[GRASSLIST:2204] Re: How to display satellite data correctly?

[Wolfgang von Hansen]

Hamish <hamish_nospam at yahoo.com> schrieb am 13.01.04 07:37:00:
> 
> > 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.
> > 
> 
> is it really bad data or just each channel using a different color scale?

I think that radiometrically it is raw sensor output. This means that each channel's histogram has got a different mean so that a direct display mainly displays the "background color" that is defined by the means values. Also the variance of the histograms is different but this should be due to little variance in the according spectral band. I guess the "noise" that I mentioned comes from equalizing a channel with only little information in it.

>From all your answers I see that a combination of r.stats and r.colors with rules should be fine. How should the rules look like:

0 black
40 black
140 white
255 white

or is

40 black
140 white

sufficient to put all other "categories" to black and white respectively?


Wolfgang

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