From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ffbox0-bg.ffmpeg.org (ffbox0-bg.ffmpeg.org [79.124.17.100]) by master.gitmailbox.com (Postfix) with ESMTPS id 3F55A4AED9 for ; Wed, 23 Jul 2025 13:58:28 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.ffmpeg.org (Postfix) with ESMTP id 6EF4568D95D; Wed, 23 Jul 2025 16:56:53 +0300 (EEST) Received: from haasn.dev (haasn.dev [78.46.187.166]) by ffbox0-bg.ffmpeg.org (Postfix) with ESMTP id 50A2368D88B for ; Wed, 23 Jul 2025 16:56:33 +0300 (EEST) Received: from haasn.dev (unknown [10.30.1.1]) by haasn.dev (Postfix) with UTF8SMTP id 3F55A481ED; Wed, 23 Jul 2025 15:56:28 +0200 (CEST) From: Niklas Haas To: ffmpeg-devel@ffmpeg.org Date: Wed, 23 Jul 2025 15:47:09 +0200 Message-ID: <20250723135626.1390296-7-ffmpeg@haasn.xyz> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250723135626.1390296-1-ffmpeg@haasn.xyz> References: <20250723135626.1390296-1-ffmpeg@haasn.xyz> MIME-Version: 1.0 Subject: [FFmpeg-devel] [PATCH v2 06/18] avcodec/png: set correct alpha mode 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: Niklas Haas Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: From: Niklas Haas PNG always uses straight alpha. cf. https://www.w3.org/TR/PNG-Rationale.html > Although each form of alpha storage has its advantages, we did not want to > require all PNG viewers to handle both forms. We standardized on non- > premultiplied alpha as being the lossless and more general case. --- libavcodec/pngdec.c | 5 +++++ libavcodec/pngenc.c | 6 ++++++ 2 files changed, 11 insertions(+) diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c index b9c997ab0e..d2a61d3bce 100644 --- a/libavcodec/pngdec.c +++ b/libavcodec/pngdec.c @@ -875,6 +875,11 @@ static int decode_idat_chunk(AVCodecContext *avctx, PNGDecContext *s, s->bpp += byte_depth; } + /* PNG spec mandates independent alpha channel */ + if (s->color_type == PNG_COLOR_TYPE_RGB_ALPHA || + s->color_type == PNG_COLOR_TYPE_GRAY_ALPHA) + avctx->alpha_mode = AVALPHA_MODE_STRAIGHT; + ff_progress_frame_unref(&s->picture); if (s->dispose_op == APNG_DISPOSE_OP_PREVIOUS) { /* We only need a buffer for the current picture. */ diff --git a/libavcodec/pngenc.c b/libavcodec/pngenc.c index 9bbb8267cf..ddafd4ed08 100644 --- a/libavcodec/pngenc.c +++ b/libavcodec/pngenc.c @@ -1239,6 +1239,9 @@ const FFCodec ff_png_encoder = { AV_PIX_FMT_GRAY8, AV_PIX_FMT_GRAY8A, AV_PIX_FMT_GRAY16BE, AV_PIX_FMT_YA16BE, AV_PIX_FMT_MONOBLACK), + .alpha_modes = (const enum AVAlphaMode[]) { + AVALPHA_MODE_STRAIGHT, AVALPHA_MODE_UNSPECIFIED + }, .p.priv_class = &pngenc_class, .caps_internal = FF_CODEC_CAP_ICC_PROFILES, }; @@ -1259,6 +1262,9 @@ const FFCodec ff_apng_encoder = { AV_PIX_FMT_PAL8, AV_PIX_FMT_GRAY8, AV_PIX_FMT_GRAY8A, AV_PIX_FMT_GRAY16BE, AV_PIX_FMT_YA16BE), + .alpha_modes = (const enum AVAlphaMode[]) { + AVALPHA_MODE_STRAIGHT, AVALPHA_MODE_UNSPECIFIED + }, .p.priv_class = &pngenc_class, .caps_internal = FF_CODEC_CAP_ICC_PROFILES, }; -- 2.50.1 _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".