Adjustments to threshold luminance calculation

src/main.tscn

@@ -56,7 +56,7 @@ shader = ExtResource("1_rg2hr")
 shader = ExtResource("1_bg1gg")
 shader_parameter/color_low = Color(0, 0, 0, 1)
 shader_parameter/color_hi = Color(1, 1, 1, 1)
-shader_parameter/threshold = 0.455
+shader_parameter/threshold = 0.174
 shader_parameter/contrast = 1.0
 shader_parameter/offset = 0.0
 

src/shaders/threshold.gdshader

@@ -1,23 +1,35 @@
-/* Binary threshold shader */
+/* Binary threshold shader
+ * See https://stackoverflow.com/a/56678483
+ */
 
 shader_type canvas_item;
 
 uniform vec4 color_low: source_color = vec4(0.0, 0.0, 0.0, 1.0);
 uniform vec4 color_hi: source_color = vec4(1.0, 1.0, 1.0, 1.0);
 
-uniform float threshold: hint_range(0.0, 1.0) = 0.5;
+uniform float threshold: hint_range(0.0, 1.0) = 0.455;
 uniform float contrast: hint_range(0.0, 1.0) = 1.0;
 uniform float offset: hint_range(-1.0, 1.0) = 0.0;
 
+float linearSRGB(float channel) {
+	if (channel <= 0.04045) {
+		return channel / 12.92;
+	} else {
+		return pow(((channel + 0.055) / 1.055), 2.4);
+	}
+}
+
+float luminance(vec3 color) {
+	return 0.2126 * linearSRGB(color.r) + 0.7152 * linearSRGB(color.g) + 0.0722 * linearSRGB(color.b);
+}
 
 void fragment() {
 	vec3 screen_col = texture(TEXTURE, UV).rgb;
 
-	// calculate pixel luminosity
-	float luminosity = (screen_col.r * 0.299) + (screen_col.g * 0.587) + (screen_col.b * 0.114);
+	float Y = luminance(screen_col);
 
 	// adjust contrast & offset
-	luminosity = clamp((luminosity - 0.5 + offset) * contrast + 0.5, 0.0, 1.0);
+	Y = clamp((Y - 0.5 + offset) * contrast + 0.5, 0.0, 1.0);
 
-	COLOR.rgba = luminosity > threshold ? color_hi : color_low;
+	COLOR.rgba = Y > threshold ? color_hi : color_low;
 }