GRASS GIS manual: i.landsat.rgb

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NAME

i.landsat.rgb - Performs auto-balancing of colors for LANDSAT images.

KEYWORDS

raster, imagery, colors

SYNOPSIS

i.landsat.rgb
i.landsat.rgb help
i.landsat.rgb [-fpr] red=string green=string blue=string [strength=float] [--verbose] [--quiet]

Flags:

-f: Extend colors to full range of data on each channel
-p: Preserve relative colors, adjust brightness only
-r: Reset to standard color range
--verbose: Verbose module output
--quiet: Quiet module output

Parameters:

red=string: LANDSAT red channel
green=string: LANDSAT green channel
blue=string: LANDSAT blue channel
strength=float: Cropping intensity (upper brightness level); Options: 0-100; Default: 98

DESCRIPTION

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.

NOTES

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 particular imagery.

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 afterwards.

EXAMPLE

North Carolina sample dataset example:

g.region rast=lsat7_2002_10 -p
d.rgb blue=lsat7_2002_10 green=lsat7_2002_20 red=lsat7_2002_30
d.barscale at=55.312500,93.125000 bcolor=white tcolor=black -t

i.landsat.rgb blue=lsat7_2002_10 green=lsat7_2002_20 red=lsat7_2002_30 strength=95
d.rgb blue=lsat7_2002_10 green=lsat7_2002_20 red=lsat7_2002_30
d.barscale at=55.312500,93.125000 bcolor=white tcolor=black -t

Uncorrected RGB composite of Landsat ETM channels B/G/R

Color corrected RGB composite of Landsat ETM channels B/G/R

TODO

The strength option requires further refinement.

AUTHORS

Markus Neteler, Trento, Italy
M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand

Last changed: $Date: 2012-02-13 08:19:58 -0800 (Mon, 13 Feb 2012) $

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