From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ffbox0-bg.mplayerhq.hu (ffbox0-bg.ffmpeg.org [79.124.17.100]) by master.gitmailbox.com (Postfix) with ESMTP id D59BB4A69D for ; Thu, 4 Jul 2024 14:32:10 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 947D568DA2E; Thu, 4 Jul 2024 17:31:24 +0300 (EEST) Received: from haasn.dev (haasn.dev [78.46.187.166]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 609DA68D9FC for ; Thu, 4 Jul 2024 17:31:12 +0300 (EEST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=haasn.xyz; s=mail; t=1720103468; bh=2khgc9946s96WOy2dLPxdNHKKZN53lzbELU1p0FVRiU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=El9KHwA1of6JoIzshou/g0VP++UthnujzGRyxDQM8b67PWp9gGfmfRd0Yj3oEY0Tj 0Eyz1HmA7K66Z5t7nKT7yhcEHhdopKZVpB9VAGF0auf9l9QEVyiPAI+8KXBssX+dgo 3YZt+Vh4127SbYc5flIl+d+1Dv32YGfnR9VSsgpA= Received: from haasn.dev (unknown [10.30.0.2]) by haasn.dev (Postfix) with ESMTP id F26B041F18; Thu, 4 Jul 2024 16:31:07 +0200 (CEST) From: Niklas Haas To: ffmpeg-devel@ffmpeg.org Date: Thu, 4 Jul 2024 16:31:02 +0200 Message-ID: <20240704143104.1821386-6-ffmpeg@haasn.xyz> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240704143104.1821386-1-ffmpeg@haasn.xyz> References: <20240704143104.1821386-1-ffmpeg@haasn.xyz> MIME-Version: 1.0 Subject: [FFmpeg-devel] [PATCH v2 6/8] avfilter/vf_scale: fix 4:1:0 interlaced chroma pos 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 The current logic hard-coded a check for v_sub == 1. We can extend this logic slightly to cover the case of interlaced 4:1:0 (which has v_sub == 2). Here is a diagram explaining this scenario (with center-siting): a a a a a a a a b b b b b b b b X X a a a a a a a a b b b b b b b b a a a a a a a a b b b b b b b b Y Y a a a a a a a a b b b b b b b b a = even luma rows b = odd luma rows X = even chroma sample Y = odd chroma sample In progressive mode, the chroma samples sit at (384, 384) respectively. Relative to the 8x4 grid of even luma samples (a), the X sample sits at: h_chr_pos = 384 v_chr_pos = 192 Relative to the 8x4 grid of odd luma samples (b), the Y sample sits at: h_chr_pos = 384 v_chr_pos = 576 The new code calculates the correct values in all circumstances. --- libavfilter/vf_scale.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/libavfilter/vf_scale.c b/libavfilter/vf_scale.c index b2c9d0b187..2d82141b70 100644 --- a/libavfilter/vf_scale.c +++ b/libavfilter/vf_scale.c @@ -642,9 +642,19 @@ static void calc_chroma_pos(int *h_pos_out, int *v_pos_out, int chroma_loc, v_pos = v_pos_override; /* Fix vertical chroma position for interlaced frames */ - if (v_sub == 1 && index > 0) { - v_pos += 256 * (index == 2); /* offset by one luma row for odd rows */ - v_pos >>= 1; /* double luma row distance */ + if (v_sub && index > 0) { + /* When vertically subsampling, chroma samples are effectively only + * placed next to even rows. To access them from the odd field, we need + * to account for this shift by offsetting the distance of one luma row. + * + * For 4x vertical subsampling (v_sub == 2), they are only placed + * next to every *other* even row, so we need to shift by three luma + * rows to get to the chroma sample. */ + if (index == 2) + v_pos += (256 << v_sub) - 256; + + /* Luma row distance is doubled for fields, so halve offsets */ + v_pos >>= 1; } /* Explicitly strip chroma offsets when not subsampling, because it -- 2.45.2 _______________________________________________ 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".