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

       Last changed: $Date: 2014-12-19 22:55:37 +0100 (Fri, 19 Dec 2014) $

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