libavcodec/pngdec.c

   1 /*
   2  * PNG image format
   3  * Copyright (c) 2003 Fabrice Bellard
   4  *
   5  * This file is part of Libav.
   6  *
   7  * Libav is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * Libav is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with Libav; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21 #include "libavutil/imgutils.h"
  22 #include "avcodec.h"
  23 #include "bytestream.h"
  24 #include "internal.h"
  25 #include "png.h"
  26 #include "pngdsp.h"
  27
  28 /* TODO:
  29  * - add 2, 4 and 16 bit depth support
  30  */
  31
  32 #include <zlib.h>
  33
  34 //#define DEBUG
  35
  36 typedef struct PNGDecContext {
  37     PNGDSPContext dsp;
  38
  39     GetByteContext gb;
  40     AVFrame picture1, picture2;
  41     AVFrame *current_picture, *last_picture;
  42
  43     int state;
  44     int width, height;
  45     int bit_depth;
  46     int color_type;
  47     int compression_type;
  48     int interlace_type;
  49     int filter_type;
  50     int channels;
  51     int bits_per_pixel;
  52     int bpp;
  53
  54     uint8_t *image_buf;
  55     int image_linesize;
  56     uint32_t palette[256];
  57     uint8_t *crow_buf;
  58     uint8_t *last_row;
  59     uint8_t *tmp_row;
  60     int pass;
  61     int crow_size; /* compressed row size (include filter type) */
  62     int row_size; /* decompressed row size */
  63     int pass_row_size; /* decompress row size of the current pass */
  64     int y;
  65     z_stream zstream;
  66 } PNGDecContext;
  67
  68 /* Mask to determine which y pixels can be written in a pass */
  69 static const uint8_t png_pass_dsp_ymask[NB_PASSES] = {
  70     0xff, 0xff, 0x0f, 0xcc, 0x33, 0xff, 0x55,
  71 };
  72
  73 /* Mask to determine which pixels to overwrite while displaying */
  74 static const uint8_t png_pass_dsp_mask[NB_PASSES] = {
  75     0xff, 0x0f, 0xff, 0x33, 0xff, 0x55, 0xff
  76 };
  77
  78 /* NOTE: we try to construct a good looking image at each pass. width
  79    is the original image width. We also do pixel format conversion at
  80    this stage */
  81 static void png_put_interlaced_row(uint8_t *dst, int width,
  82                                    int bits_per_pixel, int pass,
  83                                    int color_type, const uint8_t *src)
  84 {
  85     int x, mask, dsp_mask, j, src_x, b, bpp;
  86     uint8_t *d;
  87     const uint8_t *s;
  88
  89     mask     = ff_png_pass_mask[pass];
  90     dsp_mask = png_pass_dsp_mask[pass];
  91
  92     switch (bits_per_pixel) {
  93     case 1:
  94         /* we must initialize the line to zero before writing to it */
  95         if (pass == 0)
  96             memset(dst, 0, (width + 7) >> 3);
  97         src_x = 0;
  98         for (x = 0; x < width; x++) {
  99             j = (x & 7);
 100             if ((dsp_mask << j) & 0x80) {
 101                 b = (src[src_x >> 3] >> (7 - (src_x & 7))) & 1;
 102                 dst[x >> 3] |= b << (7 - j);
 103             }
 104             if ((mask << j) & 0x80)
 105                 src_x++;
 106         }
 107         break;
 108     default:
 109         bpp = bits_per_pixel >> 3;
 110         d   = dst;
 111         s   = src;
 112         if (color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
 113             for (x = 0; x < width; x++) {
 114                 j = x & 7;
 115                 if ((dsp_mask << j) & 0x80) {
 116                     *(uint32_t *)d = (s[3] << 24) | (s[0] << 16) | (s[1] << 8) | s[2];
 117                 }
 118                 d += bpp;
 119                 if ((mask << j) & 0x80)
 120                     s += bpp;
 121             }
 122         } else {
 123             for(x = 0; x < width; x++) {
 124                 j = x & 7;
 125                 if ((dsp_mask << j) & 0x80) {
 126                     memcpy(d, s, bpp);
 127                 }
 128                 d += bpp;
 129                 if ((mask << j) & 0x80)
 130                     s += bpp;
 131             }
 132         }
 133         break;
 134     }
 135 }
 136
 137 void ff_add_png_paeth_prediction(uint8_t *dst, uint8_t *src, uint8_t *top, int w, int bpp)
 138 {
 139     int i;
 140     for (i = 0; i < w; i++) {
 141         int a, b, c, p, pa, pb, pc;
 142
 143         a = dst[i - bpp];
 144         b = top[i];
 145         c = top[i - bpp];
 146
 147         p  = b - c;
 148         pc = a - c;
 149
 150         pa = abs(p);
 151         pb = abs(pc);
 152         pc = abs(p + pc);
 153
 154         if (pa <= pb && pa <= pc)
 155             p = a;
 156         else if (pb <= pc)
 157             p = b;
 158         else
 159             p = c;
 160         dst[i] = p + src[i];
 161     }
 162 }
 163
 164 #define UNROLL1(bpp, op) {\
 165                  r = dst[0];\
 166     if(bpp >= 2) g = dst[1];\
 167     if(bpp >= 3) b = dst[2];\
 168     if(bpp >= 4) a = dst[3];\
 169     for(; i < size; i+=bpp) {\
 170         dst[i+0] = r = op(r, src[i+0], last[i+0]);\
 171         if(bpp == 1) continue;\
 172         dst[i+1] = g = op(g, src[i+1], last[i+1]);\
 173         if(bpp == 2) continue;\
 174         dst[i+2] = b = op(b, src[i+2], last[i+2]);\
 175         if(bpp == 3) continue;\
 176         dst[i+3] = a = op(a, src[i+3], last[i+3]);\
 177     }\
 178 }
 179
 180 #define UNROLL_FILTER(op)\
 181          if(bpp == 1) UNROLL1(1, op)\
 182     else if(bpp == 2) UNROLL1(2, op)\
 183     else if(bpp == 3) UNROLL1(3, op)\
 184     else if(bpp == 4) UNROLL1(4, op)\
 185     else {\
 186         for (; i < size; i += bpp) {\
 187             int j;\
 188             for (j = 0; j < bpp; j++)\
 189                 dst[i+j] = op(dst[i+j-bpp], src[i+j], last[i+j]);\
 190         }\
 191     }
 192
 193 /* NOTE: 'dst' can be equal to 'last' */
 194 static void png_filter_row(PNGDSPContext *dsp, uint8_t *dst, int filter_type,
 195                            uint8_t *src, uint8_t *last, int size, int bpp)
 196 {
 197     int i, p, r, g, b, a;
 198
 199     switch (filter_type) {
 200     case PNG_FILTER_VALUE_NONE:
 201         memcpy(dst, src, size);
 202         break;
 203     case PNG_FILTER_VALUE_SUB:
 204         for (i = 0; i < bpp; i++) {
 205             dst[i] = src[i];
 206         }
 207         if (bpp == 4) {
 208             p = *(int*)dst;
 209             for (; i < size; i += bpp) {
 210                 int s = *(int*)(src + i);
 211                 p = ((s & 0x7f7f7f7f) + (p & 0x7f7f7f7f)) ^ ((s ^ p) & 0x80808080);
 212                 *(int*)(dst + i) = p;
 213             }
 214         } else {
 215 #define OP_SUB(x,s,l) x+s
 216             UNROLL_FILTER(OP_SUB);
 217         }
 218         break;
 219     case PNG_FILTER_VALUE_UP:
 220         dsp->add_bytes_l2(dst, src, last, size);
 221         break;
 222     case PNG_FILTER_VALUE_AVG:
 223         for (i = 0; i < bpp; i++) {
 224             p = (last[i] >> 1);
 225             dst[i] = p + src[i];
 226         }
 227 #define OP_AVG(x,s,l) (((x + l) >> 1) + s) & 0xff
 228         UNROLL_FILTER(OP_AVG);
 229         break;
 230     case PNG_FILTER_VALUE_PAETH:
 231         for (i = 0; i < bpp; i++) {
 232             p = last[i];
 233             dst[i] = p + src[i];
 234         }
 235         if (bpp > 1 && size > 4) {
 236             // would write off the end of the array if we let it process the last pixel with bpp=3
 237             int w = bpp == 4 ? size : size - 3;
 238             dsp->add_paeth_prediction(dst + i, src + i, last + i, w - i, bpp);
 239             i = w;
 240         }
 241         ff_add_png_paeth_prediction(dst + i, src + i, last + i, size - i, bpp);
 242         break;
 243     }
 244 }
 245
 246 static av_always_inline void convert_to_rgb32_loco(uint8_t *dst,
 247                                                    const uint8_t *src,
 248                                                    int width, int loco)
 249 {
 250     int j;
 251     unsigned int r, g, b, a;
 252
 253     for (j = 0; j < width; j++) {
 254         r = src[0];
 255         g = src[1];
 256         b = src[2];
 257         a = src[3];
 258         if (loco) {
 259             r = (r + g) & 0xff;
 260             b = (b + g) & 0xff;
 261         }
 262         *(uint32_t *)dst = (a << 24) | (r << 16) | (g << 8) | b;
 263         dst += 4;
 264         src += 4;
 265     }
 266 }
 267
 268 static void convert_to_rgb32(uint8_t *dst, const uint8_t *src, int width, int loco)
 269 {
 270     if (loco)
 271         convert_to_rgb32_loco(dst, src, width, 1);
 272     else
 273         convert_to_rgb32_loco(dst, src, width, 0);
 274 }
 275
 276 static void deloco_rgb24(uint8_t *dst, int size)
 277 {
 278     int i;
 279     for (i = 0; i < size; i += 3) {
 280         int g = dst[i + 1];
 281         dst[i + 0] += g;
 282         dst[i + 2] += g;
 283     }
 284 }
 285
 286 /* process exactly one decompressed row */
 287 static void png_handle_row(PNGDecContext *s)
 288 {
 289     uint8_t *ptr, *last_row;
 290     int got_line;
 291
 292     if (!s->interlace_type) {
 293         ptr = s->image_buf + s->image_linesize * s->y;
 294         /* need to swap bytes correctly for RGB_ALPHA */
 295         if (s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
 296             png_filter_row(&s->dsp, s->tmp_row, s->crow_buf[0], s->crow_buf + 1,
 297                            s->last_row, s->row_size, s->bpp);
 298             convert_to_rgb32(ptr, s->tmp_row, s->width, s->filter_type == PNG_FILTER_TYPE_LOCO);
 299             FFSWAP(uint8_t*, s->last_row, s->tmp_row);
 300         } else {
 301             /* in normal case, we avoid one copy */
 302             if (s->y == 0)
 303                 last_row = s->last_row;
 304             else
 305                 last_row = ptr - s->image_linesize;
 306
 307             png_filter_row(&s->dsp, ptr, s->crow_buf[0], s->crow_buf + 1,
 308                            last_row, s->row_size, s->bpp);
 309         }
 310         /* loco lags by 1 row so that it doesn't interfere with top prediction */
 311         if (s->filter_type == PNG_FILTER_TYPE_LOCO &&
 312             s->color_type == PNG_COLOR_TYPE_RGB && s->y > 0)
 313             deloco_rgb24(ptr - s->image_linesize, s->row_size);
 314         s->y++;
 315         if (s->y == s->height) {
 316             s->state |= PNG_ALLIMAGE;
 317             if (s->filter_type == PNG_FILTER_TYPE_LOCO &&
 318                 s->color_type == PNG_COLOR_TYPE_RGB)
 319                 deloco_rgb24(ptr, s->row_size);
 320         }
 321     } else {
 322         got_line = 0;
 323         for (;;) {
 324             ptr = s->image_buf + s->image_linesize * s->y;
 325             if ((ff_png_pass_ymask[s->pass] << (s->y & 7)) & 0x80) {
 326                 /* if we already read one row, it is time to stop to
 327                    wait for the next one */
 328                 if (got_line)
 329                     break;
 330                 png_filter_row(&s->dsp, s->tmp_row, s->crow_buf[0], s->crow_buf + 1,
 331                                s->last_row, s->pass_row_size, s->bpp);
 332                 FFSWAP(uint8_t*, s->last_row, s->tmp_row);
 333                 got_line = 1;
 334             }
 335             if ((png_pass_dsp_ymask[s->pass] << (s->y & 7)) & 0x80) {
 336                 /* NOTE: RGB32 is handled directly in png_put_interlaced_row */
 337                 png_put_interlaced_row(ptr, s->width, s->bits_per_pixel, s->pass,
 338                                        s->color_type, s->last_row);
 339             }
 340             s->y++;
 341             if (s->y == s->height) {
 342                 for (;;) {
 343                     if (s->pass == NB_PASSES - 1) {
 344                         s->state |= PNG_ALLIMAGE;
 345                         goto the_end;
 346                     } else {
 347                         s->pass++;
 348                         s->y = 0;
 349                         s->pass_row_size = ff_png_pass_row_size(s->pass,
 350                                                              s->bits_per_pixel,
 351                                                              s->width);
 352                         s->crow_size = s->pass_row_size + 1;
 353                         if (s->pass_row_size != 0)
 354                             break;
 355                         /* skip pass if empty row */
 356                     }
 357                 }
 358             }
 359         }
 360     the_end: ;
 361     }
 362 }
 363
 364 static int png_decode_idat(PNGDecContext *s, int length)
 365 {
 366     int ret;
 367     s->zstream.avail_in = FFMIN(length, bytestream2_get_bytes_left(&s->gb));
 368     s->zstream.next_in  = s->gb.buffer;
 369     bytestream2_skip(&s->gb, length);
 370
 371     /* decode one line if possible */
 372     while (s->zstream.avail_in > 0) {
 373         ret = inflate(&s->zstream, Z_PARTIAL_FLUSH);
 374         if (ret != Z_OK && ret != Z_STREAM_END) {
 375             return -1;
 376         }
 377         if (s->zstream.avail_out == 0) {
 378             if (!(s->state & PNG_ALLIMAGE)) {
 379                 png_handle_row(s);
 380             }
 381             s->zstream.avail_out = s->crow_size;
 382             s->zstream.next_out  = s->crow_buf;
 383         }
 384     }
 385     return 0;
 386 }
 387
 388 static int decode_frame(AVCodecContext *avctx,
 389                         void *data, int *got_frame,
 390                         AVPacket *avpkt)
 391 {
 392     PNGDecContext * const s = avctx->priv_data;
 393     const uint8_t *buf      = avpkt->data;
 394     int buf_size            = avpkt->size;
 395     AVFrame *picture        = data;
 396     uint8_t *crow_buf_base  = NULL;
 397     AVFrame *p;
 398     uint32_t tag, length;
 399     int ret;
 400
 401     FFSWAP(AVFrame *, s->current_picture, s->last_picture);
 402     avctx->coded_frame = s->current_picture;
 403     p = s->current_picture;
 404
 405     /* check signature */
 406     if (buf_size < 8 ||
 407         memcmp(buf, ff_pngsig, 8) != 0 &&
 408         memcmp(buf, ff_mngsig, 8) != 0)
 409         return -1;
 410
 411     bytestream2_init(&s->gb, buf + 8, buf_size - 8);
 412     s->y = s->state = 0;
 413
 414     /* init the zlib */
 415     s->zstream.zalloc = ff_png_zalloc;
 416     s->zstream.zfree  = ff_png_zfree;
 417     s->zstream.opaque = NULL;
 418     ret = inflateInit(&s->zstream);
 419     if (ret != Z_OK)
 420         return -1;
 421     for (;;) {
 422         if (bytestream2_get_bytes_left(&s->gb) <= 0)
 423             goto fail;
 424         length = bytestream2_get_be32(&s->gb);
 425         if (length > 0x7fffffff)
 426             goto fail;
 427         tag = bytestream2_get_le32(&s->gb);
 428         av_dlog(avctx, "png: tag=%c%c%c%c length=%u\n",
 429                 (tag & 0xff),
 430                 ((tag >> 8) & 0xff),
 431                 ((tag >> 16) & 0xff),
 432                 ((tag >> 24) & 0xff), length);
 433         switch (tag) {
 434         case MKTAG('I', 'H', 'D', 'R'):
 435             if (length != 13)
 436                 goto fail;
 437             s->width  = bytestream2_get_be32(&s->gb);
 438             s->height = bytestream2_get_be32(&s->gb);
 439             if (av_image_check_size(s->width, s->height, 0, avctx)) {
 440                 s->width = s->height = 0;
 441                 goto fail;
 442             }
 443             s->bit_depth        = bytestream2_get_byte(&s->gb);
 444             s->color_type       = bytestream2_get_byte(&s->gb);
 445             s->compression_type = bytestream2_get_byte(&s->gb);
 446             s->filter_type      = bytestream2_get_byte(&s->gb);
 447             s->interlace_type   = bytestream2_get_byte(&s->gb);
 448             bytestream2_skip(&s->gb, 4); /* crc */
 449             s->state |= PNG_IHDR;
 450             av_dlog(avctx, "width=%d height=%d depth=%d color_type=%d "
 451                     "compression_type=%d filter_type=%d interlace_type=%d\n",
 452                     s->width, s->height, s->bit_depth, s->color_type,
 453                     s->compression_type, s->filter_type, s->interlace_type);
 454             break;
 455         case MKTAG('I', 'D', 'A', 'T'):
 456             if (!(s->state & PNG_IHDR))
 457                 goto fail;
 458             if (!(s->state & PNG_IDAT)) {
 459                 /* init image info */
 460                 avctx->width  = s->width;
 461                 avctx->height = s->height;
 462
 463                 s->channels       = ff_png_get_nb_channels(s->color_type);
 464                 s->bits_per_pixel = s->bit_depth * s->channels;
 465                 s->bpp            = (s->bits_per_pixel + 7) >> 3;
 466                 s->row_size       = (avctx->width * s->bits_per_pixel + 7) >> 3;
 467
 468                 if (s->bit_depth == 8 &&
 469                     s->color_type == PNG_COLOR_TYPE_RGB) {
 470                     avctx->pix_fmt = AV_PIX_FMT_RGB24;
 471                 } else if (s->bit_depth == 8 &&
 472                            s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
 473                     avctx->pix_fmt = AV_PIX_FMT_RGB32;
 474                 } else if (s->bit_depth == 8 &&
 475                            s->color_type == PNG_COLOR_TYPE_GRAY) {
 476                     avctx->pix_fmt = AV_PIX_FMT_GRAY8;
 477                 } else if (s->bit_depth == 16 &&
 478                            s->color_type == PNG_COLOR_TYPE_GRAY) {
 479                     avctx->pix_fmt = AV_PIX_FMT_GRAY16BE;
 480                 } else if (s->bit_depth == 16 &&
 481                            s->color_type == PNG_COLOR_TYPE_RGB) {
 482                     avctx->pix_fmt = AV_PIX_FMT_RGB48BE;
 483                 } else if (s->bit_depth == 1 &&
 484                            s->color_type == PNG_COLOR_TYPE_GRAY) {
 485                     avctx->pix_fmt = AV_PIX_FMT_MONOBLACK;
 486                 } else if (s->bit_depth == 8 &&
 487                            s->color_type == PNG_COLOR_TYPE_PALETTE) {
 488                     avctx->pix_fmt = AV_PIX_FMT_PAL8;
 489                 } else if (s->bit_depth == 8 &&
 490                            s->color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
 491                     avctx->pix_fmt = AV_PIX_FMT_Y400A;
 492                 } else {
 493                     goto fail;
 494                 }
 495                 if (p->data[0])
 496                     avctx->release_buffer(avctx, p);
 497
 498                 p->reference = 0;
 499                 if (ff_get_buffer(avctx, p) < 0) {
 500                     av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
 501                     goto fail;
 502                 }
 503                 p->pict_type        = AV_PICTURE_TYPE_I;
 504                 p->key_frame        = 1;
 505                 p->interlaced_frame = !!s->interlace_type;
 506
 507                 /* compute the compressed row size */
 508                 if (!s->interlace_type) {
 509                     s->crow_size = s->row_size + 1;
 510                 } else {
 511                     s->pass = 0;
 512                     s->pass_row_size = ff_png_pass_row_size(s->pass,
 513                                                          s->bits_per_pixel,
 514                                                          s->width);
 515                     s->crow_size = s->pass_row_size + 1;
 516                 }
 517                 av_dlog(avctx, "row_size=%d crow_size =%d\n",
 518                         s->row_size, s->crow_size);
 519                 s->image_buf      = p->data[0];
 520                 s->image_linesize = p->linesize[0];
 521                 /* copy the palette if needed */
 522                 if (s->color_type == PNG_COLOR_TYPE_PALETTE)
 523                     memcpy(p->data[1], s->palette, 256 * sizeof(uint32_t));
 524                 /* empty row is used if differencing to the first row */
 525                 s->last_row = av_mallocz(s->row_size);
 526                 if (!s->last_row)
 527                     goto fail;
 528                 if (s->interlace_type ||
 529                     s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
 530                     s->tmp_row = av_malloc(s->row_size);
 531                     if (!s->tmp_row)
 532                         goto fail;
 533                 }
 534                 /* compressed row */
 535                 crow_buf_base = av_malloc(s->row_size + 16);
 536                 if (!crow_buf_base)
 537                     goto fail;
 538
 539                 /* we want crow_buf+1 to be 16-byte aligned */
 540                 s->crow_buf          = crow_buf_base + 15;
 541                 s->zstream.avail_out = s->crow_size;
 542                 s->zstream.next_out  = s->crow_buf;
 543             }
 544             s->state |= PNG_IDAT;
 545             if (png_decode_idat(s, length) < 0)
 546                 goto fail;
 547             bytestream2_skip(&s->gb, 4); /* crc */
 548             break;
 549         case MKTAG('P', 'L', 'T', 'E'):
 550             {
 551                 int n, i, r, g, b;
 552
 553                 if ((length % 3) != 0 || length > 256 * 3)
 554                     goto skip_tag;
 555                 /* read the palette */
 556                 n = length / 3;
 557                 for (i = 0; i < n; i++) {
 558                     r = bytestream2_get_byte(&s->gb);
 559                     g = bytestream2_get_byte(&s->gb);
 560                     b = bytestream2_get_byte(&s->gb);
 561                     s->palette[i] = (0xff << 24) | (r << 16) | (g << 8) | b;
 562                 }
 563                 for (; i < 256; i++) {
 564                     s->palette[i] = (0xff << 24);
 565                 }
 566                 s->state |= PNG_PLTE;
 567                 bytestream2_skip(&s->gb, 4); /* crc */
 568             }
 569             break;
 570         case MKTAG('t', 'R', 'N', 'S'):
 571             {
 572                 int v, i;
 573
 574                 /* read the transparency. XXX: Only palette mode supported */
 575                 if (s->color_type != PNG_COLOR_TYPE_PALETTE ||
 576                     length > 256 ||
 577                     !(s->state & PNG_PLTE))
 578                     goto skip_tag;
 579                 for (i = 0; i < length; i++) {
 580                     v = bytestream2_get_byte(&s->gb);
 581                     s->palette[i] = (s->palette[i] & 0x00ffffff) | (v << 24);
 582                 }
 583                 bytestream2_skip(&s->gb, 4); /* crc */
 584             }
 585             break;
 586         case MKTAG('I', 'E', 'N', 'D'):
 587             if (!(s->state & PNG_ALLIMAGE))
 588                 goto fail;
 589             bytestream2_skip(&s->gb, 4); /* crc */
 590             goto exit_loop;
 591         default:
 592             /* skip tag */
 593         skip_tag:
 594             bytestream2_skip(&s->gb, length + 4);
 595             break;
 596         }
 597     }
 598  exit_loop:
 599      /* handle p-frames only if a predecessor frame is available */
 600      if (s->last_picture->data[0] != NULL) {
 601          if (!(avpkt->flags & AV_PKT_FLAG_KEY)) {
 602             int i, j;
 603             uint8_t *pd      = s->current_picture->data[0];
 604             uint8_t *pd_last = s->last_picture->data[0];
 605
 606             for (j = 0; j < s->height; j++) {
 607                 for (i = 0; i < s->width * s->bpp; i++) {
 608                     pd[i] += pd_last[i];
 609                 }
 610                 pd      += s->image_linesize;
 611                 pd_last += s->image_linesize;
 612             }
 613         }
 614     }
 615
 616     *picture   = *s->current_picture;
 617     *got_frame = 1;
 618
 619     ret = bytestream2_tell(&s->gb);
 620  the_end:
 621     inflateEnd(&s->zstream);
 622     av_free(crow_buf_base);
 623     s->crow_buf = NULL;
 624     av_freep(&s->last_row);
 625     av_freep(&s->tmp_row);
 626     return ret;
 627  fail:
 628     ret = -1;
 629     goto the_end;
 630 }
 631
 632 static av_cold int png_dec_init(AVCodecContext *avctx)
 633 {
 634     PNGDecContext *s = avctx->priv_data;
 635
 636     s->current_picture = &s->picture1;
 637     s->last_picture    = &s->picture2;
 638     avcodec_get_frame_defaults(&s->picture1);
 639     avcodec_get_frame_defaults(&s->picture2);
 640     ff_pngdsp_init(&s->dsp);
 641
 642     return 0;
 643 }
 644
 645 static av_cold int png_dec_end(AVCodecContext *avctx)
 646 {
 647     PNGDecContext *s = avctx->priv_data;
 648
 649     if (s->picture1.data[0])
 650         avctx->release_buffer(avctx, &s->picture1);
 651     if (s->picture2.data[0])
 652         avctx->release_buffer(avctx, &s->picture2);
 653
 654     return 0;
 655 }
 656
 657 AVCodec ff_png_decoder = {
 658     .name           = "png",
 659     .type           = AVMEDIA_TYPE_VIDEO,
 660     .id             = AV_CODEC_ID_PNG,
 661     .priv_data_size = sizeof(PNGDecContext),
 662     .init           = png_dec_init,
 663     .close          = png_dec_end,
 664     .decode         = decode_frame,
 665     .capabilities   = CODEC_CAP_DR1 /*| CODEC_CAP_DRAW_HORIZ_BAND*/,
 666     .long_name      = NULL_IF_CONFIG_SMALL("PNG (Portable Network Graphics) image"),
 667 };