[4/7] libcamera: software_isp: Fix black level application in GPU ISP
diff mbox series

Message ID 20260621-kbingham-awb-saturation-v1-4-b91ea59c6cfb@ideasonboard.com
State New
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Series
  • softisp: Fix Saturation and Black level handling
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Commit Message

Kieran Bingham June 20, 2026, 11 p.m. UTC 
From: Milan Zamazal <mzamazal@redhat.com>

In GPU ISP fragment shaders, the black level is simply subtracted from
the pixel value.  This means the highest pixel values can never be
reached, possibly resulting in wrong brightness or colour shifts.  Fix
this by spreading the resulting value to the whole 0.0..1.0 range.

The preceding simple pipeline IPA patch ensures `blacklevel' is less
than 1.0, preventing division by zero here.

Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
---
 src/libcamera/shaders/bayer_1x_packed.frag | 6 +++++-
 src/libcamera/shaders/bayer_unpacked.frag  | 6 +++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

Patch
diff mbox series 

diff --git a/src/libcamera/shaders/bayer_1x_packed.frag b/src/libcamera/shaders/bayer_1x_packed.frag
index 23747f78a6313503a46b61ed5bae6e7c178c5745..fbd15b32e5b3b510ba0dd5a75704f9ff3942e00c 100644
--- a/src/libcamera/shaders/bayer_1x_packed.frag
+++ b/src/libcamera/shaders/bayer_1x_packed.frag
@@ -225,7 +225,11 @@  void main(void)
 			vec3(patterns.y, C, patterns.x) :
 			vec3(patterns.wz, C));
 
-	rgb = rgb - blacklevel;
+	/*
+	 * \todo: Black level normalising, AWB and digital gain could be
+	 * reworked into a single multiplication.
+	 */
+	rgb = (rgb - blacklevel) / (1.0 - blacklevel);
 
 	/*
 	 *   CCM is a 3x3 in the format
diff --git a/src/libcamera/shaders/bayer_unpacked.frag b/src/libcamera/shaders/bayer_unpacked.frag
index 1b85196ae16130670eb3d1c077ab4884119ae63c..0f85e9a4ded7f43ce4fdabf1e045275ae2bc8f53 100644
--- a/src/libcamera/shaders/bayer_unpacked.frag
+++ b/src/libcamera/shaders/bayer_unpacked.frag
@@ -128,7 +128,11 @@  void main(void) {
             vec3(PATTERN.w, C, PATTERN.z) :
             vec3(PATTERN.yx, C));
 
-    rgb = rgb - blacklevel;
+    /*
+     * \todo: Black level normalising, AWB and digital gain could be
+     * reworked into a single multiplication.
+     */
+    rgb = (rgb - blacklevel) / (1.0 - blacklevel);
 
     /*
      *   CCM is a 3x3 in the format