[PATCH v3 22/23] libtuning: lsc: Prevent negative values

[Stefan Klug]

In cases where the calibration image contains super dark areas, or when
an invalid blacklevel was supplied, the grid might get close to zero or
negative. This would have bad effects on the 1/grid later. So clamp the
values to a small positive number.

Signed-off-by: Stefan Klug <stefan.klug at ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 utils/tuning/libtuning/modules/lsc/lsc.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/utils/tuning/libtuning/modules/lsc/lsc.py b/utils/tuning/libtuning/modules/lsc/lsc.py
index 344a07a3d443..e0ca22ebe9bd 100644
--- a/utils/tuning/libtuning/modules/lsc/lsc.py
+++ b/utils/tuning/libtuning/modules/lsc/lsc.py
@@ -59,7 +59,10 @@ class LSC(Module):
     def _lsc_single_channel(self, channel: np.array,
                             image: lt.Image, green_grid: np.array = None):
         grid = self._get_grid(channel, image.w, image.h)
-        grid -= image.blacklevel_16
+        # Clamp the values to a small positive, so that the following 1/grid
+        # doesn't produce negative results.
+        grid = np.maximum(grid - image.blacklevel_16, 0.1)
+
         if green_grid is None:
             table = np.reshape(1 / grid, self.sector_shape[::-1])
         else:
-- 
2.43.0