[{"id":37347,"web_url":"https://patchwork.libcamera.org/comment/37347/","msgid":"<85ecozqwio.fsf@mzamazal-thinkpadp1gen7.tpbc.csb>","date":"2025-12-12T20:23:59","subject":"Re: [PATCH v8 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\nReviewed-by: Milan Zamazal \n\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> +\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 20F76BD1F1\n\tfor ;\n\tFri, 12 Dec 2025 20:24:07 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 363DC61893;\n\tFri, 12 Dec 2025 21:24:06 +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 53C266142F\n\tfor ;\n\tFri, 12 Dec 2025 21:24:05 +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-629-Ci363lgXMaSNS_mQEJigAw-1; Fri, 12 Dec 2025 15:24:02 -0500","by mail-wm1-f72.google.com with SMTP id\n\t5b1f17b1804b1-47a83800743so7539715e9.0\n\tfor ;\n\tFri, 12 Dec 2025 12:24:02 -0800 (PST)","from mzamazal-thinkpadp1gen7.tpbc.csb\n\t(ip-77-48-47-2.net.vodafone.cz. 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