# Re: [Gimp-user] Select by color

```Well, that was exactly what I tought...   if the threshold is zero,
only the selected colour will be selected.
But what about a RGB with R=50, G=110 and B=220, and a threshold of
10? The colour range will be something like R=40-60, G=100-120 and
B=210-230 ?
I'm trying to implement an algorithm that does almost the same of the
select-by-colour. I'm processing images taken from a microscope (I'm
not sure about how do you spell this!) where are two kinds of
structures, one painted of yellow and the other of red. I need to make
a code for measuring the percentage of yellow, red and the space
unpainted in the picture...
I've already tried the steps I told you above, without success...```
```
Do you (or anybody!) have some idea?

Thanks a lot!

[]'s

Bruno.

On 11/6/05, michael chang <[EMAIL PROTECTED]> wrote:
> On 11/2/05, Bruno Silva de Oliveira <[EMAIL PROTECTED]> wrote:
> > Hi everyone!
> >
> > I'm new in the list, but I think a can ask some things...
> >
> > Does anybody knows how the select by color, or more precisely, the
> > threshold works. How does the GIMP makes the selection using the
> > threshold interval and how does this threshlold works in the tree
> > channels (R,G and B)?
>
> I'm not sure I _fully_ understand it, but I believe I get the gist of
> the function.  When you select-by-colour, the colour under the pixel
> is selected, and all the pixels of the same colour are selected.  If
> the threshold is zero (or something like that), then only the pixels
> with the exact same RGB values are selected, and as you increase the
> threshold, it will get further away from that colour.
>
> For example, if you had a gradient that went from black to green, and
> you clicked on the greenest part of the gradient with select by
> colour, then notice how the amount you select increases as you
> increase the threshold.
>
> I don't know about it from a mathimatical perspective.
>
> If you use windows, have you considered looking at the gimpwin-users
> mailing list?
>
> --
> ~Mike
>  - Just my two cents
>  - No man is an island, and no man is unable.
>

--
/**
*  Bruno Silva de Oliveira
*  http://bsoliveira.cjb.net/
*/
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