confusion about monitor calibration and profiling

Discussion in 'Digital Photography' started by peter, Feb 5, 2007.

  1. peter

    peter Guest

    When you buy a monitor calibration software/spyder, what happens after it
    finished running?

    (1) it adds a startup software to modify the monitor's display
    characteristic -- this affects everything that is displayed, so any software
    that displays photo will display them more accurately. Specifically, it
    makes the monitor into the sRGB colorspace.

    or

    (2) no startup software to change the monitor's display characteristic; but
    a monitor ICC profile is created so that application that uses ICC profiles
    like photoshop can use it to make photos display more accurately. software
    that doesn't use the profile will continue to display photos the same old
    way

    Which of the above is correct? There seems to be conflicting evidence to
    support both scenerios.
     
    peter, Feb 5, 2007
    #1
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  2. There is startup software that simply verifies that the ICC profile is loaded
    and up-to-date. The Spyder2 software creates a customer ICC profile and
    the OS loads it at boot or login.
     
    Thomas T. Veldhouse, Feb 5, 2007
    #2
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  3. peter

    Mardon Guest

    Yes, BUT...

    The Win XP OS cannot handle loading separate colour profiles into the
    separate LUTs of dual-head video cards. In this situation, the OS loads
    the same profile into both LUTs on boot-up and the user must manually Run
    the "Profile Chooser" software that comes with the Spyder2 in order to get
    the proper profile loaded into the LUT for the second display.
     
    Mardon, Feb 5, 2007
    #3
  4. Correct. I run a Dual-Headed display so I feel this pain. However, it is not
    that big of a deal as I only preview images on one monitor and the other is
    used strictly for menus and other "off desktop" applications. So, I really
    see little need to calibrate the second monitor [which is a pain to
    recalibrate anyway to a reasonably timely schedule].
     
    Thomas T. Veldhouse, Feb 5, 2007
    #4
  5. peter

    Roy G Guest

    Hi.

    And the Spyder 2 instructions make that fact very clear.

    Roy G
     
    Roy G, Feb 6, 2007
    #5
  6. peter

    Mike Russell Guest

    Yes, it is confusing. Color management continues to get more complex, and
    the products reflect this complexity. The result is confusing and
    conflicting beliefs and practices on the part of customers, and
    manufacturers. There are several components to monitor profiling software,
    and they are generally the same for all manufacturers.

    1) The profiling software uses the associated hardware device (Spyder, Eye
    One, Huey, or other colorimeter) to measure the brightness and color of
    various colored patches on the screen.

    2) A look up table (LUT) is created to bring the monitor to a specified
    gamma and color temperature. This LUT is loaded after calibration, and at
    system startup time, and changes the appearance of the display. If you
    specified a gamma of 2.2 and a color temperature of 6500K, your display will
    be a close approximation the sRGB color space. This is normally the
    default.

    3) A profile is created that specifies the appearance of RGB values on the
    screen, based on the color measurements taken in step 1. This profile is
    used by color aware applications, such as Photoshop, to display more
    accurate colors. If your display is set to a different gamma or color
    temperature than sRGB, images will display significantly differently using
    the display profile.

    4) A reminder application may be installed that runs at system startup time,
    and tells you when you should recalibrate.

    There are additional features provided by the "pro" versions of the
    calibration software. With the slightly more elaborate versions of these
    products, you may separately measure and/or change the overall brightness or
    color temperature of your display. Some manufacturers allow you to plot a
    graph over time of your display performance, so that you can monitor the
    aging of your display.

    It is not hard to learn to adjust your monitor manually to get good color,
    and this is not a bad way to start to learn the finer points of adjusting
    color appearance. The Apple Cinema display, for example, has a manual
    procedure for adjusting brightness, gamma, and color. Even so, many people
    lack the confidence or desire to calibrate their own monitors, and monitor
    calibration devices are becoming more popular as they become higher quality,
    and less expensive.

    Manufacturers understandibly promote the virtues of their products, but
    calibration is not a universal solution for consistent color quality. It's
    important to do a sanity check after any monitor calibration. Verify that
    you can distinguish all the squares of a 11 step step wedge, that all the
    steps are close to neutral, and that skin tones and other important colors
    from known good images look as they should. Otherwise you are buying a
    false sense of security.
     
    Mike Russell, Feb 6, 2007
    #6
  7. peter

    peter Guest

    This is what I thought. Thanks for confirming.
    If after calibration the monitor approximates the sRGB color space, is there
    any need to load a monitor profile into photoshop? Why not just turn off
    color management in photoshop or use a standard sRGB colorspace. Most
    digital cameras assumes a sRGB colorspace anyway.

    Are inkjets pre-calibrated to match sRGB colorspace, or do we need to load a
    printer specific ICC profile in photoshop in order to print correctly? It
    seems that some printer driver also has a place to set ICC profile. Is it
    better to turn off the printer ICC in photoshop and use the one in printer
    driver, or the other way around?
     
    peter, Feb 6, 2007
    #7
  8. peter

    Mike Russell Guest

    [re monitor calibration]
    Theoretically, yes, but there are two factors at work here: calibration,
    which determines monitor appearance and characterization, which measures it.

    Calibration brings the monitor to a known color temperature, gamma, and
    overall brightness. This information is stored in the LUT that is loaded at
    system startup, and also reflected in manual adjustment of brightness and
    contrast, as guided by the calibration software. Keep in mind, though, that
    the LUT is a limited adjustment, affecting each of the red, green, and blue
    channels in isolation. You cannot use the LUT to, for example, change the
    amount of green in response to amount of red or blue.

    Characterization means measuring the actual performance of the display,
    generally after it has been calibrated. Since the absolute colors of the
    red, green, and blue phosphors or LCD filters will generally vary from those
    of the sRGB standard, the monitor profile is needed to characterize the
    display colors. This generally involves varying the amount of one color,
    depending on the values of the other colors, either using a 3x3 matrix, or a
    more complex multidimensional function table that allows all three colors to
    vary arbitrarily. This complex function table is called, what else, a LUT,
    LOL!
    All of these combinations work. Most inkjets have an sRGB setting, and
    printing an sRGB image will generally give good results, provided the
    manufacturer's paper and ink are being used. I usually advise people to try
    this to see if the results are acceptable. Epson printers have another
    setting, in addition to sRGB, called PhotoEnhance, which I find gives
    slightly better results than sRGB.
    When using a profile, both ways work perfectly well. I generally specify
    the profile in Photoshop, because I want to be positive that I've selected
    the correct paper profile for the printer. If you use the same paper all
    the time, there is no advantage to doing it this way, but I feel better if I
    can convert in Photoshop, and see the name of the profile at the time I
    print.

    You've touched on an important subject, though, and that is printing. Most
    people who calibrate their monitors are motivated by a desire to match their
    printer output. This is often a fruitless waste of time, because it only
    addresses half the problem. There are generally good quality "canned"
    profiles available for Epson printers - beware of the older ones for the
    1280 and earlier at the Epson site.

    Printer calibration equipment is expensive - though there are software
    solutions that use your scanner to (attempt to) generate a profile. It's
    probably better to spend the same money on a profiling service create a
    profile for your printer paper combination. Calibrating your printer
    manually is capable of excellent results, provided you use a systematic
    procedure, and are willing to be responsible for the end result.
    http://www.curvemeister.com/downloads/TestStrip/digital_test_strip.htm
     
    Mike Russell, Feb 6, 2007
    #8
  9. peter

    bugbear Guest

    Both; the current state of the art is not mature enough
    is have a single solid working practice.

    Some software wants to do its own profiling, some software
    has never heard of color profiling, some software
    wants to (correctly) allow the OS to do color profiling
    on the apps behalf.

    So getting color correction to work "nicely"
    end-to-end involves careful reading of manuals
    and careful configuration of each and every
    software component.

    Sorry.

    BugBear
     
    bugbear, Feb 6, 2007
    #9
  10. peter

    peter Guest

    Thanks to all the response, I am ready to buy a calibrator. Does anyone have
    a pointer to a review of more than one device, like this article but more
    up-to-date:
    http://www.drycreekphoto.com/Learn/monitor_calibration_tools.htm

    I want to buy one that would let me calibrate several monitors (LCD and
    CRT). If all it does is spits out an ICC profile, then I can install the
    software on a computer, calibrate, load the ICC into the display driver,
    uninstall the software, and move on to the next computer. However, I read
    that at least some package (e.g. huey) require the color sensor to be
    attached to sense ambient light -- I would gladly give up this feature in
    exchange for the ability to calibrate multiple monitors.
     
    peter, Feb 8, 2007
    #10
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