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What are the advantages of 48-bit color scanning? - Adobe Photoshop 7, CS, CS2 & CS3

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 ...

  1. #1

    Default What are the advantages of 48-bit color scanning?

    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
    [url]http://nutritionsoftware.org[/url]



    Editor www.nutritionsoftware.org Guest

  2. #2

    Default Re: What are the advantages of 48-bit color scanning?

    Editor [url]www.nutritionsoftware.org[/url] 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 Guest

  3. #3

    Default Re: What are the advantages of 48-bit color scanning?

    On Wed, 16 Jul 2003 16:54:51 GMT, "Editor www.nutritionsoftware.org"
    <nseditor2002 [email]REMOVhotmail.com[/email]> 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 ([url]www.ledet.com\margulis[/url]).

    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.
    [url]http://www.terrapinphoto.com[/url]
    Rafe B. Guest

  4. #4

    Default Re: What are the advantages of 48-bit color scanning?


    "Rafe B." <rafebadelphia.net> wrote in message
    news:9iqbhvg1jb3onsqktjjib5m3utfb0iueca4ax.com...
    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 Guest

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