src/jpeg/jcprepct.c

   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)
  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)
 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)
 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)
 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)
 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)
 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 }