"Exposing to the Right" and curves question

Discussion in 'General Technical Discussion' started by JeffKohn, May 12, 2005.

  1. JeffKohn

    JeffKohn

    Apr 21, 2005
    Houston, TX
    OK so we've all heard the advice that if the dynamic range of the scene allows it we should try to expose to the right when shooting raw, to capture more tonal detail since the upper eV stops contain more data than the lower ones. This makes a certain sense, and I try to use it when I can. Somebody brought up a point on DPR a while back about this technique though, stating that you should adjust the tonality back down to where it should be (ie move the histogram to the left) after raw conversion once you're in 16-bit gamma-corrected space (ie in photoshop post-processing). His logic was that since the lower stops have less granularity in linear space, moving the histogram to the left at that point would essentially throw away some of that extra detail you had captured, since there's nowhere for it to go. The poster even went so far as to say that for a normally-exposed shot moving the histogram to the right during RAW conversion and then moving it back to the left in post-processing was a good idea. To me that makes no sense at all, but in the case an image that started out "exposed to the right" I wonder if he may have a point.

    So the question is, if you expose to the right when shooting, when should you shift the tonality of the image back to the left - in linear space during RAW conversion, or after conversion during post-processing in gamma-corrected space?
     
  2. Iliah

    Iliah

    Jan 29, 2005
    nowhere
    Dear Jeff,

    The poster is right on first occasion, and _theoretically_ right on the second.

    But it is not necessary if the raw converter and post-processing software are using floating point - as here granularity is a non-issue. That is one of the reasons we use floating point in RML. Slow, but less noise and posterization.
     
  3. allen_a_george

    allen_a_george

    59
    Apr 30, 2005
    Waterloo
    So wait - I should intentionally overexpose the shot every chance I get?!
     
  4. Iliah

    Iliah

    Jan 29, 2005
    nowhere
    Short answer - yes, if you are shooting RAW or JPEGs with compensation curve. But you need to know how much your camera will tolerate, and how much postprocessing can you afford without being bored :)
     
  5. JeffKohn

    JeffKohn

    Apr 21, 2005
    Houston, TX
    Thanks Iliah. Hadn't considered the ramifications of floating point vs integer math here but what you say makes sense.
     
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