[RFC,v8,4/6] libcamera: shaders: Add LSC support
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Message ID 20260716222515.251464-5-mzamazal@redhat.com
State New
Headers show
Series
  • LSC for SoftISP simple pipeline
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Commit Message

Milan Zamazal July 16, 2026, 10:25 p.m. UTC 
From: Xander Pronk <xander.c.pronk@gmail.com>

Lens shading correction should be applied after black level
subtraction (in order to make the computations with meaningful values)
and before white balance (especially before white balance stats are
computed).

Note that lens shading correction depends on temperature, which is
computed from the preceding, rather than current, frame (this is due to
how white balance is currently computed).

The shaders are compiled on initialisation, while lens shading
correction can be enabled or disabled dynamically, using the
corresponding control.  The whole correction in the shader is wrapped by
a conditional macro to be able to disable it and all the related
overheads if Lsc algorithm is not enabled at all.

If Lsc algorithm is enabled, the correction is always applied, whether
the given control is enabled or not.  If it is not, 1.0 multipliers are
expected to be provided.  This is because lens shading correction is
supposed to be rarely switched off using the runtime control when Lsc
algorithm is enabled, e.g. only for demoing or debugging purposes.
We prefer accepting the performance penalty of applying a no-op
correction in such cases rather than disturbing GPU computation in the
regular flow by introducing a runtime `if'.

Co-developed-by: Rick ten Wolde <rick_libcamera@wolde.info>
Signed-off-by: Rick ten Wolde <rick_libcamera@wolde.info>
Signed-off-by: Xander Pronk <xander.c.pronk@gmail.com>
Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
---
 src/libcamera/shaders/bayer_1x_packed.frag | 8 ++++++++
 src/libcamera/shaders/bayer_unpacked.frag  | 8 ++++++++
 2 files changed, 16 insertions(+)

Patch
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diff --git a/src/libcamera/shaders/bayer_1x_packed.frag b/src/libcamera/shaders/bayer_1x_packed.frag
index 0b641a5f3..e1c6fad4c 100644
--- a/src/libcamera/shaders/bayer_1x_packed.frag
+++ b/src/libcamera/shaders/bayer_1x_packed.frag
@@ -71,6 +71,10 @@  uniform vec3 blacklevel;
 uniform float gamma;
 uniform float contrastExp;
 
+#if defined(APPLY_LSC)
+uniform sampler2D lsc_tex;
+#endif
+
 float apply_contrast(float value)
 {
 	// Apply simple S-curve
@@ -232,6 +236,10 @@  void main(void)
 	 */
 	rgb = (rgb - blacklevel) / (1.0 - blacklevel);
 
+#if defined(APPLY_LSC)
+        rgb = rgb * texture2D(lsc_tex, textureOut).rgb;
+#endif
+
 	/* Apply AWB gains, and saturate each channel at sensor range */
 	rgb = clamp(rgb * awb, vec3(0.0), vec3(1.0));
 
diff --git a/src/libcamera/shaders/bayer_unpacked.frag b/src/libcamera/shaders/bayer_unpacked.frag
index 10c5e941b..5b870fb2c 100644
--- a/src/libcamera/shaders/bayer_unpacked.frag
+++ b/src/libcamera/shaders/bayer_unpacked.frag
@@ -30,6 +30,10 @@  uniform vec3            blacklevel;
 uniform float           gamma;
 uniform float           contrastExp;
 
+#if defined(APPLY_LSC)
+uniform sampler2D lsc_tex;
+#endif
+
 float apply_contrast(float value)
 {
     // Apply simple S-curve
@@ -135,6 +139,10 @@  void main(void) {
      */
     rgb = (rgb - blacklevel) / (1.0 - blacklevel);
 
+#if defined(APPLY_LSC)
+    rgb = rgb * texture2D(lsc_tex, center.xy).rgb;
+#endif
+
     /* Apply AWB gains, and saturate each channel at sensor range */
     rgb = clamp(rgb * awb, vec3(0.0), vec3(1.0));