[GRASS-user] Slow display of images (rasters)

[Glynn Clements]

Morten Sickel wrote:

> I am working with some aerial photograps, I have sets of pancromatic
> black and white pictures and colored infrared pictures. the pan-images
> were imported directly and displays quite qickly, each image being about
> 150M. When I imported the colored IR pictures, they came in as three
> bands, each about the same size as the pancromatic picture. Then I used
> r.composite to recreate the colored picture, and got a file on about
> 500M. When I use d.rast to display the composite file, things takes
> ages, nothing seems to happen for a long while. d.rast uses more or less
> 100% of the CPU but not much memory. I recall the xdriver being slow
> when displaying rasters with a large color space as an issue some years
> ago, but I thought that worked better now.. Are there anything I can do
> to make it work better? I have presently 24 bits color depth, but that
> is going to increase to 36 bits (3x12bits) later on, if that goes even
> slower, I will have a problem...
> 
> My machine is a 1,5 GHz with 1 GB of RAM running linux, no speedmonster,
> when displaying the same maps in qgis, it goes quite a bit faster.

If possible, avoid the use of r.composite and keep the data as
separate bands. If you must use r.composite, higher values for levels=
will result in slower rendering (hence the default value being 32
rather than 256).

-- 
Glynn Clements <glynn at gclements.plus.com>