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avcodec/png: support cICP chunks

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This commit adds both decode and encode support for cICP chunks, which
allow a PNG image's pixel data to be tagged by any of the enum values in
H.273, without an ICC profile.

Upon decode, if a cICP chunk is present, the PNG decoder will tag output
AVFrames with the resulting enum color, and ignore iCCP, sRGB, gAMA, and
cHRM chunks, as per the spec.

Upon encode, if the color space is known and specified, and it is not sRGB,
the PNG encoder will output a cICP chunk containing the color space. If the
color space is sRGB, then it will output an sRGB chunk instead of a cICP
chunk. If the color space of the input is not unspecified, it will not output
a cICP chunk tagging the PNG as unspecified.

In either the sRGB case or the non-SRGB case, gAMA and cHRM are still written
as fallbacks provided the info is known.

Signed-off-by: Leo Izen <leo.izen@gmail.com>
This commit is contained in:
Leo Izen 2023-01-17 13:38:42 -05:00
parent f7bab37c8e
commit 6f79f0971e
No known key found for this signature in database
GPG Key ID: 5A71C331FD2FA19A
2 changed files with 40 additions and 3 deletions
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35
libavcodec/pngdec.c
View File

@ -76,6 +76,10 @@ typedef struct PNGDecContext {
uint32_t white_point[2];
uint32_t display_primaries[3][2];
int have_srgb;
int have_cicp;
enum AVColorPrimaries cicp_primaries;
enum AVColorTransferCharacteristic cicp_trc;
enum AVColorRange cicp_range;
enum PNGHeaderState hdr_state;
enum PNGImageState pic_state;
@ -1314,6 +1318,19 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
}
break;
}
case MKTAG('c', 'I', 'C', 'P'):
s->cicp_primaries = bytestream2_get_byte(&gb_chunk);
s->cicp_trc = bytestream2_get_byte(&gb_chunk);
if (bytestream2_get_byte(&gb_chunk) != 0)
av_log(avctx, AV_LOG_WARNING, "nonzero cICP matrix\n");
s->cicp_range = bytestream2_get_byte(&gb_chunk);
if (s->cicp_range != 0 && s->cicp_range != 1) {
av_log(avctx, AV_LOG_ERROR, "invalid cICP range: %d\n", s->cicp_range);
ret = AVERROR_INVALIDDATA;
goto fail;
}
s->have_cicp = 1;
break;
case MKTAG('s', 'R', 'G', 'B'):
/* skip rendering intent byte */
bytestream2_skip(&gb_chunk, 1);
@ -1475,6 +1492,7 @@ static void clear_frame_metadata(PNGDecContext *s)
s->have_chrm = 0;
s->have_srgb = 0;
s->have_cicp = 0;
av_dict_free(&s->frame_metadata);
}
@ -1484,7 +1502,18 @@ static int output_frame(PNGDecContext *s, AVFrame *f)
AVCodecContext *avctx = s->avctx;
int ret;
if (s->iccp_data) {
if (s->have_cicp) {
if (s->cicp_primaries >= AVCOL_PRI_NB)
av_log(avctx, AV_LOG_WARNING, "unrecognized cICP primaries\n");
else
avctx->color_primaries = f->color_primaries = s->cicp_primaries;
if (s->cicp_trc >= AVCOL_TRC_NB)
av_log(avctx, AV_LOG_WARNING, "unrecognized cICP transfer\n");
else
avctx->color_trc = f->color_trc = s->cicp_trc;
avctx->color_range = f->color_range =
s->cicp_range == 0 ? AVCOL_RANGE_MPEG : AVCOL_RANGE_JPEG;
} else if (s->iccp_data) {
AVFrameSideData *sd = av_frame_new_side_data(f, AV_FRAME_DATA_ICC_PROFILE, s->iccp_data_len);
if (!sd) {
ret = AVERROR(ENOMEM);
@ -1514,8 +1543,8 @@ static int output_frame(PNGDecContext *s, AVFrame *f)
av_log(avctx, AV_LOG_WARNING, "unknown cHRM primaries\n");
}
/* these chunks overrides gAMA */
if (s->iccp_data || s->have_srgb)
/* these chunks override gAMA */
if (s->iccp_data || s->have_srgb || s->have_cicp)
av_dict_set(&s->frame_metadata, "gamma", NULL, 0);
avctx->colorspace = f->colorspace = AVCOL_SPC_RGB;

8
libavcodec/pngenc.c
View File

@ -417,6 +417,14 @@ static int encode_headers(AVCodecContext *avctx, const AVFrame *pict)
pict->color_trc == AVCOL_TRC_IEC61966_2_1) {
s->buf[0] = 1; /* rendering intent, relative colorimetric by default */
png_write_chunk(&s->bytestream, MKTAG('s', 'R', 'G', 'B'), s->buf, 1);
} else if (pict->color_primaries != AVCOL_PRI_UNSPECIFIED ||
pict->color_trc != AVCOL_TRC_UNSPECIFIED) {
/* these values match H.273 so no translation is needed */
s->buf[0] = pict->color_primaries;
s->buf[1] = pict->color_trc;
s->buf[2] = 0; /* colorspace = RGB */
s->buf[3] = pict->color_range == AVCOL_RANGE_MPEG ? 0 : 1;
png_write_chunk(&s->bytestream, MKTAG('c', 'I', 'C', 'P'), s->buf, 4);
}
if (png_get_chrm(pict->color_primaries, s->buf))