vo_gpu: match libplacebo debanding defaults

The defaults were awful and horribly regressed many files while also not
fixing banding on files that actually needed it, sometimes even
*increasing* banding due to the low threshold.

Fixes: 12ffce0f22
See-Also: haasn/libplacebo@e1e43376d1

DOCS/interface-changes.rst

@@ -71,6 +71,7 @@ Interface changes
     - change `--dscale` default to `hermite`
     - update defaults to `--hdr-peak-decay-rate=20`, `--hdr-scene-threshold-low=1.0`,
       `--hdr-scene-threshold-high=3.0`
+    - update defaults to `--deband-threshold=48`, `--deband-grain=32`
  --- mpv 0.36.0 ---
     - add `--target-contrast`
     - Target luminance value is now also applied when ICC profile is used.

DOCS/man/options.rst

@@ -6070,7 +6070,7 @@ them.
 ``--deband-threshold=<0..4096>``
     The debanding filter's cut-off threshold. Higher numbers increase the
     debanding strength dramatically but progressively diminish image details.
-    (Default 32)
+    (Default 48)
 
 ``--deband-range=<1..64>``
     The debanding filter's initial radius. The radius increases linearly for
@@ -6083,7 +6083,7 @@ them.
 ``--deband-grain=<0..4096>``
     Add some extra noise to the image. This significantly helps cover up
     remaining quantization artifacts. Higher numbers add more noise. (Default
-    48)
+    32)
 
 ``--corner-rounding=<0..1>``
     If set to a value above 0.0, the output will be rendered with rounded

video/out/gpu/video_shaders.c

@@ -942,9 +942,9 @@ static void prng_init(struct gl_shader_cache *sc, AVLFG *lfg)
 
 const struct deband_opts deband_opts_def = {
     .iterations = 1,
-    .threshold = 32.0,
+    .threshold = 48.0,
     .range = 16.0,
-    .grain = 48.0,
+    .grain = 32.0,
 };
 
 #define OPT_BASE_STRUCT struct deband_opts