[gdal-dev] help needed with image creation

[Frank Warmerdam]

Wolfgang wrote:
> Hi,
> 
> I want to create some images where I set the pixel values manually. The 
> values are Floats that need to be mapped finally to a color map. I'm not 
> really a skilled programmer but I've managed to get a first idea how to 
> do it (in python):
> 
> from osgeo import gdal
> import numpy as Numeric
> 
> format = "GTiff"
> driver = gdal.GetDriverByName( format )
> 
> dst_filename='test.tif'
> dst_ds = driver.Create( dst_filename, 3, 2, 1, gdal.GDT_Float32 )
> raster=Numeric.array([[ 1.,  200.5 ,  3. ],[ 256. ,  5. ,  60. ]])
> dst_ds.GetRasterBand(1).WriteArray( raster )
> 
> What I don't understand is how to create/define a color map so that the 
> result looks better? I also suppose that it is not the best to create 
> float tiffs as not so many applications will support that type. It would 
> help me much if anybody could show me the steps needed to do the task.
> 
> I'm sorry if this looks too easy for skilled programmers, but I'm 
> completely new to program graphics (with GDAL) and I still don't have 
> the overview over all GDAL functions.

Wolfgang,

You can't generally assign a palette to floating point geotiff files.
There is no way for applications to understand how to apply it.

Generally speaking, in GeoTIFF, you either offer the raw floating point
science data, or you offer a version of it is that been prescaled to
integers (usually 0 to 255) with a colormap.

I'd add that it is very common for folks to distribute raw science
data in floating point, and for the decision on a colormap to be
applied being made by the user in the viewing application.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org