Henry/Kodak/Acutance tests/Edge effects
Is anyone open to a discussion regarding the acutance tests in Richard Henry's book along with some references to the Altman/Henn Kodak study - and how edge effects could be factored in? If PE is interested perhaps he could also help me to understand how KRL measured these things.
This would help me fill in some holes in a "discussion paper" on the relative importance of various factors contributing to the image definition.
I'm posting this here because exposure and densities are involved in knife edge tests, that sort of thing. So I'd rather put it here than in the B&W forum.
Any input from the usual suspects (Stephen, Bill B., Mr. Bill) is always appreciated.
Lately I've been thinking a fair bit about the subject of accutance and so-called "sharpness", and have been involved in a number of discussions about it. As a result, I'll be following this thread with interest.
I don't have the resources you are referring to. For folks like me, it would be appreciated if you can supply either accessible links or relevant excerpts.
I'll contribute as well, if I see anything that I think might be valuable from a "layperson's" perspective.
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2
Thanks, Matt. It's part of something I've been working on regarding the traditional acutance (ie without factoring in edge effects) aspect of developer choice and how it might be largely irrelevant. But there are a couple of specific things regarding the acutance formula/tests I'd like to get clarified first. I thought this would be the best sub-forum for it.
You probably won't need the actual books in order to participate. But I thought it worthwhile to reference them here since some of the other usual participants have them, and might be able to shed some light.
Basically what I wanted to discuss here is the application of the traditional acutance formula.
I will also be following along with interest. (I doubt I'll have anything to contribute, I'm posting primarily so this thread shows up in "My Posts".)
Thank you, Michael.
Perrin gave a 1956 discussion:
He did not mention the type of developer, the effect of which was mentioned by Adams:
Presumeably there must have been some later proprietary work, I have not looked through the references in Dr Henry's book.
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Alan - thanks - yes this article by Perrin is key to what I wanted to talk about but I never had the actual article!
Goodness, I would have to re-read all 30 pages of the seminal paper by Mike Kriss. If you can get a copy, it will save a lot of time in discussion here, but he did write a paper on new methods of studying image quality. I'll have to get it out I guess. I did incorporate some graphs from his paper in my book (with permission of the author).
Anyhow, we study grain and sharpness both, but you are interested in how sharp a photo is. Perrrin shows in the first figure, the cone shaped nature of an exposed image, say a dot. It should be a cylinder, but it is cone shaped and the cone can be reversed from what is shown by Perrin. In his example, attenuation makes the image form with the point down, but if you have scatter, then the image is formed with the point up. This is more the case with modern materials in which are added absorbing or acutance dyes to make the image more cylindrical.
Now, how can we observe the ideal? We use X-Ray "dots" instead of or along with light dots. The difference between them is the contribution of light vs X-Ray in scatter. X-Rays do not scatter. Thus, no cone shape.
Now Ross showed that even with ideal exposures, development posed its own problems. For example, HQ is a hardening agent (Quinone is the hardener). This causes pseudo "edges" due to hardening, and formation of Silver metal causes the swell of the gelatin into "bumps" around such a "dot" exposure.
We have to analyze all of this as we go into an R&D cycle. And, we have to compare micro and macro effects. You see, micro and macro contrast are not the same and thus images vary from 4x5 to 35mm due to these effects.
'nuff for now.
Michael, I've never had much more than a passing interest in photographic microstructure because I always thought that without a microdensitometer it was mostly theoretical. Henry's coverage of the subject; however, does look useful as he discusses a hands on approach. Another nice book is Image Clarity: High Resolution Photography by John B Williams. I've found it to be very accessible. If you want to get into the weeds of the equation, Theory of the Photographic Process 3rd edition, Chapter 23 -The Structure of the Developed Image, The Imagery of Points, Lines, and Edges. I'm afraid you're on your own with that section.
BTW, how do you plan to work around not having a microdensitometer?
Originally Posted by Alan Johnson
Well Kodak's research into High definition Developers at the Kodak Research Laboratories, Harrow, resulted in Kodak HDD their proprietary developer which was never made or sold in the US. This developer competed with Ilford Hyfin and Paterson Acutol-S.
It's often forgotten that Kodak Ltd, UK sometimes made and sold products in Europe never available in the US. In terms of developers 3 come to mind, HDD, Kodelon and D163.
Kodelon, which was Kodak's equivalent of Agfa Rodinal and Ilford Certinal was introduced some time in the 1930's and would have been based on pf CEK Mees 1908 earlier research at Wratten and Wainwright. D163 was Kodak Ltd's main Universal film and paper developer.
PE: Are you saying the most recent methods of measuring acutance (traditional) at KRL used x-ray exposure? ie: meaning the often discussed "knife edge" methods were more primitive? Was a knife edge-type procedure per se actually ever used at Kodak or were there more advanced methods even at the time Perrin wrote the particular article attached above in Alan's post (which includes a description of the knife edge approach). I'm wondering if that was just a simplified "analogy" of what was actually being done for illustrative purposes.
Another question: At the time Altman and Henn published their well known study of the effects of sulfite concentration on acutance, speed, and granularity, would their measurements of "acutance" have been based on the Perrin/Jones/Higgins approach or would they have included edge effects somehow.
Stephen, in fact I think it might require more than microdensitometry. Electron microscopy probably. Clearly I won't be providing any experimental evidence of my own . What I want to do is put forth some ideas based on some of the work that has been done (sources Haist, Henry, Altman/Henn, Perrin etc. etc. (your pal Jones might be involved).
Will post more tomorrow on the specifics.