Scanning resolution, printing resolution, and downsampling

Discussion in 'Digital Photography' started by hassy_user, Oct 18, 2004.

  1. hassy_user

    hassy_user Guest

    I just read Margulis' chapter on resolution and am somewhat confused
    (it's one of those things you have to read multiple times, I think).
    Up to now I have been scanning my 6x6 and some 35mm slides and negs at
    3000-4000dpi on a Nikon LS8000 at 14-bit depth, and manipulating
    mostly at full res, then downsampling to 300dpi before sending it to
    my Epson 2200. According to Margulis, having a resolution too high
    can soften an image, so I'm trying to find out two things:

    1. Is the softening that occurs an effect of sending too much data to
    the printer, and if so, wouldn't downsampling before printing correct
    it, or should it be scanned at a lower resolution to begin with?

    2. Where can I find a reference of starting points for optimum
    scanning resolution that considers input film size, final print size,
    and optimum print resolution?

    Thanks for any input.

    hassy_user, Oct 18, 2004
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  2. So far, you've done well.
    That is not optimal. The 2200 (like most desktop Epsons) internally
    dithers based on a 720ppi image. If the ppi for the output size
    requested is different, the printer driver will interpolate to 720
    ppi. In your case, it will more than quadruple the number of pixels
    you offered it. Interpolation will not help resolution.
    As stated above, only down-sample to 720 ppi at output size. Then
    sharpen the result, you can visually oversharpen a bit, because there
    will be losses in the printing process. Always judge the amount of
    sharpening at 100% zoom level in the photoeditor.
    Scanning film at the highest native resolution will reduce apparent
    graininess, so by all means keep doing it as you are. You can improve
    the downsampling quality by applying a little blur before
    downsampling. The amount of blur needed depends on the amount of
    downsampling. That will also help reducing apparent graininess,
    instead of increasing it due to grain-aliasing.
    Print resolution, as stated should in your case be 720 ppi after

    Grain aliasing is explained here:

    Bart van der Wolf, Oct 18, 2004
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  3. hassy_user

    Bill Hilton Guest

    From: (hassy_user)
    Dan is a member of the "scan for the target output" club, which is the way most
    book and magazine publishers and many advertising agencies work. They rarely
    print large prints (especially magazines and books) and don't spend a lot of
    time fine-tuning each image, as a general rule.

    The other side of the coin is the "scan once, output many" club which feels
    it's best to scan at high rez, do all your prep work on a master file (which is
    what you're doing) and downsample and sharpen to various output sizes ranging
    from large fine art prints to tiny web thumbnails. Here's a good explanation
    of the theory from a fine art lab I've used, West Coast Imaging ... The key
    to doing this well is to know how to downsample well and how to use USM in a
    variety of situations, typically with film using edge sharpening or something

    You should be able to run a test yourself with the 8000 and see if downsampling
    works for you ... just scan at the native rez (4,000 dpi) and downsample to say
    360 ppi for a decent sized print and print it. Also scan at the exact rez for
    this size print and print directly from that one too without downsampling ...
    if you're printing 10x10" @ 360 ppi for example you need 3600 pixels/side so
    would scan at roughly 1650 dpi (the Nikon software lets you set this exactly).

    See what looks best, the 10x10" print at 1650 or the 4000 dpi scan downsampled.
    Keep in mind Dan has access to much better scanners than your 8000 (which is
    what I use too :) and he may get a better result with his 1650 dpi scan than
    you or I with the Nikon. The Nikon will still scan internally at 4,000 dpi and
    then downsample with its software ... can you do this better in Photoshop
    You can work backwards once you know the optimal printer ppi and the desired
    print size (multiply the ppi x the print dimensions to get the pixel count and
    divide this by the size of the film to get the scan rez), but of course the
    main problem is that you'll get a different target scan rez for each print size
    and for each printer ppi. No problem if you're scanning once for a magazine
    article but a hassle if you think you'll print the same file yourself at
    various sizes or need even smaller images for the web.

    If you want to see what a real digital ace can do with the "scan once and
    resize" flow look at Bill Atkinson's work. He shoots Velvia with a Hassy and
    scans at 5,000 dpi with a Tango drum, then resizes these files for anything
    from a 24x24" fine art print at 360 ppi to thumbnails for the web that are
    100x100 pixels ...

    Bill Hilton, Oct 18, 2004
  4. hassy_user

    Ken Weitzel Guest

    Bill Hilton wrote:


    <more snipped>

    For what it's worth, I did this test using many
    variations... about 20 prints worth. (Kodak machine
    in the mall type prints)

    Blind tests for which was better was always extremely
    close. Testers (included print machine operator, the
    subject herself, neighbors and friends) after long
    consideration always concluded that the "big" scan,
    untouched by PS or PSP, was the best.

    Ken Weitzel, Oct 18, 2004
  5. hassy_user

    hassy_user Guest

    Thanks Bart, Bill, and Ken for the thoughtful responses. Bill and
    Bart, you apparently differ on the recommended output ppi (360 vs
    720). Will there be a visible difference, however subtle, in choosing
    one over the other?

    hassy_user, Oct 20, 2004
  6. SNIP
    Depends on the image processing done to the final sized file, and
    whether it had enough resolution to begin with. Assuming the file has
    enough native resolution, the 720 ppi version will allow to enhance
    edge contrast more accurately. The resulting output will look better
    in that case.

    If you use a dedicated print program like Qimage, life becomes even
    easier because it takes care of it automagically (including profile
    conversion and optimization of paper used), without altering the
    original file.

    Bart van der Wolf, Oct 20, 2004
  7. hassy_user

    hassy_user Guest

    Thanks Bart. I save all of my raw scans so I'll do a comparison at
    both print resolutions with a minimum of processing, and USM after the
    final image size is set. I'm curious to see if the difference shows
    up at 10"x10".

    Does Qimage offer any advantage besides convenience? If I already
    know how to soft proof and color manage, do I need it?


    hassy_user, Oct 22, 2004
  8. SNIP
    That also depends, on your output requirements. A common user comment
    is that when comparing the same image output from Photoshop and Qimage
    side-by-side, usually results in higher quality for Qimage. But again,
    it depends on what you start with, and what the output size is.

    The colors will be exactly the same, as both Photoshop and Qimage are
    color managed applications, but in general, when the printer driver
    causes a need to interpolate the image data, Qimage output quality
    always wins. At (very) large output sizes Qimage excels.
    The workflow benefits become apparent when you e.g. need multiple,
    different sized, versions of an image on the same page, or if you want
    to produce contact sheets, or different cropped versions of a file.
    All those different sizes are derived from the original, which remains

    Bart van der Wolf, Oct 25, 2004
  9. hassy_user

    hassy_user Guest

    Thanks. I'll see if there's a trial version and test it. If I'm
    printing at the printer's native resolution (720ppi), then there
    shouldn't be a difference, right?

    hassy_user, Oct 25, 2004
  10. SNIP
    If you supply 720 meaningful pixels for each output inch, there will
    still be a difference. This is due to Qimage compensating for the
    losses incurred in the (inkjet) printing process. The amount of
    compensation is user adjustable, and can be set to zero. When changed
    from its default to zero, then there should be no difference.

    There is a time limited demo version that only processes a few images
    per session available at . There
    are examples for common tasks in the help file, and there is a Yahoo
    forum for support.

    Bart van der Wolf, Oct 25, 2004
  11. hassy_user

    hassy_user Guest

    Excellent! I will check it out over the weekend. So a sample project
    would go something like: scan into PS, make adjustments on full size
    file, save and re-open in Qimage for printing. So then Qimage must
    have a sharpening tool, since the final resizing is done there? How
    does it compared to USM in PS? What if I need to do selective
    sharpening, or want to sharpen in LAB mode? Sorry for all the
    questions, but this is kinda complicated stuff:)

    hassy_user, Oct 27, 2004
  12. SNIP
    Correct. You save your "master"-file after Photoshopping it. It is
    best to save in compatibility mode if your file is not flattened, and
    still has layers. Qimage has several means of sharpening, USM on the
    luminance of the RGB values amongst others. You can associate a
    non-destructive filter to individual image files and/or a generic one
    for all files you're going to print. When printing, another adjustable
    sharpening step is possible, to compensate for printing losses. That
    step is also taking the amount of resizing into account.
    Depends on the source material. QI sharpens based on Luminance (like
    sharpening the L channel in Lab mode), but also has the ability to
    apply different amounts of sharpening to Red and Blue, versus green.
    That will equalize the resolution difference from Bayer CFA sensors
    used in most Digicams.

    You can do part of the sharpening in Photoshop if it is complex, and
    use that as a starting point in Qimage. Based on the final amount of
    resizing, QI compensates with sharpening to offset potential losses.
    QI always sharpens Luminance, unless instructed to handle a digicam
    file a bit different (user adjustable amount).
    Just make good use of the month's trial period, and get a bit used to
    the different, but ultimately very efficient, interface. Concentrate
    on the basics, define layout and output size(s), drag and drop to the
    queue, set printer parameters for the paper you use, and print.

    Don't hesitate to ask questions in the Yahoo forum (after trying the
    examples in the help file), and you can also search the archive there
    for explanations from the author. He's quite cooperative, but also
    very busy, so don't expect him to answer all newbie questions
    personally (especially the ones in the helpfile), but other users will
    chip in, no doubt.

    Ultimately, Qimage will take a lot of the complications out of your
    hands. Learn to trust your eyes when you see the output.

    Bart van der Wolf, Oct 27, 2004
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