16bit photoshop files: why do they bloat?

Discussion in 'Digital Photography' started by digiboy, Feb 19, 2005.

  1. digiboy

    digiboy Guest

    Here's something I've noticed: a 16 bit file with adjustment layers
    bloats really badly compared to 8 bit.

    I created a 720x576 8 bit image and drew some stuff on it. Then I added
    an adjustment layer and drew on the layer mask. The resulting file is
    shown in PS as 1.19/1.56M.

    I did the same but created as 16 bit. Now it shows as 2.37/6.33M

    So the 8 bit image with adjustment layer grows 50%, but the 16 bit
    grows roughly 3-fold.

    This is an example. I sure anyone who uses 16 bit files would notice
    similar effect with real files. Any ideas why?


    digiboy, Feb 19, 2005
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  2. digiboy

    bmoag Guest

    One advantage of using 16 bit color is that the wider data base allows for
    finer manipulation of histograms. These are mathematical adjustments, not
    adjustments done solely by eye. The fact is that when that image is printed
    it will be down converted to 8 bits by an arbitrary algorithm in the printer
    driver over which you have little or no control, other than trial and error
    manipulations to see how the final print turns out.

    Many, probably most, people cannot see the entire 16 bit gamut, their
    monitors cannot accurately reproduce that range of colors, and printing
    processes live in an 8 bit world.

    There are good reasons for using 16 bit color. However if you do not clearly
    understand why you need to use 16 bit color then 16 bit color may actually
    hinder the creation of a final printed image. It is very difficult to
    develop a color management work flow that reliably matches the monitor to
    the printed image even when you follow all the cookbook recipes. I think
    most people should stick to and understand 8 bit color and not worry about
    what they may be missing with 16 bit color, because it isn't all that much.
    bmoag, Feb 19, 2005
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  3. digiboy

    digiboy Guest

    thanks for the intro to 16 bit files, I'm OK with all that already :)

    but none of its answers why 16 but files bloat so much
    digiboy, Feb 19, 2005
  4. digiboy

    Ken Weitzel Guest


    OK, I'll give it a quick shot :)

    24 bit color is three 8 bit channels; one for each color.
    Total of 3 bytes.

    48 bit color requires two bytes per channel, for a total
    of 6 bytes.

    But you said you already knew that, so I'd suggest doing
    your experiment without that added layer, or after flattening
    it. :)

    Ken Weitzel, Feb 19, 2005
  5. digiboy

    digiboy Guest

    the 3 bytes per pixel in 8 bit and 6 bytes for 16 bit means the file in
    16 bit will be twice as large. Which we see it is because the base file
    is 1.19Mb in 8 bit and 2.37Mb 16 bit.

    fair enough.

    so I add an adjustment layer and the 8 bit goes to +50%, while the 16
    bit goes to +260% (approx)

    if I change the 16 bit file (with adjustment layer) to 8 bit then
    surprise surprise it goes to the same size as the 8 bit.

    but why the bloat when you add an adjustment layer?
    digiboy, Feb 19, 2005
  6. digiboy

    Ken Weitzel Guest


    Dunno, can't help you with that one... don't use
    Photoshop (use PSP).

    But I wonder if PS is doing some kinds of tricks with
    that added layer. Perhaps keeps track of what portions
    are actually different? Throws away transparent chunks?
    Keeps a little more undo info?

    You experiment with ps, maybe try adding a layer that's
    totally unrelated to the "real" layer. (paste a whole
    different picture onto it, or something)

    If you like I'll try it with psp and see what happens.

    Ken Weitzel, Feb 19, 2005
  7. digiboy

    digiboy Guest

    If I take a 16 bit file and simply add another layer (ie not adjustment
    or layer effect/style) it pretty much doubles in size, which is much
    what you would expect. Adding a layer style doesn't change the size at

    You have a go with PSP and see what happens
    digiboy, Feb 19, 2005
  8. digiboy

    Ken Weitzel Guest


    Arghhh, should have warned you. I'm an old guy; stroke
    damaged, easily confused and forgetful :(

    We'll have to depend on your experiments; psp doesn't
    support 48 bit.

    Sorry about that.

    Ken Weitzel, Feb 19, 2005
  9. Probably the difference is compression. Photoshop
    seems to do some lossless compression to photoshop
    files, e.g. in the layers. (I am not 100% certain
    of this, but it is my observation as some photoshop
    files are smaller than a tif equivalent, and
    layers with transparent regions are particularly
    smaller than if the layers are full of data.)

    16-bit data is very hard to compress.
    So you might be seeing an efficiency difference.

    (I work with Photoshop-CS and 16-bit a lot.)
    Roger N. Clark (change username to rnclark), Feb 21, 2005
  10. digiboy

    JPS Guest

    In message <>,
    "Roger N. Clark (change username to rnclark)" <>

    It isn't even trying, for the main layer. A solid-color 12MP image
    saves as 72M bytes in 16-bit, and 0.6M bytes in 8-bit, as .psd, but they
    should both be equally compressible. This is without layers.

    JPS, Feb 21, 2005
  11. digiboy

    digiboy Guest

    I once read in a photoshop manual that it RLEs the PSD file, so blank
    areas will cause a smaller file than busy areas.
    digiboy, Feb 21, 2005
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