Step Wedge Question

Discussion in 'Scanning and Scanners' started by bvy, Mar 28, 2015.

  1. bvy

    bvy Subscriber

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    I'm giving DPUG another go after several years. I think this question belongs here.

    I'd like to make a reflective scan of a 4x5 Stouffer step wedge alongside a 4x5 negative. I would scan the two together in one pass without any corrections. The step wedge I'm looking at is the upper right image on this page: Stouffer Industries. Part number TP4x5-21. My scanner is an Epson V500.

    Can I determine which zones different areas of the negative falls into by hovering over that area, looking at the RGB values, and then hovering over the step wedge to find the closest match?

    Is my thinking accurate? Thanks.
     
  2. jeffreyg

    jeffreyg Subscriber

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    I don't think a reflective scan of a negative or step wedge is the correct approach. I think you would have to scan as a positive transparency and then perhaps convert to positives to compare. I think the paper and inks you intend to print with will also influence you final product. The step wedge has 21 steps and I am not sure your film or paper/ink and other calibrations truly will duplicate what you see on the monitor. As I understand it a step wedge is used to standardize exposure and processing. Personally I'm not into the mathematics of photography and rely on my eye and how I want an image to look. I mainly use film and print on traditional photographic paper and pt/pd but also with a digital printer from scanned negatives. I treat each as a separate medium. Although it might be better to calibrate my monitor and printer, I find that I get good results eyeballing and tweaking when necessary.

    i probably haven't helped so maybe someone much more knowledgeable will post a better answer for you.

    HOME
     
  3. pschwart

    pschwart Member

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    - prints are scanned by reflection; negatives are scanned by transmission
    - you want to compare the values of the scanned negative with the values of the Stouffer wedge.
    You don't need to scan the Stouffer wedge -- you already know what those values are, even if it's not
    a calibrated wedge, since all the values are 0 - 3.05 in 1/2 stop increments, or log .15.
    - if you don't have a transmission densitometer, I suppose scanning your negative and the Stouffer wedge together will at least allow you to compare values. Scan as a grayscale with no adjustments and look at the K: values in the Photoshop Info tab, not the RGB values.
     
  4. RalphLambrecht

    RalphLambrecht Subscriber

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    Yes,very doable;it's a poor man's densitometer!:smile:
     
  5. OP
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    bvy

    bvy Subscriber

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    Yes, that's exactly what I'm after.

    I knew I'd be better off scanning both as transparencies, but was trying to compensate for my scanner's inability to scan 4x5. Instead, I think I could place the wedge along one side of the negative. I wouldn't be able to scan the wedge and entire negative as a transparency, but I think could get enough of the negative to glean some useful information from it.
     
    Last edited by a moderator: Mar 28, 2015
  6. RalphLambrecht

    RalphLambrecht Subscriber

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    You can also scan one and then the other as long as you don't change the settings but be aware using a real densitometer is still the best option.I recommend the once made by Heiland Electronics in Wetzlar ,Germany,very robustand never lose calibration:smile:
     
  7. L Gebhardt

    L Gebhardt Subscriber

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    I haven't tried doing it this way, but I can see one problem is that different films have different reflectivity. So your film may reflect more or less light from the surface than the step wedge. That may throw your results off. I also wouldn't expect to be able to compare results between two different films. Of course it might all be close enough for your purposes.

    Have you thought about placing a light table (LED not fluorescent) over the negative and step wedge? Might be a cheap way to get a bit more accuracy.
     
  8. JWMster

    JWMster Subscriber

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    Ancient as this thread is, I stumbled on it today and was pleased to see some discussion about how the zonie manages along in hybrid world. Books tend to assume you either shoot film and wet print, or shoot digital and ink print. Not much for the hybrid folks that do both. Thanks!
     
  9. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    Are you trying to use your scanner as a densitometer?
     
  10. JWMster

    JWMster Subscriber

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    I think that's what he was doing.

    For my part, late to the party, I'm just thinking through the elements that would work for a hybridist. Different issues, and of course typically dismissed: "You're scanning? Ah... you can print anything!" Yes, perhaps more, but unless the negative is in the ballpark, you still have a working range beyond which you have nothing. Different process, but still I think some of the same issues. Software makes for a greater degree of noise in the processing system than a straight analog process, but the idea of working through what the equipment facilitates and what it's limits are remains valid ( I think ). And either it's just clear as day so nobody writes it up like they did the Zone system, or it's so equipment specific that generic systematic approaches don't generalize, or nobody gives a rat's 'cause they went 100% digital (I think the majority) so there's not enough interest to create a market for this. Oh well.
     
  11. Billy Axeman

    Billy Axeman Subscriber

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    What are those K-values mentioned in post #3, and why are RGB values not good?
    I have no Photoshop.
     
  12. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    I think the K values are the black values. In the pigment or ink model, it's CYMK. K is the black ink or in printers terms "key line".
     
  13. Billy Axeman

    Billy Axeman Subscriber

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    Thanks, I now see that it is possible to split a photo in the editor into separate C, M, Y and K images and then use the Dropper tool on the K image to get gray values. I guess the OP is/was working with B/W negatives, so I wonder what the advantage is above directly using RGB.

    I saw there are more threads on Photrio about this subject and I'm going to read that first.
     
  14. OP
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    bvy

    bvy Subscriber

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    That was three years ago, and I think I asked a different flavor of the question more recently. But, yes, that was the goal. Trying to remember now why I explicitly said reflective scan in the OP...
     
  15. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    So you're trying to reflective reading on your 4x5 negative? If so, it doesn't make sense because normally, you do a transmission reading on negatives as well as transparencies. You do reflective reading on reflective material like prints.
     
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