[MF3D.FORUM:515] Re: stereo cards on the web

[Tom Deering <smile@xxxxxxxxxxx>]

>I agree with Tom's remarks and suggestions except one:
>
>> Then, either I would save the images as much higher quality JPEGS, or
>> I would save them as greyscale GIFS, maybe 64 or 128 color palette.
. . . .
>Never cripple high quality b/w prints by quantizing them to less
>than 8 bits (i.e. 256 grey values)!

The word "never" is too strong.  If these were full color images, I'd 
mostly agree.  But the jpeg format loses some of it's edge with 
greyscale images.  In fact, if file size were no option, then gif 
would render better greayscale stereo images than jpeg, every time.

Due to the way the two compression schemes work, gif is less 
disruptive to the stereoscopic perception than jpeg.  When comparing 
files of the same size, a "loss-less" gif with a limited color 
palette may look better than a jpeg compressed to the same file size. 
That's why I said it was a judgement call.

The reason is, jpeg compression artifacts are positioned with regard 
to the physical dimensions of the image.  On the other hand, the 
posterization  "artifacts" that can occur in gifs are positioned with 
regard to the different elements of the image itself.

Here is an analogy.  Imagine a picture printed on graph paper.  The 
lines would interfere with stereo perception because they do not 
exist in 3D space.  Now imagine the picture is printed in a way that 
makes the shadows too light.  It may not look exactly right, but the 
problem with the image does not interfere with the stereo information.

Really tough without pictures.  I guess I have a new topic for my web site.

Tom
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tmd@xxxxxxxxxxx    http://www.deering.org