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avcodec/libjxl: set correct alpha mode

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JPEG XL supports both premultiplied and straight alpha, and the basic info
struct contains signalling for this. Forward the correct tagging on decode
and encode.
This commit is contained in:
Niklas Haas
2025-07-23 12:51:26 +02:00
parent 702a5ac29b
commit a88cc0a53e
2 changed files with 21 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files
libavcodec/libjxldec.c
+6
View File
@@ -444,6 +444,12 @@ static int libjxl_receive_frame(AVCodecContext *avctx, AVFrame *frame)
if (ctx->basic_info.have_animation)
ctx->anim_timebase = av_make_q(ctx->basic_info.animation.tps_denominator,
ctx->basic_info.animation.tps_numerator);
if (ctx->basic_info.alpha_bits) {
if (ctx->basic_info.alpha_premultiplied)
avctx->alpha_mode = AVALPHA_MODE_PREMULTIPLIED;
else
avctx->alpha_mode = AVALPHA_MODE_STRAIGHT;
}
continue;
case JXL_DEC_COLOR_ENCODING:
av_log(avctx, AV_LOG_DEBUG, "COLOR_ENCODING event emitted\n");
libavcodec/libjxlenc.c
+15
View File
@@ -357,6 +357,15 @@ static int libjxl_preprocess_stream(AVCodecContext *avctx, const AVFrame *frame,
jxl_fmt->data_type = info.bits_per_sample <= 8 ? JXL_TYPE_UINT8 : JXL_TYPE_UINT16;
}
if (info.alpha_bits) {
if (avctx->alpha_mode == AVALPHA_MODE_PREMULTIPLIED ||
avctx->alpha_mode == AVALPHA_MODE_UNSPECIFIED && frame->alpha_mode == AVALPHA_MODE_PREMULTIPLIED) {
info.alpha_premultiplied = 1;
} else if (avctx->alpha_mode != AVALPHA_MODE_STRAIGHT && frame->alpha_mode != AVALPHA_MODE_STRAIGHT) {
av_log(avctx, AV_LOG_WARNING, "Unknown alpha mode, assuming straight (independent)\n");
}
}
#if JPEGXL_NUMERIC_VERSION >= JPEGXL_COMPUTE_NUMERIC_VERSION(0, 8, 0)
jxl_bit_depth.bits_per_sample = bits_per_sample;
jxl_bit_depth.type = JXL_BIT_DEPTH_FROM_PIXEL_FORMAT;
@@ -771,6 +780,9 @@ const FFCodec ff_libjxl_encoder = {
FF_CODEC_CAP_AUTO_THREADS | FF_CODEC_CAP_INIT_CLEANUP |
FF_CODEC_CAP_ICC_PROFILES,
CODEC_PIXFMTS_ARRAY(libjxl_supported_pixfmts),
.alpha_modes = (const enum AVAlphaMode[]) {
AVALPHA_MODE_STRAIGHT, AVALPHA_MODE_PREMULTIPLIED, AVALPHA_MODE_UNSPECIFIED
},
.p.priv_class = &libjxl_encode_class,
.p.wrapper_name = "libjxl",
};
@@ -791,6 +803,9 @@ const FFCodec ff_libjxl_anim_encoder = {
FF_CODEC_CAP_AUTO_THREADS | FF_CODEC_CAP_INIT_CLEANUP |
FF_CODEC_CAP_ICC_PROFILES,
CODEC_PIXFMTS_ARRAY(libjxl_supported_pixfmts),
.alpha_modes = (const enum AVAlphaMode[]) {
AVALPHA_MODE_STRAIGHT, AVALPHA_MODE_PREMULTIPLIED, AVALPHA_MODE_UNSPECIFIED
},
.p.priv_class = &libjxl_encode_class,
.p.wrapper_name = "libjxl",
};