diff --git a/rsc/shaders/filters/chromakey.glsl b/rsc/shaders/filters/chromakey.glsl
index d7b248d..dc61fe6 100644
--- a/rsc/shaders/filters/chromakey.glsl
+++ b/rsc/shaders/filters/chromakey.glsl
@@ -42,16 +42,24 @@ void mainImage( out vec4 fragColor, in vec2 fragCoord )
 {
     vec4 texColor0 = texture(iChannel0, fragCoord.xy / iResolution.xy);
 
+    // RGB is alpha-premultiplied : revert
+    vec4 col = vec4( texColor0.rgb / max(texColor0.a, 0.001), 1.0);
+
     //convert from RGB to YCvCr/YUV
     vec4 keyYUV = RGBtoYUV * chromaKey;
-    vec4 yuv = RGBtoYUV * texColor0;
+    vec4 yuv = RGBtoYUV * col;
 
+    // correction of color
     float t = (1. - Tolerance) * 0.2;
     float mask = 1.0 - colordistance(yuv.rgb, keyYUV.rgb, vec2(t, t + 0.2));
-    vec4 col = max(texColor0 - mask * chromaKey, 0.0);
+    col = max(col - mask * chromaKey, 0.0);
 
+    // correction of alpha
     t = Threshold * Threshold * 0.2;
     col.a -= 1.0 - colordistance(yuv.rgb, keyYUV.rgb, vec2(t, t + 0.25));
 
+    // restore texture alpha
+    col.a *= texColor0.a;
+
     fragColor = col;
 }
diff --git a/rsc/shaders/filters/lumakey.glsl b/rsc/shaders/filters/lumakey.glsl
index f8ab624..3ce86ad 100644
--- a/rsc/shaders/filters/lumakey.glsl
+++ b/rsc/shaders/filters/lumakey.glsl
@@ -9,40 +9,42 @@ uniform float Threshold;
 uniform float Tolerance;
 
 
-//float sRGBtoLin( in float v ) {
-//    // Send this function a decimal sRGB gamma encoded color value
-//    // between 0.0 and 1.0, and it returns a linearized value.
-//    if ( v <= 0.04045 ) {
-//        return v / 12.92;
-//    } else {
-//        return pow((( v + 0.055)/1.055),2.4);
-//    }
-//}
+float sRGBtoLin( in float v ) {
+    // Send this function a decimal sRGB gamma encoded color value
+    // between 0.0 and 1.0, and it returns a linearized value.
+    if ( v <= 0.04045 ) {
+        return v / 12.92;
+    } else {
+        return pow((( v + 0.055)/1.055),2.4);
+    }
+}
 
-//// returns L* which is "perceptual lightness"
-//float lightness ( in vec3 color )
-//{
-//    float Y = 0.2126 * sRGBtoLin(color.r)
-//            + 0.7152 * sRGBtoLin(color.g)
-//            + 0.0722 * sRGBtoLin(color.b);
+// returns L* which is "perceptual lightness"
+float lightness ( in vec3 color )
+{
+    float Y = 0.2126 * sRGBtoLin(color.r)
+            + 0.7152 * sRGBtoLin(color.g)
+            + 0.0722 * sRGBtoLin(color.b);
 
-//    if ( Y <= (216./24389.) ) {     // The CIE standard states 0.008856 but 216/24389 is the intent for 0.008856451679036
-//        Y =  Y * (24389./27.);      // The CIE standard states 903.3, but 24389/27 is the intent, making 903.296296296296296
-//    } else {
-//        Y = pow(Y,(1./3.)) * 116. - 16.;
-//    }
+    if ( Y <= (216./24389.) ) {     // The CIE standard states 0.008856 but 216/24389 is the intent for 0.008856451679036
+        Y =  Y * (24389./27.);      // The CIE standard states 903.3, but 24389/27 is the intent, making 903.296296296296296
+    } else {
+        Y = pow(Y,(1./3.)) * 116. - 16.;
+    }
 
-//    return 0.01 * Y;
-//}
+    return 0.01 * Y;
+}
 
 void mainImage( out vec4 fragColor, in vec2 fragCoord )
 {
-    vec2 fragPos =  fragCoord.xy / iResolution.xy;
-    vec3 RGB = texture(iChannel0, fragPos).rgb;
+    vec4 texColor0 = texture(iChannel0, fragCoord.xy / iResolution.xy);
 
+    // RGB is alpha-premultiplied : revert
+    texColor0 = vec4( texColor0.rgb / max(texColor0.a, 0.001), texColor0.a);
 
-    float L = dot(RGB, vec3(0.299, 0.587, 0.114));
-//    float L = lightness( RGB );
+    // modify alpha by the lightness of the image
+    float L = lightness( texColor0.rgb );
+    texColor0.a *= smoothstep( Threshold, Threshold + Tolerance * Tolerance, abs(Luminance - L) );
 
-    fragColor = vec4( RGB, smoothstep( Threshold, Threshold + Tolerance * Tolerance, abs(Luminance - L) ) );
+    fragColor = texColor0;
 }