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r.his(1)		    GRASS GIS User's Manual		      r.his(1)

       r.his   - Generates red,	green and blue (RGB) raster map	layers combin-
       ing hue,	intensity and saturation (HIS) values from user-specified  in-
       put raster map layers.

       raster, color transformation, RGB, HIS, IHS

       r.his --help
       r.his   [-c]   hue=string    [intensity=string]	   [saturation=string]
       red=string  green=string	 blue=string   [bgcolor=name]	 [--overwrite]
       [--help]	 [--verbose]  [--quiet]	 [--ui]

	   Use colors from color tables	for NULL values

	   Allow output	files to overwrite existing files

	   Print usage summary

	   Verbose module output

	   Quiet module	output

	   Force launching GUI dialog

       hue=stringA [required]
	   Name	of layer to be used for	hue

	   Name	of layer to be used for	intensity

	   Name	of layer to be used for	saturation

       red=stringA [required]
	   Name	of output layer	to be used for red

       green=stringA [required]
	   Name	of output layer	to be used for green

       blue=stringA [required]
	   Name	of output layer	to be used for blue

	   Color to use	instead	of NULL	values
	   Either a standard color name, R:G:B triplet,	or "none"

       HIS  stands  for	hue, intensity,	and saturation.	 This program produces
       red, green and blue raster map layers  providing	 a  visually  pleasing
       combination  of hue, intensity, and saturation values from two or three
       user-specified raster map layers.

       The human brain automatically interprets	the vast amount	of visual  in-
       formation  available  according to basic	rules.	Color, or hue, is used
       to categorize  objects.	 Shading,  or  intensity,  is  interpreted  as
       three-dimensional  texturing. Finally, the degree of haziness, or satu-
       ration, is associated with distance or depth. This program allows  data
       from  up	 to  three raster map layers to	be combined into a color image
       (in the form of separate	red, green and blue raster map	layers)	 which
       retains	the original information in terms of hue, intensity, and satu-

       While any raster	map layer can be used to represent  the	 hue  informa-
       tion,  map  layers  with	 a  few	 very distinct colors work best.  Only
       raster map layers representing continuously varying  data  like	eleva-
       tion,  aspect, weights, intensities, or amounts can suitably be used to
       provide intensity and saturation	information.

       For example, a visually pleasing	image can be made by using a watershed
       map  for	the hue	factor,	an aspect map for the intensity	factor,	and an
       elevation map for saturation. (The user may wish	to leave out the  ele-
       vation  information  for	 a  first  try.)  Ideally, the resulting image
       should resemble the view	from an	aircraft looking at  a	terrain	 on  a
       sunny day with a	bit of haze in the valleys.

   The Process
       Each  map  cell	is processed individually. First, the working color is
       set to the color	of the corresponding cell in the map layer  chosen  to
       represent  hue.	 Second, this color is multiplied by the red intensity
       of that cell in the intensity map layer.	 This map layer	should have an
       appropriate  gray-scale	color table associated with it.	You can	ensure
       this by using the color manipulation  capabilities  of  r.colors.   Fi-
       nally,  the  color  is made somewhat gray-based on the red intensity of
       that cell in the	saturation map layer.  Again, this  map	 layer	should
       have a gray-scale color table associated	with it.

       The name	is misleading. The actual conversion used is
	 H.i.s + G.(1-s)
	 H   is	the R,G,B color	from the hue map
	 i   is	the red	value from the intensity map
	 s   is	the red	value from the saturation map
	 G   is	50% gray (R = G	= B = 0.5)

       Either (but not both) of	the intensity or the saturation	map layers may
       be omitted. This	means that it is possible  to  produce	output	images
       that represent combinations of his, hi, or hs.  The separate red, green
       and blue	maps can be displayed on the graphics monitor using d.rgb,  or
       combined	 into  a composite RGB layer using r.composite.	 Users wishing
       to simply display an his	composite image	 without  actually  generating
       any layers should use the program d.his.

       Recreate	 the  following	 example for d.his using r.his.	 First,	create
       shaded relief and show it.
       g.region	raster=elevation
       r.relief	input=elevation	output=elevation_shaded_relief
       d.mon wx0
       d.his hue=elevation intensity=elevation_shaded_relief brighten=50
       Second, compute lighter version of color	of shaded relief.   Then  con-
       vert from HIS model to RGB and show the result.
       r.mapcalc "elevation_shaded_relief_bright_50 = #elevation_shaded_relief * 1.5"
       r.colors	elevation_shaded_relief_bright_50 color=grey255
       r.his hue=elevation intensity=elevation_shaded_relief_bright_50 \
	     red=shadedmap_r green=shadedmap_g blue=shadedmap_b
       d.mon wx1
       d.rgb red=shadedmap_r green=shadedmap_g blue=shadedmap_b

	d.his, d.colortable, d.rgb, r.blend, r.colors, r.composite, r.mapcalc,
       r.shade,	i.his.rgb, i.rgb.his

       Glynn Clements (based upon d.his)

       Available at: r.his source code (history)

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       A(C) 2003-2021 GRASS Development	Team, GRASS GIS	7.8.6 Reference	Manual

GRASS 7.8.6							      r.his(1)


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