[Qgis-developer] Raster colours

[Larry Shaffer]

On Thu, Jul 26, 2012 at 1:40 PM, Paolo Cavallini <cavallini at faunalia.it> wrote:
> Il 26/07/2012 21:29, Etienne Tourigny ha scritto:
>> Is there anything in the vector color ramps that should NOT be
>> available for raster color ramps?
> Beware that many ramps have a meaning only when applied to absolute
> values (e.g. DTM), not on a relative (0-100%) scale. This is true for
> both, probably more often for rasters.
> All the best.

Concerning color ramps, it reminds me of an article I read about
thematic maps and cross-tinting by Tom Patterson (creator of Natural
Earth) [0]. While his technique uses Photoshop, it brings up two
interesting questions:

Is blending two color ramps (maybe from different data sources)
possible on-the-fly in QGIS?

And, is it possible to set a blending mode for a layer? Qt supports
blending modes in its painting engine [1], but I only see alpha
blending (transparency) supported. Example of needed use: create
hillshaded or thematic raster (overlay) from DEM, import above other
background layers, set overlay layer to blend mode in layer properties
(e.g. multiply for hillshade).

[0] http://www.shadedrelief.com/hypso/hypso.html
[1] http://doc.qt.nokia.com/4.7-snapshot/painting-imagecomposition.html

Regards,

Larry Shaffer
Dakota Cartography
Black Hills, South Dakota