What are the advantages of 48-bit color scanning?

Discussion in 'Digital Photography' started by Editor www.nutritionsoftware.org, Jul 16, 2003.

  1. When I use PhotoShop 6 and can only edit using 24-bit color? (Am I wrong
    about this?)
    Shouldn't I just scan in 24-bit mode to save time and space?

    I just got an Epson 3200 scanner which is capable of 48-bit color mode. If I
    use Silverfast, I see a scan mode listed as "48->24 bit color". Does this
    mean the scanner uses 48-bit mode but the software converts to 24-bit for
    output?

    When I use Epson Scan, the 48- and 24-bit modes are listed separatedly. If I
    use the 48-bit mode, I can see the file in Photoshop but cannot copy and
    paste, etc.

    Thanks for any enlightenment. A few years ago I had some bad experience with
    scanning, but am giving it another try. Scanners are getting so much better
    and cheaper these days.

    --
    Editor, Internet's Convenient and Unbiased Directory of Nutrition Software
    http://nutritionsoftware.org
     
    Editor www.nutritionsoftware.org, Jul 16, 2003
    #1
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  2. Editor  www.nutritionsoftware.org

    Bill Hilton Guest

    >From: "Editor www.nutritionsoftware.org"

    >When I use PhotoShop 6 and can only edit using 24-bit color? (Am I wrong
    >about this?)


    You can use most of the key color correction tools in 48 bit mode in Photoshop,
    like Levels, Curves, Hue/Sat etc. But you can't use most of the filters, nor
    layers, nor adjustment layers.

    >Shouldn't I just scan in 24-bit mode to save time and space?


    You can do that if you wish. It probably won't save you much scan time (on my
    scanners it takes the same amount of time to scan in either mode) but will save
    you disk space.

    >I just got an Epson 3200 scanner which is capable of 48-bit color mode. If I
    >use Silverfast, I see a scan mode listed as "48->24 bit color". Does this
    >mean the scanner uses 48-bit mode but the software converts to 24-bit for
    >output?


    Yes, the scanner internally scans in high bit mode and then converts to 24 bit
    mode. That's why it doesn't save you any time to just scan in 24 bits :)

    >When I use Epson Scan, the 48- and 24-bit modes are listed separatedly. If I
    >use the 48-bit mode, I can see the file in Photoshop but cannot copy and
    >paste, etc.


    You can do many things in 48 bit mode, but not copy/paste.

    The normal flow for people using 48 bit mode is to make the major overall tonal
    corrections in high bit mode and then convert to 24 bit mode for local
    corrections.

    Here' are two explanations of why high bit mode is better in theory, if you
    make a lot of changes to the colors, etc. At least the histograms look better
    (grin).

    http://www.creativepro.com/story/feature/7627.html
    http://www.inkjetart.com/2450/48bit/page4.html

    In theory this makes a lot of sense, in practice it's often hard to see any
    differences in the final output and some people feel it's not worth the extra
    disk space and effort, Dan Margulis being the most well-known proponent of this
    view.

    Bill
     
    Bill Hilton, Jul 16, 2003
    #2
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  3. Editor  www.nutritionsoftware.org

    Tony Spadaro Guest

    The only controls you have in Photoshop seven on images over 24 bit are the
    colour adjustments and a couple others (like crop). These are all converted
    to 16 bits per channel, no matter what they were from the scanner (12 bit,
    14 bit, etc) and must be converted down to 8 bit before most tools will work
    on them.
    So start your work by adjusting colours (you can use selections, although
    you have very few options with them) and then convert down for other work.
    There is an article on the subject here:
    http://www.chapelhillnoir.com/mani/digi/mhibit.html
    --
    http://www.chapelhillnoir.com
    home of The Camera-ist's Manifesto
    The Improved Links Pages are at
    http://www.chapelhillnoir.com/links/mlinks00.html
    New email - Contact on the Menyou page.
    "Bill Hilton" <> wrote in message
    news:...
    > >From: "Editor www.nutritionsoftware.org"

    >
    > >When I use PhotoShop 6 and can only edit using 24-bit color? (Am I wrong
    > >about this?)

    >
    > You can use most of the key color correction tools in 48 bit mode in

    Photoshop,
    > like Levels, Curves, Hue/Sat etc. But you can't use most of the filters,

    nor
    > layers, nor adjustment layers.
    >
    > >Shouldn't I just scan in 24-bit mode to save time and space?

    >
    > You can do that if you wish. It probably won't save you much scan time

    (on my
    > scanners it takes the same amount of time to scan in either mode) but will

    save
    > you disk space.
    >
    > >I just got an Epson 3200 scanner which is capable of 48-bit color mode.

    If I
    > >use Silverfast, I see a scan mode listed as "48->24 bit color". Does

    this
    > >mean the scanner uses 48-bit mode but the software converts to 24-bit for
    > >output?

    >
    > Yes, the scanner internally scans in high bit mode and then converts to 24

    bit
    > mode. That's why it doesn't save you any time to just scan in 24 bits :)
    >
    > >When I use Epson Scan, the 48- and 24-bit modes are listed separatedly.

    If I
    > >use the 48-bit mode, I can see the file in Photoshop but cannot copy and
    > >paste, etc.

    >
    > You can do many things in 48 bit mode, but not copy/paste.
    >
    > The normal flow for people using 48 bit mode is to make the major overall

    tonal
    > corrections in high bit mode and then convert to 24 bit mode for local
    > corrections.
    >
    > Here' are two explanations of why high bit mode is better in theory, if

    you
    > make a lot of changes to the colors, etc. At least the histograms look

    better
    > (grin).
    >
    > http://www.creativepro.com/story/feature/7627.html
    > http://www.inkjetart.com/2450/48bit/page4.html
    >
    > In theory this makes a lot of sense, in practice it's often hard to see

    any
    > differences in the final output and some people feel it's not worth the

    extra
    > disk space and effort, Dan Margulis being the most well-known proponent of

    this
    > view.
    >
    > Bill
     
    Tony Spadaro, Jul 16, 2003
    #3
  4. Editor www.nutritionsoftware.org wrote:
    > When I use PhotoShop 6 and can only edit using 24-bit color? (Am I wrong
    > about this?)


    I think you are. I have Photoshop 6, and I'm pretty sure I can edit in
    48 bit color, at least for the most common operations. I don't use
    Photoshop very often, so I would have to check. But there are certainly
    some operations I perform fairly regularly which can only be done in 24
    bit color depth in Photoshop. Photoshop 7 does more in 48 bit, but not
    everything.

    > Shouldn't I just scan in 24-bit mode to save time and space?


    In prinicple you should do as many editing operations in 48 bit color
    depth as you can, particular operations which spread values. The reason
    is that you start with a certain number of distinct possible values, 256
    for 24 bit and 65536 for 48 bit. Some operations, such as expanding
    contrast will cut down the size of the range and spread the values
    apart. You can see this often as gaps in the histogram. If the
    changes are not too large, your eye can't detect them, but it is still a
    good idea to avoid too large gaps. With 65336 values you have much more
    room to work without producing any noticeable effect. So you should
    probably scan in 48 bit color depth and do as many operations as you can
    in 48 color depth. Before printing or archiving the result, it is
    probably okay to switch to 24 bit. Also, some of the operations you
    want to do in Photoshop may have to be done in 24 bit, but you can save
    those for last.

    >
    > I just got an Epson 3200 scanner which is capable of 48-bit color mode. If I
    > use Silverfast, I see a scan mode listed as "48->24 bit color". Does this
    > mean the scanner uses 48-bit mode but the software converts to 24-bit for
    > output?


    Yes.

    >
    > When I use Epson Scan, the 48- and 24-bit modes are listed separatedly. If I
    > use the 48-bit mode, I can see the file in Photoshop but cannot copy and
    > paste, etc.


    ???

    >
    > Thanks for any enlightenment. A few years ago I had some bad experience with
    > scanning, but am giving it another try. Scanners are getting so much better
    > and cheaper these days.


    I use Vuescan to scan, but I edit in the Gimp under Linux, which does
    only 24 bit color depth. I scan in Vuescan at 48 bit depth, do some
    preliminary operations such as choosing black and white points, and
    making an initial choice for gamma, all in Vuescan, and I save in 24 bit
    depth. I do my remaining editing in the Gimp. So far it seems to
    work fine. I don't detect any degradation of the image.

    >
     
    Leonard Evens, Jul 16, 2003
    #4
  5. Editor  www.nutritionsoftware.org

    Rafe B. Guest

    On Wed, 16 Jul 2003 16:54:51 GMT, "Editor www.nutritionsoftware.org"
    <nseditor2002 > wrote:

    >When I use PhotoShop 6 and can only edit using 24-bit color? (Am I wrong
    >about this?)
    >Shouldn't I just scan in 24-bit mode to save time and space?



    Scanning in 48-bit (16 bits per color) is popular but IMHO
    wasteful. Some people consider it "key" to getting good
    color, and that's hogwash.

    Do a google search on Dan Marguls for some expert
    opinion on this (www.ledet.com\margulis).

    What 48-bit does do for you is it allows you to carry some
    sloppiness up the signal-processing chain before critical
    image data is irretrievably lost. I would argue that that's
    a poor reason to use it.

    However, if you take reasonable care with your scans
    in the first place, and reasonable care afterward in your
    image editor (with regard to tonal manipulatin) there is
    little or no advantage to scanning in 48-bit.


    rafe b.
    http://www.terrapinphoto.com
     
    Rafe B., Jul 17, 2003
    #5
  6. "Rafe B." <> wrote in message
    news:...
    SNIP
    > Scanning in 48-bit (16 bits per color) is popular but IMHO
    > wasteful. Some people consider it "key" to getting good
    > color, and that's hogwash.


    Assuming you mean scanning in 48-bit and not output in 48-bit, I have to
    disagree. Scanning in 48-bits allows to do inevitable gamma correction
    without causing posterization.
    Whether 48-bit output after the major tonal corrections is wasteful, depends
    on the capabilities of the scanner software. Not all software e.g. allows to
    apply Curves corrections / Histogram Equalizations, so they need to be
    applied afterwards.
    Should significant additional correction be needed, 48-bits is unavoidable.
    If you don't need to adjust the file, 24-bits is probably fine in 90% of the
    cases, although I prefer to do things like sharpening and noise suppression
    in a 16-bit Luminance channel.

    So to make a long story short: It depends.

    Bart
     
    Bart van der Wolf, Jul 17, 2003
    #6
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