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i.landsat.rgb.1grass

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

i.landsat.rgb red=tm.3 green=tm.2 blue=tm.1

TODO

The strength option requires further refinement.

SEE ALSO

d.rgb, g.region, i.oif, r.colors, r.composite, r.univar,

AUTHORS

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

Last changed: $Date: 2006-09-07 11:24:10 +0200 (gio, 07 set 2006) $

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