images/io-libjpeg.c

   1 /*
   2  *      Image Library -- libjpeg
   3  *
   4  *      (c) 2006 Pavel Charvat <pchar@ucw.cz>
   5  *
   6  *      This software may be freely distributed and used according to the terms
   7  *      of the GNU Lesser General Public License.
   8  */
   9
  10 #undef LOCAL_DEBUG
  11
  12 #include "lib/lib.h"
  13 #include "lib/mempool.h"
  14 #include "lib/fastbuf.h"
  15 #include "images/images.h"
  16 #include "images/error.h"
  17 #include "images/color.h"
  18 #include "images/io-main.h"
  19
  20 #include <stdio.h>
  21 #include <sys/types.h>
  22 #include <jpeglib.h>
  23 #include <jerror.h>
  24 #include <setjmp.h>
  25
  26 struct libjpeg_err {
  27   struct jpeg_error_mgr pub;
  28   jmp_buf setjmp_buf;
  29   struct image_io *io;
  30 };
  31
  32 struct libjpeg_read_internals {
  33   struct jpeg_decompress_struct cinfo;
  34   struct jpeg_source_mgr src;
  35   struct libjpeg_err err;
  36   struct fastbuf *fastbuf;
  37   byte *fastbuf_pos;
  38 };
  39
  40 struct libjpeg_write_internals {
  41   struct jpeg_compress_struct cinfo;
  42   struct jpeg_destination_mgr dest;
  43   struct libjpeg_err err;
  44   struct fastbuf *fastbuf;
  45   byte *fastbuf_pos;
  46 };
  47
  48 static void NONRET
  49 libjpeg_read_error_exit(j_common_ptr cinfo)
  50 {
  51   DBG("libjpeg_error_exit()");
  52   struct libjpeg_err *e = (struct libjpeg_err *)cinfo->err;
  53   byte buf[JMSG_LENGTH_MAX];
  54   e->pub.format_message(cinfo, buf);
  55   IMAGE_ERROR(e->io->context, IMAGE_ERROR_READ_FAILED, "libjpeg: %s", buf);
  56   longjmp(e->setjmp_buf, 1);
  57 }
  58
  59 static void NONRET
  60 libjpeg_write_error_exit(j_common_ptr cinfo)
  61 {
  62   DBG("libjpeg_error_exit()");
  63   struct libjpeg_err *e = (struct libjpeg_err *)cinfo->err;
  64   byte buf[JMSG_LENGTH_MAX];
  65   e->pub.format_message(cinfo, buf);
  66   IMAGE_ERROR(e->io->context, IMAGE_ERROR_WRITE_FAILED, "libjpeg: %s", buf);
  67   longjmp(e->setjmp_buf, 1);
  68 }
  69
  70 static void
  71 libjpeg_emit_message(j_common_ptr cinfo UNUSED, int msg_level UNUSED)
  72 {
  73 #ifdef LOCAL_DEBUG
  74   byte buf[JMSG_LENGTH_MAX];
  75   cinfo->err->format_message(cinfo, buf);
  76   DBG("libjpeg_emit_message(): [%d] %s", msg_level, buf);
  77 #endif
  78 #if 0
  79   // Terminate on warning?
  80   if (unlikely(msg_level == -1))
  81     {
  82       struct libjpeg_err *e = (struct libjpeg_err *)cinfo->err;
  83       byte buf[JMSG_LENGTH_MAX];
  84       cinfo->err->format_message(cinfo, buf);
  85       IMAGE_ERROR(e->io->context, 0, "libjpeg: %s", buf);
  86       longjmp(e->setjmp_buf, 1);
  87     }
  88 #endif
  89 }
  90
  91 static inline uns
  92 libjpeg_fastbuf_read_prepare(struct libjpeg_read_internals *i)
  93 {
  94   DBG("libjpeg_fb_read_prepare()");
  95   byte *start;
  96   uns len = bdirect_read_prepare(i->fastbuf, &start);
  97   if (!len)
  98     {
  99       // XXX: maybe only generate a warning and return EOI markers to recover from such errors (also in skip_input_data)
 100       IMAGE_ERROR(i->err.io->context, IMAGE_ERROR_READ_FAILED, "Incomplete JPEG file");
 101       longjmp(i->err.setjmp_buf, 1);
 102     }
 103   i->fastbuf_pos = start + len;
 104   i->src.next_input_byte = start;
 105   i->src.bytes_in_buffer = len;
 106   return len;
 107 }
 108
 109 static inline void
 110 libjpeg_fastbuf_read_commit(struct libjpeg_read_internals *i)
 111 {
 112   DBG("libjpeg_fb_read_commit()");
 113   bdirect_read_commit(i->fastbuf, i->fastbuf_pos);
 114 }
 115
 116 static void
 117 libjpeg_init_source(j_decompress_ptr cinfo)
 118 {
 119   DBG("libjpeg_init_source()");
 120   libjpeg_fastbuf_read_prepare((struct libjpeg_read_internals *)cinfo);
 121 }
 122
 123 static void
 124 libjpeg_term_source(j_decompress_ptr cinfo UNUSED)
 125 {
 126   DBG("libjpeg_term_source()");
 127   //libjpeg_fastbuf_read_commit((struct libjpeg_read_internals *)cinfo);
 128 }
 129
 130 static boolean
 131 libjpeg_fill_input_buffer(j_decompress_ptr cinfo)
 132 {
 133   DBG("libjpeg_fill_input_buffer()");
 134   struct libjpeg_read_internals *i = (struct libjpeg_read_internals *)cinfo;
 135   libjpeg_fastbuf_read_commit(i);
 136   return 1;
 137 }
 138
 139 static void
 140 libjpeg_skip_input_data(j_decompress_ptr cinfo, long num_bytes)
 141 {
 142   DBG("libjpeg_skip_input_data(num_bytes=%d)", (int)num_bytes);
 143   if (num_bytes > 0)
 144     {
 145       struct libjpeg_read_internals *i = (struct libjpeg_read_internals *)cinfo;
 146       if ((unsigned long)num_bytes <= i->src.bytes_in_buffer)
 147         {
 148           i->src.next_input_byte += num_bytes;
 149           i->src.bytes_in_buffer -= num_bytes;
 150         }
 151       else
 152         {
 153           num_bytes -= i->src.bytes_in_buffer;
 154           libjpeg_fastbuf_read_commit(i);
 155           if (!bskip(i->fastbuf, num_bytes))
 156             {
 157               IMAGE_ERROR(i->err.io->context, IMAGE_ERROR_READ_FAILED, "Incomplete JPEG file");
 158               longjmp(i->err.setjmp_buf, 1);
 159             }
 160           libjpeg_fastbuf_read_prepare(i);
 161         }
 162     }
 163 }
 164
 165 static inline void
 166 libjpeg_fastbuf_write_prepare(struct libjpeg_write_internals *i)
 167 {
 168   byte *start;
 169   uns len = bdirect_write_prepare(i->fastbuf, &start);
 170   i->fastbuf_pos = start + len;
 171   i->dest.next_output_byte = start;
 172   i->dest.free_in_buffer = len;
 173   if (!len)
 174     {
 175       IMAGE_ERROR(i->err.io->context, IMAGE_ERROR_WRITE_FAILED, "Unexpected end of stream");
 176       longjmp(i->err.setjmp_buf, 1);
 177     }
 178 }
 179
 180 static void
 181 libjpeg_init_destination(j_compress_ptr cinfo)
 182 {
 183   DBG("libjpeg_init_destination()");
 184   libjpeg_fastbuf_write_prepare((struct libjpeg_write_internals *)cinfo);
 185 }
 186
 187 static void
 188 libjpeg_term_destination(j_compress_ptr cinfo)
 189 {
 190   DBG("libjpeg_term_destination()");
 191   struct libjpeg_write_internals *i = (struct libjpeg_write_internals *)cinfo;
 192   bdirect_write_commit(i->fastbuf, (byte *)i->dest.next_output_byte);
 193 }
 194
 195 static boolean
 196 libjpeg_empty_output_buffer(j_compress_ptr cinfo)
 197 {
 198   DBG("libjpeg_empty_output_buffer()");
 199   struct libjpeg_write_internals *i = (struct libjpeg_write_internals *)cinfo;
 200   bdirect_write_commit(i->fastbuf, i->fastbuf_pos);
 201   libjpeg_fastbuf_write_prepare(i);
 202   return TRUE;
 203 }
 204
 205 static inline uns
 206 libjpeg_read_byte(struct libjpeg_read_internals *i)
 207 {
 208   DBG("libjpeg_read_byte()");
 209   if (!i->src.bytes_in_buffer)
 210     if (!libjpeg_fill_input_buffer(&i->cinfo))
 211       ERREXIT(&i->cinfo, JERR_CANT_SUSPEND);
 212   i->src.bytes_in_buffer--;
 213   return *i->src.next_input_byte++;
 214 }
 215
 216 static inline void
 217 libjpeg_read_buf(struct libjpeg_read_internals *i, byte *buf, uns len)
 218 {
 219   DBG("libjpeg_read_buf(len=%u)", len);
 220   while (len)
 221     {
 222       if (!i->src.bytes_in_buffer)
 223         if (!libjpeg_fill_input_buffer(&i->cinfo))
 224           ERREXIT(&i->cinfo, JERR_CANT_SUSPEND);
 225       uns buf_size = i->src.bytes_in_buffer;
 226       uns read_size = MIN(buf_size, len);
 227       memcpy(buf, i->src.next_input_byte, read_size);
 228       i->src.bytes_in_buffer -= read_size;
 229       i->src.next_input_byte += read_size;
 230       len -= read_size;
 231     }
 232 }
 233
 234 static byte libjpeg_exif_header[6] = { 'E', 'x', 'i', 'f', 0, 0 };
 235
 236 static boolean
 237 libjpeg_app1_preprocessor(j_decompress_ptr cinfo)
 238 {
 239   struct libjpeg_read_internals *i = (struct libjpeg_read_internals *)cinfo;
 240   struct image_io *io = i->err.io;
 241   uns len = libjpeg_read_byte(i) << 8;
 242   len += libjpeg_read_byte(i);
 243   DBG("Found APP1 marker, len=%u", len);
 244   if (len < 2)
 245     return TRUE;
 246   len -= 2;
 247   if (len < 7 /*|| io->exif_size*/)
 248     {
 249       libjpeg_skip_input_data(cinfo, len);
 250       return TRUE;
 251     }
 252   byte header[6];
 253   libjpeg_read_buf(i, header, 6);
 254   if (memcmp(header, libjpeg_exif_header, 6))
 255     {
 256       libjpeg_skip_input_data(cinfo, len - 6);
 257       return TRUE;
 258     }
 259   io->exif_size = len;
 260   io->exif_data = mp_alloc(io->internal_pool, len);
 261   memcpy(io->exif_data, header, 6);
 262   libjpeg_read_buf(i, io->exif_data + 6, len - 6);
 263   DBG("Parsed EXIF of length %u", len);
 264   return TRUE;
 265 }
 266
 267 static void
 268 libjpeg_read_cancel(struct image_io *io)
 269 {
 270   DBG("libjpeg_read_cancel()");
 271   struct libjpeg_read_internals *i = io->read_data;
 272   jpeg_destroy_decompress(&i->cinfo);
 273 }
 274
 275 int
 276 libjpeg_read_header(struct image_io *io)
 277 {
 278   DBG("libjpeg_read_header()");
 279   struct libjpeg_read_internals *i = io->read_data = mp_alloc(io->internal_pool, sizeof(*i));
 280   i->fastbuf = io->fastbuf;
 281
 282   /* Create libjpeg read structure */
 283   DBG("Creating libjpeg read structure");
 284   i->cinfo.err = jpeg_std_error(&i->err.pub);
 285   i->err.pub.error_exit = libjpeg_read_error_exit;
 286   i->err.pub.emit_message = libjpeg_emit_message;
 287   i->err.io = io;
 288   if (setjmp(i->err.setjmp_buf))
 289     {
 290       DBG("Libjpeg failed to read the image, longjump saved us");
 291       jpeg_destroy_decompress(&i->cinfo);
 292       return 0;
 293     }
 294   jpeg_create_decompress(&i->cinfo);
 295
 296   /* Initialize source manager */
 297   i->cinfo.src = &i->src;
 298   i->src.init_source = libjpeg_init_source;
 299   i->src.fill_input_buffer = libjpeg_fill_input_buffer;
 300   i->src.skip_input_data = libjpeg_skip_input_data;
 301   i->src.resync_to_restart = jpeg_resync_to_restart;
 302   i->src.term_source = libjpeg_term_source;
 303
 304   if (io->flags & IMAGE_IO_WANT_EXIF)
 305     jpeg_set_marker_processor(&i->cinfo, JPEG_APP0 + 1, libjpeg_app1_preprocessor);
 306
 307   /* Read JPEG header and setup decompression options */
 308   DBG("Reading image header");
 309   jpeg_read_header(&i->cinfo, TRUE);
 310   switch (i->cinfo.jpeg_color_space)
 311     {
 312       case JCS_GRAYSCALE:
 313         io->flags = COLOR_SPACE_GRAYSCALE;
 314         break;
 315       case JCS_RGB:
 316         io->flags = COLOR_SPACE_RGB;
 317         break;
 318       case JCS_YCbCr:
 319         io->flags = COLOR_SPACE_YCBCR;
 320         break;
 321       case JCS_CMYK:
 322         io->flags = COLOR_SPACE_CMYK;
 323         break;
 324       case JCS_YCCK:
 325         io->flags = COLOR_SPACE_YCCK;
 326         break;
 327       default:
 328         if (unlikely(i->cinfo.num_components < 1 || i->cinfo.num_components > 4))
 329           {
 330             jpeg_destroy_decompress(&i->cinfo);
 331             IMAGE_ERROR(io->context, IMAGE_ERROR_INVALID_PIXEL_FORMAT, "Invalid color space.");
 332             return 0;
 333           }
 334         io->flags = COLOR_SPACE_UNKNOWN + i->cinfo.num_components;
 335         break;
 336     }
 337   if (unlikely(i->cinfo.num_components != (int)color_space_channels[io->flags]))
 338     {
 339       jpeg_destroy_decompress(&i->cinfo);
 340       IMAGE_ERROR(io->context, IMAGE_ERROR_INVALID_PIXEL_FORMAT, "Invalid number of color channels.");
 341       return 0;
 342     }
 343   io->cols = i->cinfo.image_width;
 344   io->rows = i->cinfo.image_height;
 345   io->number_of_colors = (i->cinfo.num_components < 4) ? (1U << (i->cinfo.num_components * 8)) : 0xffffffff;
 346   io->read_cancel = libjpeg_read_cancel;
 347   return 1;
 348 }
 349
 350 int
 351 libjpeg_read_data(struct image_io *io)
 352 {
 353   DBG("libjpeg_read_data()");
 354
 355   struct libjpeg_read_internals *i = io->read_data;
 356   uns read_flags = io->flags;
 357
 358   /* Select color space */
 359   switch (read_flags & IMAGE_COLOR_SPACE)
 360     {
 361       case COLOR_SPACE_GRAYSCALE:
 362         i->cinfo.out_color_space = JCS_GRAYSCALE;
 363         break;
 364       case COLOR_SPACE_YCBCR:
 365         i->cinfo.out_color_space = JCS_YCbCr;
 366         break;
 367       case COLOR_SPACE_CMYK:
 368         i->cinfo.out_color_space = JCS_CMYK;
 369         break;
 370       case COLOR_SPACE_YCCK:
 371         i->cinfo.out_color_space = JCS_YCCK;
 372         break;
 373       default:
 374         switch (i->cinfo.jpeg_color_space)
 375           {
 376             case JCS_CMYK:
 377               read_flags = (read_flags & ~IMAGE_COLOR_SPACE & IMAGE_CHANNELS_FORMAT) | COLOR_SPACE_CMYK;
 378               i->cinfo.out_color_space = JCS_YCbCr;
 379               break;
 380             default:
 381               read_flags = (read_flags & ~IMAGE_COLOR_SPACE & IMAGE_CHANNELS_FORMAT) | COLOR_SPACE_RGB;
 382               i->cinfo.out_color_space = JCS_RGB;
 383               break;
 384           }
 385         break;
 386     }
 387
 388   /* Prepare the image  */
 389   struct image_io_read_data_internals rdi;
 390   if (io->cols <= (i->cinfo.image_width >> 3) && io->rows <= (i->cinfo.image_height >> 3))
 391     {
 392       DBG("Scaling to 1/8");
 393       i->cinfo.scale_num = 1;
 394       i->cinfo.scale_denom = 8;
 395     }
 396   else if (io->cols <= (i->cinfo.image_width >> 2) && io->rows <= (i->cinfo.image_height >> 2))
 397     {
 398       DBG("Scaling to 1/4");
 399       i->cinfo.scale_num = 1;
 400       i->cinfo.scale_denom = 4;
 401     }
 402   else if (io->cols <= (i->cinfo.image_width >> 1) && io->rows <= (i->cinfo.image_height >> 1))
 403     {
 404       DBG("Scaling to 1/2");
 405       i->cinfo.scale_num = 1;
 406       i->cinfo.scale_denom = 2;
 407     }
 408   jpeg_calc_output_dimensions(&i->cinfo);
 409   DBG("Output dimensions %ux%u", (uns)i->cinfo.output_width, (uns)i->cinfo.output_height);
 410   if (unlikely(!image_io_read_data_prepare(&rdi, io, i->cinfo.output_width, i->cinfo.output_height, read_flags)))
 411     {
 412       jpeg_destroy_decompress(&i->cinfo);
 413       return 0;
 414     }
 415
 416   /* Setup fallback */
 417   if (setjmp(i->err.setjmp_buf))
 418     {
 419       DBG("Libjpeg failed to read the image, longjump saved us");
 420       jpeg_destroy_decompress(&i->cinfo);
 421       image_io_read_data_break(&rdi, io);
 422       return 0;
 423     }
 424
 425   /* Decompress the image */
 426   struct image *img = rdi.image;
 427   jpeg_start_decompress(&i->cinfo);
 428   if ((int)img->pixel_size == i->cinfo.output_components)
 429     {
 430       byte *pixels = img->pixels;
 431       for (uns r = img->rows; r--; )
 432         {
 433           jpeg_read_scanlines(&i->cinfo, (JSAMPLE **)&pixels, 1);
 434           pixels += img->row_size;
 435         }
 436     }
 437   else
 438     {
 439       switch (img->pixel_size)
 440         {
 441           case 2: /* Grayscale -> Grayscale+Alpha */
 442             {
 443               ASSERT(i->cinfo.output_components == 1);
 444               byte buf[img->cols], *src;
 445 #             define IMAGE_WALK_PREFIX(x) walk_##x
 446 #             define IMAGE_WALK_INLINE
 447 #             define IMAGE_WALK_IMAGE img
 448 #             define IMAGE_WALK_UNROLL 4
 449 #             define IMAGE_WALK_COL_STEP 2
 450 #             define IMAGE_WALK_DO_ROW_START do{ src = buf; jpeg_read_scanlines(&i->cinfo, (JSAMPLE **)&src, 1); }while(0)
 451 #             define IMAGE_WALK_DO_STEP do{ walk_pos[0] = *src++; walk_pos[1] = 255; }while(0)
 452 #             include "images/image-walk.h"
 453             }
 454             break;
 455           case 4: /* * -> *+Alpha or aligned * */
 456             {
 457               ASSERT(i->cinfo.output_components == 3);
 458               byte buf[img->cols * 3], *src;
 459 #             define IMAGE_WALK_PREFIX(x) walk_##x
 460 #             define IMAGE_WALK_INLINE
 461 #             define IMAGE_WALK_IMAGE img
 462 #             define IMAGE_WALK_UNROLL 4
 463 #             define IMAGE_WALK_COL_STEP 4
 464 #             define IMAGE_WALK_DO_ROW_START do{ src = buf; jpeg_read_scanlines(&i->cinfo, (JSAMPLE **)&src, 1); }while(0)
 465 #             define IMAGE_WALK_DO_STEP do{ *(u32 *)walk_pos = *(u32 *)src; walk_pos[3] = 255; src += 3; }while(0)
 466 #             include "images/image-walk.h"
 467             }
 468             break;
 469           default:
 470             ASSERT(0);
 471         }
 472
 473     }
 474
 475   ASSERT(i->cinfo.output_scanline == i->cinfo.output_height);
 476
 477   /* Destroy libjpeg object */
 478   jpeg_finish_decompress(&i->cinfo);
 479   jpeg_destroy_decompress(&i->cinfo);
 480
 481   /* Finish the image */
 482   return image_io_read_data_finish(&rdi, io);
 483 }
 484
 485 int
 486 libjpeg_write(struct image_io *io)
 487 {
 488   DBG("libjpeg_write()");
 489   struct libjpeg_write_internals i;
 490   i.fastbuf = io->fastbuf;
 491
 492   /* Create libjpeg write structure */
 493   DBG("Creating libjpeg write structure");
 494   i.cinfo.err = jpeg_std_error(&i.err.pub);
 495   i.err.pub.error_exit = libjpeg_write_error_exit;
 496   i.err.pub.emit_message = libjpeg_emit_message;
 497   i.err.io = io;
 498   if (setjmp(i.err.setjmp_buf))
 499     {
 500       DBG("Libjpeg failed to write the image, longjump saved us");
 501       jpeg_destroy_compress(&i.cinfo);
 502       return 0;
 503     }
 504   jpeg_create_compress(&i.cinfo);
 505
 506   /* Initialize destination manager */
 507   i.cinfo.dest = &i.dest;
 508   i.dest.init_destination = libjpeg_init_destination;
 509   i.dest.term_destination = libjpeg_term_destination;
 510   i.dest.empty_output_buffer = libjpeg_empty_output_buffer;
 511
 512   /* Set output parameters */
 513   struct image *img = io->image;
 514   i.cinfo.image_width = img->cols;
 515   i.cinfo.image_height = img->rows;
 516   switch (img->flags & IMAGE_COLOR_SPACE)
 517     {
 518       case COLOR_SPACE_GRAYSCALE:
 519         i.cinfo.in_color_space = JCS_GRAYSCALE;
 520         break;
 521       case COLOR_SPACE_RGB:
 522         i.cinfo.in_color_space = JCS_RGB;
 523         break;
 524       case COLOR_SPACE_YCBCR:
 525         i.cinfo.in_color_space = JCS_YCbCr;
 526         break;
 527       case COLOR_SPACE_CMYK:
 528         i.cinfo.in_color_space = JCS_CMYK;
 529         break;
 530       case COLOR_SPACE_YCCK:
 531         i.cinfo.in_color_space = JCS_YCCK;
 532         break;
 533       default:
 534         jpeg_destroy_compress(&i.cinfo);
 535         IMAGE_ERROR(io->context, IMAGE_ERROR_INVALID_PIXEL_FORMAT, "Unsupported pixel format.");
 536         return 0;
 537     }
 538   i.cinfo.input_components = color_space_channels[img->flags & IMAGE_COLOR_SPACE];
 539   jpeg_set_defaults(&i.cinfo);
 540   if (io->jpeg_quality)
 541     jpeg_set_quality(&i.cinfo, MIN(io->jpeg_quality, 100), 1);
 542   if (io->exif_size)
 543     {
 544       /* According to the Exif specification, the Exif APP1 marker has to follow immediately after the SOI,
 545        * just as the JFIF specification requires the same for the JFIF APP0 marker!
 546        * Therefore a JPEG file cannot legally be both Exif and JFIF.  */
 547       i.cinfo.write_JFIF_header = FALSE;
 548       i.cinfo.write_Adobe_marker = FALSE;
 549     }
 550
 551   /* Compress the image */
 552   jpeg_start_compress(&i.cinfo, TRUE);
 553   if (io->exif_size)
 554     {
 555       DBG("Writing EXIF");
 556       jpeg_write_marker(&i.cinfo, JPEG_APP0 + 1, io->exif_data, io->exif_size);
 557     }
 558   if ((int)img->pixel_size == i.cinfo.input_components)
 559     {
 560       byte *pixels = img->pixels;
 561       for (uns r = img->rows; r--; )
 562         {
 563           jpeg_write_scanlines(&i.cinfo, (JSAMPLE **)&pixels, 1);
 564           pixels += img->row_size;
 565         }
 566     }
 567   else
 568     {
 569       switch (img->pixel_size)
 570         {
 571           case 2: /* Grayscale+Alpha -> Grayscale */
 572             {
 573               ASSERT(i.cinfo.input_components == 1);
 574               byte buf[img->cols], *dest = buf;
 575 #             define IMAGE_WALK_PREFIX(x) walk_##x
 576 #             define IMAGE_WALK_INLINE
 577 #             define IMAGE_WALK_IMAGE img
 578 #             define IMAGE_WALK_UNROLL 4
 579 #             define IMAGE_WALK_COL_STEP 2
 580 #             define IMAGE_WALK_DO_ROW_END do{ dest = buf; jpeg_write_scanlines(&i.cinfo, (JSAMPLE **)&dest, 1); }while(0)
 581 #             define IMAGE_WALK_DO_STEP do{ *dest++ = walk_pos[0]; }while(0)
 582 #             include "images/image-walk.h"
 583               break;
 584             }
 585           case 4: /* *+Alpha or aligned * -> * */
 586             {
 587               ASSERT(i.cinfo.input_components == 3);
 588               byte buf[img->cols * 3], *dest = buf;
 589 #             define IMAGE_WALK_PREFIX(x) walk_##x
 590 #             define IMAGE_WALK_INLINE
 591 #             define IMAGE_WALK_IMAGE img
 592 #             define IMAGE_WALK_UNROLL 4
 593 #             define IMAGE_WALK_COL_STEP 4
 594 #             define IMAGE_WALK_DO_ROW_END do{ dest = buf; jpeg_write_scanlines(&i.cinfo, (JSAMPLE **)&dest, 1); }while(0)
 595 #             define IMAGE_WALK_DO_STEP do{ *dest++ = walk_pos[0]; *dest++ = walk_pos[1]; *dest++ = walk_pos[2]; }while(0)
 596 #             include "images/image-walk.h"
 597               break;
 598             }
 599           default:
 600             ASSERT(0);
 601         }
 602     }
 603   ASSERT(i.cinfo.next_scanline == i.cinfo.image_height);
 604   jpeg_finish_compress(&i.cinfo);
 605   jpeg_destroy_compress(&i.cinfo);
 606   return 1;
 607 }