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Chromakey fix for pre-multiplied Alpha #643

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merged 2 commits into from
Mar 12, 2021
Merged

Chromakey fix for pre-multiplied Alpha #643

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62a69e4
Fixing logic when applying chromakey logic with pre-multiplied alpha.…
jonoomph Mar 12, 2021
6b845c0
Increasing max fuzz for Chromakey
jonoomph Mar 12, 2021
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32 changes: 19 additions & 13 deletions src/effects/ChromaKey.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -83,18 +83,24 @@ std::shared_ptr<openshot::Frame> ChromaKey::GetFrame(std::shared_ptr<openshot::F
for (int pixel = 0, byte_index=0; pixel < image->width() * image->height(); pixel++, byte_index+=4)
{
// Get the RGB values from the pixel
unsigned char R = pixels[byte_index];
unsigned char G = pixels[byte_index + 1];
unsigned char B = pixels[byte_index + 2];
unsigned char A = pixels[byte_index + 3];

// Get distance between mask color and pixel color
long distance = Color::GetDistance((long)R, (long)G, (long)B, mask_R, mask_G, mask_B);

// Alpha out the pixel (if color similar)
if (distance <= threshold)
// MATCHED - Make pixel transparent
pixels[byte_index + 3] = 0;
// Remove the premultiplied alpha values from R,G,B
float A = float(pixels[byte_index + 3]);
unsigned char R = (pixels[byte_index] / A) * 255.0;
unsigned char G = (pixels[byte_index + 1] / A) * 255.0;
unsigned char B = (pixels[byte_index + 2] / A) * 255.0;

// Get distance between mask color and pixel color
long distance = Color::GetDistance((long)R, (long)G, (long)B, mask_R, mask_G, mask_B);

if (distance <= threshold) {
// MATCHED - Make pixel transparent
// Due to premultiplied alpha, we must also zero out
// the individual color channels (or else artifacts are left behind)
pixels[byte_index] = 0;
pixels[byte_index + 1] = 0;
pixels[byte_index + 2] = 0;
pixels[byte_index + 3] = 0;
}
}

// return the modified frame
Expand Down Expand Up @@ -168,7 +174,7 @@ std::string ChromaKey::PropertiesJSON(int64_t requested_frame) const {
root["color"]["red"] = add_property_json("Red", color.red.GetValue(requested_frame), "float", "", &color.red, 0, 255, false, requested_frame);
root["color"]["blue"] = add_property_json("Blue", color.blue.GetValue(requested_frame), "float", "", &color.blue, 0, 255, false, requested_frame);
root["color"]["green"] = add_property_json("Green", color.green.GetValue(requested_frame), "float", "", &color.green, 0, 255, false, requested_frame);
root["fuzz"] = add_property_json("Fuzz", fuzz.GetValue(requested_frame), "float", "", &fuzz, 0, 25, false, requested_frame);
root["fuzz"] = add_property_json("Fuzz", fuzz.GetValue(requested_frame), "float", "", &fuzz, 0, 125, false, requested_frame);

// Return formatted string
return root.toStyledString();
Expand Down