Soft Proofing: Light Booth and Monitor Luminance

Discussion in 'Digital Darkroom' started by paul_dixon|3, Aug 23, 2005.

  1. Hello,

    I am calibrating a Apple Cinema (the new 20" model). I am using Eye-One Display 2 with
    Eye-One Match Software.

    I am following guidelines published in ISO 12646, with some modifications for LCD. Here
    are the settings I am optimizing for:

    Monitor Luminance: Target 140 cd/m2
    Monitor Gamma: 1.8 (mac)
    Monitor White Point/Temp: 5000K

    Room Ambient Light: 32 lux
    Light Booth Light: 2000 lux
    Light Booth White Point/Temp: 5000K

    And to get to the point, my question is, it seems that even at 140 cd/m2, my monitor does
    not match the overall brightness of the Light Booth at 2000 lux. I find it to be too dark
    overall, and have to either turn up the monitor brightness, or turn down the light booth
    dimmer.

    I find this interesting with the Apple LCD because CRTs have typically had an even lower
    target (around 100 cd/m2) for soft proofing. Is 2000 lux too high for the light booth (even
    though recommended by ISO 12646)? It seems accurate in that the color temp is right on
    5000K at that level...

    Is there some other target level other than 2000 lux that I should shoot for on the light
    booth? Or should I pump up the brightness on the display? And to what luminance?

    Thanks in advance to any responses.
     
  2. According to Bruce Fraser (a recognised authority on colour management), the standards that you're talking about are designed for the graphic arts. I'm not sure about ISO 12646 but ISO 3664 calls for 500 lux for practical appraisal and 2000 lux for critical comparison. If the same holds true for 12646 as 3664 Fraser has this to say:

    "...the standard wasn't created with monitor to print matching in mind- it mandates that the ambient illumination for color monitors should be less than or equal to 32 lux and must be less than or equal to 64 lux. For monitor to print matching, all these values are way too high- the ISO has acknowledged this and is still working on standards for this kind of match" (pg 210, Real World Color Management, ISBN 0-201-77340-6) Book is highly recommended.

    Most color management experts that I've read set their LCDs to the following:
    1) around 100 cd/m2 depending on ambient light
    2) Gamma 2.2 (yes even for apple, the native gamma of the apple lcd range is 2.2 not 1.8)
    3) Color temp at 6500k

    From what I've read, the best technique to compare on screen images to your light box is to try to balance the light box illumination to roughly that of your screen and when looking between the monitor and paper print, either close your eyes for a second or look at some neutral coloured wall.

    The reason is that a) 5000k on a monitor makes everything look a bit yellow and most people find 6500k a more natural monitor temp and b) your eye/brain quickly adjusts its sense of white balance to compensate for the difference in colour temp dif between the monitor and light box.
     
  3. Those ISO spec?s are old and not taking the very high luminance levels possible with an
    LCD into account. Your ambient light is pretty low (good). You should be in the
    neighborhood of 95cd/m2 for a setting in the 16-25lux levels. 140cd/m2 is WAY too
    high. The luminance is based on the environment; you want the blackest black/whitest
    white to be the display. So you?ll probably want to try a value of 100cd/m2. Also, you want
    to be at a TRC gamma of 2.2 and whenever possible, select a white point using a D
    illuminant not a color temperature value (that?s way to ambiguous, many colors correlate
    to the same kelvin value).
     
  4. Thanks for all the great advice.

    To add to the information I provided, yes I am doing soft proofing for graphic arts
    purposes (i.e. SWOP color space). That being said, do I still really want to be at 6500K for
    temp? Seems like 5000K is not too yellow on the monitor vs. light booth. It just looks a
    little dark.

    Weird that Gretag EyeOne has 140cd/m2 as the target for LCD, but I guess they are just
    providing calibration norms...not necessarily with soft proofing in mind. I'll try a
    calibration at gamma 2.2, 6500k, and 100cd/m2. Keeping light booth at 2000lux. The
    proof is in the pudding...
     
  5. For a yellow paper stock, 5000K can work fine although at least on CRTs, the luminance can
    be on the low side to get that. So stick with 5000K (I?d use D50) and if it still looks dim, try
    and up the luminance but better, dim the light booth (assuming it has a dimmer).
     

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