Henry/Kodak/Acutance tests/Edge effects

Discussion in 'Exposure Discussion' started by michael_r, Jun 14, 2013.

  1. michael_r

    michael_r Subscriber

    Messages:
    6,539
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    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.

    Thanks
     
  2. MattKing

    MattKing Subscriber

    Messages:
    16,816
    Joined:
    Apr 24, 2005
    Location:
    Delta, BC, Canada
    Shooter:
    Multi Format
    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.
     
  3. michael_r

    michael_r Subscriber

    Messages:
    6,539
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    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.
     
  4. Shawn Dougherty

    Shawn Dougherty Member

    Messages:
    4,184
    Joined:
    Jul 22, 2004
    Location:
    Pennsylvania
    Shooter:
    4x5 Format
    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.
     
  5. Alan Johnson

    Alan Johnson Subscriber

    Messages:
    1,514
    Joined:
    Nov 16, 2004
  6. michael_r

    michael_r Subscriber

    Messages:
    6,539
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    Alan - thanks - yes this article by Perrin is key to what I wanted to talk about but I never had the actual article!
     
  7. Photo Engineer

    Photo Engineer Subscriber

    Messages:
    25,774
    Joined:
    Apr 19, 2005
    Location:
    Rochester, NY
    Shooter:
    Multi Format
    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.

    PE
     
  8. Stephen Benskin

    Stephen Benskin Member

    Messages:
    1,646
    Joined:
    Jan 7, 2005
    Location:
    Los Angeles
    Shooter:
    4x5 Format
    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?
     
  9. Ian Grant

    Ian Grant Subscriber

    Messages:
    18,035
    Joined:
    Aug 2, 2004
    Location:
    West Midland
    Shooter:
    Multi Format

    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.

    Ian
     
  10. michael_r

    michael_r Subscriber

    Messages:
    6,539
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    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 :laugh:. 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.
     
  11. Photo Engineer

    Photo Engineer Subscriber

    Messages:
    25,774
    Joined:
    Apr 19, 2005
    Location:
    Rochester, NY
    Shooter:
    Multi Format
    Before I even joined Kodak, the standard method comprised of slits, not knife edges. And the slits were used to create images with Xrays and with visible light as a measure of turbulence in the emulsions.

    The light exposures were both negative and positive, and we used several slit widths. In the example it is 10, 100 and 1000 microns but I have used 1 micron as well. The height of these at different exposures will give the relative contrasts as seen in the second image. This difference represents say 35mm vs 4x5 images and thus you "see" the image differently.

    In 35mm, the 10 micron line may represent a telephone line, but in 4x5 that might be a 1000 micron line.

    So, we never (AFAIK) used knife edges because they were not very revealing in many ways.

    Pictures courtesy of Mike Kriss.

    PE
     

    Attached Files:

  12. Alan Johnson

    Alan Johnson Subscriber

    Messages:
    1,514
    Joined:
    Nov 16, 2004
    In 2003 Geoffrey Crawley was publishing film test results using a microdensitometer scanning negatives of lines of decreasing separation, see attachment of my tracing of one.
    On the LHS of this diagram apparently the amplitude (height) of the trace is proportional to the ability of the film to resolve what he calls "overall main subject outlines".
    I believe the little peaks at the top corners of the curve on the first cycle are some kind of measure of adjacency effects.
    On the RHS of this diagram the amplitude is apparently higher with films having superior fine detail definition.
    So Crawley could get on one diagram evaluation of acutance and resolution but no numbers for either.

    IDK if this method is used by film manufacturers more recently.
     

    Attached Files:

  13. Mustafa Umut Sarac

    Mustafa Umut Sarac Member

    Messages:
    4,574
    Joined:
    Oct 29, 2006
    Location:
    İstanbul
    Shooter:
    35mm RF
    This graph confirms that you must expose the film for the shadows and develop for the highlights.
     
  14. Sponsored Ad
  15. Photo Engineer

    Photo Engineer Subscriber

    Messages:
    25,774
    Joined:
    Apr 19, 2005
    Location:
    Rochester, NY
    Shooter:
    Multi Format
    Since apparent sharpness is linked to the ability to resolve items, and this is linked to contrast, then the Crawley method will miss any image effects linked to contrast.

    There are many ways to measure apparent sharpness, but it must be done at the scale at which you intend to work, and at the contrast you are using. The technical data are hard to interpret, when in actual fact one image may appear sharper than another when the data says the opposite must be true. Nothing beats the eye for telling what is "right", and if your test print vs your test subjects pick one over another, then that is the way to go.

    Ok, so, Kriss points out that the grain (or noise in the measurements) also contributes to image sharpness or overall quality and he uses the term "Film Information Capacity" to express all aspects of the quality of a film. In his article, he cites 103 references.

    PE
     
  16. Alan Johnson

    Alan Johnson Subscriber

    Messages:
    1,514
    Joined:
    Nov 16, 2004
    PE.
    Do you know what method Kodak used when IIRC they put the words "Worlds Sharpest" on the new version TMY2 of the 400 ISO TMY film?

    Crawley's method, Amateur Photographer 10 May 2008 confirmed that TMY2 gave a higher amplitude at both high and low frequencies, agreeing with this although as you indicate other factors are involved (probably outside the scope of this discussion but interesting to know what Kodak did.)

    He noted other 400 ISO films have different advantages.
     
  17. markbarendt

    markbarendt Subscriber

    Messages:
    7,516
    Joined:
    May 18, 2008
    Location:
    Beaverton, OR
    Shooter:
    Multi Format
    I got to see some prints of the Degas made from cancelled (scored) plates a month or so ago. Very interesting indeed.
     
  18. Photo Engineer

    Photo Engineer Subscriber

    Messages:
    25,774
    Joined:
    Apr 19, 2005
    Location:
    Rochester, NY
    Shooter:
    Multi Format
    Alan, AFAIK, the method Kodak is using n ow is the same as what we used as far back as the 60s. The algorithms have improved and thus data gathering and presentation is far superior.

    So, on a 35 mm x 12" strip, the 1000 micron down to the 1 micron slid exposures appear as about 1/2" square "boxes" containing all 4 exposures, and there are 11 of these per strip, each box having 1 stop more exposure. They are all plotted as I have shown above in an exposure series, and they are treated mathematically to give a large set of data presentations, some of which are shown on the Kodak web site. Grain is introduced and this is then treated to give the result Kriss describes as "Film Information Capacity".

    With color, it is done with R/G/B/N, and of course a set of X-Ray data accompanies all of this so that we can determine turbidity and the proper level of acutance dyes.

    PE
     
  19. michael_r

    michael_r Subscriber

    Messages:
    6,539
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    PE, in the first graph you posted, would it be fair to say the different slit widths also illustrate the Eberhard effect?

    I’d like to look a little at the math now, in the context of the acutance formula (and variations) from Higgins/Jones and Higgins/Perrin/Wolfe.

    The basic formula discussed by Perrin, and used by Richard Henry in his book is the mean square gradient for the transition from high to low density. I’m assuming the basic math would be the same whether the exposure is with x-rays, visible light, through a slit, or using a knife edge test (Perrin, Henry). So, G2x. Henry then explains Higgins and Jones thought the total change in density should also be a factor so they proposed G2x * DS where DS is Dhi-Dlo. Apparently based on experimental data Higgins/Perrin/Wolfe later modified the formula to be G2x / DS , but that’s a separate issue I’m unclear on.

    Here is what puzzles me. Perrin (and later Henry in his tests) says that edge effects need to be accounted for by modifying the formula, but that nobody has figured out how to do it. I don’t understand why this is so difficult. It is even more odd that as late as 1986 Henry would say it still has not been done. By introducing DS, weren’t they almost there? While Jones, Higgins, Perrin etc. Were undoubtedly a lot smarter than I am, why didn’t they just convert DS into some sort of “factor”? For example, suppose we have a given acutance experiment (either comparing two films, or the same film with different developers, or different exposures etc.), for each trace why couldn’t we multiply G2x by something like C (for Contrast) where:

    Acutance = G2x * C

    C = delta Dedge / delta Dexp

    delta Dedge = (max Dhi – min Dlo) across the transition

    delta Dexp = (Dhi – Dlo) away from the transition based on the high and low exposures given.

    Thoughts?
     
    Last edited by a moderator: Jun 17, 2013
  20. Photo Engineer

    Photo Engineer Subscriber

    Messages:
    25,774
    Joined:
    Apr 19, 2005
    Location:
    Rochester, NY
    Shooter:
    Multi Format
    Michael, this work moved far beyond Higgin's work. There was the work of Bartleson and Breneman, the work of DeMarsh and the work of Kriss. And, much of this was never published outside of EK. So,yes the slit exposures show what we now call "edge effects". These are the "ears" on the exposure. Those who worked with knife edge exposures missed a lot of information such as fill in and bloom.

    Kriss' method of defining "image content" codifies all of these into an appropriate equation which I would have to scan in, but the explanation is nearly 30 pages long in his article. It can be found in the bok "Color Thory and Imaging Systems" published by the SPSE.

    PE
     
  21. michael_r

    michael_r Subscriber

    Messages:
    6,539
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    I'll have to look into that. When was this work done?

    What sort of techniques and calculations would Altman/Henn been using in their famous developer study (1950s)?

    Of course I suspected much more had been done on this after the initial work. The problem is for the most part none of us know of any of that stuff, nor is anyone in the position to run such tests at this point. So I figured I would tackle the traditional or "classical" :laugh: notions of acutance, edge effects, resolution, and granularity without a unified field theory of image structure. The reason is that these are the ways formulators and laymen have referred to the working characteristics of developers and developed negatives, and still do (rightly or wrongly).

    Where I'm ultimately going with all this is to suggest acutance as it has traditionally been characterized by people (ie edge sharpness of "grains") is virtually meaningless in the selection of a developer. There are a variety of reasons for this. I just don't think it makes much sense when people talk about a certain developer giving a sharp edge to a grain vs an etched edge. Among other things, Haist's discussion regarding the formation of metallic silver during development, and the microscopic images of developed silver would seem to suggest this notion of etching = unsharp image is rather silly.
     
  22. Photo Engineer

    Photo Engineer Subscriber

    Messages:
    25,774
    Joined:
    Apr 19, 2005
    Location:
    Rochester, NY
    Shooter:
    Multi Format
    Michael, there is no magic developer. You have the triad of speed, grain and sharpness and you can only improve on 2 at one time. So, you are technically barred from reaching the peak of this pyramid.

    As we worked on imaging even earlier than the '60s when I arrived, it was apparent that the knife edge was self limiting as it only gave information on the boundary of an image at infinite width on either side. But pictures are made up of bounded areas and thus the slits came into vogue. They gave far more information and still allowed the examination of the edge effects. Kriss published his first work on this in the '70s and work has since sped up. The reason? Total image content is a very important method of comparison with digital. With aliasing, and R/G/B separations it is the content of the image which is important.

    Kriss' work is based on the work of Higgins, Perrin and others, but is the next step forward from the early knife edge exposures. I cannot hope to explain this unless I scan in the whole article and post it. It is packed with a lot of calculus. All I can say is that we used the methods I described and out the other end came figures relating to overall image quality based on these mathematical geniuses.

    PE
     
  23. Alan Johnson

    Alan Johnson Subscriber

    Messages:
    1,514
    Joined:
    Nov 16, 2004
    As Dr Henry pointed out the word acutance (A1) was originally as defined in the early Kodak work but is now also used (A2) to mean perceived sharpness which combines this with adjacency effects (A3).
    To define (A3) would need another 4 numbers to show the height and slope of the fringe and border effects.
    (A2) for each film developer combination would then involve 5 numbers. IMO nobody would use such a complex label.
     
  24. michael_r

    michael_r Subscriber

    Messages:
    6,539
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    PE: Interesting that this work continued as a result of digital.

    Absolutely agree there is no magic developer (I'm actually trying to simplify the choice a little). However many things are said, not only by laypeople but by people formulating these things, and there are some claims I just don't think hold much water based on the mechanisms at work. This seems particularly to be the case concerning "sharp" developers such as Rodinal, Crawley's FXs and tanning/staining formulas. Not a new story I know, but I wanted to approach a few image structure characteristics from a critical perspective. Sharpness (or definition) is complex, but as far as the influence of developer/development goes, I'd like to question the concept of traditional acutance - ie the idea that solvent action per se has any significant influence on sharpness.

    I agree introducing a lot of calculus is probably beyond what many people will find interesting so let's leave that for now (unless people want to get into it).

    Alan: Why would A3 be so complicated? It is basically the idea I proposed (simplistic) but with more "factors" to account for the 4 gradients of the edge effects individually and separately from the gradient G2x in A2. Actually this is helpful since it points out a flaw in my simplified formula (ie no consideration of the edge effect gradients).
     
    Last edited by a moderator: Jun 17, 2013
  25. Photo Engineer

    Photo Engineer Subscriber

    Messages:
    25,774
    Joined:
    Apr 19, 2005
    Location:
    Rochester, NY
    Shooter:
    Multi Format
    Michael, just FYI, Crawley's early developers with iodide worked because the iodide adsorbed to the early bromide emulsions and then was released during development to cause edge effects. In modern, high iodide (up to 10%) emulsions, the Crawley developers have little or no effect.

    I have been discussing this with Bill Troop. I am not sure he agrees but he was on board with a positive reaction last we discussed this.

    PE
     
  26. michael_r

    michael_r Subscriber

    Messages:
    6,539
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    That would be pretty important given how much there is about Crawley's developers in the FDC. On the other hand Iodide was only in the FX1 formula as far as I know (although it may have been in some of his Paterson FX and/or Acu developers).

    What is your view on current films (including tabular-grain emulsions) vs older style films when it comes to how readily they produce edge effects in general? Some people have said films like TMax for example "resist" the formation of edge effects even in highly dilute developers. Is there any truth to this?

    Edge effects are one thing, "grain etching" by sulfite is another. That's the effect I question when it comes to the relative acutance (ie excluding edge effects) of low pH solvent vs high pH non-solvent developers. Simply put, I don't see how the grain etching argument makes much sense when it comes to image structure. For one thing the scale is too small if we're talking about individual grains. Then there is the fact the shape of a grain is only barely maintained under typical development circumstances. Then, even where the overall shape of the grain is maintained, most development results in the formation of filamentary silver, so the edges of what was the silver halide grain have a rough appearance anyway.