[Qgis-developer] Multiband grey in master?

[Radim Blazek]

On Tue, Dec 18, 2012 at 4:52 PM, HAUBOURG
<regis.haubourg at eau-adour-garonne.fr> wrote:
>> So probably just a new options for multiband color and color data renderers
>> should be implemented.
>
> Thanks radim for your feedback
> Why not 'multiband gray' just like multiband color? It makes sense to me.
> Or maybe some users would rather have a checkbox 'show in grayscale' in multiband color screen.

Your "just like" means a lot of work: new GUI widget, new renderer,
support for this new renderer in raster layer (save restor in/from
project), in renderers registry, in raster layer properties etc.
Technically the renderer would be still multiband color but with
additional grayscale mode flag, but still, it is enough work to do. On
the contrary, to add grayscale flag to multiband color renderer and
widget is easy, because it is only limited to those two classes.

Note also, that the values must first be converted to RGB and then to
grayscale, so all to options for stretching of individual bands must
be there.

In addition, for images which are not in RGB true colors, a user
should have a possibility to tune first bands selection and contrast
enhancement with colors and once the colors are tuned, switch to
grayscale.

It may also be be handy to switch to grayscale and back, according to
situation, without a necessity to change renderer. This could be
useful even for single band pseudocolor and paletted. So it seems
useful for all renderers apart single band gray.

Radim

> Other opinions?
> Régis
>
>> -----Message d'origine-----
>> De : Radim Blazek [mailto:radim.blazek at gmail.com]
>> Envoyé : mardi 18 décembre 2012 16:49
>> À : HAUBOURG
>> Cc : qgis-developer at lists.osgeo.org
>> Objet : Re: [Qgis-developer] Multiband grey in master?
>>
>> On Tue, Dec 18, 2012 at 2:23 PM, haubourg <regis.haubourg at eau-adour-
>> garonne.fr> wrote:
>> > Hi all,
>> > regarding to recent modifications in raster styling [0], I was
>> > wondering if multiband grey is possible in QGIS.
>> >
>> > I usually have topo maps in RGB. It is very handy to switch them to
>> > grayscale styling so that vector overlays are well highlighted. I
>> > currently didn't find how to do this. I can only have grayscale for
>> > one band. The result is not good since red , green or blue band
>> > signals are really not supporting the right info. This is existing in
>> > Mapinfo and other softs seamlessly.
>> > Did I miss something?
>>
>> Currently that is not possible, AFAIK. I am not sure where it should go. It may
>> be also useful for color data sources (WMS). In theory it is possible to add a
>> new filter implementing raster interface and plug it into the pipe after
>> renderer, but it seems to be overkill too me.
>> So probably just a new options for multiband color and color data renderers
>> should be implemented.
>>
>> Radim
>>
>> >
>> >
>> > [0] http://hub.qgis.org/issues/6598 <http://hub.qgis.org/issues/6598>
>> >
>> >
>> >
>> > --
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