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From: osmoviita@cc.helsinki.fi
Newsgroups: comp.graphics
Subject: Re: Psycho Graphics (was: Subjective Graphics)
Message-ID: <1991Feb17.031043.4897@cc.helsinki.fi>
Date: 17 Feb 91 03:10:43 GMT
References: <1991Feb1.082556.8553@agate.berkeley.edu> <2899@charon.cwi.nl> <1991Feb7.093627.3734@santra.uucp> <27B9DF69.11406@ics.uci.edu>
Organization: University of Helsinki
Lines: 32

In article <27B9DF69.11406@ics.uci.edu>, honig@ics.uci.edu (David Honig) writes:
> 
> Indeed, established psychophysics (from the sensory psychology area) has
> been used by computer graphicists et al. ---e.g., the MTF of the human
                                                    ^^^^^^^^^^^^^^^^^^^^
> eye tells you that you don't need as many bits for higher or lower spatial
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> frequencies.  (Of course, the MTF shifts as luminance varies, its not
  ^^^^^^^^^^^^
> linear you know....) 

True for stationary images, not for moving or flickering images.
Also if you change viewing distance spatial frequencies change. So it is
not wise to cut bits off if you need high quality images. At least 14 bits
per gun is needed to match human vision. So there is already a big cut in
todays "photo-realistic" 24 bit graphics which has only 8 bits per gun.
It is not yet clear where is the limit although so many seem to believe to 
some old misleading results made in simplified conditions. Indeed,
psychophysics has been misused by computer graphicists. So many computer
graphics books tell pure rubbish about human vision.

There is not good enough commercial computer graphics systems to make
psychophysical measurements to show what amount of data human being can see
from image. --- As far as I know. But somebody shoud build an accuracy
graphics card around TriQuint Semiconductors 14-bit, 1 GHz DACs (Computer
Design, Feb 1, 1991).

BTW, was it you, David Honig, who asked about people who study ray traced
images by psychophysics? I would be interested if somebody can give me
images calculated with enough accuracy.

Kari Osmoviita				osmoviita@cc.Helsinki.Fi