[GRASS-user] Adjust opacity in command line

[Markus Neteler]

On Tue, Aug 28, 2012 at 4:19 PM, Glynn Clements
<glynn at gclements.plus.com> wrote:
>
> Andy Wickert wrote:
>
>> I have been trying to find a way to adjust the opacity (or
>> transparency, to throw another key word in there) of raster and vector
>> layers using the command line. This is possible in the wxPython GUI,
>> but I have a large number of maps to produce, and would like to script
>> it. So if anyone knows if this is possible with the standard d.*
>> commands, ps.map, or something else I don't know about - thanks in
>> advance!
>
> It isn't possible to directly generate images with partial opacity.
> wxGUI (via g.pnmcomp) uses the opacity values when compositing the
> layers to form the displayed image.
>
> You'll need to use general-purpose image-processing tools such as
> ImageMagick, netpbm or Python+PIL. Blending between an empty
> (fully-transparent) image and the source image is probably the easiest
> approach.

Perhaps "r.blend" could be of interest to some extent.

Markus