How to calculate an RGB colour by specifying an alpha blending amount?

Question

I\'m writing a colour picker that gets the pixel RGB values from wherever you point to on the screen. I want to also have the option of specifying that the colour I picked

Answer 1

The following pseudo-code resolves your problem:

    CalculateSolidColorFromTransparentColor(Color color, Color background)
    {
        alpha = color.A / 255;
        oneminusalpha = 1 - alpha;

        newR = ((color.R * alpha) + (oneminusalpha * background.R));
        newG = ((color.G * alpha) + (oneminusalpha * background.G));
        newB = ((color.B * alpha) + (oneminusalpha * background.B));
    }

Note that input color and backgroud has values expressed in [0..255]