1 /*
2  * jcprepct.c
3  *
4  * This file is part of the Independent JPEG Group's software:
5  * Copyright (C) 1994-1996, Thomas G. Lane.
6  * It was modified by The libjpeg-turbo Project to include only code relevant
7  * to libjpeg-turbo.
8  * For conditions of distribution and use, see the accompanying README file.
9  *
10  * This file contains the compression preprocessing controller.
11  * This controller manages the color conversion, downsampling,
12  * and edge expansion steps.
13  *
14  * Most of the complexity here is associated with buffering input rows
15  * as required by the downsampler.  See the comments at the head of
16  * jcsample.c for the downsampler's needs.
17  */
18 
19 #define JPEG_INTERNALS
20 #include "jinclude.h"
21 #include "jpeglib.h"
22 
23 
24 /* At present, jcsample.c can request context rows only for smoothing.
25  * In the future, we might also need context rows for CCIR601 sampling
26  * or other more-complex downsampling procedures.  The code to support
27  * context rows should be compiled only if needed.
28  */
29 #ifdef INPUT_SMOOTHING_SUPPORTED
30 #define CONTEXT_ROWS_SUPPORTED
31 #endif
32 
33 
34 /*
35  * For the simple (no-context-row) case, we just need to buffer one
36  * row group's worth of pixels for the downsampling step.  At the bottom of
37  * the image, we pad to a full row group by replicating the last pixel row.
38  * The downsampler's last output row is then replicated if needed to pad
39  * out to a full iMCU row.
40  *
41  * When providing context rows, we must buffer three row groups' worth of
42  * pixels.  Three row groups are physically allocated, but the row pointer
43  * arrays are made five row groups high, with the extra pointers above and
44  * below "wrapping around" to point to the last and first real row groups.
45  * This allows the downsampler to access the proper context rows.
46  * At the top and bottom of the image, we create dummy context rows by
47  * copying the first or last real pixel row.  This copying could be avoided
48  * by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
49  * trouble on the compression side.
50  */
51 
52 
53 /* Private buffer controller object */
54 
55 typedef struct {
56   struct jpeg_c_prep_controller pub; /* public fields */
57 
58   /* Downsampling input buffer.  This buffer holds color-converted data
59    * until we have enough to do a downsample step.
60    */
61   JSAMPARRAY color_buf[MAX_COMPONENTS];
62 
63   JDIMENSION rows_to_go;        /* counts rows remaining in source image */
64   int next_buf_row;             /* index of next row to store in color_buf */
65 
66 #ifdef CONTEXT_ROWS_SUPPORTED   /* only needed for context case */
67   int this_row_group;           /* starting row index of group to process */
68   int next_buf_stop;            /* downsample when we reach this index */
69 #endif
70 } my_prep_controller;
71 
72 typedef my_prep_controller * my_prep_ptr;
73 
74 
75 /*
76  * Initialize for a processing pass.
77  */
78 
79 METHODDEF(void)
start_pass_prep(j_compress_ptr cinfo,J_BUF_MODE pass_mode)80 start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
81 {
82   my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
83 
84   if (pass_mode != JBUF_PASS_THRU)
85     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
86 
87   /* Initialize total-height counter for detecting bottom of image */
88   prep->rows_to_go = cinfo->image_height;
89   /* Mark the conversion buffer empty */
90   prep->next_buf_row = 0;
91 #ifdef CONTEXT_ROWS_SUPPORTED
92   /* Preset additional state variables for context mode.
93    * These aren't used in non-context mode, so we needn't test which mode.
94    */
95   prep->this_row_group = 0;
96   /* Set next_buf_stop to stop after two row groups have been read in. */
97   prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
98 #endif
99 }
100 
101 
102 /*
103  * Expand an image vertically from height input_rows to height output_rows,
104  * by duplicating the bottom row.
105  */
106 
107 LOCAL(void)
expand_bottom_edge(JSAMPARRAY image_data,JDIMENSION num_cols,int input_rows,int output_rows)108 expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols,
109                     int input_rows, int output_rows)
110 {
111   register int row;
112 
113   for (row = input_rows; row < output_rows; row++) {
114     jcopy_sample_rows(image_data, input_rows-1, image_data, row,
115                       1, num_cols);
116   }
117 }
118 
119 
120 /*
121  * Process some data in the simple no-context case.
122  *
123  * Preprocessor output data is counted in "row groups".  A row group
124  * is defined to be v_samp_factor sample rows of each component.
125  * Downsampling will produce this much data from each max_v_samp_factor
126  * input rows.
127  */
128 
129 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)130 pre_process_data (j_compress_ptr cinfo,
131                   JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
132                   JDIMENSION in_rows_avail,
133                   JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
134                   JDIMENSION out_row_groups_avail)
135 {
136   my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
137   int numrows, ci;
138   JDIMENSION inrows;
139   jpeg_component_info * compptr;
140 
141   while (*in_row_ctr < in_rows_avail &&
142          *out_row_group_ctr < out_row_groups_avail) {
143     /* Do color conversion to fill the conversion buffer. */
144     inrows = in_rows_avail - *in_row_ctr;
145     numrows = cinfo->max_v_samp_factor - prep->next_buf_row;
146     numrows = (int) MIN((JDIMENSION) numrows, inrows);
147     (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
148                                        prep->color_buf,
149                                        (JDIMENSION) prep->next_buf_row,
150                                        numrows);
151     *in_row_ctr += numrows;
152     prep->next_buf_row += numrows;
153     prep->rows_to_go -= numrows;
154     /* If at bottom of image, pad to fill the conversion buffer. */
155     if (prep->rows_to_go == 0 &&
156         prep->next_buf_row < cinfo->max_v_samp_factor) {
157       for (ci = 0; ci < cinfo->num_components; ci++) {
158         expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
159                            prep->next_buf_row, cinfo->max_v_samp_factor);
160       }
161       prep->next_buf_row = cinfo->max_v_samp_factor;
162     }
163     /* If we've filled the conversion buffer, empty it. */
164     if (prep->next_buf_row == cinfo->max_v_samp_factor) {
165       (*cinfo->downsample->downsample) (cinfo,
166                                         prep->color_buf, (JDIMENSION) 0,
167                                         output_buf, *out_row_group_ctr);
168       prep->next_buf_row = 0;
169       (*out_row_group_ctr)++;
170     }
171     /* If at bottom of image, pad the output to a full iMCU height.
172      * Note we assume the caller is providing a one-iMCU-height output buffer!
173      */
174     if (prep->rows_to_go == 0 &&
175         *out_row_group_ctr < out_row_groups_avail) {
176       for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
177            ci++, compptr++) {
178         expand_bottom_edge(output_buf[ci],
179                            compptr->width_in_blocks * DCTSIZE,
180                            (int) (*out_row_group_ctr * compptr->v_samp_factor),
181                            (int) (out_row_groups_avail * compptr->v_samp_factor));
182       }
183       *out_row_group_ctr = out_row_groups_avail;
184       break;                    /* can exit outer loop without test */
185     }
186   }
187 }
188 
189 
190 #ifdef CONTEXT_ROWS_SUPPORTED
191 
192 /*
193  * Process some data in the context case.
194  */
195 
196 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)197 pre_process_context (j_compress_ptr cinfo,
198                      JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
199                      JDIMENSION in_rows_avail,
200                      JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
201                      JDIMENSION out_row_groups_avail)
202 {
203   my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
204   int numrows, ci;
205   int buf_height = cinfo->max_v_samp_factor * 3;
206   JDIMENSION inrows;
207 
208   while (*out_row_group_ctr < out_row_groups_avail) {
209     if (*in_row_ctr < in_rows_avail) {
210       /* Do color conversion to fill the conversion buffer. */
211       inrows = in_rows_avail - *in_row_ctr;
212       numrows = prep->next_buf_stop - prep->next_buf_row;
213       numrows = (int) MIN((JDIMENSION) numrows, inrows);
214       (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
215                                          prep->color_buf,
216                                          (JDIMENSION) prep->next_buf_row,
217                                          numrows);
218       /* Pad at top of image, if first time through */
219       if (prep->rows_to_go == cinfo->image_height) {
220         for (ci = 0; ci < cinfo->num_components; ci++) {
221           int row;
222           for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
223             jcopy_sample_rows(prep->color_buf[ci], 0,
224                               prep->color_buf[ci], -row,
225                               1, cinfo->image_width);
226           }
227         }
228       }
229       *in_row_ctr += numrows;
230       prep->next_buf_row += numrows;
231       prep->rows_to_go -= numrows;
232     } else {
233       /* Return for more data, unless we are at the bottom of the image. */
234       if (prep->rows_to_go != 0)
235         break;
236       /* When at bottom of image, pad to fill the conversion buffer. */
237       if (prep->next_buf_row < prep->next_buf_stop) {
238         for (ci = 0; ci < cinfo->num_components; ci++) {
239           expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
240                              prep->next_buf_row, prep->next_buf_stop);
241         }
242         prep->next_buf_row = prep->next_buf_stop;
243       }
244     }
245     /* If we've gotten enough data, downsample a row group. */
246     if (prep->next_buf_row == prep->next_buf_stop) {
247       (*cinfo->downsample->downsample) (cinfo,
248                                         prep->color_buf,
249                                         (JDIMENSION) prep->this_row_group,
250                                         output_buf, *out_row_group_ctr);
251       (*out_row_group_ctr)++;
252       /* Advance pointers with wraparound as necessary. */
253       prep->this_row_group += cinfo->max_v_samp_factor;
254       if (prep->this_row_group >= buf_height)
255         prep->this_row_group = 0;
256       if (prep->next_buf_row >= buf_height)
257         prep->next_buf_row = 0;
258       prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
259     }
260   }
261 }
262 
263 
264 /*
265  * Create the wrapped-around downsampling input buffer needed for context mode.
266  */
267 
268 LOCAL(void)
create_context_buffer(j_compress_ptr cinfo)269 create_context_buffer (j_compress_ptr cinfo)
270 {
271   my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
272   int rgroup_height = cinfo->max_v_samp_factor;
273   int ci, i;
274   jpeg_component_info * compptr;
275   JSAMPARRAY true_buffer, fake_buffer;
276 
277   /* Grab enough space for fake row pointers for all the components;
278    * we need five row groups' worth of pointers for each component.
279    */
280   fake_buffer = (JSAMPARRAY)
281     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
282                                 (cinfo->num_components * 5 * rgroup_height) *
283                                 sizeof(JSAMPROW));
284 
285   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
286        ci++, compptr++) {
287     /* Allocate the actual buffer space (3 row groups) for this component.
288      * We make the buffer wide enough to allow the downsampler to edge-expand
289      * horizontally within the buffer, if it so chooses.
290      */
291     true_buffer = (*cinfo->mem->alloc_sarray)
292       ((j_common_ptr) cinfo, JPOOL_IMAGE,
293        (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
294                       cinfo->max_h_samp_factor) / compptr->h_samp_factor),
295        (JDIMENSION) (3 * rgroup_height));
296     /* Copy true buffer row pointers into the middle of the fake row array */
297     MEMCOPY(fake_buffer + rgroup_height, true_buffer,
298             3 * rgroup_height * sizeof(JSAMPROW));
299     /* Fill in the above and below wraparound pointers */
300     for (i = 0; i < rgroup_height; i++) {
301       fake_buffer[i] = true_buffer[2 * rgroup_height + i];
302       fake_buffer[4 * rgroup_height + i] = true_buffer[i];
303     }
304     prep->color_buf[ci] = fake_buffer + rgroup_height;
305     fake_buffer += 5 * rgroup_height; /* point to space for next component */
306   }
307 }
308 
309 #endif /* CONTEXT_ROWS_SUPPORTED */
310 
311 
312 /*
313  * Initialize preprocessing controller.
314  */
315 
316 GLOBAL(void)
jinit_c_prep_controller(j_compress_ptr cinfo,boolean need_full_buffer)317 jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
318 {
319   my_prep_ptr prep;
320   int ci;
321   jpeg_component_info * compptr;
322 
323   if (need_full_buffer)         /* safety check */
324     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
325 
326   prep = (my_prep_ptr)
327     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
328                                 sizeof(my_prep_controller));
329   cinfo->prep = (struct jpeg_c_prep_controller *) prep;
330   prep->pub.start_pass = start_pass_prep;
331 
332   /* Allocate the color conversion buffer.
333    * We make the buffer wide enough to allow the downsampler to edge-expand
334    * horizontally within the buffer, if it so chooses.
335    */
336   if (cinfo->downsample->need_context_rows) {
337     /* Set up to provide context rows */
338 #ifdef CONTEXT_ROWS_SUPPORTED
339     prep->pub.pre_process_data = pre_process_context;
340     create_context_buffer(cinfo);
341 #else
342     ERREXIT(cinfo, JERR_NOT_COMPILED);
343 #endif
344   } else {
345     /* No context, just make it tall enough for one row group */
346     prep->pub.pre_process_data = pre_process_data;
347     for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
348          ci++, compptr++) {
349       prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
350         ((j_common_ptr) cinfo, JPOOL_IMAGE,
351          (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
352                         cinfo->max_h_samp_factor) / compptr->h_samp_factor),
353          (JDIMENSION) cinfo->max_v_samp_factor);
354     }
355   }
356 }
357