[comp.windows.x] Images in files.

rrs+@andrew.cmu.edu (Robert R. Shank) (04/25/89)

The documentation I have available says the the format for storing images
in files has not been defined.  Can someone advise me of the status of a
standard format?  What are the issues?

Thanks,

Bob Shank
send replies to rrs@cerc.wvu.wvnet.edu

raveling@venera.isi.edu (Paul Raveling) (04/27/89)

In article <cYJ9Gcy00VE60b8JAU@andrew.cmu.edu> rrs+@andrew.cmu.edu (Robert R. Shank) writes:
>The documentation I have available says the the format for storing images
>in files has not been defined.  Can someone advise me of the status of a
>standard format?  What are the issues?


	There are probably at least a couple dozen "standard"
	formats.  Naturally I've added my own nomination (Img format),
	but only after a couple years' experience with various others.

	My view of the main issues, approximately in order of their
	importance, is:

	1.  Complexity of software using images:

	    The interface from application code should be as simple
	    as possible.  This in turn requires careful design to keep
	    the software layer supporting images as simple as possible
	    (but not simpler).
	
	2.  Disk space:  Image files can consume lots if not compressed
	    efficiently.  Approximate statistics for our collection of
	    files in compressed Img color-mapped format are:

	Image type			   Color   Grayscale  Monochrome
	Mean Img file size per image	  105,400   128,300    12,679
	Mean number of pixels per image	  382,790   385,853   151,092
	Pixels per byte			      3.6       3.0      11.9

		* Subset:  Only checked a couple dozen monochrome images
		  rather than all 834 in the collection.

	3.  Processing speed:  With large amounts of data, even simple
	    functions such as copying the data can be slow.
	
	4.  Color quantization for display:  We have many raw RGB
	    images with >200,000 unique colors, and we have displays
	    variously capable of handling 2, 16, 64, and 256 colors.
	    Trying to retain as much image quality when few colors
	    are available is both necessary and challenging.  Doing
	    it fast is more challenging.

	5.  Associated data:  Some applications need to store data
	    of an unpredictable nature with images.


----------------
Paul Raveling
Raveling@isi.edu