Newsgroups: sci.image.processing
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From: jlavi@cs.joensuu.fi (Jarkko Lavinen)
Subject: Re: Are 24-bit video adapters toys?
Message-ID: <1994Oct31.110610.10808@cs.joensuu.fi>
Organization: University of Joensuu
References: <1994Oct13.121017.481@cs.joensuu.fi> <37m17b$mh6@kodak.rdcs.Kodak.COM> <usenet-1410941051060001@lowry.eche.ualberta.ca> <37uo35$2vb@kodak.rdcs.Kodak.COM> <usenet-1910941241490001@lowry.eche.ualberta.ca> <388gj0$k0c@kodak.rdcs.Kodak.COM> <1994Oct25.113957.13989@cs.joensuu.fi> <Cy8E0r.FEB@bbc.co.uk>
Date: Mon, 31 Oct 1994 11:06:10 GMT
Lines: 37

alanr@dd.eng.bbc.co.uk (Alan Roberts) writes:

>about 1%. That means _within_a_picture_. There is no point providing
>contrast of greater than 100:1 within a picture because the eye responds
>to the mean (or possibly weighted peak) brightness and adjusts its gain
>accordingly. Greater contrast means that the blacks gets darker, and below
>1% the eye [produces no response from them. If you increase (or reduce)

I find this part a little unpalatable. I mean, on a bright day the
contrast outdoors can be as large as 9..10 steps and I think I can
still see the scale. When I read Ansel Adams (et al) texts, one can
clearly see they handle scenary with dynamic range more than 1:100 and
that they perceive somehow this range. Perhaps they don't see it in
a one glimpse, but they can visualize it. Perhaps this 1% applies to
TV screen viewed from normal distance so the viewing angle is limited?

I have taken many slides where scenary contrast is 1:100 and more. There
are bright areas and deep shades together in the image. When I view the
slide I can see details both in shade and in bright areas. Perhaps it
is that projected image has decreased contrast due flare and because
it is magnified one can concentrate separately to highlights and
shades. Now I should have actually a densitometer to really know whats 
the contrast in a slide and a photometer to know whats the contrast in 
a viewed image!

I also find it a little hard to take that human eye couldn't handle 
optically more contrast than 1:100. There is a single lens in eye and 
I don't see why more than 1:100 couldn't be projected into retina.

Nevertheless this is interesting point to consider. I never thought
that human eye itself could be the bottleneck. I am quite used to
idea that human senses are fine intruments which are hard to beat.
My forthcoming monitor purchase is now becoming more and more difficult
all the time.

	Jarkko Lavinen
jlavi@cs.joensuu.fi, http://balrog.joensuu.fi/~jlavi/
