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  1. #11

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    Curve section - here you go completely wrong. Typical color neg films might have wide exposure latitude overall, but just look at the published dye curves and see just how fast that color spikes
    intersect and cross-talk. You can't clean up things at that point in the curve, Photoshop or otherwise. And to get a crisp scan of what's left requires either a large sample size (i.e., large film)or a very high quality drum scan because the curve shape of the geometry changes rapidly. But what do I know? I only spent a week with a spectophotometer making a true gray card that is actually 18% gray all the way from IR to UV. Commercial gray cards aren't even 18% at the middle.
    I probably have a different concept of a lightbox than most folks too.

  2. #12
    Diapositivo's Avatar
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    The general problem with negative film is that if there is no colour reference in the picture (if there is no test frame with a known colour patch target) then the 1-hour printer is left in the cold about filtration, and takes all the brown stuff when the result is disappointing the client.

    Negative films sadly need a colour reference. Tourists don't put colour references in their shots and they happen to be disappointed by the prints they receive from the shop. It's not the shop fault, it's the medium. Professionals working in a colour "managed" environment use colour charts as a matter of fact and might prefer negative film.

    I didn't scan negatives a lot, but I did discover that's a lot of head scratching involved when filtering without a reference, at least a neutral grey.

    I don't know about how exact can slide film be in their "best" part of the characteristic curve. I think that when one works in a studio under controlled light (catalogue work or things like that) it's not uncommon that film is used on its linear part of the characteristic curve, where slide film can be on par with negative film.

    Negative film has better characteristic curves on the film sheet, but they do extend much more than with slide film (wider dynamic range), and all that dynamic range is not necessarily used in a controlled-light situation, in the studio.

    So I am not surprised to hear that slide film, when used in its limited "best" part, is on par with negative film for exactitude of colour rendition. But negative film is chromatically "correct" on a much broader dynamic range than slides which makes it an easier choice.

    I have always preferred "neutral" films like Astia and I do think that their appeal rests on their fidelity, not on the surprise-surprise effect (which can be said for "saturated" film like Velvia).
    Fabrizio Ruggeri fine art photography site: http://fabrizio-ruggeri.artistwebsites.com
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  3. #13

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    Color neg film has more range - way more than one actually needs in a critical studio environment.
    This stuff is engineered for pleasing skintones first, everything else second. If you want accurate
    colors in a high contrast environment there's only one way to get it - a tricolor camera using straight
    line black and white film! But if you want to get into copying museum painting nowdays go get a
    Beterlight scanning back before they themselves go extinct and put a good Apo El Nikkor on it for
    only another three grand. Or buy some of the real-deal chrome 8X10 dupe film from my freezer, though I suspect some it has already gone bad, at least for critical work. End of an era. So time to
    apply a crowbar to Portra 160 and leverage some new tricks (I've already started).

  4. #14
    Photo Engineer's Avatar
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    I think that HRST has it right and Drew has it wrong. I have run literally thousands of comparisons between E6 type films and C41 type films when designing color negative film and being responsible for color reproduction. The masks and DIR couplers give C41 films a color fidelity that cannot even be approached by any reversal film.

    Yes, slide films look beautiful, but they are not accurate which is the essence of the question in the OP. I vote for the Portra family. And, you get 2 shots at correction, the original auto corrects and you can make corrections in the print.

    Before you ask, I'll answer. The comparisons were all Kodak C41 films ve Fuji, Konica and Agfa color C41 films, and all Kodak E6 films, Kodachrome, and again Fuji, Konica and Agfa E6 films. They were printed and viewed. Prints were made on type R, C and Cibachrome print materials, and also using Ektaflex R and C materials. As I said, it was a huge comparison.

    I might add that part of this test also compared two sensitizing dyes and two magenta couplers in the paper and C41 film, and two cyan couplers in the paper. It also spanned 2 color developers for the paper. Did I mention that this was a huge test? Drew, you have not done one tenth of one percent of the tests I have. And, you have not had to have your results passed by a panel of observers.

    Is that enough for you guys? Geez, no wonder Kodak film is so expensive. We did (and do) it right!

    PE

  5. #15
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    Quote Originally Posted by Photo Engineer View Post
    I think that HRST has it right and Drew has it wrong. I have run literally thousands of comparisons between E6 type films and C41 type films when designing color negative film and being responsible for color reproduction. The masks and DIR couplers give C41 films a color fidelity that cannot even be approached by any reversal film.
    You can take that to the bank!

    The most accurate color print film for portrait work is the Kodak Porta Series. If the skin tones are correct, then anything else you shoot will be correct. But what do I know, I have only been doing this for five decades.
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

  6. #16
    Athiril's Avatar
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    Quote Originally Posted by hrst View Post
    Which is completely untrue and an urban myth. Any color neg film is much more accurate in color than any color slide film from obvious technical reasons. You can verify this very easily from the curve sets.

    Slide films are completely based on HUGE color errors. RGB curves are all far from linear and differ in shape for every color record. The dyes are unmasked and produce unwanted absorptions. These problems are practically non-existent in color negative films, with at least 10x or so more linearity and much more color purity because of masking.

    This is also one of the reasons people use slide film -- they have a more interesting "color palette" or "look" to them, exactly due to these color errors. For example, in landscape images, certain color crossovers may render the images more appealing and a look of higher saturation.

    Mostly, the reason slide films are considered more "saturated" than negatives, is not the saturation itself, but a combination of high contrast and severe color errors - because color errors create color in scenes that otherwise looked dull gray!

    I'm a big fan of slide films, but I like to state the real reason I like them, and it's completely opposite from being "accurate". If I want accurate look and don't have any preference of the output medium (slide/negative) (in practice, if I'm going to scan them), then I naturally pick color negative, which can be in order of 10-100x more "accurate".

    The reason why slide films were preferred in some situations when accurate colors were needed were mostly non-technical choices made by non-technical people and that's perfectly fine; but that still does not change the truth.

    Also, the accuracy of slide films has not progressed at all in the last decade or so, but the color negatives have advanced more.

    If you ever sc*n your images, this is instantly obvious; the slides always show some crossover and other color problems, whereas negative image is pure and clinical. There are some pieces of broken hardware and software sold to customers with a label of "scanner", causing the color-CORRECTING orange mask to actually cause color errors, but that is a different story. Unfortunately, this farce has thrown some gasoline on the flames of the traditional myth of color-inaccurate negative film. The original cause for the myth are the automatic 1-hr labs that autoadjusted color neg images, trying to make "average customer" satisfied. For a "typical" customer without a darkroom or money to pay a pro, shooting slide film was one of the ways to skip those automatic, unmaintained machines run by untrained operators.
    This. Unmasked films cannot match masked films. The dyes are not perfect. Therefore unmasked films cannot produce accurate results. You don't need any tests to tell you this, other than very simple logic and a little bit of math.



    "The multiple generations of film involved in the color neg-
    pos process (as many as four in the motion picture chain)
    served, however, to emphasize the colorimetric imperfec-
    tions of the subtractive primary dyes
    . Ideally, a cyan dye, for
    example, should control only red light by absorbing between
    600 and 700 nm. But virtually all cyan dyes also had significant
    unwanted absorptions in the blue-green. This led to desatu-
    rated or “muddy” colors, especially in successive generations of
    film. The ingenious solution to this problem was a technology
    called “integral color masking,” invented by W. T. “Bunny”
    Hanson of Kodak and introduced in Ektacolor films in 1949.
    The technique added “colored couplers,” which bore an
    attached pre-formed azo dye, to the normal colorless coupler
    in the layer. For example, the added cyan dye-forming colored
    coupler carried a blue-green dye that would be released and
    washed out of the film to the extent that cyan dye with its
    unwanted blue-green absorption was formed. The result
    was equivalent to a “perfect” cyan image dye overlaid with a
    uniform density to blue green. While this gave the negative an
    orange cast, it required only a longer cyan exposure in making
    the positive print. So revolutionary was this improvement that
    virtually all negative films would adopt this technology once it
    was free of patent restrictions."
    Last edited by Athiril; 06-07-2012 at 09:07 PM. Click to view previous post history.

  7. #17
    polyglot's Avatar
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    Quote Originally Posted by Athiril View Post
    This. Unmasked films cannot match masked films. The dyes are not perfect. Therefore unmasked films cannot produce accurate results. You don't need any tests to tell you this, other than very simple logic and a little bit of math.
    Exactly this. Astia looks nice and is very accurate for a chrome, but it is not nearly as accurate as Portra.

    Next thing to keep in mind is that films have only three (sometimes four) output channels (dyes) and reproduce colour "accurately" only to human eyes. A "perfectly accurate" tri-colour film would have three photosensitive dyes, each with the same spectral sensitivity as one of the cone-types in a human eye, and with an absorption spectrum to match and therefore expose the paper appropriately. So colour accuracy is heavily dependent on the papers used too, as well as how the film exposes the paper (correspondence between absorption spectra in the film and sensitivity spectra in the paper). Masking is necessary to deal with differences in both the sensitivity and absorption spectra of the film with respect to human vision.

    Obviously the RA4 cannot be masked for the same reason a chrome cannot be masked, however my understanding is that the masking in the film is designed to make up for dye deficiencies in both the film and the paper. If you have no mask at all (i.e. a chrome), a whole bunch of colour errors will creep in.

    We differentiate slightly different hues (wavelengths) by comparison of intensity of response from different cone types, which means we cannot differentiate between mixtures of light (a little blue plus a little green) and a monochromatic source somewhere between the two. Films have the same issues. When you look at a print or chrome, it's showing a few narrow spikes of fairly monochromatic light, with magnitudes chosen so as to excite cones in the eyes at the right ratios to believe that there is a full spectrum present when there is not. If you had non-human eyes, a colour print designed for humans would look totally wrong.

    Edit: I see Athiril has posted in a section about the reason for the mask being mostly-orange. The primary correction is to the cyan dye but there are other, more-subtle spectral corrections used in modern films.
    Last edited by polyglot; 06-07-2012 at 09:36 PM. Click to view previous post history.

  8. #18
    amsp's Avatar
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    I never thought my seemingly simple question would spark such an interesting discussion

  9. #19
    polyglot's Avatar
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    Nerds. No one expects nerds on the internet

  10. #20
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    Drew, it seems to me that while you have real hands-on experience on the topic, it also seems you have some problems in the very basics of color theory. Or then, I might be misreading you.

    Quote Originally Posted by DREW WILEY View Post
    Typical color neg films might have wide exposure latitude overall, but just look at the published dye curves and see just how fast that color spikes intersect and cross-talk.
    And they NEED to intersect and "cross-talk". It is the only way to give good color accuracy in a tricolor RGB system! It simulates the eye. We come to the very basics of the color theory here; the optimum RGB system would use wide band "input" filters when capturing the images, to simulate how the eye works, and when presenting the image, narrow band "output" filters to eliminate any crosstalk happening in the eye at that stage.

    It is actually a common misconception to think that the input stage would use narrow filters too.

    If the coupler dye absorption spectra would not intersect and "cross-talk" at all, some yellow objects would be rendered black and some yellow! We cannot tell the difference of these objects by eye when looking at them, but a narrow-band RGB imaging system would show it. This system would not be called "accurate".

    Wavelengths between the primaries have to expose both of the records in order to be reproduced in the RGB system.

    You can't clean up things at that point in the curve, Photoshop or otherwise. And to get a crisp scan of what's left requires either a large sample size (i.e., large film)or a very high quality drum scan because the curve shape of the geometry changes rapidly.
    Not a single word here makes any sense to me, sorry!

    It is a bit arrogant to assume that others here have no hands-on experience on these topics. For example, I have built a film scanner from scratch (for my motion picture laboratory) and am currently building version 2, as well as motion picture contact printer etc, not to mention the lab. I had no problems getting good color fidelity and accuracy out of 16mm motion picture color neg from the first try. It was as simple as adjusting the RGB levels of the light to get a neutral near-white gray from Dmin. In this sense, color negative has as much "reference" as color slide does.

    The reference can be a neutral print with neutral filtration, or a positive copy on a print film if it is to be viewed on a light table. It only necessitates SOME bookkeeping and laboratory discipline skills, and some calibrated equipment to do this well.

    The difference is just that color negative film ALLOWS corrections and some people get confused with this possibility!

    In a real-world photography anyway, corrections are almost ALWAYS needed. The only real reference was the scene when it was photographed. The slide may look completely different, so it makes no sense to call it reference. Actually, shooting in studio is the only exception and even that requires a lot of skill to make the slide have the desired color and contrast. Maybe some people, again, are lost when they have learned that skill with a lot of hard work and forget it is only for one specific corner case and not very descriptive on the theory of color imaging.

    If the aim is to have something to look at light table, then you have to compare slide film with a print of a color negative made on print film (in the correct meaning of the words) stock.

    Do you know how motion picture films are/were produced? Do you know that everything is shot on negative, and that they can copy original negative to a negative-working interpositive, that being copied on an internegative, copied on a release print film? There can be four color "negative" film copies in a row, and the end result can still have astonishing life-like color accuracy. Try copying a slide three times.

    This all comes back to linear curves and color masking. Please take a look at the curves of any today's color negative film. You will see they are unbelievably linear. More linear than most B&W stock available. Also, the spectral sensitivity set is so good that you wouldn't gain that much benefit from using B&W separations. After all, you would probably end up choosing too narrow bands and get an interesting effect of increased saturation and false color, like slide film. This is, however, not called "accuracy".

    I agree that for a studio lighting conditions, a certain slide film designed for just this special purpose can do remarkably well. And it probably does better than those color negatives NOT designed for this purpose, especially if you shoot those without 80A or 80B filter. So we have a general product having 10x to 100x more accurate colors, and then we have a very special corner case with a specifically engineered product just for this purpose, and it can do better in this case than the general product. And there's nothing wrong using it, quite the opposite.

    Also, we all are leaving out the fact that if we need a specific output format, the game changes. If we NEED a projectable slide, then slide film is a very natural choice. If we NEED a print, then color negative film is a very natural choice. If we need a digital file and if we have a usable scanner with a usable software, color negative film gives better color accuracy for most purposes, but slide film might still look better if that look is desired.

    We are lucky to still have so many choices left.

    One more question to digest; have you looked at the same slide
    (1) on a small light table
    (2) on a large light table
    (3) on a light table, with everything except the slide masked black
    (4) on a light table with 2800K tubes
    (5) on a light table with 4000K tubes
    (6) on a light table with 5600K tubes
    (7) on a light table with 9000K tubes
    (8) on a light table with poor color rendition index
    (9) on a light table with good color rendition index
    (10) with a projector equipped with a 110V or 220V mains halogen bulb
    (11) with a projector equipped with a 24V halogen bulb
    (12) with a projector equipped with a xenon arc bulb

    I have a slide which has absolutely stunning delicate light-blue hues. It looks very good scanned or on a light table with 5600K tubes, but horrible with a halogen projector. Completely different image. It was supposed to be a REFERENCE as it is a SLIDE! Go figure. I ended up cutting a piece of light-blue wratten filter with the slide for projection.
    Last edited by hrst; 06-08-2012 at 02:06 AM. Click to view previous post history.

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