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

       North Carolina sample dataset example:
       g.region rast=lsat7_2002_10 -p
       d.rgb blue=lsat7_2002_10 green=lsat7_2002_20 red=lsat7_2002_30
       d.barscale at=55.312500,93.125000 bcolor=white tcolor=black -t
       i.landsat.rgb 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=55.312500,93.125000 bcolor=white tcolor=black -t
        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: 2012-02-13 08:19:58 -0800 (Mon, 13 Feb 2012) $

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