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 8200740131 for ; Sat, 5 Nov 2022 15:28:11 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 5815F68B4FD; Sat, 5 Nov 2022 17:26:46 +0200 (EET) Received: from ssq0.pkh.me (laubervilliers-656-1-228-164.w92-154.abo.wanadoo.fr [92.154.28.164]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id 4DD5A68B3E7 for ; Sat, 5 Nov 2022 17:26:41 +0200 (EET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pkh.me; s=selector1; t=1667661982; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=n1OyaAQq87iiEE2XLvuqG94Vopy9hh+rhmOfKdxlAxA=; b=X6x1gqUjSpI3mCUa1Qp42jvBG7NMSNswP7OxudmHsE3wqdv4iiDeK56W15Q9ou/kQLohl1 YSXDHry4WCOjcWVgtnvhNd3wduR0Cl+mK6j/06ZyPl/REIfLjdaK1q/GFb8bNSTNUPEcLr oC9zk5yPTyBcGiQ22NfVVMoXzKFTY7M= Received: from localhost (ssq0.pkh.me [local]) by ssq0.pkh.me (OpenSMTPD) with ESMTPA id 66408e5d; Sat, 5 Nov 2022 15:26:22 +0000 (UTC) From: =?UTF-8?q?Cl=C3=A9ment=20B=C5=93sch?= To: ffmpeg-devel@ffmpeg.org Date: Sat, 5 Nov 2022 16:26:13 +0100 Message-Id: <20221105152617.1809282-12-u@pkh.me> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20221105152617.1809282-1-u@pkh.me> References: <20221105152617.1809282-1-u@pkh.me> MIME-Version: 1.0 Subject: [FFmpeg-devel] [PATCH 11/15] avfilter/palettegen: comment on the unnormalized variance 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: =?UTF-8?q?Cl=C3=A9ment=20B=C5=93sch?= 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: --- libavfilter/vf_palettegen.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/libavfilter/vf_palettegen.c b/libavfilter/vf_palettegen.c index 2b412cdb55..b8e4463539 100644 --- a/libavfilter/vf_palettegen.c +++ b/libavfilter/vf_palettegen.c @@ -152,6 +152,24 @@ static void compute_box_variance(PaletteGenContext *s, struct range_box *box) const struct color_ref *ref = s->refs[box->start + i]; variance += diff(ref->color, box->color) * ref->count; } + /* + * The variance is computed as a Mean Squared Error of the distance of the + * current color to the box color average, with an important difference: + * the final sum is not normalized using the total weight of the box (the + * sum of the ref->count). + * + * One may expect that in order to compare the variance of the boxes + * between each others a normalization makes sense. Unfortunately, the + * normalization has the side effect of taking the "size" of the box out of + * the equation. In practice, this has a tendency to cause dramatic banding + * effects (in particular without dithering). Typically a scene where the + * sky is omnipresent may get much less colors assigned than its + * surroundings. + * + * Not normalizing causes a bias towards boxes with many colors, but that's + * exactly what we want. The downside is that vivid/accent colors found in + * small quantities tend to disappear. + */ box->variance = variance; } -- 2.38.1 _______________________________________________ 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".