[GRASS5] Driver Update

[Markus Neteler]

On Tue, Jun 26, 2001 at 02:58:08AM +0100, Glynn Clements wrote:
> 
> Glynn Clements wrote:
> 
> > > Any help would be welcome to fix d.his,
> > 
> > I'll fix this in a similar manner to d.rgb, i.e. scrap the misguided
> > attempt to generate a composite "RGB" output layer and just display
> > the result of HIS->RGB conversion using R_RGB_raster().
> 
> Having looked into this, the name is somewhat misleading:
> 
> 1. The "hue" map is only really a hue map if used with a colour table
> such as "rainbow" where all entries have 100% intensity and
> saturation. Otherwise the intensity and saturation values are used to
> scale those provided by the i_map and s_map parameters.
> 
> 2. The "saturation" map isn't. An all-black saturation map would
> result in grey-scale output, but specifying an all-black for the
> "s_map" parameter will actually output solid 50% grey. "haze map"
> would be more accurate.
> 
> From reading the d.his manpage, I'm assuming that the behaviour is
> correct and the name isn't, so I'll maintain the existing behaviour.
> 
> Would there be any value in a program which displays (or converts)
> actual HIS layers? Is HIS ever used for geographical raster data?

Glynn,

thanks for your fixes. Now color quality is as expected (no more odd
dithering). However, unfortunately the "output" option is gone which
is needed - or do you know a different way to store such images?

An example, where this is needed: If you want to create shaded maps
(as done in my example from yesterday), you need the "output" parameter
to store the result. This feature is also implemented in "tcltkgrass"
(Display -> shaded map).

Another example, where the RGB/IHS transform is used (i.rgb.his, i.his.rgb)
is resolution improvement of satellite images:


low.res Image                    I2: high res. pan image     high res. image
    
  red   ---|         |-- I      replace |- I2 --|         |--- R
           |         |                          |         |
  green ---| RGB/IHS |-- H ---------------------| IHS/RGB |--- G
           |         |                          |         |
  blue  ---|         |-- S ---------------------|         |--- B
                                     g.region
                                     res change
                                     here

This approach needs low.res multispectral and outputs "high res"
multispectral using the high res. geometrical information and
low res. multispectral color information.

But for above (shaded maps), the d.his approach was much more convenient.

Regards

 Markus