Geografic-Information-System/scripts/i.colors.enhance/i.colors.enhance.html

<h2>DESCRIPTION</h2>

<em>i.colors.enhance</em> 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.
<p>
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 <em>r.colors</em>.
<p>
<!-- limitation still true ? -->
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.

<h2>NOTES</h2>

Depending on the image, it may or may not be advantageous to use the <b>-p</b>
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.
<p>
The <b>strength</b> 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.
<p>
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 <em>g.region</em>) and then back to the original resolution
afterwards.

<h2>EXAMPLE</h2>

North Carolina sample dataset example with Landsat data:

<div class="code"><pre>
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
</pre></div>

<center>
<img src="i_colors_enhance_uncorrected.jpg" alt="Uncorrected RGB composite of Landsat ETM channels B/G/R"><br>
Uncorrected RGB composite of Landsat ETM channels B/G/R
<p>
<img src="i_colors_enhance_corrected.jpg" alt="Color corrected RGB composite of Landsat ETM channels B/G/R"><br>
Color corrected RGB composite of Landsat ETM channels B/G/R
</center>

<h2>TODO</h2>

The <b>strength</b> option requires further refinement.

<h2>SEE ALSO</h2>

<em>
<a href="d.rgb.html">d.rgb</a>,
<a href="g.region.html">g.region</a>,
<a href="i.oif.html">i.oif</a>,
<a href="r.colors.html">r.colors</a>,
<a href="r.composite.html">r.composite</a>,
<a href="r.univar.html">r.univar</a>
</em>


<h2>AUTHORS</h2>

Markus Neteler, Trento, Italy<br>
M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand

<p><i>Last changed: $Date$</i>