Degradation with

Martin Ameskamp ma at
Thu Jan 16 09:17:17 EST 1997

> Hello all
> I have a TIFF image that I have converted to GRASS raster with the
> command from the SCS contributed software. Unfortunately when I display the
> raster file in GRASS, the image has been degraded. An example of the
> degradation can be seen at
> The command reported that the bits/sample of the original TIFF image
> was 8. Also the original image had only 64 shades of gray requiring only 6
> bits. My question is how did the image become so degraded if the
> command can easily handle 64 shades of gray? Or maybe the command is
> not the problem but the XDRIVER or d.mon is?

	Have you tried to set the colormode to float? In fixed colormode,
	you use a standard list of colors (computed from a 6x6x6 cube
	of red, green, and blue values) that is adequate for most
	purposes. This means that you only have 6 gret values, however.

	If you switch to float colormode, you get a new colormap
	that is optimized for the map being displayed, i.e. you should
	see all 64 grey values as different colours on the screen.
	The downside of this is that on normal 8bit/pixel graphics
	hardware, ALL screen windows change colours (often to something
	truely horrible) when you move into and out of the monitor window.


	PS Oh, yes, the command name is d.colormode

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