.TH i.colors.enhance 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH NAME
\fI\fBi.colors.enhance\fR\fR  \- Performs auto\-balancing of colors for RGB images.
.SH KEYWORDS
imagery, RGB, satellite, colors
.SH SYNOPSIS
\fBi.colors.enhance\fR
.br
\fBi.colors.enhance \-\-help\fR
.br
\fBi.colors.enhance\fR [\-\fBfprs\fR] \fBred\fR=\fIname\fR \fBgreen\fR=\fIname\fR \fBblue\fR=\fIname\fR  [\fBstrength\fR=\fIfloat\fR]   [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-f\fR" 4m
.br
Extend colors to full range of data on each channel
.IP "\fB\-p\fR" 4m
.br
Preserve relative colors, adjust brightness only
.IP "\fB\-r\fR" 4m
.br
Reset to standard color range
.IP "\fB\-s\fR" 4m
.br
Process bands serially (default: run in parallel)
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBred\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of red channel
.IP "\fBgreen\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of green channel
.IP "\fBblue\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of blue channel
.IP "\fBstrength\fR=\fIfloat\fR" 4m
.br
Cropping intensity (upper brightness level)
.br
Options: \fI0\-100\fR
.br
Default: \fI98\fR
.SH DESCRIPTION
\fIi.colors.enhance\fR 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.
.PP
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 \fIr.colors\fR.
.PP
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.
.SH NOTES
Depending on the image, it may or may not be advantageous to use the \fB\-p\fR
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.
.PP
The \fBstrength\fR 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.
.PP
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 \fIg.region\fR) and then back to the original resolution
afterwards.
.SH EXAMPLE
North Carolina sample dataset example with Landsat data:
.br
.nf
\fC
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
\fR
.fi
.br
Uncorrected RGB composite of Landsat ETM channels B/G/R
.PP
.br
Color corrected RGB composite of Landsat ETM channels B/G/R
.SH TODO
The \fBstrength\fR option requires further refinement.
.SH SEE ALSO
\fI
d.rgb,
g.region,
i.oif,
r.colors,
r.composite,
r.univar
\fR
.SH AUTHORS
Markus Neteler, Trento, Italy
.br
M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand
.SH SOURCE CODE
.PP
Available at: i.colors.enhance source code (history)
.PP
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.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual