[FFmpeg-devel] [PATCH v6 1/2] avcodec/libjxldec: properly tag output colorspace

[Leo Izen]

Whether an ICC profile is present or not, the decoder
should now properly tag the colorspace of pixel data
received by the decoder.
---
 libavcodec/libjxldec.c | 113 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 105 insertions(+), 8 deletions(-)

diff --git a/libavcodec/libjxldec.c b/libavcodec/libjxldec.c
index cd4bca3343..813ee279fe 100644
--- a/libavcodec/libjxldec.c
+++ b/libavcodec/libjxldec.c
@@ -135,6 +135,7 @@ static int libjxl_decode_frame(AVCodecContext *avctx, AVFrame *frame, int *got_f
     uint8_t *buf = avpkt->data;
     size_t remaining = avpkt->size, iccp_len;
     JxlDecoderStatus jret;
+    JxlColorEncoding jxl_encoding;
     int ret;
     *got_frame = 0;
 
@@ -189,16 +190,112 @@ static int libjxl_decode_frame(AVCodecContext *avctx, AVFrame *frame, int *got_f
             continue;
         case JXL_DEC_COLOR_ENCODING:
             av_log(avctx, AV_LOG_DEBUG, "COLOR_ENCODING event emitted\n");
-            jret = JxlDecoderGetICCProfileSize(ctx->decoder, &ctx->jxl_pixfmt, JXL_COLOR_PROFILE_TARGET_ORIGINAL, &iccp_len);
-            if (jret == JXL_DEC_SUCCESS && iccp_len > 0) {
-                av_buffer_unref(&ctx->iccp);
-                ctx->iccp = av_buffer_alloc(iccp_len);
-                if (!ctx->iccp)
-                    return AVERROR(ENOMEM);
-                jret = JxlDecoderGetColorAsICCProfile(ctx->decoder, &ctx->jxl_pixfmt, JXL_COLOR_PROFILE_TARGET_ORIGINAL, ctx->iccp->data, iccp_len);
-                if (jret != JXL_DEC_SUCCESS)
+            jret = JxlDecoderGetColorAsEncodedProfile(ctx->decoder, NULL, JXL_COLOR_PROFILE_TARGET_ORIGINAL, &jxl_encoding);
+            if (jret == JXL_DEC_SUCCESS)
+                jret = JxlDecoderSetPreferredColorProfile(ctx->decoder, &jxl_encoding);
+            if (jret == JXL_DEC_SUCCESS)
+                jret = JxlDecoderGetColorAsEncodedProfile(ctx->decoder, &ctx->jxl_pixfmt, JXL_COLOR_PROFILE_TARGET_DATA, &jxl_encoding);
+
+            avctx->color_range = frame->color_range = AVCOL_RANGE_JPEG;
+
+            if (jret == JXL_DEC_SUCCESS) {
+                if (ctx->jxl_pixfmt.num_channels >= 3) {
+                    avctx->colorspace = AVCOL_SPC_RGB;
+                    switch (jxl_encoding.primaries) {
+                    case JXL_PRIMARIES_SRGB:
+                        avctx->color_primaries = AVCOL_PRI_BT709;
+                        break;
+                    case JXL_PRIMARIES_2100:
+                        /* BT2020 and BT2100 use the same primaries */
+                        avctx->color_primaries = AVCOL_PRI_BT2020;
+                        break;
+                    case JXL_PRIMARIES_P3:
+                        /* DCI P3 uses DCI, Display P3 uses D65 */
+                        if (jxl_encoding.white_point == JXL_WHITE_POINT_DCI) {
+                            avctx->color_primaries = AVCOL_PRI_SMPTE431;
+                        } else if (jxl_encoding.white_point == JXL_WHITE_POINT_D65) {
+                            avctx->color_primaries = AVCOL_PRI_SMPTE432;
+                        } else {
+                            av_log(avctx, AV_LOG_WARNING, "Unsupported JXL white point: %d\n", jxl_encoding.white_point);
+                            jret = JXL_DEC_ERROR;
+                        }
+                        break;
+                    case JXL_PRIMARIES_CUSTOM:
+                        av_log(avctx, AV_LOG_WARNING, "Custom primaries are unsupported without an ICC profile\n");
+                        jret = JXL_DEC_ERROR;
+                        break;
+                    default:
+                        av_log(avctx, AV_LOG_WARNING, "Unknown JXL color primaries: %d\n", jxl_encoding.primaries);
+                        jret = JXL_DEC_ERROR;
+                    }
+                }
+
+                switch (jxl_encoding.transfer_function) {
+                case JXL_TRANSFER_FUNCTION_709:
+                    avctx->color_trc = AVCOL_TRC_BT709;
+                    break;
+                case JXL_TRANSFER_FUNCTION_LINEAR:
+                    avctx->color_trc = AVCOL_TRC_LINEAR;
+                    break;
+                case JXL_TRANSFER_FUNCTION_SRGB:
+                    avctx->color_trc = AVCOL_TRC_IEC61966_2_1;
+                    break;
+                case JXL_TRANSFER_FUNCTION_PQ:
+                    avctx->color_trc = AVCOL_TRC_SMPTE2084;
+                    break;
+                case JXL_TRANSFER_FUNCTION_DCI:
+                    avctx->color_trc = AVCOL_TRC_SMPTE428;
+                    break;
+                case JXL_TRANSFER_FUNCTION_HLG:
+                    avctx->color_trc = AVCOL_TRC_ARIB_STD_B67;
+                    break;
+                case JXL_TRANSFER_FUNCTION_GAMMA:
+                    if (jxl_encoding.gamma == 2.2) {
+                        avctx->color_trc = AVCOL_TRC_GAMMA22;
+                    } else if (jxl_encoding.gamma == 2.8) {
+                        avctx->color_trc = AVCOL_TRC_GAMMA28;
+                    } else {
+                        av_log(avctx, AV_LOG_WARNING, "Unsupported gamma transfer: %f\n", jxl_encoding.gamma);
+                        jret = JXL_DEC_ERROR;
+                    }
+                    break;
+                default:
+                    av_log(avctx, AV_LOG_WARNING, "Unknown transfer function: %d\n", jxl_encoding.transfer_function);
+                    jret = JXL_DEC_ERROR;
+                }
+            }
+
+            /* fall back on ICCP if enum values fail */
+            if (jret != JXL_DEC_SUCCESS) {
+                jret = JxlDecoderGetICCProfileSize(ctx->decoder, &ctx->jxl_pixfmt, JXL_COLOR_PROFILE_TARGET_DATA, &iccp_len);
+                if (jret == JXL_DEC_SUCCESS && iccp_len > 0) {
                     av_buffer_unref(&ctx->iccp);
+                    ctx->iccp = av_buffer_alloc(iccp_len);
+                    if (!ctx->iccp)
+                        return AVERROR(ENOMEM);
+                    jret = JxlDecoderGetColorAsICCProfile(ctx->decoder, &ctx->jxl_pixfmt, JXL_COLOR_PROFILE_TARGET_DATA, ctx->iccp->data, iccp_len);
+                    if (jret != JXL_DEC_SUCCESS) {
+                        av_log(avctx, AV_LOG_WARNING, "Unable to obtain ICCP from header\n");
+                        av_buffer_unref(&ctx->iccp);
+                    }
+                }
             }
+
+            if (ctx->iccp) {
+                /* if the ICCP is present, libjxl outputs sRGB */
+                if (ctx->jxl_pixfmt.num_channels >= 3) {
+                    avctx->colorspace = AVCOL_SPC_RGB;
+                    avctx->color_primaries = AVCOL_PRI_BT709;
+                }
+                /* linear sRGB if float values, standard sRGB if int values */
+                avctx->color_trc = ctx->jxl_pixfmt.data_type == JXL_TYPE_FLOAT
+                                    || ctx->jxl_pixfmt.data_type == JXL_TYPE_FLOAT16
+                                    ? AVCOL_TRC_LINEAR : AVCOL_TRC_IEC61966_2_1;
+            }
+
+            frame->color_trc = avctx->color_trc;
+            frame->color_primaries = avctx->color_primaries;
+            frame->colorspace = avctx->colorspace;
             continue;
         case JXL_DEC_NEED_IMAGE_OUT_BUFFER:
             av_log(avctx, AV_LOG_DEBUG, "NEED_IMAGE_OUT_BUFFER event emitted\n");
-- 
2.36.0