i.landsat.rgb - Auto-balancing of colors for LANDSAT images
raster, imagery, colors
i.landsat.rgb [-fpr] red=string green=string blue=string [strength=integer]
- Extend colors to full range of data on each channel
- Preserve relative colors, adjust brightness only
- Reset to standard color range
- LANDSAT red channel
- LANDSAT green channel
- LANDSAT blue channel
- Cropping intensity (upper brightness level)
- Options: 0-100
- Default: 98
i.landsat.rgb auto-balances and enhances the color channels of a
LANDSAT RGB image to provide a more natural color mixture. Only the color
table of each image band is modified, the base data remains untouched.
The module works by calculating a histogram for each color channel and
removing an adjustable amount of outliers from either end before recalibrating
the color scale with r.colors.
It will work with any 8-bit RGB imagery set and the script is easily modified
to work with other datasets of greater band-depth.
Depending on the image, it may or may not be advantageous to use the -p
flag to preserve the relative color scaling. You will have to experiment
with the different options to find a setting that works best for your
The strength option should generally be set in the 90-99 range. The
lower the number, the more saturated the image becomes. It represents the
percentage cut-off for the top end of the color histogram curve. The lower
end is fixed at 2% of the area under the curve.
For quicker execution of this module on large images you can achieve largely
similar results by switching to a coarser resolution before the running of
the module (using g.region) and then back to the original resolution
i.landsat.rgb red=tm.3 green=tm.2 blue=tm.1
The strength option requires further refinement.
Update to use r.univar instead of r.univar.sh once
r.univar receives extended statistics support.
M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand
Last changed: $Date: 2007/03/08 13:51:30 $
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