[Qgis-developer] Re: [Qgis-user] raster display properties

[William Kyngesburye]

Ah, this must be why my GRASS raster GROUPs don't work (I was getting  
an email to the list ready to ask about it).

To properly display in GRASS, an RGB image GROUP must have a  
greyscale palette defined for each band in its COLR definition, even  
if they already are integers within 0..255, like 0:0 255:255.   
Without it you get psychadelic colors.

In Qgis they become paletted bands, like Jonathon's ERDAS bands.  All  
I get is a grey image.  Odd thing, without the COLR definitions in  
GRASS, the become Gray bands in Qgis, and it still doesn't work.

Bummer that it must wait until after 0.8.  I'll see what Jonathon  
does about a bug report and add a comment about GRASS GROUPs.


On Jun 19, 2006, at 9:24 PM, Tim Sutton wrote:

> Hi Jonathon
>
> I had a look at your sample. Running
>
> gdalinfo temp_harmonics.img > temp_harmonics.txt
>
> From the command line produces the attached output. You will see  
> gdal identifies each band as 'undefined' (you get similar info from  
> the raster properties dialog). QGIS uses gdal for its underlying  
> data access mechanism. I think there are additional issues at work  
> here though.  Each of your bands is a paletted layer so it wouldnt  
> really make sense to treat the data as a three band image. Putting  
> the layer into grayscale mode shows better structure to your image.  
> The logic in raster layer looks for the keyword 'PALETTE' in the  
> band name (as reported by GDAL). If its that keyword is not there  
> and there are more than two bands it tries to assign sensible  
> defaults to the RGB components. The snippet below illustrates this.
>
...

> The best resolution to your issue is for us to improve the logic  
> that detects Palletted layers - but Im afraid that I cant do this  
> now until after 0.8 is release. It would be great if you could file  
> a bug report for this at http://svn.qgis.org/trac and attach the  
> piece of sample data (if you dont mind it getting out into the wild).
>
> Best regards
>

-----
William Kyngesburye <kyngchaos at kyngchaos.com>
http://www.kyngchaos.com/

"Mon Dieu! but they are all alike.  Cheating, murdering, lying,  
fighting, and all for things that the beasts of the jungle would not  
deign to possess - money to purchase the effeminate pleasures of  
weaklings.  And yet withal bound down by silly customs that make them  
slaves to their unhappy lot while firm in the belief that they be the  
lords of creation enjoying the only real pleasures of existence....

- the wisdom of Tarzan