i.colors.enhance(1grass) GRASS GIS User's Manual i.colors.enhance(1grass)
NAME
i.colors.enhance - Performs auto-balancing of colors for RGB images.
KEYWORDS
imagery, RGB, satellite, colors
SYNOPSIS
i.colors.enhance
i.colors.enhance --help
i.colors.enhance [-fprs] red=name green=name blue=name
[strength=float] [--help] [--verbose] [--quiet] [--ui]
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
-s
Process bands serially (default: run in parallel)
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
red=name [required]
Name of red channel
green=name [required]
Name of green channel
blue=name [required]
Name of blue channel
strength=float
Cropping intensity (upper brightness level)
Options: 0-100
Default: 98
DESCRIPTION
i.colors.enhance auto-balances and enhances the color channels of a RGB
image (e.g. from Landsat) 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 recal-
ibrating 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 experi-
ment 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 with Landsat data:
g.region raster=lsat7_2002_10 -p
d.rgb blue=lsat7_2002_10 green=lsat7_2002_20 red=lsat7_2002_30
d.barscale at=55.3125,93.125 bcolor=white text_pos=over
i.colors.enhance 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=55.3125,93.125 bcolor=white text_pos=over
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.
SEE ALSO
d.rgb, g.region, i.oif, r.colors, r.composite, r.univar
AUTHORS
Markus Neteler, Trento, Italy
M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand
SOURCE CODE
Available at: i.colors.enhance source code (history)
Accessed: unknown
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