libtuning: agc: rkisp1: Increase y-target

With the addition of gamma out correction the relative luminance target
was set too low. As brightness is a bit subjective it is difficult to
come up with the "correct" value. With 0.5 the patch 22 on the macbeth
chart (neutral grey, 18% reflectance) ended up a bit below 50% grey,
which seems reasonable.

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>

utils/tuning/libtuning/modules/agc/rkisp1.py

@@ -64,7 +64,7 @@ class AGCRkISP1(AGC):
         return {'ConstraintNormal': normal, 'ConstraintHighlight': highlight}
 
     def _generate_y_target(self) -> list:
-        return 0.16
+        return 0.5
 
     def process(self, config: dict, images: list, outputs: dict) -> dict:
         output = {}