16bit vs 8bit for prints

Discussion in 'Digital Cameras' started by Terry, Feb 14, 2006.

  1. Terry

    Terry Guest

    A photographer friend of mine processes everything in Photoshop in 16 bit
    RAW. When he wants to have a print made he changes the image to an 8 bit
    tif. He says that the reason for dropping to 8 bit is that most photo labs
    have 8 bit printers.

    It seems to me if you are going to switch to 8 bit for the print, you might
    as well have never started in 16 bit in the first place. Don't you lose the
    extra dynamic range, etc. as soon as you make the change? It doesn't makes
    sense to me. What would happen if you sent a 16 bit file to be printed?
    How much larger would the file size be - twice the size?
     
    Terry, Feb 14, 2006
    #1
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  2. Terry

    rafe b Guest


    I doubt there are any inkjet printers that can use
    16-bits and in any case, the Windows driver interface
    doesn't allow 16-bit print files -- at least that's
    what I've heard.

    A 16 bit workflow is another matter -- easier to
    defend on theoretical grounds if not from actual
    observable benefits.

    The idea behind the 16-bit workflow is that the
    extra bits will minimize the cumulative effects
    of rounding/truncation error in the course of
    several radical color transformations (eg.,
    curves/levels/saturation, etc.)


    rafe b
    www.terrapinphoto.com
     
    rafe b, Feb 14, 2006
    #2
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  3. Terry

    HornBlower Guest

    16-bit is great for color and exposure adjustments, but for printing it is
    100% pointless. Print drivers convert to 8-bit when you send a 16-bit image.
    There are currently no 16-bit printers. Now does the printer driver do a
    better job of converting the image data to 8-bit than say Photoshop? Can't
    say. The chances are you will never notice a difference. So why waste time
    converting to 8-bit when you print.

    R
     
    HornBlower, Feb 14, 2006
    #3
  4. 8-bit/ch files still have a gamma of around 2.2. Paper typically has a
    contrast range about 100:1.

    This basically means that an 8-bit/ch file is precise enough for prints.
    More bits don't really help.

    8-bit/ch is just enough for a print. When an image needs lots of edits,
    you need extra bits to compensate for the loss of accuracy as a result of
    the editing operations. Furthermore, if you need significant changes to the
    contrast of an image, you need extra bits as well, otherwise you will
    get banding.

    If you are essentially printing straight from the camera, you can just as
    well use 8-bit/ch for the entire process.
     
    Philip Homburg, Feb 14, 2006
    #4
  5. Terry

    Andrew Haley Guest

    This is a very contentious topic, and there is no agreement amongst
    the experts. Lat time I looked, Dan Margulis was arguing one way and
    Andrew Rodney the other, and if they can't come to any agreement after
    years of arguing there's no hope that you'll get any simple answers
    here.

    Andrew.
     
    Andrew Haley, Feb 14, 2006
    #5
  6. Terry

    Hunt Guest

    If one is not going to post-process the image, especially Levels, Curves, or
    Color correction, then 8-bit is fine. If you are doing work in, say Photoshop,
    then 16-bit to start is the better choice, if you have it. I (almost) always
    shoot RAW, Open as 16-bit and do all corrections, saving as PSD. Convert to 8
    -bit and do any operations that require 8-bit (Filters mostly), then Save as
    xxxxx 8-bit.PSD. Finially, I'll run Neat Image, then Sharpen, saving as xxxx
    8-bit Final.PSD. Flatten and possibly convert to CMYK (depends on where the
    image goes next), saving as TIF.

    Hunt
     
    Hunt, Feb 14, 2006
    #6
  7. Terry

    Keith Guest

    If you shoot RAW then you can choose to convert to 8 or 16 bit as you
    see fit.

    Thinking about archive and longevity - I prefer to capture at the
    highest possible quality always - ie RAW. Why do anything else with all
    that expensive kit!

    We can't tell what kind of devices we'll be displaying the images we
    capture today on in the distant future.
     
    Keith, Feb 14, 2006
    #7
  8. Philip seems to have been the only responder to raise the significant
    issue of the different gamma between output and input in digital image
    processing. However, at a gamma of 2.2, 8 bits is capable of yielding a
    contrast of (1/256)^2.2, which is a lot more than the paper is capable
    of. It is the minimum perceivable contrast ratio that drives the 8-bit
    criteria, not the total contrast range.

    It is also why those holding out for a 16-bit printer driver will have a
    long wait - there simply is no need for it since 8 bits with the
    appropriate gamma is already well in excess of what you can see in any
    case and certainly well above what even the best papers can reproduce.

    The reason for 16-bit processing is two fold: the actual data
    acquisition from the camera/scanner sensor is in linear space, not gamma
    compensated space, and this requires more bits to address the same
    dynamic range (which I think was what Philip was alluding to in the
    first sentence of his post) and, as others have mentioned, to provide
    additional dynamic range headroom for editing.

    RAW is essentially your digital negative - it *must* capture more
    dynamic range than you can see to be of any value over simpler outputs.
    If you want to do the same processes as darkroom dodging and burning in
    digital then you need more than 8-bits in the original, but you don't
    need that in the output - just as photographic paper doesn't have the
    same SNR or dynamic range as film.

    It will be several million years before humans evolve adequate vision to
    *require* 16-bit print drivers. ;-)
     
    Kennedy McEwen, Feb 15, 2006
    #8
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