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 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 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)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual