What manipulations are adversely affected by 8bit images?

Discussion in 'Digital Cameras' started by Mueen Nawaz, Oct 9, 2006.

  1. Mueen Nawaz

    Mueen Nawaz Guest

    Hi,

    I use Linux for pretty much everything, and am in the process of
    getting a new camera after all these years. I'll be using RAW fairly
    frequently, and want to ensure I take advantage of the increased bit depth.

    However, the main software I use, Gimp, currently does all its
    operations in 8 bits. Looking around, I often see people saying, "Do the
    relevant operations where 16 bits matter (e.g. Levels adjustment) in
    another program (e.g. Bibble, Cinepaint), and then use GIMP for the rest".

    The question is, "For what digital manipulations does it matter if you
    have 8 or 16 bits?" I know of Levels, and Curves. What else? How would I
    know - is there a rule of thumb to follow?

    Thanks.

    --
    Cartoon Law: Any violent rearrangement of feline matter is impermanent.


    /\ /\ /\ /
    / \/ \ u e e n / \/ a w a zanl
     
    Mueen Nawaz, Oct 9, 2006
    #1
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  2. Mueen Nawaz

    Rod Williams Guest

    Photoshop is really missing the boat not having a Linux version.
    To my untrained but fairly critical eye, I can not see much difference
    between 8 and 16 bits, using a Canon i960 printer. I don't use 16 bits.
    It also slows things down a lot with my aging computer.
     
    Rod Williams, Oct 10, 2006
    #2
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  3. Mueen Nawaz

    Mueen Nawaz Guest

    Photoshop is really missing the boat not having a Linux version.
    I think generally, few can tell the difference. That's not the reason
    people use 16 bits. When does some level adjustments - say to stretch
    the histogram to get better contrast, a lot of interpolation goes on,
    and the results aren't as accurate in 8 bit mode. Supposedly, if done in
    16 bits, you get better (and probably more noticeable) results.

    --
    Cartoon Law: Any violent rearrangement of feline matter is impermanent.


    /\ /\ /\ /
    / \/ \ u e e n / \/ a w a zanl
     
    Mueen Nawaz, Oct 10, 2006
    #3
  4. Mueen Nawaz

    Mueen Nawaz Guest

    I know - the problem is that other than levels and curves, I don't know
    what else creates such gaps (I suppose I could just "do" it and compare
    before and after histograms...). Would sharpening do that, for example?

    --
    Laugh alone and the world thinks you're an idiot.


    /\ /\ /\ /
    / \/ \ u e e n / \/ a w a zanl
     
    Mueen Nawaz, Oct 10, 2006
    #4
  5. SNIP
    With 16-bits/channel, you can avoid cumulating rounding errors at each
    subsequent correction/adjustment you make. Then finally when it comes
    to outputting the image, you'll have less chance on posterization
    artifacts showing up.
     
    Bart van der Wolf, Oct 10, 2006
    #5
  6. Mueen Nawaz

    Lionel Guest

    In general, the more 8-bit operations you do to your starting image,
    the more damage you'll get, because it's due to clipping & rounding
    errors at each operation, which accumulate with each operation. It
    shows up in the form of posterisation in one or more colour channels,
    most visibly in highlights & shadow areas.

    I run Linux myself for many things, but unfortunately, Gimp just isn't
    capable (yet!) of doing high quality photo work.
     
    Lionel, Oct 12, 2006
    #6
  7. Mueen Nawaz

    Lionel Guest

    Yes, absolutely. Really, almost anything you're likely to want to do
    to a photo (other than clipping) will introduce errors if done in 8
    bits. This is why professional image or cine editing systems all
    operate in 16 or 32 bits per channel, per pixel.
     
    Lionel, Oct 12, 2006
    #7
  8. Mueen Nawaz

    Mueen Nawaz Guest

    So what do you use?

    --
    Mary had a little lamb, a little beef, and a little ham.


    /\ /\ /\ /
    / \/ \ u e e n / \/ a w a zanl
     
    Mueen Nawaz, Oct 12, 2006
    #8
  9. Mueen Nawaz

    Lionel Guest

    Photoshop, or one of several RAW image processing packages.
     
    Lionel, Oct 13, 2006
    #9
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