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  1. #71
    Stephen Benskin's Avatar
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    Quote Originally Posted by sanking
    I am perplexed as to why you believe this comment contributes to the discussion? The issue of whether the phrase "developing to a given CI" exists in the literature has not been in question, either in the previous thread or this one. So far as I can recall no one has claimed that the phrase does not exist in the literature. I certainly have not, and in fact I alluded to it in at least one previous message in this thread, for example where I wrote: “Even in cases where the term is used to in such a way that might suggest that it is a control or index number for processing, subsequent explanation always makes it clear that that CI is something to be obtained, not the process itself.”

    Sandy
    I probably just misinterpreted your comments.

  2. #72

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    Quote Originally Posted by Sanking

    Kirk,

    My connect is with the literature. I have looked carefully at the definition of CI in quite a number of technical books, including several devoted entirely to sensitometry, in order to better understand the issue, and I can find no example where the term CI, when defined, is not associated with a slope or gradient, which clearly shows that it is a result, not a process.

    Even in cases where the term is used to in such a way that might suggest that it is a control or index number for processing, subsequent explanation always makes it clear that that CI is something to be obtained, not the process itself. I could agree that the phrase "to develop film to a given CI" describes a process, but the phrase does not redefine the meaning of CI. It describes only the reality of the phrase itself as something that takes place. And even within the context of the phrase in question the literature reaffirms the definition of CI itself as a result, i.e. a slope or gradient that defines two different points of density. Blank film, unless it is unevenly fogged, can not have two different points of density; it can not have a slope or gradient.

    OK, I'm setting aside Davis. I’m satisfied with Sandy’s description of how to meter BTZS style for low contrast scenes. And I understand that Sandy is bowing out of the discussion – that’s fine.

    Since I started this thread, I’ll take the liberty to officially hijack it and get back to my original contention about CI and blank film. See http://www.apug.org/forums/forum37/14389-ci-blank-film.html if you missed it.

    Many opinions have been expressed that CI is dependant on exposure. It is not. They have infact gone on to tie this requirement for exposure to CI by saying if there is no exposure, there is no CI. That is wrong as well. And finally, there has been the claim that using the term/concept of CI as a level development or to describe a particular aspect of development, is incorrect or at least a perversion of the term. Let’s see.

    I don’t know which technical literature Sandy was looking in – but I just grabbed a couple of them for here – “Photographic Sensitometry” by Todd and Zakia, and also the original paper on “Contrast Index”, published in the Jan-Feb 1966 issue of Photographic Science and Engineering, by C.J. Neiderpruem, Nelson, and Yale of the Kodak Research Lab.

    So here’s a few quotes from Todd and Zakia –

    “Gamma is the slope of the straight line of the characteristic curve.”

    “Contrast Index is an average slope, as distinct from the straight-line slope specified as gamma. An average slope in this context is merely the slope of the straight line drawn between two defined points on the curve.”

    As Sandy pointed out in the other thread, “Definitions of gamma, CI, and C-Bar always include the use of one of these two words, either slope or gradient.” And I DO agree. These are descriptions of the method of measuring the gamma or CI of a particular film. Let’s move on.

    Also, for the rest of this discussion, keep in mind that when Todd and Zakia wrote this book in 1969, the term CI was quite new, and typically used the term “gamma” in instances where it would be custom to now use the term “CI”. They do say, “Recently the use of contrast index has come fro many purposes to replace gamma.”


    CI is not dependant on exposure -

    Todd and Zakia continue:

    “[…] Gamma is a useful measure of the degree or extent of development. For this reason gamma is often used as a processing control index. If we want, for example, to maintain a replenished developer at a constant activity, we test this consistency by finding out whether or not the gamma, obtained from test strips, remains nearly the same. […] If gamma differs, we suspect that the difference is associated with the different degree of development, instead of with the factor we are really trying to test.”

    Note that they say nothing about exposure here. They also flat out state that it is used as a process control index. That is a significant step beyond the simple definition of gamma or CI. In fact, it is an extremely useful definition, and allows a great deal of useful data to be applied to the act of developing film. The CI or gamma is not just a slope, it is a valuable property of processed film.

    They continue, “Contrast index has the same uses of gamma: it is an index number that can be used for processing control purposes; when films (or developers) are compared, the test images should be developed to the same contrast index. Like gamma, obtaining a consistent contrast index will not insure all negatives will have the same total contrast, nor that all negatives will print similarly.”

    Again they are using the term CI as a number, not as a slope. It is certainly derived from the calculation used to measure the slope associated with the definition of CI, but it is being used as a descriptive property of the processed film or processing.

    They also did not require that the test films mentioned in the last quote, all have the same total contrast. This means that some films may have a larger or smaller level of total contrast. Some may have enough total contrast to actually perform a CI or gamma calculation – and some may not. Some may have half as much as needed, and some may be unexposed or completely overexposed. But is does not matter, as the level of exposure is an unrelated factor to gamma as will be shown in the next quote, and it is also unrelated to CI as well.

    Todd and Zakia: “The value of the total negative contrast is dependant upon many factors. Among these are: subject luminance ratio; camera exposure level; color of light; gamma.”

    Gamma and camera exposure level are two independent factors. They would not list gamma and exposure as separate issues if they were not. The same goes for CI as it does with gamma.

    CI (or gamma) is not dependant on exposure.

    If there is no exposure, is there no CI?

    Now it was agued, that a sheet of unexposed film which has been developed for a period of time will graph on a horizontal line, i.e. at right angle to the vertical or parallel with the horizon - no slope, no gradient, and no CI.

    This conclusion if false. Simply put, the math used to make this conclusion is incorrect. An unexposed sheet of film will give us one data point – written as a data pair - (exposure, film density). Since we understand that determining the slope or gradient requires a minimum of two data points, we should be able to understand that there is simply insufficient data to even attempt to draw any one line with only one data point. (Interestingly, there are an infinite number of lines that can be drawn through one data point.)

    With only one data point, we simply cannot calculate the CI of this sheet of film. But this is not the same thing as saying that it has no gradient or CI as was claimed. The issue is there is just not enough data to calculate it here.

    In fact, we don’t even need to have sufficient exposure in a frame or roll to have a film achieve a particular CI. (The film does have to be capable of actually achieving the CI, but any particular sheet or roll of film doesn’t have to have received some minimum amount of exposure to get processed to a particular CI.

    Todd and Zakia say “In roll film, we may develop all the frames uniformly to a gamma of 0.75, but the negatives will no doubt have different total contrasts because of the variations in subject matter at least.” This also includes any blank frames or any overexposed areas – they mean the entire roll of film. They do not list any requirement for the number of points of density in the film because there is no requirement for this. Remember, both gamma and CI, are a property of the film development, and not the exposure. That entire roll of film they mention has a CI of 0.75, not just the parts with the “right” exposure. The blank parts have a CI of 0.75 too!

    Please go back to the link I gave above and carefully read the example I gave of the step tablet that was being cut into smaller and smaller pieces. That entire sheet of film has a CI of some particular value, and even if we cut it into small bits, each of those bits still have that same CI. The CI of that film is an innate property of that film.

    End Part I

  3. #73

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    Part II -

    Using CI as a term describing the development process -
    Finally, as to the question of the use - whether the term CI (or gamma) can be used to describe a process, and not just the slope or gradient of a line derived from a film curve, Todd and Zakia have several examples of this type of use. Even my use of the phrase “to develop to a CI” was questioned. (Keep in mind that gamma and CI are interchangeable for the concepts described here. Sorry I don’t have any more recent references nearby.)

    “In roll film, we may develop all the frames uniformly to a gamma of 0.75, but the negatives will no doubt have different total contrasts because of the variations in subject matter at least.” Develop to a gamma of 0.75, not for a gamma.

    “We may, develop a negative exposed on a foggy day to a high gamma, say 1.5, and still have a flat negative because the subject has a small luminance range.”

    “We may make a negative of another scene, with a large luminance range, develop it to a small gamma, and still have a negative of so great contrast that it requires a very soft paper for printing.”

    “It is true that if we make two negatives of the same scene and develop them to two different gammas, we expect the negative developed to the higher gamma to have more contrast.”

    “If we develop to a gamma of 0.5, the negative will have the same contrast as the subject for all straight line exposures. If we develop to a gamma of 0.5, the negative will have half as much contrast as the subject, but again only for the straight line.”

    Let’s see what Nelson has to say: “For Film A, development to a gamma of 0.65 produces the desired range. However, developing Film B to a gamma of 0.65 produces a negative having a short density range.”

    And here’s one where they use CI – “Using development to a contrast index of 0.56 (for portrait work) as the criterion for choosing the development times…”

    I hope these are sufficient examples of the use of the term CI and gamma to describe a process or index value, and not just a simple result that is obtained by making measurements of the film curve. It is consistently used to describe the level of development to be given a film. It is a goal of the processing step, and not always an act of measurement of some piece of film.

    You can see that there is no “suggestion” that the use of gamma and CI in these examples is as a term describing a control process, it is being used exactly for that description – these examples are way beyond mere suggestion. This is a “redefining” of the meaning - and one that has been in use for many decades.

    Kirk

  4. #74
    smieglitz's Avatar
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    ...But is does not matter, as the level of exposure is an unrelated factor to gamma as will be shown in the next quote, and it is also unrelated to CI as well.

    Todd and Zakia: “The value of the total negative contrast is dependant upon many factors. Among these are: subject luminance ratio; camera exposure level; color of light; gamma.”

    Gamma and camera exposure level are two independent factors. They would not list gamma and exposure as separate issues if they were not. The same goes for CI as it does with gamma.

    CI (or gamma) is not dependant on exposure.



    Kirk,

    You are drawing an invalid conclusion. You cannot properly draw the conclusion that CI is not dependent on exposure just because your premise that gamma, CI, spectral properties, camera exposure, etc., are not the same thing. Doesn't follow.

    If you reread what they are saying with an open mind, you will discover they are in fact discussing more than a single point whenever they discuss exposure in relation to CI or gamma. For example your quote of them:

    “ In roll film, we may develop all the frames uniformly to a gamma of 0.75, but the negatives will no doubt have different total contrasts because of the variations in subject matter at least"

    implies a subject with an inherent exposure variation ("variations in subject matter") instead of a single exposure value (as in a blank frame).


    Did you ever consider that Todd and Zakia may have made an error of omission by not simply stating that CI (or gamma) was dependent on 2 (or actually 3 in the case of CI) data points? I would bet that they thought the concept of a measurement of slope (a contrast) was so straightforwardly dependent on two or more data points that they just never mentioned it. Nothing you have said above changes that fact.

    You've not given any example by any of these sensitometrists where a variation/difference/contrast in exposure isn't implied in their discussion of developing a film "TO" a certain CI rather than "FOR" a certain CI. You are just choosing to overlook the implication that, for example, a portrait has many different exposures which have been taken simultaneously and from which one can develop TO a certain CI as well as FOR a certain CI and derive the measure. Nowhere have you *proven* a blank frame can be developed TO a certain CI.

    And why do you choose to dwell on this totally impractical and irrelevant point??? B-O-R-I-N-G. You can go on with this if you wish but I too have had enough of this absolutely meaningless debate.

    Go take some pictures or pay your taxes or something.

    Later.

    Joe

  5. #75

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    You know, getting out the books and quoting those passages that only support your argument and dismissing the rest is really a silly way to argue.

    Now that you have quoted Todd and Zakia, I decided to go get my book out and quote them. Here is their definition for contrast index:

    Page 71 Photographic sensitometry:

    "Contrast Index is an average slope. An average slope in this context is merely the slope of the straight line drawn between two defined points on the curve. Since the value of the slope will vary with the points that are chosen, some decision muxt be made about the definition of the two points"

    Since your blank film has no curve and it has no two points, you have no CI in a blank piece of film as quoted by your sources. QED.

    And yeah...I agree with Joe, you are not showing that you are smarter than all here, only that you are a greater PITA.....

  6. #76

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    Oh yeah, and before I forget...first thread on the "ignore thread list".....

  7. #77

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    Joe - I have read it with an open mind. And Joe, If you find this B-O-R-I-N-G, then why reply? Anyway, I have paid my taxes, thanks for the reminder though.

    Quote Originally Posted by smieglitz
    You cannot properly draw the conclusion that CI is not dependent on exposure just because your premise that gamma, CI, spectral properties, camera exposure, etc., are not the same thing. Doesn't follow.
    Please explain how these factors are the same thing - subject luminance ratio; camera exposure level; color of light; gamma? They are not. They are independant variables. I can pretty much set each one of them to nearly any value I wish. They are not dependant on each other.

    Todd and Zakia said: “ In roll film, we may develop all the frames uniformly to a gamma of 0.75, but the negatives will no doubt have different total contrasts because of the variations in subject matter at least"

    Quote Originally Posted by smieglitz
    implies a subject with an inherent exposure variation ("variations in subject matter") instead of a single exposure value (as in a blank frame)..
    They refer to the subject luminance range here and they are making a general case. I am using a specific case in this thread where the subject luminance range is zero.

    So let's use BTZS-type terms here: You surely agree that they are discussing SBRs at 7, right? How about 6, or 5, or 4? Still lots of variation there in the "inherent exposure variation" as you put it.

    Here's a question - at what subject luminance range or SBR did that film, which they said was developed uniformly to a gamma of 0.75, loose the gamma of 0.75? They said that the entire roll was at 0.75. Is it at SBR 3, or 2, or 1, or 0.1, or 0.001? When did the gamma drop to zero? Where?

    At no point do they mention that what the level of the subject luminance range was, or even what the actual expsoure was. That is because they understand that gamma or CI is, in addition to a measure of a film curves gradient, it is also a measure of development. Not exposure, not subject luminance range.

    Quote Originally Posted by smieglitz
    If you reread what they are saying with an open mind, you will discover they are in fact discussing more than a single point whenever they discuss exposure in relation to CI or gamma.
    They are not discussing exposure range here. They are discussing development.

    Quote Originally Posted by smieglitz
    Did you ever consider that Todd and Zakia may have made an error of omission by not simply stating that CI (or gamma) was dependent on 2 (or actually 3 in the case of CI) data points? I would bet that they thought the concept of a measurement of slope (a contrast) was so straightforwardly dependent on two or more data points that they just never mentioned it. Nothing you have said above changes that fact.
    Sure, I can consider it. But they had already clearly discussed the mathematical technique needed to calculate gamma or CI earlier in the book, and they appearantly felt they did not need to repeat it. It is straight forward, as you say.

    Did you ever consider that they are discussing an index for the measure of development, as they say they are discussing?

    Quote Originally Posted by smieglitz
    You've not given any example by any of these sensitometrists where a variation/difference/contrast in exposure isn't implied in their discussion of developing a film "TO" a certain CI rather than "FOR" a certain CI. You are just choosing to overlook the implication that, for example, a portrait has many different exposures which have been taken simultaneously and from which one can develop TO a certain CI as well as FOR a certain CI and derive the measure. Nowhere have you *proven* a blank frame can be developed TO a certain CI.
    I see you included the words "and derive the measure {of the CI}." I think you will find I have never argued that you can calculate there actual CI of a sheet of film if it is blank. I have repeated this several times. Please note that. I agree that you can not.

    But it is a different thing to process a film to a desired level. Just because you can't prove it directly from that piece of film, because it did not contain the necessary levels of exposure needed to generate sufficient data points to directly calculate it, does not mean it did not recieve the desired level of development, the desired CI or gamma.

    You may be able to measure it indirectly, say if you processed a control strip along side your roll. Or you may need to infer it from the information that you have gained through process control - you ran a control strip 15 minutes before and it achieved your desired level of CI and you ran one 15 minutes after your roll of film and it also achieved your desired level of CI. You can be pretty safe in inferring that your roll of film also recieved that level of processing. Regardless of the exposure that the film recieved.

    It's not a trivial, nit-picking point, as some have made it out. It is a basic concept of film processing that I would have thought would be more appearant given some thought. (I do agree it may not be immediately appearant though.)

    And as far as not quoting any of these sensitometerist giving a quote "where a variation/difference/contrast in exposure isn't implied", I did. How about

    Tood and Zakia, "Gamma is a useful measure of the degree or extent of development."

    They say nothing about variation/difference/contrast in exposure there.

    How about from "View Camera Technique", 6th ed. by Leslie Stroebel. "Gamma is defined as the slope of the straight line of the characteristic curve, and it is useful because it is a simple objective concept that takes into account the various factors that determine the degree of development - developer activity, time, temperature, and agitation - for a given emulsion."

    Stroebel does not mention anything about variation/difference/contrast in exposure. He does not even mention exposure! Only factors of development.

    And please consider this - From "The Theory of the Photographic Process", 3rd Ed. by C.E.K. Mees and T.H. James, "Any value of fog given for a photographic material must obviously be accompianied by some specification of the development time or the degree of development (in terms of gamma) for it to have any definite significance".

    Perhaps that quote clears it up. Mees and James recognize that a piece of film with no exposure has a gamma (and therfore a CI). Do they say there must be a range of densities - no. Do they discuss the variation/difference/contrast in exposure - no.

    So what do Mees and James understand that seems to not be appearant to some of the participants in the thread? They understand that blank, unexposed film has the property of gamma, and that the gamma is dependant on the degree of development. Not exposure.

    Kirk

  8. #78

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    Quote Originally Posted by Jorge
    Since your blank film has no curve and it has no two points, you have no CI in a blank piece of film as quoted by your sources.
    You just can't calculate it directly from that sheet of film. See the previous post.

  9. #79

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    Quote Originally Posted by Kirk Keyes
    You just can't calculate it directly from that sheet of film. See the previous post.
    LOL...well if you cant measure it, then you dont have it......

    Look, if it makes you feel good to have the last word, I hope you realize that you are not "winning" any discussions by the power of your reasoning, but by attrition. People are gettring tired of reading your 2 page long foolishness in an effort to prove a stupid point anybody can see you are wrong.

    What you are displaying here is not a command of the subject, but a childish stubburness to be always right and "show" the rest of us. Let me assure you, you are becoming the laughing stock of this site very fast judging by the amount of PMs I have been getting about you. As Donald wrote, your notoriety is not one of admiration but one of "there goes this a**hole again."

    I know that as far as I am concerned my opinion of you has radically changed, and from the messages I have gotten you jdef and Beskin are very quickly being lumped with the likes of scarpitti/ornello. If you want people to respect your point of views, you should learn to give it a rest once the thread has grown to 11 pages of endless repetition.

    In the end , I have yet to see you "win" a discussion, what I have seen is you drown people with endless meaningless facts that it becomes too tedious and boring.

    Dont bother on replying, I have placed this thread in the ignore section....I am just giving you a friendly advice in return for the help you provided to me in the past. As far as I am concerned we are even....I wish you luck and hope you heed my advice.

  10. #80

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    Do you actually read the posts? If not, please block them.

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