[{"id":37426,"web_url":"https://patchwork.libcamera.org/comment/37426/","msgid":"<85ldj1b6l0.fsf@mzamazal-thinkpadp1gen7.tpbc.csb>","date":"2025-12-17T13:06:51","subject":"Re: [PATCH v9 10/26] libcamera: shaders: Add support for contrast","submitter":{"id":177,"url":"https://patchwork.libcamera.org/api/people/177/","name":"Milan Zamazal","email":"mzamazal@redhat.com"},"content":"Bryan O'Donoghue writes:\n\n> Apply contrast after black-level and CCM operations.\n>\n> Suggested-by: Milan Zamazal \n> Signed-off-by: Bryan O'Donoghue \n> ---\n> src/libcamera/shaders/bayer_1x_packed.frag | 21 +++++++++++++++++++++\n> src/libcamera/shaders/bayer_unpacked.frag | 21 +++++++++++++++++++++\n> 2 files changed, 42 insertions(+)\n>\n> diff --git a/src/libcamera/shaders/bayer_1x_packed.frag b/src/libcamera/shaders/bayer_1x_packed.frag\n> index 77d9fbfa7..0b730070e 100644\n> --- a/src/libcamera/shaders/bayer_1x_packed.frag\n> +++ b/src/libcamera/shaders/bayer_1x_packed.frag\n> @@ -68,6 +68,16 @@ uniform sampler2D tex_y;\n> uniform mat3 ccm;\n> uniform vec3 blacklevel;\n> uniform float gamma;\n> +uniform float contrast;\n> +\n> +float apply_contrast(float value, float contrastExp)\n> +{\n> +\t// Apply simple S-curve\n> +\tif (value < 0.5)\n> +\t\treturn 0.5 * pow(value / 0.5, contrastExp);\n> +\telse\n> +\t\treturn 1.0 - 0.5 * pow((1.0 - value) / 0.5, contrastExp);\n> +}\n> \n> void main(void)\n> {\n> @@ -261,6 +271,17 @@ void main(void)\n> \trgb.g = (rin * ccm[1][0]) + (gin * ccm[1][1]) + (bin * ccm[1][2]);\n> \trgb.b = (rin * ccm[2][0]) + (gin * ccm[2][1]) + (bin * ccm[2][2]);\n> \n> +\t/*\n> +\t * Contrast\n> +\t * contrastExp 0..2 contrast to 0..infinity; avoid actual infinity at tan(pi/2)\n> +\t */\n> +\tfloat contrastExp = tan(clamp(contrast * 0.78539816339744830962, 0.0, 1.5707963267948966 - 0.00001));\n\nAs discussed at the sync, the constants should be either computed from\nnamed constants or explained in a source code comment (here and in the\nunpacked shader).\n\n0.78539816339744830962 = pi / 4\n1.5707963267948966 = pi / 2\n\nPassing contrastExp value as a uniform is another option.\n\nWith either of these:\n\nReviewed-by: Milan Zamazal \n\n> +\n> +\trgb = clamp(rgb, 0.0, 1.0);\n> +\trgb.r = apply_contrast(rgb.r, contrastExp);\n> +\trgb.g = apply_contrast(rgb.g, contrastExp);\n> +\trgb.b = apply_contrast(rgb.b, contrastExp);\n> +\n> \t/* Apply gamma after colour correction */\n> \trgb = pow(rgb, vec3(gamma));\n> \n> diff --git a/src/libcamera/shaders/bayer_unpacked.frag b/src/libcamera/shaders/bayer_unpacked.frag\n> index aba11a87f..114e32058 100644\n> --- a/src/libcamera/shaders/bayer_unpacked.frag\n> +++ b/src/libcamera/shaders/bayer_unpacked.frag\n> @@ -27,6 +27,16 @@ varying vec4 xCoord;\n> uniform mat3 ccm;\n> uniform vec3 blacklevel;\n> uniform float gamma;\n> +uniform float contrast;\n> +\n> +float apply_contrast(float value, float contrastExp)\n> +{\n> + // Apply simple S-curve\n> + if (value < 0.5)\n> + return 0.5 * pow(value / 0.5, contrastExp);\n> + else\n> + return 1.0 - 0.5 * pow((1.0 - value) / 0.5, contrastExp);\n> +}\n> \n> void main(void) {\n> vec3 rgb;\n> @@ -156,6 +166,17 @@ void main(void) {\n> rgb.g = (rin * ccm[1][0]) + (gin * ccm[1][1]) + (bin * ccm[1][2]);\n> rgb.b = (rin * ccm[2][0]) + (gin * ccm[2][1]) + (bin * ccm[2][2]);\n> \n> + /*\n> + * Contrast\n> + * Convert 0..2 contrast to 0..infinity; avoid actual infinity at tan(pi/2)\n> + */\n> + float contrastExp = tan(clamp(contrast * 0.78539816339744830962, 0.0, 1.5707963267948966 - 0.00001));\n> +\n> + rgb = clamp(rgb, 0.0, 1.0);\n> + rgb.r = apply_contrast(rgb.r, contrastExp);\n> + rgb.g = apply_contrast(rgb.g, contrastExp);\n> + rgb.b = apply_contrast(rgb.b, contrastExp);\n> +\n> /* Apply gamma after colour correction */\n> rgb = pow(rgb, vec3(gamma));","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id 1C1CFBD7D8\n\tfor ;\n\tWed, 17 Dec 2025 13:07:01 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 1F44D61A4E;\n\tWed, 17 Dec 2025 14:07:00 +0100 (CET)","from us-smtp-delivery-124.mimecast.com\n\t(us-smtp-delivery-124.mimecast.com [170.10.129.124])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 4204761A35\n\tfor ;\n\tWed, 17 Dec 2025 14:06:58 +0100 (CET)","from mail-wm1-f72.google.com (mail-wm1-f72.google.com\n\t[209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS\n\t(version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id\n\tus-mta-593-lWVA9gPKOjiqHkPm1UCkQw-1; 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\n\tWed, 17 Dec 2025 05:06:53 -0800 (PST)","by 2002:a05:600d:8401:b0:47a:935f:61a0 with SMTP id\n\t5b1f17b1804b1-47a935f64f6mr142969675e9.0.1765976813071; \n\tWed, 17 Dec 2025 05:06:53 -0800 (PST)"],"X-Google-Smtp-Source":"AGHT+IGfLxEtSqivQY8Fq95K6h42yEV0NcdPMss1/eyPoZglvIiPjzEQu0c8xfI7atCNElIihGtlig==","From":"Milan Zamazal ","To":"Bryan O'Donoghue ","Cc":"libcamera-devel@lists.libcamera.org, pavel@ucw.cz","Subject":"Re: [PATCH v9 10/26] libcamera: shaders: Add support for contrast","In-Reply-To":"<20251217100138.82525-11-bryan.odonoghue@linaro.org> (Bryan\n\tO'Donoghue's message of \"Wed, 17 Dec 2025 10:01:22 +0000\")","References":"<20251217100138.82525-1-bryan.odonoghue@linaro.org>\n\t<20251217100138.82525-11-bryan.odonoghue@linaro.org>","Date":"Wed, 17 Dec 2025 14:06:51 +0100","Message-ID":"<85ldj1b6l0.fsf@mzamazal-thinkpadp1gen7.tpbc.csb>","User-Agent":"Gnus/5.13 (Gnus v5.13)","MIME-Version":"1.0","X-Mimecast-Spam-Score":"0","X-Mimecast-MFC-PROC-ID":"A05DVfoIuTYyJjoITRB88bv71ZhcSsG9GQ1NTnkPYUI_1765976813","X-Mimecast-Originator":"redhat.com","Content-Type":"text/plain","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}}]