Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,854   Posts: 1,582,920   Online: 993
      
Page 1 of 8 1234567 ... LastLast
Results 1 to 10 of 76
  1. #1
    RalphLambrecht's Avatar
    Join Date
    Sep 2003
    Location
    Central florida,USA
    Shooter
    Multi Format
    Posts
    6,813
    Images
    1

    Why is Zone V 50% gray?

    Why does a digital camera record a Kodak Gray Card (Zone V) as 50% gray?

    A Kodak Gray Card represents an 'average' scene of 18% reflectance, but that has nothing to do with a mean or medium on a grayscale. A gray card has an absolute log reflectance density of about 0.75. Medium gray on a 2.2-gamma monitor and a calibrated print thereof is about 0.66. So the image of the card is lighter than the card itself. Why? Who came up with this assumption or standard? Is it a mistake? Did someone assume 'average gray' meant 50%?



    Disclaimer:

    I'm aware that this is a mainly or exclusively analog forum, but I doubt to get a satisfying answer for my question in a digital forum, since they usually understand little about the Zone System. That's why I post the question here. Besides, I need this to work out some details about making digital negatives, which will be used to make pure-silver contact prints. So, it's an analog question in a way.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  2. #2
    David A. Goldfarb's Avatar
    Join Date
    Sep 2002
    Location
    Honolulu, Hawai'i
    Shooter
    Large Format
    Posts
    17,485
    Images
    20
    A perfect question for the "Gray Area."
    flickr--http://www.flickr.com/photos/davidagoldfarb/
    Photography (not as up to date as the flickr site)--http://www.davidagoldfarb.com/photo
    Academic (Slavic and Comparative Literature)--http://www.davidagoldfarb.com

  3. #3

    Join Date
    May 2006
    Location
    Aurora, IL
    Shooter
    35mm
    Posts
    1,983
    I don't know either. I had a question for a long time and I asked many so called experts in the digital field and get no real answer. The question is if we use spotmeter and meter an evenly lit gray card and set the exposure according to this reading what do we get in term of RGB values in the resulting image file? I got chewed out for asking dumb questions by these so called experts because they said that they can change this value in post processing so why care?

  4. #4
    RalphLambrecht's Avatar
    Join Date
    Sep 2003
    Location
    Central florida,USA
    Shooter
    Multi Format
    Posts
    6,813
    Images
    1
    Nice to hear from you again Chan.

    Let's make a deal. You and I will never stop asking 'dumb' question. By the way, I'm pretty sure this one doesn't belong into this group anyway. I suspect, a so-called-expert made a mistake, but I'm happy to be proven wrong. Just hang in there!
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  5. #5
    John Jarosz's Avatar
    Join Date
    May 2006
    Location
    Chicago area
    Shooter
    Large Format
    Posts
    148
    I'll just ask a question that may help.

    If you meter the card with a spotmeter and then use the digital camera, does the camera exposure agree with the spotmeter?

    John

  6. #6
    RalphLambrecht's Avatar
    Join Date
    Sep 2003
    Location
    Central florida,USA
    Shooter
    Multi Format
    Posts
    6,813
    Images
    1
    John

    That's a very question. Unfortunately, the difference between 0.66 and 0.75 density is a little more than 1/6 stop in analog photography, so I can't tell for sure (my meters differe more from one to the other). Anyway, let's assume they do. Still, I can develop my film to give me 0.75 in density, but my gamma-calibrated digital system insists on giving me a print with 0.66, which again, is too light for the gray card. It's not much, but why is it there?
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  7. #7

    Join Date
    May 2006
    Location
    Aurora, IL
    Shooter
    35mm
    Posts
    1,983
    Do you know when we send out a digital file for printing, how are the tones be interpreted? In another word what is the RGB values in the file that will produce say a 0.75 density tone on the print?

  8. #8
    RalphLambrecht's Avatar
    Join Date
    Sep 2003
    Location
    Central florida,USA
    Shooter
    Multi Format
    Posts
    6,813
    Images
    1
    I do know that. It depends on the gamma setting of the attached profile, but most are set to gamma 2.2, which returnd about 53 - 54 % for 0.75 density. I've seen some go as high as 58%.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  9. #9
    L Gebhardt's Avatar
    Join Date
    Jun 2003
    Location
    NH - Live Free or Die
    Shooter
    Large Format
    Posts
    1,723
    Blog Entries
    1
    Images
    18
    Is this a problem with all cameras or just one in particular? I imagine each manufacturer "tunes" the output to make what they consider a good image. I know that the JPG images I get out of my DSLR are much different looking than the JPG images out of the digital point and shoot. The RAW images as opened by default are also quite different.

    How are you determining density from the RGB values?

    Just curious, but why do you need this info to make digital negatives? Wouldn't you just make your curves match the screen output to the final print output?
    Last edited by L Gebhardt; 08-30-2006 at 02:49 PM. Click to view previous post history. Reason: Puctuation

  10. #10
    RalphLambrecht's Avatar
    Join Date
    Sep 2003
    Location
    Central florida,USA
    Shooter
    Multi Format
    Posts
    6,813
    Images
    1
    It is a 'problem' with all digital cameras that I could get my hands on. Take a picture of the sky, gray card, white wall, all out-of-focus, it doesn't matter, always 50% in the jpg image (not the raw file, that's a different matter).

    I determined the density by measuring the lumination on the monitor with a densitometer, and this matches exactly the gamma 2.2 theory (at least from 30 to 70% the rest must be different for different reasons). Also, the calibrated lab print comes back with the same relative reflection density of 0.66. Print and screen match at 50%.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

Page 1 of 8 1234567 ... LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin