Re: Grayscale perception
Re: Grayscale perception
- Subject: Re: Grayscale perception
- From: Marco Ugolini <email@hidden>
- Date: Mon, 05 Dec 2005 19:42:39 -0800
In a message dated Mon, Dec 5, 2005 2:52 PM, Mark Rice wrote:
> It is true that there are an infinite number of points along a line, but in
> 16 bit, there are only 65,536 points on the line.
Hi, Mark.
Please allow me to clarify: when I wrote that "from my limited
understanding, it seems obvious that mathematical precision requires that
many steps in 16 bits," I meant the number of steps implicit in a 16-bit
architecture, that is 2 to the power of 16 = 65,536 (though Photoshop only
uses 15 bits, or 32,768 steps).
Though that was what I had in mind, I understand that it may have seemed
that I was saying that a 16-bit architecture implies an infinite number of
points, which was not my intention.
Sorry for the confusion.
> Different people can see considerably different amounts of discrimination,
> so it is impossible to answer the question: "What different values can
> people see?"
The answer is not exactly quantifiable, if not, possibly, by assuming an
abstraction similar to the "standard observer" established by the CIE in
1931 for the sake of quantifying the human color matching functions.
> One measure of this is the Munsell color test. I took it when I got my first
> job in the photo lab business to see what my color discrimination was. It
> consisted of 256 color chips, mounted on wooden circles. The examiner mixed
> them up, and then asked the examinee to put them in order. They used subtly
> different hues - light desaturated green to light desaturated cyan, for
> instance. The differences between colors were VERY subtle.
Was that a variation of the Farnsworth-Munsell 100-Hue Test? I myself took
the 100-hue test several years ago at UC Berkeley.
> I think the only way to truly answer the question would be to give a large
> group of users a gray scale discrimination test similar to the Munsell test,
> and tabulating the results. It would also be necessary to generate a series
> of smoothly gradated gray values, as the eye may be more sensitive to smooth
> changes than it is to discreet samples. I do not know how one could create
> the latter test, as I know of no printers that can generate prints with more
> than 8 bits without dithering.
A test like that would require a lot of chips...
I actually think that there is at least one application, ImagePrint, that
can print at 16 bits on Epson inkjets. I am not sure whether the actual
final print is restricted to 8 bits, though.
Best regards.
--------------
Marco Ugolini
Mill Valley, CA
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