Re: Only shades of gray...

From: steves ^lt;[email protected]>
Date: 06/09/04-01:37:43 PM Z
Message-id: <004a01c44e59$3cedf4a0$>

Those comparative luminance perception levels were Hannah's experiments.
The boxes inside boxes with various colors surrounding the gray center were
done by Jay.

----- Original Message -----
From: "Ryuji Suzuki" <>
To: <>
Sent: Tuesday, June 08, 2004 9:49 PM
Subject: Re: Only shades of gray...

> From: Richard Knoppow <>
> Subject: Re: Only shades of gray...
> Date: Tue, 08 Jun 2004 21:07:48 -0700
> I wasn't going to get into this thread but since you are into details...
> > Since the paper gradation is continuous the perceived
> > separation of tones depends on the visual system and the
> > things which affect it, like illumination level. There is
> > really no such thing as a minimum difference in tone, at
> > least in relation to anything practical in making good
> > prints.
> As you said, average density (or reflection/transmission luminance in
> relation to incident luminance) of some area is practically speaking a
> continuous quantity although individual constituents of the density is
> discrete grains. This is a physical quantity, and should accompany
> measurement error whenever experimental values are discussed. These
> measurements are in units of candela per square meter or foot candles.
> On the other hand, perceived quantity (brightness) is a psychophysical
> quantity, and its accuracy is limited by the errors in our sensory
> system, which is larger than errors due to decent physical measurements.
> On brightness, various things are of importance, but in this
> particular context, "difference limen" or "just noticeable difference"
> are in question. These things are very well studied in vision
> psychophysical community and published in their journals as well as
> numerous textbooks. The JND depends on various factors including the
> size of the targets, target separation, baseline luminance, duration
> of the stimulus presentation, etc. The JND is measured as the minimum
> difference in luminance that can be detected by visual system to a
> certain probability criterion.
> In average viewing conditions and typical density range of prints, the
> print's range would translate to some 100 JND's or on that
> order. Slides would have some 10x more. However, actual JND's vary at
> dark end, midtone, and highlights and spacing would not be equal.
> Analogously, sound intensity is a physical quantity, and loudness is
> psychophysical quantity. Fletcher at Bell Labs in 1930's is also
> analogous to Jones at Kodak Labs.
> I don't know much about olfactory system. Together with gustatory
> system, these chemosensory systems are much less understood
> scientifically.
> I don't think the work of Jones is considered obscure. There are
> zillions of things that we should know better, and it's just one of
> them :-)
> Journal of the Franklin Institute is a fun reading, at least from
> 1930's and 1940's. I just learned that B-29 was basically a huge air
> conditioner that happened to fly (well, not quite). That's the kind of
> stuff that my dentist's waiting room should have. (Actually my dentist
> has no waiting time because appointments are efficiently made online
> or by email with no overlap, and he locks the door in other times.)
> --
> Ryuji Suzuki
> "You have to realize that junk is not the problem in and of itself.
> Junk is the symptom, not the problem."
> (Bob Dylan 1971; source: No Direction Home by Robert Shelton)
Received on Wed Jun 9 13:37:01 2004

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