There's "no difference" in the file format for the z being either elevation or a value between 0-255. The formula works the same. Therefore all you have to do is to write the formula for each of the three bands RGB (not just one band) and filter out the value in each band that makes up blue...
Jean-Yves
At 12:27 2001-06-22 -0400, you wrote:
Hello List:
I have imported into ERMapper a USGS DRG (Digital Rater Graphic). These
files are 8-bit index colored files. Each indexed color value is comprised
of a R, G, and B value. When I show a cell value in the .ERS for the green
pixels for instance I see displayed the value for each of the R,G and B
components. Ultimately my goal is to turn all pixels that are not green to
null and leave just those that are green . I am very familiar with writing
formulas when the pixel has only one value such as a height, but not sure
what to do when a pixel has a value for R,G and B. I do not really care
what the exact new value would be just so I could differentiate from other
pixels that are blue or red, etc.
Any help would be appreciated.
Greg
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