OpenEuphoria

Re: difference between two colors

• Posted by Derek Parnell <ddparnell at bigpond.com> Jun 09, 2001
• 388 views

----- Original Message -----
From: rforno at tutopia.com
Subject: Re: difference between two colors


>I'd assume r, g, b are the axis of a 3-dimensional
>space, and so their possible values span a cube.
>Then I would compute the geometrical distance
>between the 2 points in such a space, but I am
>too lazy to write the function...


This seems reasonable, especially when you factor in the way the eye
perceives colors. Here's one attempt at this algorithm.

----------------------------
function RFORNO_difference(sequence rgb1, sequence rgb2)

    sequence colorfactors
    atom diff, brightness

    -- Set color band ranges
    -- ie. Red needs 16 values difference before the eye registers it,
    --     Green needs 12, and Blue needs 10
    colorfactors = {16, 12, 10}

    -- Set brightness factor
    -- Tune this to your liking.
    brightness = 1.0

    -- Calc relative luminosity difference of raw colors.
    lum = abs((rgb1[1] + rgb1[2] + rgb1[3])-(rgb2[1] + rgb2[2] + rgb2[3]))

    -- Adjust raw colors into color bands.
    rgb1 = floor(rgb1 / colorfactors) * colorfactors
    rgb2 = floor(rgb2 / colorfactors) * colorfactors

    -- Calc 3d-space distance.
    diff = power( power(rgb1[1] - rgb2[1], 2) +
                  power(rgb1[2] - rgb2[2], 2) +
                  power(rgb1[3] - rgb2[3], 2)
            , 0.5)

    -- Adjust dist with brightness,
    -- Convert to integer and return
    return floor(diff + (lum * brightness))

end function
----------------------------

Of course, one could also debate the color band factors, as each person sees
color differently. There is an interesting discussion on this at
http://www.firelily.com/opinions/color.html


---
cheers,
Derek Parnell
Melbourne, Australia
"To finish a job quickly, go slower."