[Qgis-user] Four band raster displaying funny

[Andrew Harfoot]

PS. gdalwarp offers more flexibility when mosaicing rasters, and is 
better at memory management. I have just noticed that in GDAL 1.10 and 
above there is an gdalwarp option -setci that 'Sets the color 
interpretation of the bands of the target dataset from the source 
dataset'. This could be used to remove the assignment of the alpha 
channel to the IR band on merging. Sadly there isn't an example of its 
usage!

Cheers,

Andy

On 02/12/2013 11:53, Jonathan Moules wrote:
> Hi List,
> I've got a 4 band raster aerial photography (RGBI) that comprises lots 
> of tiles. I've merged some of the tiles together with:
>
>     gdal_merge -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co
>     COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co
>     BLOCKYSIZE=512 --optfile tiff_list.txt
>
>
> But the resultant file looks funny in QGIS.
> This is what the source file looks like (correct):
> Inline images 1
>
> This is what the merged file looks like (wrong):
> Inline images 2
>
> All the shadows are a whitey colour. This doesn't happen with 3-band 
> (RGB) images.
> I've tried comparing individual bands; they all look different in the 
> 4-band.
>
> However, if I open the four-band in ArcGIS, it looks fine (both source 
> and original).
>
> Anyone know what's going on? Is it a QGIS bug or is it doing something 
> "smart"; I can't see anything odd going on with symbology.
>
> Thanks,
> Jonathan
>
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-- 
Andy Harfoot

GeoData Institute
University of Southampton
Southampton
SO17 1BJ

Tel:  +44 (0)23 8059 2719
Fax:  +44 (0)23 8059 2849

www.geodata.soton.ac.uk

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