[gdal-dev] RGB + Grayscale in gdalwarp

[Even Rouault]

Le mardi 11 octobre 2011 22:09:02, Jay Jennings a écrit :
> Hi folks,
> I am trying to merge a grayscale (1-band) image with RGB (3-band) imagery
> using 'gdalwarp', the hope being that the grayscale image would be
> converted on-the-fly to RGB by duplicating the one band 3 times, thus
> ending up still grayscale visually. But 'gdalwarp' doesn't seem to do
> that; instead the grayscale image comes out recognizable but dark reddish,
> as if the one input band is being used as the Red band on output, with the
> Green and Blue output bands getting all zeroes.
> 
> Looking at the 'gdalwarp' documentation, I don't see any options to treat
> this (admittedly unusual) case as I'm expecting.  Did I miss anything ?
> 
> ( I see that the 1-band image can be made compatible by preprocessing it
> like this: gdal_translate -b 1 -b 1 -b 1 gray.tif  RGB_still_gray.tif
> 
> That will be my fallback if there are no special tricks in 'gdalwarp' )

I can understand your wish, but gdalwarp has probably already enough special 
tricks to justify adding a new one for which you have found by yourself a 
perfectly simple solution.

"Write programs that do one thing and do it well." -Doug McIlroy

PS:  If you really want to do it in a single step, you could probably easily 
convince the warping algorithm to do the RGB expansion directly by setting 
psWO->panSrcBands[i] = 1 and assigning psWO->nBandCount to 3 . (hack in 
apps/gdalwarp.cpp).


> .........................................................
> Jay Jennings
> GeoEye, Inc.
> (NASDAQ: GEOY)