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  1. #1
    Dave Krueger's Avatar
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    Zonemaster calibration using scanner as reflection densitometer

    This question is primarily for those who are familiar with the calibration process of the RH Designs Zonemaster or Analyzer Pro enlarging meters.

    I'm going through the above mentioned calibration process and I now have a bunch of test strips that need to be evaluated by comparing them the highlight and shadow tones on the provided reference tile. In other words, I need to identify which tones on my test strips come closest to matching the reference tones that came with the product.

    My paper tone is slightly warmer than the tone of the tile adding another variable to fool my already easily fooled eye balls. I was thinking that I might be able to use my flatbed scanner to scan the test strips and tile and match the tones that way. Furthermore, I was thinking it might be possible to improve the calibration by determining intermediate tonal values. In other words, if the reference tone falls between two tones on my test strip, perhaps the scanner would allow me to find out what the intermediate value would be for purposes of fine tuning the calibration values a bit. My test strip tones are 1/4 stop apart, but the calibration values are in increments of 1/12th stop, permitting more precision.

    Has anyone done this before? Does it make sense to use a scanner to quantify differences in density like this? My thinking is that it would have to be an improvement over just just eyeballing it. By using the scanner in gray scale mode, I would also be eliminating the possible subjective error introduced by the warm tone of the paper.

  2. #2
    ath
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    I think the visually evaluation makes sense because that is the way one views a print.
    Instead of comparing to the reference I simply chose the field which showed the first tone separation from black resp. white.
    After all it's a personal thing what tone to choose - with this choice you set the tone you will get at the extreme ends of the displayed grey scale. Some (like me) prefer nearly black and nearly white, others want more separation and choose a very light and very dark grey.
    Regards,
    Andreas

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    Quote Originally Posted by Dave Krueger View Post
    Does it make sense to use a scanner to quantify differences in density like this? My thinking is that it would have to be an improvement over just just eyeballing it. By using the scanner in gray scale mode, I would also be eliminating the possible subjective error introduced by the warm tone of the paper.
    I do use scanner as a densitometer and I've tried to estimate its accuracy. Check it out:

    http://sites.google.com/site/negfix/scan_dens

    JaZ

  4. #4
    Dave Krueger's Avatar
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    Quote Originally Posted by ath View Post
    I think the visually evaluation makes sense because that is the way one views a print.
    Instead of comparing to the reference I simply chose the field which showed the first tone separation from black resp. white.
    After all it's a personal thing what tone to choose - with this choice you set the tone you will get at the extreme ends of the displayed grey scale. Some (like me) prefer nearly black and nearly white, others want more separation and choose a very light and very dark grey.
    That's a great point. All I really need to do is get a little bit up off the toe of the curve rather than being precise about using the .04 density point. I suspect I will probably develop a preference of some kind as I become more familiar with the meter.

  5. #5
    Dave Krueger's Avatar
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    OK, I fooled around with it a little bit and found that scanning was helpful in the sense of getting rid of the tonal distraction. The meter calibrates in increments of 1/12th stop, so I only need limited numerical precision for the tone matching. For some reason I find it very difficult to match tones by eyeballing them, so it was comforting to use a numerical value. Also, it didn't take very long. I could, of course, rerun the test strips at a finer step size and get even closer, but the scanner allowed me to estimate intermediate values, so I will run with this and see how it works.

    Thanks for the opinions. Also, thanks for the link, JaZ. I downloaded ImageJ and will check it out Aside from doing low res scans to put on Flickr, I don't do any picture scanning, so I'm pretty ignorant in that regard. I don't even know if my scanner will do 16-bit linear.



 

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