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avcodec/pngdec: support sBIT chunks 

Add support for reading sBIT chunks, which mark the significant
bit depth of the PNG file. This passes the metadata using the field
bits_per_raw_sample of AVCodecContext.

Signed-off-by: Leo Izen <leo.izen@gmail.com>
This commit is contained in:
Leo Izen 2023-03-21 23:26:25 -04:00
parent 113f684271
commit 84b454935f
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GPG Key ID: 5A71C331FD2FA19A
1 changed files with 48 additions and 0 deletions
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48
libavcodec/pngdec.c
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@ -98,6 +98,7 @@ typedef struct PNGDecContext {
int bpp;
int has_trns;
uint8_t transparent_color_be[6];
int significant_bits;
uint32_t palette[256];
uint8_t *crow_buf;
@ -716,6 +717,14 @@ static int populate_avctx_color_fields(AVCodecContext *avctx, AVFrame *frame)
avctx->colorspace = frame->colorspace = AVCOL_SPC_RGB;
avctx->color_range = frame->color_range = AVCOL_RANGE_JPEG;
/*
* tRNS sets alpha depth to full, so we ignore sBIT if set.
* As a result we must wait until now to set
* avctx->bits_per_raw_sample in case tRNS appears after sBIT
*/
if (!s->has_trns && s->significant_bits > 0)
avctx->bits_per_raw_sample = s->significant_bits;
return 0;
}
@ -996,6 +1005,41 @@ fail:
return ret;
}
static int decode_sbit_chunk(AVCodecContext *avctx, PNGDecContext *s,
GetByteContext *gb)
{
int bits = 0;
int channels;
if (!(s->hdr_state & PNG_IHDR)) {
av_log(avctx, AV_LOG_ERROR, "sBIT before IHDR\n");
return AVERROR_INVALIDDATA;
}
if (s->pic_state & PNG_IDAT) {
av_log(avctx, AV_LOG_ERROR, "sBIT after IDAT\n");
return AVERROR_INVALIDDATA;
}
channels = ff_png_get_nb_channels(s->color_type);
if (bytestream2_get_bytes_left(gb) != channels)
return AVERROR_INVALIDDATA;
for (int i = 0; i < channels; i++) {
int b = bytestream2_get_byteu(gb);
bits = FFMAX(b, bits);
}
if (bits < 0 || bits > s->bit_depth) {
av_log(avctx, AV_LOG_ERROR, "Invalid significant bits: %d\n", bits);
return AVERROR_INVALIDDATA;
}
s->significant_bits = bits;
return 0;
}
static void handle_small_bpp(PNGDecContext *s, AVFrame *p)
{
if (s->bits_per_pixel == 1 && s->color_type == PNG_COLOR_TYPE_PALETTE) {
@ -1440,6 +1484,10 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
break;
}
case MKTAG('s', 'B', 'I', 'T'):
if ((ret = decode_sbit_chunk(avctx, s, &gb_chunk)) < 0)
goto fail;
break;
case MKTAG('g', 'A', 'M', 'A'): {
AVBPrint bp;
char *gamma_str;