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<em>i.colors.enhance</em> auto-balances and enhances the color channels of a
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RGB image (e.g. from Landsat) to provide a more natural color mixture. Only
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the color table of each image band is modified, the base data remains untouched.
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The module works by calculating a histogram for each color channel and
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removing an adjustable amount of outliers from either end before recalibrating
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the color scale with <em>r.colors</em>.
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<!-- limitation still true ? -->
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It will work with any 8-bit RGB imagery set and the script is easily modified
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to work with other datasets of greater band-depth.
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Depending on the image, it may or may not be advantageous to use the <b>-p</b>
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flag to preserve the relative color scaling. You will have to experiment
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with the different options to find a setting that works best for your
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The <b>strength</b> option should generally be set in the 90-99 range. The
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lower the number, the more saturated the image becomes. It represents the
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percentage cut-off for the top end of the color histogram curve. The lower
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end is fixed at 2% of the area under the curve.
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For quicker execution of this module on large images you can achieve largely
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similar results by switching to a coarser resolution before the running of
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the module (using <em>g.region</em>) and then back to the original resolution
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North Carolina sample dataset example with Landsat data:
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<div class="code"><pre>
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g.region raster=lsat7_2002_10 -p
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d.rgb blue=lsat7_2002_10 green=lsat7_2002_20 red=lsat7_2002_30
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d.barscale at=55.3125,93.125 bcolor=white text_pos=over
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i.colors.enhance blue=lsat7_2002_10 green=lsat7_2002_20 red=lsat7_2002_30 strength=95
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d.rgb blue=lsat7_2002_10 green=lsat7_2002_20 red=lsat7_2002_30
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d.barscale at=55.3125,93.125 bcolor=white text_pos=over
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<img src="i_col_enh_uncorr.jpg" alt="Uncorrected RGB composite of Landsat ETM channels B/G/R"><br>
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Uncorrected RGB composite of Landsat ETM channels B/G/R
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<img src="i_col_enh_corr.jpg" alt="Color corrected RGB composite of Landsat ETM channels B/G/R"><br>
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Color corrected RGB composite of Landsat ETM channels B/G/R
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The <b>strength</b> option requires further refinement.
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<a href="d.rgb.html">d.rgb</a>,
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<a href="g.region.html">g.region</a>,
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<a href="i.oif.html">i.oif</a>,
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<a href="r.colors.html">r.colors</a>,
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<a href="r.composite.html">r.composite</a>,
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<a href="r.univar.html">r.univar</a>
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Markus Neteler, Trento, Italy<br>
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M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand
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<p><i>Last changed: $Date: 2014-12-19 22:55:37 +0100 (Fri, 19 Dec 2014) $</i>