honig@ICS.UCI.EDU (David Honig) (01/01/91)
A while ago I asked the Net if anyone was formally evaluating image
compression schemes. The answer is: a few. I said I'd post my
responses, so here they are. Thanks to all.
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I asked those who responded,
What do *you* evaluate exactly? With what goal in mind? What is your
backround? (Your address indicates affiliation with an EECS dept; do
you work with psychophysicists or manage on your own?)
And introduced myself:
I'm a grad student studying computational vision, with a backround in
computer science and cognitive science/perceptual psych. A few days a
week I'm a programmer in the research part of a medical physics &
imaging dept of a hospital.
There, we have been thinking about running some experiments on the
perception of compressed medical images and I was wondering if there
were others out there who were willing to share their experiences. By
"experiences" I mean experimental methods that they used or pointers
to published work where they explain this; also unpublished hints and
pitfalls they've found. Technical stuff. E.g., "if you make it
brighter, it looks better, so you've gotta normalize..." [when
comparing stereos, this is a problem ---the louder one sounds better
even if it distorts and shapes the sound...] Did you know that the
brightness of a Sony monitor can vary significantly over the face of
the tube, but that you don't notice without a photometer?
We already have experiences of our own in doing psychophysics on
dynamic images, and a "perceptual workstation" (color Sun 4/370, and
growing :-) suited to the task. But our experiences were with very
simple signal-detection style tasks. Psychophysics traditionally
shuns complex, real-world stimuli, due to their uncontrollability.
Perhaps there are ways around this problem, eg., by using many images
and well-defined (but perhaps realistically complex) tasks?
-David Honig
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From: dlluner@mspvmic1.iinus1.ibm.COM
To: honig@ICS.UCI.EDU
Subject: Psychophysical evaluation of image compression
I suspect your conjecture is correct ("Hey Joe -- how's this one look?").
There is a "major" effort underway in the international standards community
for the compression of (color) images. The proposed standard (or, almost
proposed standard, as the case may be), JPEG, has a number of transmission
and/or compression modes based on the DCT (Discrete Cosine Transform --
amusingly engough I just got one of those packets of book RSVP cards
from some publisher and, sure enough, there's a book on the DCT now).
The DCT is tuneable for varying levels of quality vs. compression. I would
hope (though don't expect) there is some work going on in the committee.
(Net: I don't know, I'm just pointing to a possibility.)
-- David
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From: "Bart M. ter Haar Romeny" <bart@cv.ruu.nl>
Subject: Re: anyone doing PSYCHOPHYSICAL testing of image compression???
I know of two groups working in this field, on primarily medical
images:
prof. George Seeley, Univ. of Arizona, Tucson, Az. is one of the
leading experts in this field,
prof. Bernie Huang, UCLA, Medical School, Dept. of Radiology and
Digital Imaging has done many radiological studies, and built
compression routines and hardware himself, for PACS purposes.
Good luck.
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From: <haim@hawk.ulowell.edu>
Take a look at:
``Performance consequences of two types of stereo picture
compression,''
by J. Tselgov, A. Henik, I. Dinstein, and J. Rabany
Human Factors, 32(2):173-182, April 1990.
--hl
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From: David McLaren <mclaren@tasis.eecs.utas.edu.au>
Subject: Re: Psychovisual Compression
I am a postgraduate student in the EECS department here. My research involves
the compression of images for telecommunication applications. I mainly use
the psychophysics of human vision to decide what information I can remove from
an image in the compression process (the major characteristics used so far
being : spatial frequency response, luminance effects, and spatial masking).
No, I don't actually work with any pschophysicists - I get all my
information from journals, etc...