[mapserver-users] TIFFs and ECWs rasters get a monochrome output - why?

[Andrew Hallam]

Alexander,

Can you tell me how the TIFFs were compressed into ECW format? There are 
two compression modes that are used for colour imagery - RGB and multiband 
(plus grayscale).

RGB is optimised for colour imagery and produces the smallest file size. 
However, if you use it to compress cartographic images (topo maps, 
rasterised vectors, etc) it does not produce an image that looks as good as 
the multiband equivalent. (Multiband results in a larger ECW file size.)

If your images were compressed using multiband you may find that MapServer 
will produce grayscale output. I've written my own WMS image server using 
ECW data (completely independent of MapServer) and I also have this 
problem. As yet, I haven't worked out whether the problem is in my code or 
the ECW SDK.

So, were your ECW images compressed as RGB, multiband or grayscale? If it 
was multiband, try compressing a TIFF file using RGB and see if it works.

Regards
Andrew Hallam

Digital Earth Pty Ltd
http://www.digitalearth.com.au



--On Monday, September 23, 2002 23:28 +0200 Alexander Gleyzer 
<agleyzer at bezeqint.net> wrote:

>
> Hi!
>
> I'm using MapServer raster layers to present large background images.
> When I got to large TIFFs (>200 MB) the server displayed an error message
> (unsupported image format or smth.).  I tried to download the GDAL
> support version (precompiled Win-32 binaries),  which also supports ECW
> (I have those TIFFs compressed to ECWs).  But when I fired it up - all
> the output turned out black-and-white, never mind the output format (GIF,
> JPG, PNG)!  Why is that happening? Is there a way to normally present
> large TIFFs or their ECW equivalents?
> Thanks!
>
> Alexander Gleyzer.
>
>