buf_row == cinfo->max_v_samp_factor) {
163       (*cinfo->downsample->downsample) (cinfo,
164 					prep->color_buf, (JDIMENSION) 0,
165 					output_buf, *out_row_group_ctr);
166       prep->next_buf_row = 0;
167       (*out_row_group_ctr)++;
168     }
169     /* If at bottom of image, pad the output to a full iMCU height.
170      * Note we assume the caller is providing a one-iMCU-height output buffer!
171      */
172     if (prep->rows_to_go == 0 &&
173 	*out_row_group_ctr < out_row_groups_avail) {
174       for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
175 	   ci++, compptr++) {
176 	expand_bottom_edge(output_buf[ci],
177 			   compptr->width_in_blocks * DCTSIZE,
178 			   (int) (*out_row_group_ctr * compptr->v_samp_factor),
179 			   (int) (out_row_groups_avail * compptr->v_samp_factor));
180       }
181       *out_row_group_ctr = out_row_groups_avail;
182       break;			/* can exit outer loop without test */
183     }
184   }
185 }
186 
187 
188 #ifdef CONTEXT_ROWS_SUPPORTED
189 
190 /*
191  * Process some data in the context case.
192  */
193 
194 METHODDEF(void)
pre_process_context(j_compress_ptr cinfo,JSAMPARRAY input_buf,JDIMENSION * in_row_ctr,JDIMENSION in_rows_avail,JSAMPIMAGE output_buf,JDIMENSION * out_row_group_ctr,JDIMENSION out_row_groups_avail)195 pre_process_context (j_compress_ptr cinfo,
196 		     JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
197 		     JDIMENSION in_rows_avail,
198 		     JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
199 		     JDIMENSION out_row_groups_avail)
200 {
201   my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
202   int numrows, ci;
203   int buf_height = cinfo->max_v_samp_factor * 3;
204   JDIMENSION inrows;
205 
206   while (*out_row_group_ctr < out_row_groups_avail) {
207     if (*in_row_ctr < in_rows_avail) {
208       /* Do color conversion to fill the conversion buffer. */
209       inrows = in_rows_avail - *in_row_ctr;
210       numrows = prep->next_buf_stop - prep->next_buf_row;
211       numrows = (int) MIN((JDIMENSION) numrows, inrows);
212       (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
213 					 prep->color_buf,
214 					 (JDIMENSION) prep->next_buf_row,
215 					 numrows);
216       /* Pad at top of image, if first time through */
217       if (prep->rows_to_go == cinfo->image_height) {
218 	for (ci = 0; ci < cinfo->num_components; ci++) {
219 	  int row;
220 	  for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
221 	    jcopy_sample_rows(prep->color_buf[ci], 0,
222 			      prep->color_buf[ci], -row,
223 			      1, cinfo->image_width);
224 	  }
225 	}
226       }
227       *in_row_ctr += numrows;
228       prep->next_buf_row += numrows;
229       prep->rows_to_go -= numrows;
230     } else {
231       /* Return for more data, unless we are at the bottom of the image. */
232       if (prep->rows_to_go != 0)
233 	break;
234       /* When at bottom of image, pad to fill the conversion buffer. */
235       if (prep->next_buf_row < prep->next_buf_stop) {
236 	for (ci = 0; ci < cinfo->num_components; ci++) {
237 	  expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
238 			     prep->next_buf_row, prep->next_buf_stop);
239 	}
240 	prep->next_buf_row = prep->next_buf_stop;
241       }
242     }
243     /* If we've gotten enough data, downsample a row group. */
244     if (prep->next_buf_row == prep->next_buf_stop) {
245       (*cinfo->downsample->downsample) (cinfo,
246 					prep->color_buf,
247 					(JDIMENSION) prep->this_row_group,
248 					output_buf, *out_row_group_ctr);
249       (*out_row_group_ctr)++;
250       /* Advance pointers with wraparound as necessary. */
251       prep->this_row_group += cinfo->max_v_samp_factor;
252       if (prep->this_row_group >= buf_height)
253 	prep->this_row_group = 0;
254       if (prep->next_buf_row >= buf_height)
255 	prep->next_buf_row = 0;
256       prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
257     }
258   }
259 }
260 
261 
262 /*
263  * Create the wrapped-around downsampling input buffer needed for context mode.
264  */
265 
266 LOCAL(void)
create_context_buffer(j_compress_ptr cinfo)267 create_context_buffer (j_compress_ptr cinfo)
268 {
269   my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
270   int rgroup_height = cinfo->max_v_samp_factor;
271   int ci, i;
272   jpeg_component_info * compptr;
273   JSAMPARRAY true_buffer, fake_buffer;
274 
275   /* Grab enough space for fake row pointers for all the components;
276    * we need five row groups' worth of pointers for each component.
277    */
278   fake_buffer = (JSAMPARRAY)
279     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
280 				(cinfo->num_components * 5 * rgroup_height) *
281 				SIZEOF(JSAMPROW));
282 
283   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
284        ci++, compptr++) {
285     /* Allocate the actual buffer space (3 row groups) for this component.
286      * We make the buffer wide enough to allow the downsampler to edge-expand
287      * horizontally within the buffer, if it so chooses.
288      */
289     true_buffer = (*cinfo->mem->alloc_sarray)
290       ((j_common_ptr) cinfo, JPOOL_IMAGE,
291        (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
292 		      cinfo->max_h_samp_factor) / compptr->h_samp_factor),
293        (JDIMENSION) (3 * rgroup_height));
294     /* Copy true buffer row pointers into the middle of the fake row array */
295     MEMCOPY(fake_buffer + rgroup_height, true_buffer,
296 	    3 * rgroup_height * SIZEOF(JSAMPROW));
297     /* Fill in the above and below wraparound pointers */
298     for (i = 0; i < rgroup_height; i++) {
299       fake_buffer[i] = true_buffer[2 * rgroup_height + i];
300       fake_buffer[4 * rgroup_height + i] = true_buffer[i];
301     }
302     prep->color_buf[ci] = fake_buffer + rgroup_height;
303     fake_buffer += 5 * rgroup_height; /* point to space for next component */
304   }
305 }
306 
307 #endif /* CONTEXT_ROWS_SUPPORTED */
308 
309 
310 /*
311  * Initialize preprocessing controller.
312  */
313 
314 GLOBAL(void)
jinit_c_prep_controller(j_compress_ptr cinfo,boolean need_full_buffer)315 jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
316 {
317   my_prep_ptr prep;
318   int ci;
319   jpeg_component_info * compptr;
320 
321   if (need_full_buffer)		/* safety check */
322     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
323 
324   prep = (my_prep_ptr)
325     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
326 				SIZEOF(my_prep_controller));
327   cinfo->prep = (struct jpeg_c_prep_controller *) prep;
328   prep->pub.start_pass = start_pass_prep;
329 
330   /* Allocate the color conversion buffer.
331    * We make the buffer wide enough to allow the downsampler to edge-expand
332    * horizontally within the buffer, if it so chooses.
333    */
334   if (cinfo->downsample->need_context_rows) {
335     /* Set up to provide context rows */
336 #ifdef CONTEXT_ROWS_SUPPORTED
337     prep->pub.pre_process_data = pre_process_context;
338     create_context_buffer(cinfo);
339 #else
340     ERREXIT(cinfo, JERR_NOT_COMPILED);
341 #endif
342   } else {
343     /* No context, just make it tall enough for one row group */
344     prep->pub.pre_process_data = pre_process_data;
345     for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
346 	 ci++, compptr++) {
347       prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
348 	((j_common_ptr) cinfo, JPOOL_IMAGE,
349 	 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
350 			cinfo->max_h_samp_factor) / compptr->h_samp_factor),
351 	 (JDIMENSION) cinfo->max_v_samp_factor);
352     }
353   }
354 }
355