finding "distance" between two pixel's colors

Question

Once more something relatively simple, but confused as to what they want.

the method to find distance on cartesian coordinate system is distance=sqrt[(x2-x1)^2 + (y2-y1)^2]

but how do i apply it here?

    //Requires: testColor to be a valid Color
    //Effects: returns the "distance" between the current Pixel's color and  
    //         the passed color
    //         uses the standard method to calculate "distance"
    //         uses the same formula as finding distance on a
    //         Cartesian coordinate system
    double colorDistance(Color testColor) const;

The color class has defined colors: int red,green,blue

Do i define something like 'oldGreen' 'oldRed' 'oldBlue' and get the distance that way? The passed color being red,green,blue ?

http://pastebin.com/v9K30dc7

Answer 1

I'm guessing they want you to use:

distance = sqrt[(r2-r1)^2 + (g2-g1)^2 + (b2-b1)^2]

Answer 2

break the color into it's red green and blue components, and use the same method, ie sqrt(sqr(delta red)+sqr(delta blue)+sqr(delta green))

note, this is not a really great method, as it doesn't allow for gamma or even the more complicated case of human perception. read http://en.wikipedia.org/wiki/Color_difference for more exotic methods.