[{"id":38632,"web_url":"https://patchwork.libcamera.org/comment/38632/","msgid":"<85pl3tiibb.fsf@mzamazal-thinkpadp1gen7.tpbc.csb>","date":"2026-04-20T18:43:20","subject":"Re: [RFC PATCH v2 5/8] libcamera: shaders: Add LSC support","submitter":{"id":177,"url":"https://patchwork.libcamera.org/api/people/177/","name":"Milan Zamazal","email":"mzamazal@redhat.com"},"content":"Milan Zamazal writes:\n\n> From: Xander Pronk \n>\n> Lens shading correction should be applied after black level\n> subtraction (in order to make the computations with meaningful values)\n> and before white balance (especially before white balance stats are\n> computed).\n>\n> Note that lens shading correction depends on temperature, which depends\n> on white balance, so there is a chicken-egg problem. Currently, we\n> determine white balance and temperature from the preceding frame.\n>\n> TODO: It's unknown why the LSC is computed in the shader the way it is.\n>\n> Co-developed-by: Rick ten Wolde \n> Signed-off-by: Rick ten Wolde \n> Signed-off-by: Xander Pronk \n> Signed-off-by: Milan Zamazal \n> ---\n> src/libcamera/shaders/bayer_1x_packed.frag | 8 ++++++++\n> src/libcamera/shaders/bayer_unpacked.frag | 8 ++++++++\n> 2 files changed, 16 insertions(+)\n>\n> diff --git a/src/libcamera/shaders/bayer_1x_packed.frag b/src/libcamera/shaders/bayer_1x_packed.frag\n> index 23747f78a..efc2fec72 100644\n> --- a/src/libcamera/shaders/bayer_1x_packed.frag\n> +++ b/src/libcamera/shaders/bayer_1x_packed.frag\n> @@ -70,6 +70,10 @@ uniform vec3 blacklevel;\n> uniform float gamma;\n> uniform float contrastExp;\n> \n> +#if defined(DO_LSC)\n> +uniform sampler2D lsc_tex;\n> +#endif\n> +\n> float apply_contrast(float value)\n> {\n> \t// Apply simple S-curve\n> @@ -227,6 +231,10 @@ void main(void)\n> \n> \trgb = rgb - blacklevel;\n> \n> +\t#if defined(DO_LSC)\n> +\trgb = rgb + rgb * 3.0 * texture2D(lsc_tex, textureOut).rgb;\n\nCould anybody explain this formula, please?\n\n> +\t#endif\n> +\n> \t/*\n> \t * CCM is a 3x3 in the format\n> \t *\n> diff --git a/src/libcamera/shaders/bayer_unpacked.frag b/src/libcamera/shaders/bayer_unpacked.frag\n> index 1b85196ae..cc82e656c 100644\n> --- a/src/libcamera/shaders/bayer_unpacked.frag\n> +++ b/src/libcamera/shaders/bayer_unpacked.frag\n> @@ -29,6 +29,10 @@ uniform vec3 blacklevel;\n> uniform float gamma;\n> uniform float contrastExp;\n> \n> +#if defined(DO_LSC)\n> +uniform sampler2D lsc_tex;\n> +#endif\n> +\n> float apply_contrast(float value)\n> {\n> // Apply simple S-curve\n> @@ -130,6 +134,10 @@ void main(void) {\n> \n> rgb = rgb - blacklevel;\n> \n> + #if defined(DO_LSC)\n> + rgb = rgb + rgb * 3.0 * texture2D(lsc_tex, center.xy).rgb;\n> + #endif\n> +\n> /*\n> * CCM is a 3x3 in the format\n> *","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 1C6EAC324E\n\tfor ;\n\tMon, 20 Apr 2026 18:43:36 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 91D4162EF2;\n\tMon, 20 Apr 2026 20:43:35 +0200 (CEST)","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 7F02D62EE0\n\tfor ;\n\tMon, 20 Apr 2026 20:43:33 +0200 (CEST)","from mail-pj1-f70.google.com (mail-pj1-f70.google.com\n\t[209.85.216.70]) by relay.mimecast.com with ESMTP with STARTTLS\n\t(version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id\n\tus-mta-17-07Po6C8hMhWDAsyHlCjokw-1; Mon, 20 Apr 2026 14:43:30 -0400","by mail-pj1-f70.google.com with SMTP id\n\t98e67ed59e1d1-358e95e81aeso7251808a91.0\n\tfor ;\n\tMon, 20 Apr 2026 11:43:30 -0700 (PDT)","from mzamazal-thinkpadp1gen7.tpbc.csb\n\t(ip-77-48-47-2.net.vodafone.cz. 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