[Mapserver-users] tiffs and 256 colors

[Dylan Keon]

Hi Ed,

No, I'm not using transparency...I don't want to blend the images.  The 
shaded relief image is much larger than the DRG (it covers about 20 
quads), and gives the map some context of the larger area.  I just want 
to display the DRG on top of the shaded relief image.  Actually, the DRG 
is just a test image that I'm using to get the application running. 
What I'll really be doing is displaying a single flight line of 
false-color AVIRIS-derived data on top of other layers.  Another 
application will pass the filename to my MapServer app, which will then 
display the image in context of the greater surroundings.  So, I'd like 
to be able to display the single, small AVIRIS image on top of the 
larger shaded relief image at small scales (at large scales, the shaded 
relief image is turned off).

Shouldn't that be possible?

Thanks,
Dylan

Ed McNierney wrote:
> Dylan -
> 
> Are you using transparency to blend the two images?  I assume so, otherwise you wouldn't need to display them both at once.
> 
> If you have a 64-color grayscale layer and want to display a 12-color image blended with it, the resulting image will require 64 * 12 = 768 colors, not counting duplicates.
> 
> However, it can be done....
> 
> http://test.topozone.com/map.asp?z=10&n=5189336&e=594639&s=200&size=m&layer=DRGSR
> 
> 	- Ed
> 
> Ed McNierney
> President and Chief Mapmaker
> TopoZone.com / Maps a la carte, Inc.
> 73 Princeton Street, Suite 305
> North Chelmsford, MA  01863
> ed at topozone.com
> (978) 251-4242 
> 
> -----Original Message-----
> From: Dylan Keon [mailto:keon at nacse.org]
> Sent: Wednesday, March 05, 2003 5:38 PM
> To: mapserver-users
> Subject: [Mapserver-users] tiffs and 256 colors
> 
> 
> I'm trying to display a colored tiff (single DRG 1:24K quad) on top of a 
> grayscale shaded relief tiff.  When using 8-bit PNG output, the DRG 
> appears as grayscale if both layers are displayed at the same time.  If 
> I turn off the shaded relief layer, the DRG is colored correctly.
> 
> I've reduced the color depth of the grayscale shaded relief image to 64 
> colors using Imagemagick, but still have the same problem.  Shouldn't 
> that make enough colors available between the shaded relief (64 colors) 
> and the DRG (12 colors)?
> 
> I've experimented with both 3.6.4 and today's 3.7 CVS version.  I'm 
> doing this through a PHP MapScript application, but I get the same 
> result with each version's shp2img.  It does work ok if I use 24-bit 
> output in 3.7, but I'd like to stick with 8-bit if I can.
> 
> Thanks for any tips.
> 
> --Dylan
> 
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