media/libjpeg/jcprepct.c

   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  * libjpeg-turbo Modifications:
   7  * Copyright (C) 2022, D. R. Commander.
   8  * For conditions of distribution and use, see the accompanying README.ijg
   9  * file.
  10  *
  11  * This file contains the compression preprocessing controller.
  12  * This controller manages the color conversion, downsampling,
  13  * and edge expansion steps.
  14  *
  15  * Most of the complexity here is associated with buffering input rows
  16  * as required by the downsampler.  See the comments at the head of
  17  * jcsample.c for the downsampler's needs.
  18  */
  19
  20 #define JPEG_INTERNALS
  21 #include "jinclude.h"
  22 #include "jpeglib.h"
  23
  24
  25 /* At present, jcsample.c can request context rows only for smoothing.
  26  * In the future, we might also need context rows for CCIR601 sampling
  27  * or other more-complex downsampling procedures.  The code to support
  28  * context rows should be compiled only if needed.
  29  */
  30 #ifdef INPUT_SMOOTHING_SUPPORTED
  31 #define CONTEXT_ROWS_SUPPORTED
  32 #endif
  33
  34
  35 /*
  36  * For the simple (no-context-row) case, we just need to buffer one
  37  * row group's worth of pixels for the downsampling step.  At the bottom of
  38  * the image, we pad to a full row group by replicating the last pixel row.
  39  * The downsampler's last output row is then replicated if needed to pad
  40  * out to a full iMCU row.
  41  *
  42  * When providing context rows, we must buffer three row groups' worth of
  43  * pixels.  Three row groups are physically allocated, but the row pointer
  44  * arrays are made five row groups high, with the extra pointers above and
  45  * below "wrapping around" to point to the last and first real row groups.
  46  * This allows the downsampler to access the proper context rows.
  47  * At the top and bottom of the image, we create dummy context rows by
  48  * copying the first or last real pixel row.  This copying could be avoided
  49  * by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
  50  * trouble on the compression side.
  51  */
  52
  53
  54 /* Private buffer controller object */
  55
  56 typedef struct {
  57   struct jpeg_c_prep_controller pub; /* public fields */
  58
  59   /* Downsampling input buffer.  This buffer holds color-converted data
  60    * until we have enough to do a downsample step.
  61    */
  62   JSAMPARRAY color_buf[MAX_COMPONENTS];
  63
  64   JDIMENSION rows_to_go;        /* counts rows remaining in source image */
  65   int next_buf_row;             /* index of next row to store in color_buf */
  66
  67 #ifdef CONTEXT_ROWS_SUPPORTED   /* only needed for context case */
  68   int this_row_group;           /* starting row index of group to process */
  69   int next_buf_stop;            /* downsample when we reach this index */
  70 #endif
  71 } my_prep_controller;
  72
  73 typedef my_prep_controller *my_prep_ptr;
  74
  75
  76 /*
  77  * Initialize for a processing pass.
  78  */
  79
  80 METHODDEF(void)
  81 start_pass_prep(j_compress_ptr cinfo, J_BUF_MODE pass_mode)
  82 {
  83   my_prep_ptr prep = (my_prep_ptr)cinfo->prep;
  84
  85   if (pass_mode != JBUF_PASS_THRU)
  86     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
  87
  88   /* Initialize total-height counter for detecting bottom of image */
  89   prep->rows_to_go = cinfo->image_height;
  90   /* Mark the conversion buffer empty */
  91   prep->next_buf_row = 0;
  92 #ifdef CONTEXT_ROWS_SUPPORTED
  93   /* Preset additional state variables for context mode.
  94    * These aren't used in non-context mode, so we needn't test which mode.
  95    */
  96   prep->this_row_group = 0;
  97   /* Set next_buf_stop to stop after two row groups have been read in. */
  98   prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
  99 #endif
 100 }
 101
 102
 103 /*
 104  * Expand an image vertically from height input_rows to height output_rows,
 105  * by duplicating the bottom row.
 106  */
 107
 108 LOCAL(void)
 109 expand_bottom_edge(JSAMPARRAY image_data, JDIMENSION num_cols, int input_rows,
 110                    int output_rows)
 111 {
 112   register int row;
 113
 114   for (row = input_rows; row < output_rows; row++) {
 115     jcopy_sample_rows(image_data, input_rows - 1, image_data, row, 1,
 116                       num_cols);
 117   }
 118 }
 119
 120
 121 /*
 122  * Process some data in the simple no-context case.
 123  *
 124  * Preprocessor output data is counted in "row groups".  A row group
 125  * is defined to be v_samp_factor sample rows of each component.
 126  * Downsampling will produce this much data from each max_v_samp_factor
 127  * input rows.
 128  */
 129
 130 METHODDEF(void)
 131 pre_process_data(j_compress_ptr cinfo, JSAMPARRAY input_buf,
 132                  JDIMENSION *in_row_ctr, 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 && *out_row_group_ctr < out_row_groups_avail) {
 175       for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 176            ci++, compptr++) {
 177         expand_bottom_edge(output_buf[ci], 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)
 195 pre_process_context(j_compress_ptr cinfo, JSAMPARRAY input_buf,
 196                     JDIMENSION *in_row_ctr, JDIMENSION in_rows_avail,
 197                     JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
 198                     JDIMENSION out_row_groups_avail)
 199 {
 200   my_prep_ptr prep = (my_prep_ptr)cinfo->prep;
 201   int numrows, ci;
 202   int buf_height = cinfo->max_v_samp_factor * 3;
 203   JDIMENSION inrows;
 204
 205   while (*out_row_group_ctr < out_row_groups_avail) {
 206     if (*in_row_ctr < in_rows_avail) {
 207       /* Do color conversion to fill the conversion buffer. */
 208       inrows = in_rows_avail - *in_row_ctr;
 209       numrows = prep->next_buf_stop - prep->next_buf_row;
 210       numrows = (int)MIN((JDIMENSION)numrows, inrows);
 211       (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
 212                                          prep->color_buf,
 213                                          (JDIMENSION)prep->next_buf_row,
 214                                          numrows);
 215       /* Pad at top of image, if first time through */
 216       if (prep->rows_to_go == cinfo->image_height) {
 217         for (ci = 0; ci < cinfo->num_components; ci++) {
 218           int row;
 219           for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
 220             jcopy_sample_rows(prep->color_buf[ci], 0, prep->color_buf[ci],
 221                               -row, 1, cinfo->image_width);
 222           }
 223         }
 224       }
 225       *in_row_ctr += numrows;
 226       prep->next_buf_row += numrows;
 227       prep->rows_to_go -= numrows;
 228     } else {
 229       /* Return for more data, unless we are at the bottom of the image. */
 230       if (prep->rows_to_go != 0)
 231         break;
 232       /* When at bottom of image, pad to fill the conversion buffer. */
 233       if (prep->next_buf_row < prep->next_buf_stop) {
 234         for (ci = 0; ci < cinfo->num_components; ci++) {
 235           expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
 236                              prep->next_buf_row, prep->next_buf_stop);
 237         }
 238         prep->next_buf_row = prep->next_buf_stop;
 239       }
 240     }
 241     /* If we've gotten enough data, downsample a row group. */
 242     if (prep->next_buf_row == prep->next_buf_stop) {
 243       (*cinfo->downsample->downsample) (cinfo, prep->color_buf,
 244                                         (JDIMENSION)prep->this_row_group,
 245                                         output_buf, *out_row_group_ctr);
 246       (*out_row_group_ctr)++;
 247       /* Advance pointers with wraparound as necessary. */
 248       prep->this_row_group += cinfo->max_v_samp_factor;
 249       if (prep->this_row_group >= buf_height)
 250         prep->this_row_group = 0;
 251       if (prep->next_buf_row >= buf_height)
 252         prep->next_buf_row = 0;
 253       prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
 254     }
 255   }
 256 }
 257
 258
 259 /*
 260  * Create the wrapped-around downsampling input buffer needed for context mode.
 261  */
 262
 263 LOCAL(void)
 264 create_context_buffer(j_compress_ptr cinfo)
 265 {
 266   my_prep_ptr prep = (my_prep_ptr)cinfo->prep;
 267   int rgroup_height = cinfo->max_v_samp_factor;
 268   int ci, i;
 269   jpeg_component_info *compptr;
 270   JSAMPARRAY true_buffer, fake_buffer;
 271
 272   /* Grab enough space for fake row pointers for all the components;
 273    * we need five row groups' worth of pointers for each component.
 274    */
 275   fake_buffer = (JSAMPARRAY)
 276     (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
 277                                 (cinfo->num_components * 5 * rgroup_height) *
 278                                 sizeof(JSAMPROW));
 279
 280   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 281        ci++, compptr++) {
 282     /* Allocate the actual buffer space (3 row groups) for this component.
 283      * We make the buffer wide enough to allow the downsampler to edge-expand
 284      * horizontally within the buffer, if it so chooses.
 285      */
 286     true_buffer = (*cinfo->mem->alloc_sarray)
 287       ((j_common_ptr)cinfo, JPOOL_IMAGE,
 288        (JDIMENSION)(((long)compptr->width_in_blocks * DCTSIZE *
 289                      cinfo->max_h_samp_factor) / compptr->h_samp_factor),
 290        (JDIMENSION)(3 * rgroup_height));
 291     /* Copy true buffer row pointers into the middle of the fake row array */
 292     memcpy(fake_buffer + rgroup_height, true_buffer,
 293            3 * rgroup_height * sizeof(JSAMPROW));
 294     /* Fill in the above and below wraparound pointers */
 295     for (i = 0; i < rgroup_height; i++) {
 296       fake_buffer[i] = true_buffer[2 * rgroup_height + i];
 297       fake_buffer[4 * rgroup_height + i] = true_buffer[i];
 298     }
 299     prep->color_buf[ci] = fake_buffer + rgroup_height;
 300     fake_buffer += 5 * rgroup_height; /* point to space for next component */
 301   }
 302 }
 303
 304 #endif /* CONTEXT_ROWS_SUPPORTED */
 305
 306
 307 /*
 308  * Initialize preprocessing controller.
 309  */
 310
 311 GLOBAL(void)
 312 jinit_c_prep_controller(j_compress_ptr cinfo, boolean need_full_buffer)
 313 {
 314   my_prep_ptr prep;
 315   int ci;
 316   jpeg_component_info *compptr;
 317
 318   if (need_full_buffer)         /* safety check */
 319     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
 320
 321   prep = (my_prep_ptr)
 322     (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
 323                                 sizeof(my_prep_controller));
 324   cinfo->prep = (struct jpeg_c_prep_controller *)prep;
 325   prep->pub.start_pass = start_pass_prep;
 326
 327   /* Allocate the color conversion buffer.
 328    * We make the buffer wide enough to allow the downsampler to edge-expand
 329    * horizontally within the buffer, if it so chooses.
 330    */
 331   if (cinfo->downsample->need_context_rows) {
 332     /* Set up to provide context rows */
 333 #ifdef CONTEXT_ROWS_SUPPORTED
 334     prep->pub.pre_process_data = pre_process_context;
 335     create_context_buffer(cinfo);
 336 #else
 337     ERREXIT(cinfo, JERR_NOT_COMPILED);
 338 #endif
 339   } else {
 340     /* No context, just make it tall enough for one row group */
 341     prep->pub.pre_process_data = pre_process_data;
 342     for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 343          ci++, compptr++) {
 344       prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
 345         ((j_common_ptr)cinfo, JPOOL_IMAGE,
 346          (JDIMENSION)(((long)compptr->width_in_blocks * DCTSIZE *
 347                        cinfo->max_h_samp_factor) / compptr->h_samp_factor),
 348          (JDIMENSION)cinfo->max_v_samp_factor);
 349     }
 350   }
 351 }