Add color correction to the gles shader

data/debayer.frag

@@ -5,6 +5,7 @@ precision highp float;
 uniform sampler2D texture;
 uniform mat3 color_matrix;
 uniform float inv_gamma;
+uniform float blacklevel;
 #ifdef BITS_10
 uniform float row_length;
 uniform float padding_ratio;
@@ -59,16 +60,9 @@ main()
         vec3 color = vec3(samples.x, (samples.y + samples.z) / 2.0, samples.w);
 #endif
 
-        // Some crude blacklevel correction to make the preview a bit nicer, this
-        // should be an uniform
-        vec3 corrected = color - 0.02;
-
-        /*
-        // Fast SRGB estimate. See https://mimosa-pudica.net/fast-gamma/
-        vec3 gamma_color =
-                (vec3(1.138) * inversesqrt(corrected) - vec3(0.138)) * corrected;
-        */
-        color = color * color_matrix;
+        color -= blacklevel;
+        color *= 1.0-(1.0/blacklevel);
+        color *= color_matrix;
 
         vec3 gamma_color = pow(color, vec3(inv_gamma));
         gl_FragColor = vec4(gamma_color, 1);