[GRASSLIST:6004] Re: r.his and i.his.rgb confusion

[Maciek Sieczka]

Thanks, I get it now.

Maciek

----- Original Message ----- 
From: "Glynn Clements" <glynn at gclements.plus.com>
To: "Maciek Sieczka" <werchowyna at pf.pl>
Cc: <grasslist at baylor.edu>
Sent: Friday, March 04, 2005 9:17 AM
Subject: [GRASSLIST:6001] Re: r.his and i.his.rgb confusion


>
> Maciek Sieczka wrote:
>
>> The outputs of r.his and i.his.rgb are completely different but according
>> the manual and the comands' syntax I can't understand why. They seem to
>> provide exactly the same functionality. Could somebody clear it out to 
>> dumb
>> me?
>
> AFAICT, i.his.rgb does correct HIS->RGB translation, while r.his is a
> fudge. I believe that the hsv.rgb.sh script in 5.3 (omitted from
> 5.7/6.0 for some reason) will produce results similar to i.his.rgb.
>
> For i.his.rgb, the three input maps correspond directly to the Hue,
> Saturation and Intensity (aka Value or Brightness) components of the
> HIS (aka HSV or HSB) colour space. The values should lie in the range
> 0-255, corresponding to 0-360 degrees for the hue map and 0-100% for
> the other two. The maps' colour tables are ignored.
>
> OTOH, r.his obtains an (R,G,B) colour triplet from the colour table
> for the "hue" map, then modifies the intensity and saturation of the
> colour according to the intensities from the colour tables of the
> intensity and saturation maps (which should have grey-scale colour
> tables).
>
> Intensities of 255 for both maps will result in the output map
> essentially being a copy of the hue map, split into separate R/G/B
> components. A lower intensity for the intensity map will result in the
> output colour being a darker version of the input colour, while a
> lower intensity for the saturation map will produce a lighter version.
>
> AFAIK, r.his exists solely to provide a specific visual effect. If you
> use an existing coloured map as the hue map, create an intensity map
> which simulates solar illumination (e.g. by obtaining the slope from a
> DEM using r.slope.aspect) and a saturation map by scaling a DEM, the
> end result looks (slightly) like an illuminated relief map, tinted
> according to the hue map and with "fog" in the valleys.
>
> -- 
> Glynn Clements <glynn at gclements.plus.com>
>
>
>