i.colors.enhance(1grass) | GRASS GIS User's Manual | i.colors.enhance(1grass) |
i.colors.enhance - Performs auto-balancing of colors for RGB images.
imagery, RGB, satellite, colors
i.colors.enhance
i.colors.enhance --help
i.colors.enhance [-fprs] red=name
green=name blue=name
[strength=float] [--help] [--verbose]
[--quiet] [--ui]
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 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 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.
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
The strength option requires further refinement.
d.rgb, g.region, i.oif, r.colors, r.composite, r.univar
Markus Neteler, Trento, Italy
M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand
Available at: i.colors.enhance source code (history)
Accessed: Sunday Jan 22 07:37:42 2023
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