Re: Which scanners REALLY provide 36 bit output? HP?

From: Bob Washburne (
Date: Thu Dec 07 2000 - 21:17:17 PST

  • Next message: Nick Lamb: "Re: Which scanners REALLY provide 36 bit output? HP?"


    Thanks for the responce. Please see comments below.

    "Jeffrey H. Ingber" wrote:
    > I have a 6350 and can confirm that it will scan at 1200dpi optical
    > resolution. Any resolution thereafter will be handled in software. If
    > I do a 1200dpi color scan uncropped, the resulting image saved in
    > xscanimage is *huge*, roughly 800MB or so.
    > I just fired up xscanimage and noticed that the "bit depth" option in
    > "Advanced Properties" only contains "8, 10, and 12" for the selection?

    I believe that this referes to the individual colors. Scanners work
    like monitors with R(ed)G(reen)B(lue). When all the colors have the
    same value you get a greyscale. So 8 bits per "gun" gives you 24 bpp
    color. 10 gives you 30. 12 gives you 36.

    I'll try to find the docs for xscanimage to comfirm this.

    Here is the definitive test:
    1) scan an image at 1200 dpi and 12 bit depth.
    2) crop the scan to a small, even size. One inch by one inch would be
    3) calculate the number of pixels. This would be X x 1200 x Y x 1200.
    If you cropped to exactly one inch each way it would be 1 x 1200 x 1 x
    1200 = 1,440,000 or about 1.4 Meg.
    4) 8 bits is one byte. So if you had set the bit depth to 8 the
    resulting scan would be about 1.4 MB (raw, not compressed via png, gif,
    etc.) If you set the bit depth to 12, that would be half again as large
    as 8 so the resulting scan would be about 2.1 MB (X x 1200 x Y x 1200 x
    1.5). However, this assumes that the output is packed tight. The
    software might use an entire 16 bit word to store each 12 bit pixel
    (this would be a lot easier to program). In that case, the scan would
    be about 2.8 MB. So the result, if we really received 12 bpp, would be
    1.5/2.0 times the result of step three for greyscale and 4.5/6.0 time
    for color.

    Pumping your numbers for a full, uncropped scan through the equations...
    1.4 MPixels/SqIn x 8.5" x 11" x 6 Bytes/Pixel = 785.4 MB
    Very close to the 800 MB you said that you saw.

    This is very encourageing. But perhaps not definitive (darn, this is
    making me paranoid).

    My Linux is down for the moment (I just upgraded my CPU to an AMD K7
    650MHz and RH 6.2 can't deal with it. RH 7.0 with Duron support is
    sitting here waiting to be installed) so could you perform a quick
    experiment for me?

    Scan a small image with bit depth set to 12 and save it as a png file.
    Then look at that file with gimp and examine its properties. I believe
    gimp will tell you what the color depth is. That should pretty much
    confirm what is happening.

    > From the box:
    > 1200 dpi optical resolution
    > 1200x2400 dpi hardware resolution
    > 36-bit color

    Yah, the box for my 5370C says the same thing. The razlesnatzin liars.

    What they, and others, appear to be doing is scanning 36 bit internally
    and using that data to calculate an "optimised" 24 bits. So only 24
    bits ever leave the scanner. But they don't come right out and say

    > I'm not an expert on some of this marketing spin, so make of this what
    > you will. The resolution seems a no-brainer, but the bit depth may need
    > further investivation. FWIW, for the price of this scanner, you
    > *should* get true 36-bit color, but I don't know for sure. Sorry.

    Amen, brother.

    > Jeffrey H. Ingber (

    Thanks again,

    Bob Washburne -

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