CHROMiX

Monitor Calibration White Luminance #'s for LCD

Hi,

I’m curious what the suggested white luminance numbers would be for calibrating an LCD monitor so that it would provide the most accurate display… Do these numbers apply for pre-press as well as inkjet and photographic reproduction? Also are there any guidelines regarding what is acceptable for an LCD Black Luminance point? Separately if you calibrate a CRT to a white luminance of 85cd/m2 (in a dark room) is it okay to also calibrate an LCD to the same white luminance of 85cd/m2 so they somewhat match?

informed replies only please…

TIA,

Keith

Keith,
There really is no hard and fast correct luminance target for monitor calibration. A rather general rule that was created for the film retouching industry was that the brightness of the monitor white should be about 80% greater than the surrounding environment. Now they were in a darkened room and were not comparing the monitor to printed output so they could work with the relatively low 85cdm/2 targets with no problem. 85 would be rather low when comparing an on-screen image to a printout in a viewbooth. I doubt you could even get a viewbooth that dim. With the new LCDs it is a lot easier to achieve print matches because of the higher luminance capabilities. What I would suggest is to find a luminance that works for your needs. If that is 85cdm/2 then there really is nothing wrong with that. Just be aware that if you are sharing the image with someone viewing on a monitor that is calibrated significantly brighter there could be large differences in appearance.
I would also strongly suggest that if you are bringing the brightness of a monitor down that you do so via the brightness controls and not rely on the calibration software to make the correction via the graphics card luts. If you have a DDC/CI capable monitor/software combination this may not be a problem but it is something you should be aware of.

An actual benefit to calibrating an LCD to a reduced luminance is that as the monitor’s backlights degrade over time, and they all will, you will still be able to achieve the same target luminance. If your always calibrating to the monitor’s maximum luminance then as the monitor dims so will your calibration results.

Good luck!
Bob Burnett

On Mar 29, 2007, at 10:55 AM, keith wrote:

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[There really is no hard and fast correct luminance target for monitor calibration. A rather general rule that was created for the film retouching industry was that the brightness of the monitor white should be about 80% greater than the surrounding environment.]

I can see there is a lot of room for interpretation but am curious, on a day to day basis is a white Luminance of 100cd/m2 a realistic target for an LCD?

Also how critical is the advertised contrast range of an LCD? If based on my CRT (Artisan) one might assume that an LCD with a contrast range of 400:1 or 450:1 would be in the ballpark… is that the case?

Thanks!

Keith
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Contrast ratio of LCD monitors, as its been explained to me by some monitor manufacturers, is a constant regardless of the white point luminance. That is, as you bring down the brightness of the monitor, the black and white point luminances will reduce at the same relative rate. Lets say a monitor with a 400:1 ratio has a starting white luminance of 400cd/m2. It’s black point should then be about 1cd/m2. If you lower the brightness so that the white point is 100cd/m2 then the black point should be about 0.25cd/m2. I’ve found this to be only somewhat true because as you get lower and lower in brightness there is a floor that you just cannot seem to go under with LCDs.

100cdm/2 is a fine target and should be steadily achievable on an LCD for years. As for making the LCD and CRT monitors match, contrast ratio or the relative black point of the monitor will have a big affect to how close you can get. CRT monitors have a much darker black point when compared to LCDs. If the black ends are left alone then even if the monitors’ white points match, as you go down the tonal scale the two will start to diverge and your eye will easily pick that up.
To match technologies you basically have to break both down to the weakest points. This means reducing the white point of the LCD to meet the CRT and raising the black point of the CRT to meet the LCD. Some calibration software packages allow you to control the black point as well as the white point so it can be handled automatically. With the CRT you’d want to use the brightness controls to affect the black point. (opposite of how brightness works on LCDs). Again, strive to make as much of the change in the monitor’s hardware as possible.

Bob

On Mar 29, 2007, at 11:41 AM, keith wrote:

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Hi,

Does that mean that LCD’s with a contrast range of 400:1 or 500:1 are ideal and that LCD’s with a contrast range of 1000:1 or so are less desirable?

Thanks for your help!

Keith

I’m always looking for the biggest and baddest and there’s a definite advantage to the higher contrast ratio monitors,especially when your keeping your white point targets high. With you looking at 100cd/m2 as a target your not going to get a 0.1cdm/2 black point. Your therefore not getting the advertised 1000:1 and so it might be overkill. But then again you have to look at it in combination with the maximum luminance for the monitor and how dark your CRT’s black point is.

Bob

On Mar 29, 2007, at 12:23 PM, keith wrote:

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Hi Bob,

Without all the CRT matching considerations, what would the specs of an “ideal” LCD monitor for photography and graphics be… at least a good guess if you can?

Keith