8 bit vs 16 bit color

Discussion in 'Digital Cameras' started by Fred, Feb 15, 2004.

  1. Fred

    Fred Guest

    I have been shooting in RAW mode with an Oly E-20 camera. I have a small
    program which converts Raw to Tiff or JPEG after allowing editing. In the
    TIFF format option, one can save as 8 bit or 16 bit color. The file size
    for 16 bit is double the size of 8 bit. Is there any advantage in using 16
    bit color? Also, my image editor can open the 16 bit file, but the image,
    upon initial opening is completely black. It can be lightened and edited.
    Any insite would be appreciated.
    Best,
    Fred Dwight
     
    Fred, Feb 15, 2004
    #1
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  2. Yes, there are advantages to saving as 16 bit color.
    You will lose information when coding to 8 bit.
    If that loss is important or not, only you can decide.
    The RAW E-20 format is only 10 bits though, so it might
    not be all that important, maybe ....
    Hmmm ... strange. This hints at your conversion program using
    the 10 lower bits instead of the 10 higher bits when converting
    to 16 bit TIF. I don't think it really should do that.


    /Roland
     
    Roland Karlsson, Feb 15, 2004
    #2
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  3. I have an article on my web site called 'A Practical Guide to Interpreting
    RGB Histograms'. The third page of this article has an explanation and some
    graphic illustrations of the advantages of working with 16 bit color. This
    is a four page tutorial. If you want to see the info on 16 bit vs. 8 bit
    issue, click this link
    http://www.sphoto.com/techinfo/histograms/histograms3.htm and scroll down
    the 'Working with 16 bit Color' heading. If you want to start at the
    beginning of the histogram article, click this link
    http://www.sphoto.com/techinfo/histograms/histograms.htm
     
    Steve Hoffmann, Feb 15, 2004
    #3
  4. The 16 bit format has the advantage, that it prevents banding etc
    when you adjust levels, brightness, contrast etc.

    The main advantage in 16-bit is as input to your RAW converter,
    where you will probably do most of such large alterations. Then
    you can often save in 8-bit for photoshop if all the rest you are
    doing is resizing, cropping, sharpening etc.
     
    Povl H. Pedersen, Feb 15, 2004
    #4
  5. Fred

    Fred Guest

    Thank you, Roland. the camera output is 10 bits but the program can convert
    it to 16 bits.
    Best,
    Fred Dwight
     
    Fred, Feb 15, 2004
    #5
  6. (Bill Hilton) wrote in
    I have seen both arguments before. And, just as you say - working
    in 16 bits at least makes the histogram look nicer. That is enough
    to convince me. I think that Dan Marguilis' arguments are somewhat
    weak. If you cannot see it, it does not matter. Hmmm ... that is not
    always true. A measurable difference may show up later when you want
    to manipulate the picture further or maybe be seen by someone
    with a better sight than me.


    /Roland
     
    Roland Karlsson, Feb 15, 2004
    #6
  7. Fred

    Fred Guest

    Thank you for the links, Steve. I am in the process of reading through the
    material now.
    Fred Dwight
     
    Fred, Feb 15, 2004
    #7
  8. Fred

    Fred Guest

    Than you for your input, Povl.
    Fred Dwight
     
    Fred, Feb 15, 2004
    #8
  9. It's probably doing the same thing as the Canon raw converter in "16 bit
    linear" mode. In that mode, the 10 or 12 bits of real data are shifted
    up to the high-order end of the 16-bit word, so they span the whole
    16-bit space, but they're still linear not gamma corrected. The first
    thing you need to do to get a viewable picture is gamma correct the data
    (in Photoshop, do Levels and set the middle box to 2.2). Or you can do
    the gamma correction with your graphics card adjustments.

    If you don't do the gamma correction, the image will look incredibly
    dark. That doesn't mean there's anything wrong with your image, just
    that it's not ready for display.

    Dave
     
    Dave Martindale, Feb 16, 2004
    #9
  10. Fred

    Jim Davis Guest

    I believe one day we will be able to see a difference. When printing
    machines get better.

    Right now, I do all my manipulations in 16 bit space but only save a
    TIF if I've done a lot of work to an image. Othewise I only save the
    RAW file and a small JPG for previewing. I can always convert the RAW
    file again. I don't want to save tons of 16 bit TIFs and have no
    reason to do so. At 36 meg a file, that would really add up.
     
    Jim Davis, Feb 16, 2004
    #10
  11. Fred

    Giles Morant Guest

    If you are using the program dcraw (BTW the free RAW conversion used in
    most RAW programs) you should read the manual; this is an FAQ.

    If not, the information on the site (look up dcraw in Google) may very
    well help you.

    Giles Morant
     
    Giles Morant, Feb 16, 2004
    #11
  12. Fred

    Fred Guest

    Thank you, Dave. I'll give it a try.
    Fred
     
    Fred, Feb 16, 2004
    #12
  13. This does not sound right.

    When I read a 16 bit linear file into Photoshop and then
    save it as an 8 bit file, it does the gamma correction
    automatically.


    /Roland
     
    Roland Karlsson, Feb 16, 2004
    #13
  14. How would it know to do it "automatically"? What if you wanted an 8-bit
    linear file?

    All of the Photoshop versions I've used (2.5 through 6.0) do not do
    anything like this without being asked. If you want to convert from
    linear to gamma-corrected encoding, you have to tell it to do so.

    Converting 16-bit to 8-bit via Image->Mode just rescales the values,
    dividing by 256 or 257 - no gamma correction.

    Dave
     
    Dave Martindale, Feb 17, 2004
    #14
  15. Fred

    Fred Guest

    Thank you, Giles.
    Fred
     
    Fred, Feb 17, 2004
    #15
  16. Fred

    Fred Guest

    Thanks, Steve. I am reading up on your articles. I found much more than I
    originally had a question about. Very good articles. I am learning a lot
    about histograms.
    Best,
    Fred Dwight
     
    Fred, Feb 17, 2004
    #16
  17. Fred

    Fred Guest

    I want to thank all those that responded with their input.
    Best,
    Fred Dwight
     
    Fred, Feb 17, 2004
    #17
  18. Fred

    JPS Guest

    In message <c0sest$fhl$>,
    That's my experience as well, in 5.5, 7, and CS.
    --
     
    JPS, Feb 18, 2004
    #18
  19. Fred

    Jim Davis Guest

    Scans? Yuck :)
     
    Jim Davis, Feb 20, 2004
    #19
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