Extract Drop Shadow (Gradient-to-Color vs Gradient-to-Alpha)

[aaronhoffman]

Is there a way "Extract" a drop shadow in Paint.net?

For example:

I have a Gradient that is from Black to White. It represents a Drop Shadow on top of a White Background, (All in one layer. no transparency. kinda like if the Drop Shadow was "flattened", or you took a "Print Screen" of it). (left half of attached image)

How would you Convert that to a Gradient that is from Black to Transparent? Basically I want to replace White, and any level of "white" within the image, with that same level of Transparency. (right half of attached image)

Color Crosswalk:

Initial color -- post-extract color

(RRR-GGG-BBB-AAA) -- (RRR-GGG-BBB-AAA)

000-000-000-255 -- 000-000-000-255 (black stays black)

093-093-093-255 -- 000-000-000-163 (black, but a little bit transparent)

212-212-212-255 -- 000-000-000-044 (black, a little more transparent)

255-255-255-255 -- 000-000-000-000 (white turns into black, fully transparent)

Thank You,

Aaron

[Ash]

Color to Alpha plugin.

Uncheck Hue and Saturation, Try setting Brightness, Keep From @ 0, and slide To.

And you also have to adjust the Feather, if you don't, you won't get the gradient, you only get a hard edge.

Trial and error, you will get it.

[BoltBait]

Here is a CodeLab script to do what you want:

#region UICode
byte Amount1 = 0; // [1] Delete|White|Black
#endregion

private UnaryPixelOps.Desaturate desaturateOp = new UnaryPixelOps.Desaturate();

void Render(Surface dst, Surface src, Rectangle rect)
{
   ColorBgra CurrentPixel;
   for (int y = rect.Top; y     {
       for (int x = rect.Left; x         {
           CurrentPixel = desaturateOp.Apply(src[x,y]);
           switch (Amount1) {
           case 0:
               CurrentPixel.A = (byte)(255-CurrentPixel.R);
               CurrentPixel.R = 0;
               CurrentPixel.G = 0;
               CurrentPixel.B = 0;
           break;
           case 1:
               CurrentPixel.A = CurrentPixel.R;
               CurrentPixel.R = 255;
               CurrentPixel.G = 255;
               CurrentPixel.B = 255;
           break;
           }
           dst[x,y] = CurrentPixel;
       }
   }
}

[aaronhoffman]

Thanks Ash, I feel like "Color to Alpha" should work as well. But I just can't seem to get it to work.

Thanks BoltBait, that code worked perfectly. (CodeLab Plugin required http://www.boltbait.com/pdn/codelab/ )