Re: Problem reading depth 16 gray image.

* Bob Friesenhahn <[email protected]> [040813 20:11]:
> 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).
> 

Hi,

Yes I did build GM with the default QuantumDepth=8, I tried to rebuild
it using --with-quantum-depth=16 and the results are different but still
wrong, now it seems mostly random noise, maybe only the LSB is used? 
By the way that was the same result I had with the old ImageMagick I had
around.

I can send you an image but it's rather big (2MB) you can get it from 
http://www.ino.it/~gip/files/images/uv600_360.raw
or just tell me and I'll send it by E-Mail.

> 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).
> 

If you mean for showing the image, it's no problem, the human eye doesn't
even see 256 levels of grey so not having 65.000+ is fine. But if
internally for elaboration and other stuff all 16 bits could be kept
that would be better.


Thanks for the help.

GianPiero


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