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[68.41.54.207]) by smtp.gmail.com with ESMTPSA id r7-20020a92d987000000b0030f43cefc4bsm6570122iln.53.2023.02.02.07.09.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Feb 2023 07:09:42 -0800 (PST) From: Leo Izen To: ffmpeg-devel@ffmpeg.org Date: Thu, 2 Feb 2023 10:09:38 -0500 Message-Id: <20230202150938.22297-4-leo.izen@gmail.com> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230202150938.22297-1-leo.izen@gmail.com> References: <20230202150938.22297-1-leo.izen@gmail.com> MIME-Version: 1.0 Subject: [FFmpeg-devel] [PATCH v3 3/3] avcodec/pngdec: populate enum transfer values from gAMA chunk X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: FFmpeg development discussions and patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: FFmpeg development discussions and patches Cc: Leo Izen Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" X-TUID: xD/B1HBBNvzp If the gAMA chunk is present, the gamma-transfer described by it often matches one of our enum values (e.g. gamma = 2.2). If so, we should populate the corresponding fields in AVCodecContext and AVFrame, provided that some other chunk isn't already providing that info. --- libavcodec/pngdec.c | 27 ++++++++++++++++++++++++--- 1 file changed, 24 insertions(+), 3 deletions(-) diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c index a80e0d15bb..b7751c64d8 100644 --- a/libavcodec/pngdec.c +++ b/libavcodec/pngdec.c @@ -75,6 +75,7 @@ typedef struct PNGDecContext { int have_chrm; uint32_t white_point[2]; uint32_t display_primaries[3][2]; + int gamma; int have_srgb; int have_cicp; enum AVColorPrimaries cicp_primaries; @@ -1259,6 +1260,7 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s, case MKTAG('s', 'R', 'G', 'B'): case MKTAG('c', 'I', 'C', 'P'): case MKTAG('c', 'H', 'R', 'M'): + case MKTAG('g', 'A', 'M', 'A'): break; default: continue; @@ -1361,10 +1363,10 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s, case MKTAG('g', 'A', 'M', 'A'): { AVBPrint bp; char *gamma_str; - int num = bytestream2_get_be32(&gb_chunk); + s->gamma = bytestream2_get_be32(&gb_chunk); av_bprint_init(&bp, 0, AV_BPRINT_SIZE_UNLIMITED); - av_bprintf(&bp, "%i/%i", num, 100000); + av_bprintf(&bp, "%i/%i", s->gamma, 100000); ret = av_bprint_finalize(&bp, &gamma_str); if (ret < 0) return ret; @@ -1429,8 +1431,27 @@ exit_loop: } /* these chunks override gAMA */ - if (s->iccp_data || s->have_srgb || s->have_cicp) + if (s->iccp_data || s->have_srgb || s->have_cicp) { av_dict_set(&s->frame_metadata, "gamma", NULL, 0); + } else if (s->gamma) { + /* + * These values are 100000/2.2, 100000/2.8, 100000/2.6, and + * 100000/1.0 respectively. 45455, 35714, and 38462, and 100000. + * There's a 0.001 gamma tolerance here in case of floating + * point issues when the PNG was written. + * + * None of the other enums have a pure gamma curve so it makes + * sense to leave those to sRGB and cICP. + */ + if (s->gamma > 45355 && s->gamma < 45555) + avctx->color_trc = p->color_trc = AVCOL_TRC_GAMMA22; + else if (s->gamma > 35614 && s->gamma < 35814) + avctx->color_trc = p->color_trc = AVCOL_TRC_GAMMA28; + else if (s->gamma > 38362 && s->gamma < 38562) + avctx->color_trc = p->color_trc = AVCOL_TRC_SMPTE428; + else if (s->gamma > 99900 && s->gamma < 100100) + avctx->color_trc = p->color_trc = AVCOL_TRC_LINEAR; + } avctx->colorspace = p->colorspace = AVCOL_SPC_RGB; avctx->color_range = p->color_range = AVCOL_RANGE_JPEG;