Christina Seabra writes:
> I'm a little confused with all the commands that change the colors!!
> 
> When running r.support, there is an option to update the statistics (histogram
> and range). I've looked at those. The histogram gives the number of pixels for
> each category (that is each intensity level?), is this right?
> 
	Right.

> I tried to do a contrast stretching; i.grey.scale and grey.eq (from r.colors)
> do the same. What I expect from a contrast stretch is that the intensity values
> are "stretch" to use the entire available range (that is 0-255). When I display the image
> it looks like it has been stretched, but the number of categories doesn't change.

	Only the colors are stretched with these two commands. True stretching
	is done with r.rescale.

> This works fine if it is a single band (I'm using Landsat TM images), but if I try it in a
> color composite the image becomes black and white. So maybe what happens is that when
> running i.composite the result is already "stretched". Is it?
> 
> If that color composite image is already stretched, that range of categories it has is the
> maximum that it handles. Right?
> What type of stretching is it applying? Linear or equalized?

	If I read the manual well, i.composite is not stretching the values. It
	does create its own color space (read the manual). Use d.colormode to
	reduce the number of colors used to the maximum your display is capable
	of.

> Is there any way to control (or change) the stretching? Let's say the range is from 1 to
> 215, but I want it 10-250. Is it possible?

	R.rescale.

Martijn van Leusen

