http://imagej.273.s1.nabble.com/Filtering-certain-color-range-tp3696226p3696233.html
> Hi there everyone,
>
> I would like to know if it is possible to subtract or filter a certain color
> range. I have attached a photograph of a core(acquired while drilling the
> hole looking for oil). From the image, three different major features (in
> terms of color) can be seen, light brown, dark brown and gray.
>
>
http://www.nabble.com/file/p17182225/2010.00-2020.00%2Bm.jpg> 2010.00-2020.00+m.jpg .
>
> What I would like to do is to know the total height of the sand(light and
> dark brown) in the image removing the gray stuff which is shale/clay.
> Therefore, if I could filter the gray stuff out, I can then plot a profile,
> knowing that the low value(or black) is the shale/clay and the rest is sand.
>
> The problem I have now is, when I plot a gray scale profile, it will not be
> possible to differentiate the shale from sand as the shale seem to be
> brighter than the dark brown sand.
>
> Any advice on this matter is very much appreciated. Thanks guys/gals.
>