Re: Problem reading depth 16 gray image.

On Fri, 13 Aug 2004, GianPiero Puccioni wrote:

> I have some images in raw format 16 bits per pixel and when I try to
> read them with
>
> gm display -depth 16 -size 1024x1024 gray:b400_02.RAW
>
> I get a completely black image. The images are fine as I can read them
> with a C program I wrote myself to reduce to 8 bits and display them,
> but I'd like to do some processing with GM.
>
> Am I doing something wrong?

From looking at the supportive code, I suspect that your 
GraphicsMagick is built with QuantumDepth=8.  It appears that if 
GraphicsMagick is built with less depth than the image being read, it 
is likely to produce an all-black image since the input quantums are 
not down-scaled and therefore will exceed the colormap index range 
(gray images are read as PseudoClass) and be reset to zero (black).

I do plan to substantially re-write the code which supports this so 
that a QuantumDepth=8 GraphicsMagick can still usefully read 16-bit 
images (but loosing 8 bits of resolution).

Bob
======================================
Bob Friesenhahn
[email protected]
http://www.simplesystems.org/users/bfriesen


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