Re: Digital negative novice needs help.

If Ektaflex prints look sharper at 65 lppm than at 20 lppm it is
because of accutance, not resolution.

Although it is true that the methods used to measure resolution are
subjective in that they depend on human judgement they are
nevertheless relevant since photographic sharpness is ultimately
determined by human beings with their eyes rather than by scientific
methods. It is important to keep this fact in mind, because studies
have shown that the limits of human vision are determined by
separation of light receptors in the fovea of the retina, and that
separation suggests an absolutely maximum resolution of something on
the order of 25 lppm. This takes into consideration both point source
and line discrimination. So regardless of what Ctein may say I
personally do not believe that resolution greater than 20-25 lppm can
be the cause of the greater sharpness apparently observed in the
testes to which Gregory refers.

Regardless, all of this is totally irrelevant to the the original
question, which was about making digital negatives with desktop
scanners and inkjet printers. In any imaging system the maximum
information that can be obtained is determined by the weakest link in
the chain, and in this case it is either the printer or the paper
(assuming alternative printing on art and drawing papers), since both
limit resolution to 10 lppm or less. And you can get 10 lppm or more
from some inexpensive flatbed scanners (Epson 4870, 4990 etc.),
assuming you don't plan to enlarge the file more than about 2.5X.

Sandy

>From: Gregory Popovitch <greg@gpy.com>
>Subject: RE: Digital negative novice needs help.
>Date: Fri, 21 Apr 2006 21:21:15 -0400
>
>> Also, there are some facts. Ektaflex prints known to resolve 20 lp/mm
>> are visibly less sharp to the eye that other types of RA4 paper prints
>> resolving 65 lp/mm. How do you explain this if 10 lp/mm is the resolution
>> limit of the eye?
>
>Again, resolution limit and accutance are very different matters. You
>should be discussing these matters in terms of MTF (modulation
>transfer function) instead of resolvability and accutance, both of
>which are rather subjective matters. (resolvability is often given in
>numbers but there is no single established scientific method to
>measure those numbers without human judgement, not that it matters a
>lot in most practical cases.)
>
>There are two important papers on this topic published in volume 15,
>issue 2 of Photographic Science and Engineering (1971). One is by
>Nelson and the other Higgins.
>
>> I think that your statement "increased resolution does
>> not necessarily mean the edge contrast is greater", while correct,
>> is misleading. I doubt that in practice you will be able to produce
>> high acutance, low resolution prints. If the resolution is low, then the
>> edge sharpness will not be satisfactory to the eye, and I think that's
>> what Ctein was saying.
>
>It's easy to make high accutance, low resolution image. Using
>old technology film developed in accutance developers, and then
>magnify by a large factor.
>
>On the other hand, if you develop T-MAX 100 in D-76 and print it at
>moderate magnification, you get low accutance, high resolution image.
>
>With digital signal processing based image processing on computers,
>any of these things is possible.
Received on Sat Apr 22 10:33:54 2006