Photoshop resizes my images against my will

Discussion in 'Scanners' started by ray, Oct 4, 2005.

  1. ray

    ray Guest

    I scan an image at 300 DPI. Using Photoshop I save
    it as a GIF. When I reopen it is set to 72 DPI.
    I then have to resize it to print at proper size.
    Is there any way to tell Photoshop that I know
    what DPI I want and don't be smarter than me and
    change it?
     
    ray, Oct 4, 2005
    #1
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  2. ray

    Wayne Guest



    GIF is the problem, so dont use GIF. GIF files are not designed to have
    any way to store the scaled dpi value, so no program can store the dpi
    value in a GIF file. In the absense of any dpi info, most photo
    programs will make up either 72 dpi or 96 dpi to tell you.

    A TIF file can save the dpi value, and TIF will support anything GIF
    will, including GIF's indexed color, if you actually need to limit the
    colors in your image. TIF with indexed color and LZW compresson will be
    a similar quality and file size as GIF (GIF uses LZW too). The only
    real difference then is that web browsers dont do TIF, but if for a web
    page, then dpi is not used anyway.

    If it is a photo image instead of graphics, you surely dont want indexed
    color anyway.. it is limited to a maximum of only 256 colors. This can
    be very appropriate for graphics, but rarely suitable for photo images.
     
    Wayne, Oct 4, 2005
    #2
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  3. ray

    ray Guest

    Thanks for the reply. What I an scanning are woodworking plans.
    I just want 256 gray scale. I want sharp lines which JPEG does not
    give me. I want small size files that GIF gives. Tiff files are quite
    a bit larger. Is there a way to get TIFF files of comparable size to
    the GIF file

    Thanks

    Ray
     
    ray, Oct 5, 2005
    #3
  4. ray

    Wayne Guest


    Agreed, GIF indexed mode should not be a limitation for 256 shades of
    grayscale. And agreed, JPG is not so great for line drawings.
    But, I wondered if line drawings even needed 256 shades? Possibly 16
    shades would show all you have to show? (and would be about half size in
    the file). Or perhaps more likely, if true line drawings, black ink on
    white paper, then 2 color indexed (everything is either fully black or
    fully white) ought to do it best, and will be a smaller file yet.

    2 colors (B or W) has potential to look better, sharper and more clear,
    than grayscale, when the original is actually line art anyway (no gray
    tones to be retained). You would want to use at least 300 dpi for B&W line
    art scans. Fax for example is only 200 dpi line art, and could be better.

    GIF images are indexed color mode (which causes the limitation of 256
    colors maximum), and GIF stores this in the file with LZW compression.
    However GIF offers no way to save the scaled dpi value for printing,
    because CompuServe designed GIF files only for video screen presentation,
    and video has no use at all for dpi.

    You can change the same grayscale image to indexed color mode, and save it
    in a TIF file, and can specify the same LZW compression. This will be
    about the same file size as GIF. If both are indexed color and LZW
    compression, then there will be little file size difference. It wont be
    exact same size, but very close, cant matter.

    Yes, TIF can be be much a larger file, but not if same mode as GIF. Indexed
    color mode and LZW is fully automatic in GIF, it is unavoidable, there are
    no other choices if GIF. TIF files have many more choices, so you must
    specify this choice if you want it. It is not automatic with TIF, but
    the same thing is available with TIF.

    What photo editor are you using? Photo programs do vary, and it is not
    always straightforward. For one example, the free program Irfanview from
    www.irfanview.com. Its menu for indexed color is Image - Decrease Color
    Depth. It doesnt call it indexed, but it speaks of bits per pixel, and
    that is what it means. It does have a limitation that it doesnt allow
    changing grayscale to 256 color indexed. Technically it shouldnt matter,
    but practically it does. But you can change it to RGB color first, and
    then to indexed 256 colors, and then convert to grayscale, and get 256
    indexed that way, same mode as GIF (and the file will be substantially
    smaller than grayscale that way). Or its menu will change to 16 color or 2
    color indexed too.

    Or PNG file type also supports indexed color mode, and uses a compression
    possibly smaller than LZW, and PNG will also save the dpi print value too.

    But bottom line, there is no way to save the dpi value in a GIF file.
    It is more nuisance, but you can however simply open the GIF file, and then
    rescale the image to print the right size again, just before you print it.
     
    Wayne, Oct 5, 2005
    #4
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