## NAME

blend.sh - Combines the red, green, and blue color components of two raster map layers.
(GRASS Shell Script)

## SYNOPSIS

blend.sh file1 file2 perc outbase

## DESCRIPTION

blend.sh is a Bourne shell (sh(1)) script that extracts the red (R), green (G), and blue (B) color components from each of two raster map layers, and creates three new raster map layers whose category values respectively represent the combined red, combined blue, and combined green color values from the two input layers. Category values in each of the output map layers will fall within the range of 0 - 255.

The R,G,B values from the two input map layers (file1 and file2) are not simply added together, but are instead combined by a user-named percentage (perc) of the R,G,B values in file1. Specifically, blend.sh executes three r.mapcalc statements that:

1. convert the R,G,B values in file1 and file2 to the range 0 - 255;
2. multiply the R, G, and B values in file1 by a user-named percentage (perc);
3. multiply the R, G, and B values in file2 by (100 - perc)%;
4. create three new raster map layers, whose category values represent the summed R, summed G, or summed B values resulting from (2) and (3). Resulting R, G, and B values will respectively be stored in three new raster map layers named outbase.r, outbase.g and outbase.b.

## OPTIONS

This program runs non-interactively; the user must state all parameter values on the command line.

### Parameters:

file1
  Name of a first raster map layer, whose R, G, and B color components will be combined with those of the second raster map layer (file2) named. The percent value (perc) given will apply to file1.
file2
  Name of a second raster map layer, whose color components will be combined with those of file1. The percent value (perc) given will apply to the R,G,B values in file1. The R, G, and B values in file2 will be multiplied by (100 - perc)%.
perc
  Percentage or amount of the color contribution in terms of color intensity. This value is multiplied by the R,G,B values in file1.
outbase
  The root name assigned to each of the three output files created. A suffix is added to each file name, indicating which hold the red, green, and blue color values.

## NOTES

blend.sh executes three r.mapcalc statements:

  r.mapcalc "outbase.r = r#file1 * .perc + (1.0 - .perc) * r#file2"
  r.mapcalc "outbase.g = g#file1 * .perc + (1.0 - .perc) * g#file2"
  r.mapcalc "outbase.b = b#file1 * .perc + (1.0 - .perc) * b#file2"

It uses the # operator to separately extract the red, green, and blue components in the named raster map layers, essentially allowing color separates to be made.

## EXAMPLE

Typing the following at the command line:

  blend.sh aspect elevation 40 elev.asp

will create three new raster map layers named elev.asp.r, elev.asp.g, and elev.asp.b, that, respectively, contain 40% of the red, green, and blue components of the elevation map layer and contain 60% of the red, green, and blue components of the aspect map layer.

## FILES

This program is simply a shell script. Users are encouraged to make their own shell scripts using similar techniques. See `$GISBASE/scripts/blend.sh`.

## SEE ALSO

r.colors,
r.mapcalc

## AUTHOR

Dave Gerdes, U.S.Army Construction Engineering Research Laboratory

Last changed: $Date: 2002/01/25 05:45:32 $