[GRASSLIST:2202] Re: How to display satellite data correctly?

[Hamish]

> currently I am doing some first steps with GRASS to see how it all
> works. I've got some sample data (Landsat TM) that I would like to
> analyze with some of the available functions. However it seems that
> GRASS is not very good at displaying color images -- at least not if
> the histograms of the individual channels aren't properly equalized.
> 
> There is r.colors that should do the trick (I've tried grey.eq) but
> the results weren't too good. To my opinion the histogram is
> transformed to be a little like black-and-white but the dynamics
> aren't well. The display of d.rgb is extremely bright colored but it
> is difficult to see the real structure -- there are quite a few
> colored noise pixels that also degrade the quality.
> 
> Are there better ways to display and visually analyze satellite data?
> What I am especially missing is a simple linear stretch of the
> histogram with a 1% cutoff at each end.

is it really bad data or just each channel using a different color scale?

see
http://article.gmane.org/gmane.comp.gis.grass.user/2836


then use d.rgb, not r.composite.

A custom color map is a less destructive way if you aren't sure..

If it is bad data, you can use r.mapcalc or r.null to get rid of it.


?
Hamish