[FWTools] accessing the histogram

[Greg Fiske]

Thanks Frank.  I couldn't get the -hist switch to work for
gdalinfo, maybe because our cluster is running an old version of
FWTools...  But the histrep.py example is exactly what we were
looking for.

Best regards,

Greg

-----Original Message-----
From: Frank Warmerdam [mailto:warmerdam at pobox.com] 
Sent: Wednesday, January 21, 2009 11:41 AM
To: Greg Fiske
Cc: fwtools at lists.maptools.org
Subject: Re: [FWTools] accessing the histogram

Greg Fiske wrote:
> Hello folks,
> 
> Can somebody demonstrate how I can access the histogram of a
> raster image.  Ultimately, I'd like to dump it to a text file
as
> well (I have many images to assess).

Greg,

You can get gdalinfo to report the histogram details using the
-hist
option.

The results (mixed into the gdalinfo report) look like:

   256 buckets from -0.5 to 255.5:
   5824 0 0 0 0 0 0 0 4892 0 0 0 0 0 0 0 6665 0 0 0 0 0 0 0 0
8432 0 0 0 0 0 0 
0 9026 0 0 0 0 0 0 0 8988 0 0 0 0 0 0 0 9651 0 0 0 0 0 0 0 0
11196 0 0 0 0 0 0 
0 13316 0 0 0 0 0 0 0 14152 0 0 0 0 0 0 0 13986 0 0 0 0 0 0 0
14118 0 0 0 0 0 0 
0 0 15181 0 0 0 0 0 0 0 15247 0 0 0 0 0 0 0 14278 0 0 0 0 0 0 0
13076 0 0 0 0 0 
0 0 0 12244 0 0 0 0 0 0 0 11412 0 0 0 0 0 0 0 10168 0 0 0 0 0 0 0
8505 0 0 0 0 
0 0 0 0 6909 0 0 0 0 0 0 0 5860 0 0 0 0 0 0 0 4797 0 0 0 0 0 0 0
3864 0 0 0 0 0 
0 0 3348 0 0 0 0 0 0 0 0 2774 0 0 0 0 0 0 0 2368 0 0 0 0 0 0 0
2027 0 0 0 0 0 0 
0 1611 0 0 0 0 0 0 0 0 1306 0 0 0 0 0 0 0 1080 0 0 0 0 0 0 0 5843

If you need more control, and are willing to write a python
script you
can adapt the one at:

 
http://svn.osgeo.org/gdal/trunk/gdal/swig/python/samples/histrep.
py

Underlying this is the C++ method GDALRasterBand::GetHistogram():

http://www.gdal.org/classGDALRasterBand.html#3f8889607d3b2294f7e0
f11181c201c8

Good luck,
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