[pure-silver] Re: Ruminations On Subject Brightness Range In The Real World
- From: Laurence Cuffe <cuffe@xxxxxxx>
- To: "pure-silver@xxxxxxxxxxxxx" <pure-silver@xxxxxxxxxxxxx>
- Date: Tue, 11 Sep 2012 23:07:02 +0100
As just a grey scale the number is surprisingly small, circa 450 different
levels. For further reading on this i would recommend looking up the DICOM grey
scale standard,
http://medical.nema.org/Dicom/2011/11_14pu.pdf
And the research reported therein.
this scale does seem limited by the concept of simultaneously able to
distinguish, that is, if we take the full range of light conditions from
extreme tropical sunlight to a fully dark adapted eye, then the eye can operate
over a larger range of light levels than those defined by the scale, however
the scale does seem to give a fair representation of the ability of the eye to
distinguish light levels in one image.
Another interesting concept in this area is Kardas's concept of an information
volume for a given film and developer combination, which I encountered in
Hyzer's excellent 1962 book on engineering and scientific high speed
photography. Thevreference given there is
Kardas the photographic information volume, photo engr vol 5 no 2 1954, and I
can find no convenient online source.
For colour work, it would seem logical to assume that the maximum number of
distinguishable colours would be around (450)^3
All the best
Laurence Cuffe
Sent from an iPad,
On 11 Sep 2012, at 21:09, Jean-David Beyer <jeandavid8@xxxxxxxxxxx> wrote:
> Tim Daneliuk wrote:
>
>> Film, of course, is analog and has no notion of a "discrete" tone. It
>> would be interesting to know - if anyone does - how many shades from
>> pure black to pure white the human eye can distinguish. It would seem
>> THAT would define what an equivalent digital system has to do to
>> compete with film fidelity.
>
> I do not know the numbers, but it is A LOT.
>
> If you memorize a step tablet, and I show you a grey patch, you might be
> able to get to the nearest step. And that does not sound like much. And
> it isn't. In a project I had to memorize the entire Munsell Book of
> Color, about 4000 color chips. They were in a three dimensional color
> solid. One axis was hue (e.g., red, green, blue), one was lightness
> (black, the various grays, white)., and one was saturation (e.g., red,
> pinks, white). We had 40 hues, 10 lightnesses and 10 saturations
> (roughly). We could memorize those to be within one step in hue, one
> step in lightness, and two steps in saturation. That was pretty good.
>
> But what a human can remember, and what (s)he can distinguish are very
> different things. If you match things up and put two things immediately
> adjacent to each other, you can make extremely fine distinctions. This
> was all in the 1970s, so my memory may not be all that good. But it
> seems to me 8-bits were the minimum you could tolerate in lineally coded
> black and white, and 24 bits or so for color. You could use perhaps 4
> bits for blue and 6 bits for color, but you needed about 9 bits for
> green. And this was satisfactory only for still images. For moving
> images, you needed far more bits or the edges of things were "busy"
> because of the noise in the coders, the environmental illumination, etc.
> For really good color work, 48 bits were required.
>
> --
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