How many bits per color are needed

Discussion in '35mm Cameras' started by Scott W, Feb 1, 2006.

  1. Scott W

    Scott W Guest

    One of the questions that gets debated from time to time is how many
    bits / color are needed for an image. The debate is usually between 8
    and 16 bit per color with the argument that 8 bits is not enough to
    handle the shadow part of the image. I got playing around with this
    and under the right conditions it is pretty amazing just how good the
    shadow detail can be using 8 bits.

    Whereas 8bits/color is enough for great shadow detail the jpeg file
    format tends to trash the dark parts of the image. If you want to have
    very good shadow detail a lossless format such as tiff is needed.

    This is an image where the whole of it is jammed into the bottom 32
    levels.
    http://www.sewcon.com/temp/shadow.tif
    This of course looks very dark but using levels the detail can be
    extracted to look like this.
    http://www.sewcon.com/temp/shadow expanded.tif

    Trying to store this same image as a jpeg and expanding it does not
    work nearly as well.
    http://www.sewcon.com/temp/jpg_shadow_expanded.jpg

    I should point out that the only reason you would need this level of
    detail in the shadows is if you are going to be making some pretty
    extreme adjustments to the photo.

    Scott
     
    Scott W, Feb 1, 2006
    #1
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  2. Scott W

    Alan Meyer Guest

    That is truly amazing. I hadn't realized how much detail was there.

    I just downloaded your shadow.tif and used the GIMP's "curves"
    control to bring out the detail and, sure enough, it was all right
    there.

    In case anyone thinks Scott was cheating, he wasn't. The beautiful
    image in "shadow expanded.tif" really is hiding in shadow.tif.

    Alan
     
    Alan Meyer, Feb 1, 2006
    #2
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  3. Scott W

    no_name Guest

    Expand first and then save as a jpeg.
     
    no_name, Feb 1, 2006
    #3
  4. Scott W

    Gordon Moat Guest


    Room for adjustments is one reason. Changing conversion to CMYK for
    another type of printing method can be another. Nearly all commercial
    printing and layout software only handles 8 bit images. It could be
    argued that an 8 bit workflow could save some time. At least with
    scanning, most scanners are faster handling an 8 bit scan. Another
    aspect of this to consider is that some scanners (and some digital
    cameras) are actually only 10 bit or 12 bit, even though in PhotoShop
    anything more than 8 bits is worked in 16 bit mode. Given a 10 bit
    scanner or digital camera, there might not be much benefit for going to
    some printing types.
     
    Gordon Moat, Feb 1, 2006
    #4
  5. Scott W

    bugbear Guest

    Heh. It also depends wether the colour space
    is linear or logarithmic.

    BugBear
     
    bugbear, Feb 1, 2006
    #5
  6. Scott W

    Greg Guest

    Why???????

    Why be a smart ass unless you're prepared to share your knowledge?

    Or have I answered that question myself?
     
    Greg, Feb 1, 2006
    #6
  7. Why do I want a JPEG which will just throw away data? PSD or TIFF
    are far better.

    The only reason one would want a JPEG is for the web where quality
    doesn't matter.


    *********************************************************

    "It looked like the sort of book described in library
    catalogues as "slightly foxed", although it would be
    more honest to admit that it looked as though it had
    been badgered, wolved and possibly beared as well."

    _Light Fantastic_
    Terry Pratchett
     
    John A. Stovall, Feb 1, 2006
    #7
  8. Scott W

    Xiaoding Guest

    What you are really talking about here is exposure, not color.
     
    Xiaoding, Feb 1, 2006
    #8
  9. Scott W

    bugbear Guest

    That's because the JPEG quantisation figures
    used in "Normal" desktop applications
    are tuned for natural (real world) images
    with "normal" colour distributions.
    JPEG (in the abstract) could handle your example
    just fine, but you'd need a JPEG guru to work
    out good quantization figures.

    (and I don't just mean thr "quality" number)
    http://www.impulseadventure.com/photo/jpeg-quantization.html

    BugBear
     
    bugbear, Feb 1, 2006
    #9
  10. I can't save either one of these images. I get a message that says, "buy
    Quick time", and when I click on OK, I'll buy" nothing happens......
     
    William Graham, Feb 1, 2006
    #10
  11. Scott W

    Walter Banks Guest

    This thread is recognizing the differences between implimentations of jpeg compression on different cameras. My kodak DX 7590 has two different jpeg compression levels and no raw :( the best (most detailed image) jpeg compression removes a lot of detail
    from the image including brightness information on bright objects that appears in the electronic viewfinder not not in the stored image. An old small canon S110 that I have uses a much better jpeg compression implementation and seems to preserve the
    dynamic range. Both camera's have 8 bit color levels.

    To get back to the real thread for general use 8 bits are enough in the same way that the S110's 2M pixels is enough. Properly framed so that cropping is not needed 2M pixels produces nice images.

    Properly exposed so post processing light levels are not needed 8 bits is enough for some very good images. If recovering washed out detail or if brightness/contrast is an issue then 8 bits are not enough. The next digital camera I will want more color
    levels over more pixels.

    w..
     
    Walter Banks, Feb 1, 2006
    #11
  12. Scott W

    Scott W Guest

    You may have to download the images and then open them in the viewer of
    your choice.
    Right click on the links and choose Save Target as.

    Scott
     
    Scott W, Feb 1, 2006
    #12
  13. That was my first step.....But when I right click on the targets, saving
    them isn't one of the options I get.....I get five choices:
    1. About Quick Time plug in.
    2. Save as source.
    3. Save as QT movie.
    4. Plug in settings.
    5. Connection speed.

    When I click on either of the two "save as...."
    I get a Get Quick Time Pro ad, and when I click on OK, I'll buy now.....I
    get nothing....It just acts like it didn't see my click, and stays there
    until I click on "Not now".
     
    William Graham, Feb 1, 2006
    #13
  14. Scott W

    Paul Furman Guest

    Right-click the links in the message above.
     
    Paul Furman, Feb 1, 2006
    #14
  15. Nope....That don't work either....Is this "Quick Time" something for Apple
    computers only? - If it is, then that's why I can't buy it for my MS-DOS
    Windows machine........
     
    William Graham, Feb 1, 2006
    #15
  16. Scott W

    Scott W Guest

    In reality it shows that if everything is done just right you only need
    5 bits for a good image. Of course making adjustments of the 5 bit
    image is pretty limited.

    For my own workflow I use 16 bits/color while making adjustments and
    then will save the image in 8 bits/color. I edit in 16 bit space
    simply because it is easy to do so. But the truth is that if I do the
    exact same operations on an 8 bit/color version of the image that I do
    on the 16 bit / version in the end it is hard to tell them apart. I
    find this to be true for both scan film and digital images.

    This is a pretty easy test to do, take a 16 bit/color image that you
    feel has a lot of dynamic range and make a 8 bit / color version of it.
    Do the same edits to both images and in the end it will be hard to
    tell them apart.

    Scott
     
    Scott W, Feb 1, 2006
    #16
  17. Scott W

    Scott W Guest

    Quick Time runs on the PC as well as Mac.

    I am surprised that you can't simply download the image to disk by
    right clicking on it.

    Here are photoshops version of the same files, give these a try.
    http://www.sewcon.com/temp/shadow.psd
    http://www.sewcon.com/temp/shadow_expanded.psd

    Scott
     
    Scott W, Feb 1, 2006
    #17
  18. Thanks....The first like works, I was able to save it to disk, and opened it
    with Photoshop 7. the other link doesn't work....I get the standard "page is
    not available" message. - but that's OK. I wanted to see if I could extract
    an image out of the blackness of the first picture with my PS7 program, and
    I can....But the water in the foreground is still black, so it needs some
    work....I am not very good at using my PS7 program, especially when it comes
    to color balance issues, so I try to work with it every chance I get.....
     
    William Graham, Feb 1, 2006
    #18
  19. Scott W

    Xiaoding Guest

    I think, if I understand you correctly, that this shows that 16 bits
    really does not make much difference, but with the caveat, that the
    color space is the same. Which makes sense, since I shoot in 8 bit
    currently, and it seems good enough for most situations. My question
    would be, then, why hasn't the color space increased, if you are taking
    pictures in 16 bit? Then it would make a great deal of difference.
     
    Xiaoding, Feb 2, 2006
    #19
  20. Scott W

    Scott W Guest

    The color space does not necessarily increase when you go from 8
    bits/color to 16/color. What you do get is more precession in the
    color within the space. An 8 bit/color image in sRGB and a 16
    bit/color image in sRGB will both have the same size color space.

    Scott
     
    Scott W, Feb 2, 2006
    #20
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