[Mapserver-users] help with ImageMagick & gdal utilities

[Jan Hartmann]

Benjamin Thelen wrote:

> 
> I have 300 24bit tif images (6400x6400) which need to be resized and 
> converted to 8bit.
> 
> There are some problems and I suppose that most of you might have quite 
> an experience with ImageMagick and the gdal utilities.
> 
> 
> Converting & resizing (convert / mogrify) with ImageMagick stops with 
> "Memory allocation failed", allthough it is a machine with 512M of RAM, 
> enough swap (1G) and enough /tmp (60G). Converting an image with a size 
> up to 5400x5400 runs through (I resized one tif with IrfanView), but it 
> takes incredible long, compared to gdal_translate or Windows IrfanView.
> 
> Also all the tiff-headers (tags) are lost, see the tiffinfo output 
> below. This is also true for both gdal utilies (gdal_translate and 
> rgb2pct.py).
> 
> 
> I would be happy about some general feedback, experiences, tips and of 
> course solutions :-)!
> 

I have done this for lots of rasters up to 30000*30000 pixels with 
GRASS. Resizing gets done line by line, so there is no limit to the size 
of the raster. I think the same is true for converting to 8bits. For 
operations that require the whole image in memory, like rectifying, you 
can very easily split the image up, manipulate the parts, and stitch it 
back together. IMHO for working with large rasters, nothing beats GRASS, 
if only because it can be scripted so easily.

HTH,

Jan