what RGB is blue?

[Mark Schonewille]

Tiemo,

The distance between any colour (1) and a colour chosen by you (2; e.g. r=0, g=0, b=255) can be calculated as

sqrt((r1-r2)^2+(g1-g2)^2+(b1-b2)^2) <= T

where T is a threshold between 0 and 442 set by you. Change the colour of the background pixel whenever the distance between the colour of that pixel and your selected colour is less than the threshold.

I use this technique in Color Converter http://www.color-converter.com

--
Best regards,

Mark Schonewille

Economy-x-Talk Consulting and Software Engineering
Homepage: http://economy-x-talk.com
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On 1 jul 2011, at 11:39, Tiemo Hollmann TB wrote:

> Hello,
> 
> I am taking the mousecolor at different points from an image by script (not
> by clicking). I would like to analyse if the color I've taken is a "kind of
> blue", or another color. I want to change the backgroundcolor of an image.
> The background is always blue, but different blues and changing over the
> background. So what I want to do is to verify, what is background and what
> is foreground of my image.
> 
> 100% pure blue would be 0,0,255. But for a human being 25,75,130 (greyblue)
> is also still blue, but 240,20,180 is pink, though the third RGB value is
> higher as in my greyblue.
> 
> So I can't just check only the third RGB value, neither the sum or cross
> total. Has anybody ever heard, if you can define at all by math "what is
> blue"?
> 
> Any color specialist around here?
> 
> Tiemo
>