libs/jpeg/jcprepct.c

   1 /*
   2  * jcprepct.c
   3  *
   4  * Copyright (C) 1994-1996, Thomas G. Lane.
   5  * Modified 2003-2020 by Guido Vollbeding.
   6  * This file is part of the Independent JPEG Group's software.
   7  * For conditions of distribution and use, see the accompanying README file.
   8  *
   9  * This file contains the compression preprocessing controller.
  10  * This controller manages the color conversion, downsampling,
  11  * and edge expansion steps.
  12  *
  13  * Most of the complexity here is associated with buffering input rows
  14  * as required by the downsampler.  See the comments at the head of
  15  * jcsample.c for the downsampler's needs.
  16  */
  17
  18 #define JPEG_INTERNALS
  19 #include "jinclude.h"
  20 #include "jpeglib.h"
  21
  22
  23 /* At present, jcsample.c can request context rows only for smoothing.
  24  * In the future, we might also need context rows for CCIR601 sampling
  25  * or other more-complex downsampling procedures.  The code to support
  26  * context rows should be compiled only if needed.
  27  */
  28 #ifdef INPUT_SMOOTHING_SUPPORTED
  29 #define CONTEXT_ROWS_SUPPORTED
  30 #endif
  31
  32
  33 /*
  34  * For the simple (no-context-row) case, we just need to buffer one
  35  * row group's worth of pixels for the downsampling step.  At the bottom of
  36  * the image, we pad to a full row group by replicating the last pixel row.
  37  * The downsampler's last output row is then replicated if needed to pad
  38  * out to a full iMCU row.
  39  *
  40  * When providing context rows, we must buffer three row groups' worth of
  41  * pixels.  Three row groups are physically allocated, but the row pointer
  42  * arrays are made five row groups high, with the extra pointers above and
  43  * below "wrapping around" to point to the last and first real row groups.
  44  * This allows the downsampler to access the proper context rows.
  45  * At the top and bottom of the image, we create dummy context rows by
  46  * copying the first or last real pixel row.  This copying could be avoided
  47  * by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
  48  * trouble on the compression side.
  49  */
  50
  51
  52 /* Private buffer controller object */
  53
  54 typedef struct {
  55   struct jpeg_c_prep_controller pub; /* public fields */
  56
  57   /* Downsampling input buffer.  This buffer holds color-converted data
  58    * until we have enough to do a downsample step.
  59    */
  60   JSAMPARRAY color_buf[MAX_COMPONENTS];
  61
  62   JDIMENSION rows_to_go;        /* counts rows remaining in source image */
  63   int next_buf_row;             /* index of next row to store in color_buf */
  64
  65 #ifdef CONTEXT_ROWS_SUPPORTED   /* only needed for context case */
  66   int this_row_group;           /* starting row index of group to process */
  67   int next_buf_stop;            /* downsample when we reach this index */
  68 #endif
  69 } my_prep_controller;
  70
  71 typedef my_prep_controller * my_prep_ptr;
  72
  73
  74 /*
  75  * Initialize for a processing pass.
  76  */
  77
  78 METHODDEF(void)
  79 start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
  80 {
  81   my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
  82
  83   if (pass_mode != JBUF_PASS_THRU)
  84     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
  85
  86   /* Initialize total-height counter for detecting bottom of image */
  87   prep->rows_to_go = cinfo->image_height;
  88   /* Mark the conversion buffer empty */
  89   prep->next_buf_row = 0;
  90 #ifdef CONTEXT_ROWS_SUPPORTED
  91   /* Preset additional state variables for context mode.
  92    * These aren't used in non-context mode, so we needn't test which mode.
  93    */
  94   prep->this_row_group = 0;
  95   /* Set next_buf_stop to stop after two row groups have been read in. */
  96   prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
  97 #endif
  98 }
  99
 100
 101 /*
 102  * Expand an image vertically from height input_rows to height output_rows,
 103  * by duplicating the bottom row.
 104  */
 105
 106 LOCAL(void)
 107 expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols,
 108                     int input_rows, int output_rows)
 109 {
 110   register int row;
 111
 112   for (row = input_rows; row < output_rows; row++) {
 113     jcopy_sample_rows(image_data + input_rows - 1,
 114                       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)
 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         numrows = (compptr->v_samp_factor * compptr->DCT_v_scaled_size) /
 179                   cinfo->min_DCT_v_scaled_size;
 180         expand_bottom_edge(output_buf[ci],
 181                            compptr->width_in_blocks * compptr->DCT_h_scaled_size,
 182                            (int) (*out_row_group_ctr * numrows),
 183                            (int) (out_row_groups_avail * numrows));
 184       }
 185       *out_row_group_ctr = out_row_groups_avail;
 186       break;                    /* can exit outer loop without test */
 187     }
 188   }
 189 }
 190
 191
 192 #ifdef CONTEXT_ROWS_SUPPORTED
 193
 194 /*
 195  * Process some data in the context case.
 196  */
 197
 198 METHODDEF(void)
 199 pre_process_context (j_compress_ptr cinfo,
 200                      JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
 201                      JDIMENSION in_rows_avail,
 202                      JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
 203                      JDIMENSION out_row_groups_avail)
 204 {
 205   my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
 206   int numrows, ci;
 207   int buf_height = cinfo->max_v_samp_factor * 3;
 208   JDIMENSION inrows;
 209
 210   while (*out_row_group_ctr < out_row_groups_avail) {
 211     if (*in_row_ctr < in_rows_avail) {
 212       /* Do color conversion to fill the conversion buffer. */
 213       inrows = in_rows_avail - *in_row_ctr;
 214       numrows = prep->next_buf_stop - prep->next_buf_row;
 215       numrows = (int) MIN((JDIMENSION) numrows, inrows);
 216       (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
 217                                          prep->color_buf,
 218                                          (JDIMENSION) prep->next_buf_row,
 219                                          numrows);
 220       /* Pad at top of image, if first time through */
 221       if (prep->rows_to_go == cinfo->image_height) {
 222         for (ci = 0; ci < cinfo->num_components; ci++) {
 223           int row;
 224           for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
 225             jcopy_sample_rows(prep->color_buf[ci],
 226                               prep->color_buf[ci] - row,
 227                               1, cinfo->image_width);
 228           }
 229         }
 230       }
 231       *in_row_ctr += numrows;
 232       prep->next_buf_row += numrows;
 233       prep->rows_to_go -= numrows;
 234     } else {
 235       /* Return for more data, unless we are at the bottom of the image. */
 236       if (prep->rows_to_go != 0)
 237         break;
 238       /* When at bottom of image, pad to fill the conversion buffer. */
 239       if (prep->next_buf_row < prep->next_buf_stop) {
 240         for (ci = 0; ci < cinfo->num_components; ci++) {
 241           expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
 242                              prep->next_buf_row, prep->next_buf_stop);
 243         }
 244         prep->next_buf_row = prep->next_buf_stop;
 245       }
 246     }
 247     /* If we've gotten enough data, downsample a row group. */
 248     if (prep->next_buf_row == prep->next_buf_stop) {
 249       (*cinfo->downsample->downsample) (cinfo,
 250                                         prep->color_buf,
 251                                         (JDIMENSION) prep->this_row_group,
 252                                         output_buf, *out_row_group_ctr);
 253       (*out_row_group_ctr)++;
 254       /* Advance pointers with wraparound as necessary. */
 255       prep->this_row_group += cinfo->max_v_samp_factor;
 256       if (prep->this_row_group >= buf_height)
 257         prep->this_row_group = 0;
 258       if (prep->next_buf_row >= buf_height)
 259         prep->next_buf_row = 0;
 260       prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
 261     }
 262   }
 263 }
 264
 265
 266 /*
 267  * Create the wrapped-around downsampling input buffer needed for context mode.
 268  */
 269
 270 LOCAL(void)
 271 create_context_buffer (j_compress_ptr cinfo)
 272 {
 273   my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
 274   int rgroup_height = cinfo->max_v_samp_factor;
 275   int ci, i;
 276   jpeg_component_info * compptr;
 277   JSAMPARRAY true_buffer, fake_buffer;
 278
 279   /* Grab enough space for fake row pointers for all the components;
 280    * we need five row groups' worth of pointers for each component.
 281    */
 282   fake_buffer = (JSAMPARRAY) (*cinfo->mem->alloc_small)
 283     ((j_common_ptr) cinfo, JPOOL_IMAGE,
 284      (cinfo->num_components * 5 * rgroup_height) * SIZEOF(JSAMPROW));
 285
 286   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 287        ci++, compptr++) {
 288     /* Allocate the actual buffer space (3 row groups) for this component.
 289      * We make the buffer wide enough to allow the downsampler to edge-expand
 290      * horizontally within the buffer, if it so chooses.
 291      */
 292     true_buffer = (*cinfo->mem->alloc_sarray)
 293       ((j_common_ptr) cinfo, JPOOL_IMAGE,
 294        (JDIMENSION) (((long) compptr->width_in_blocks *
 295                       cinfo->min_DCT_h_scaled_size *
 296                       cinfo->max_h_samp_factor) / compptr->h_samp_factor),
 297        (JDIMENSION) (3 * rgroup_height));
 298     /* Copy true buffer row pointers into the middle of the fake row array */
 299     MEMCOPY(fake_buffer + rgroup_height, true_buffer,
 300             3 * rgroup_height * SIZEOF(JSAMPROW));
 301     /* Fill in the above and below wraparound pointers */
 302     for (i = 0; i < rgroup_height; i++) {
 303       fake_buffer[i] = true_buffer[2 * rgroup_height + i];
 304       fake_buffer[4 * rgroup_height + i] = true_buffer[i];
 305     }
 306     prep->color_buf[ci] = fake_buffer + rgroup_height;
 307     fake_buffer += 5 * rgroup_height; /* point to space for next component */
 308   }
 309 }
 310
 311 #endif /* CONTEXT_ROWS_SUPPORTED */
 312
 313
 314 /*
 315  * Initialize preprocessing controller.
 316  */
 317
 318 GLOBAL(void)
 319 jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
 320 {
 321   my_prep_ptr prep;
 322   int ci;
 323   jpeg_component_info * compptr;
 324
 325   if (need_full_buffer)         /* safety check */
 326     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
 327
 328   prep = (my_prep_ptr) (*cinfo->mem->alloc_small)
 329     ((j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF(my_prep_controller));
 330   cinfo->prep = &prep->pub;
 331   prep->pub.start_pass = start_pass_prep;
 332
 333   /* Allocate the color conversion buffer.
 334    * We make the buffer wide enough to allow the downsampler to edge-expand
 335    * horizontally within the buffer, if it so chooses.
 336    */
 337   if (cinfo->downsample->need_context_rows) {
 338     /* Set up to provide context rows */
 339 #ifdef CONTEXT_ROWS_SUPPORTED
 340     prep->pub.pre_process_data = pre_process_context;
 341     create_context_buffer(cinfo);
 342 #else
 343     ERREXIT(cinfo, JERR_NOT_COMPILED);
 344 #endif
 345   } else {
 346     /* No context, just make it tall enough for one row group */
 347     prep->pub.pre_process_data = pre_process_data;
 348     for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 349          ci++, compptr++) {
 350       prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
 351         ((j_common_ptr) cinfo, JPOOL_IMAGE,
 352          (JDIMENSION) (((long) compptr->width_in_blocks *
 353                         cinfo->min_DCT_h_scaled_size *
 354                         cinfo->max_h_samp_factor) / compptr->h_samp_factor),
 355          (JDIMENSION) cinfo->max_v_samp_factor);
 356     }
 357   }
 358 }