Color Math

Hello, just wanted to get your opinion on something:

http://littlemofo.soap.com.au/gamedev/color/

here you can see 4 colored circles over an image. The color of the circle changes the image underneath based on that color. Now does this seem correct to you guys? The blue color is very dark over yellow and red is very dark over blue and green is very dark over red. White is always the same.

I think its correct, but not sure. The effect I am trying to achieve is to have the color show up on top of every other color but I think this is going beyond simple multiplication.

The code is actually running from pixel bender, its implemented as a blendMode. Here is the pixel bender kernel, very straightforward.

Code:

---

<languageVersion : 1.0;>

kernel ColorFilter
<  namespace : "Flash";
    vendor : "Chris Foulston";
    version : 1;
    description : "performs colour overlay blending";
>
{
    input image4 background;
    input image4 foreground;
    output pixel4 result;

    void evaluatePixel() {
   
        float2 pos = outCoord();
       
        pixel4 pix1 = sampleNearest(background, pos);
        pixel4 pix2 = sampleNearest(foreground, pos);
     
        float a = 1.0 - pix2.a;
        float r = (pix1.r * a) + (pix1.r * pix2.r);
        float g = (pix1.g * a) + (pix1.g * pix2.g);
        float b = (pix1.b * a) + (pix1.b * pix2.b);
       
        result = pixel4(r, g, b, pix1.a);
    }
}

---

Hopefully someone can understand my ramblings

Looks fine here, isn't there a way you could produce the image in red green and blue in something like photoshop and check your results against that?

Wikipedia's entry is confusing:p: http://en.wikipedia.org/wiki/Blend_modes#Overlay

Quote:

---

Originally Posted by wikipedia

Overlay combines Multiply and Screen blend modes. Light parts of the picture become lighter and dark parts become darker. An overlay with the same picture looks like an S-curve.

---

And they give definitions for Multiply and Screen but I am confused what they mean by "combine". (I mean, I suppose it could just be the result of the first is the background of the other, but seems ambiguous to me)

I think the blue is very dark over the flower because there's very little blue in that part of the image ( It's fine up against the blue wall for example ).

If it's just pulling out the amount of that colour underneath it, then 'cause it's pulling out very little blue you're left with a "low" amount of blue, which makes it so dark.

Squize.

yeah, I'm trying to add blue (red or green too) to a color. As if a colored light was pointed at the image.

desaturate it, then add the colour

I think the blue is too dark, rest is ok!