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I have a pair of pretty nice monitors (HP ZR30w) which I calibrated with a pretty good calibrator (i1-Pro) and after I calibrated both they still show colors every so slightly differently. My left monitor has a little more magenta color to it in photos.

Is monitor calibration only ment to get things 'close'? Other people in the office have experienced similar issues with their pairs of monitors, both HP ZR30w and Dell 3007WFP-HC monitors.

If I can't even get colors to match between my two exact same monitors connected to the same computer I have little confidence that colors on my monitors will look the same on somebody else's calibrated monitor :p

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2 Answers 2

up vote 9 down vote accepted

It looks like the ZR30W uses a fluorescent backlight. Although it's a cold-cathode fluorescent, the color still changes a little with the temperature. You want to be sure you let the display warm up for quite a while before profiling it to be sure the temperature is stable. The usual recommendation is something like 20 minutes as a minimum, but from what I've seen an hour is considerably better; if you have really good color discrimination, two or three hours wouldn't hurt.

I should also point out that some monitors (even some that otherwise seem pretty "high end") don't seem to have very stable backlights no matter how long you let them run. I don't know if I applies to your HP monitor or not, but (just for one example) at work I used to have an Apple Cinema display. I could run it for eight hours straight, profile it, and then profile it again 20 minutes later, and both the color and the brightness were quite noticeably wrong. OTOH, even though it also uses a CCFL backlight, I have a LaCie 321 that's so stable I can actually measure seasonal variation. During the summer my office gets hot enough that its temperature shifts a bit, but when I re-profile it again in the fall, it goes back to where it had been a year before.

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Warm up time is a good suggestion, I calibrated these in the afternoon on a work day so they'd probably been running for 6-7 hours. I hadn't considered that the backlight would affect color (duh) and that 'Pro Editing' monitors have to add value somehow and color consistency would obviously be one spot to do that. –  Shizam Nov 22 '10 at 18:28
1  
@Shizam: One thing I forgot to mention (but should have) is that this is a real benefit of LED backlights -- they're extremely stable. –  Jerry Coffin Nov 22 '10 at 18:30
    
Well I think this is certainly the answer to why so I'm markin' this solved. Hopefully jrista's suggestion for a fix will work out. Thanks! –  Shizam Nov 23 '10 at 18:10

Jerry Coffin's answer was excellent, and I can't add a whole lot more. One other possibility may be the calibration hardware itself. There are two fundamental types of calibration devices: Colorimiters and Spectrophotometers. A Colorimiter is a "scientifically subjective" device. It uses an approach to calibration called "tristimulus", and is designed to mimic how the human eye perceives color. The human eye's cone cells are sensitive to specific peaks of color (blue, green, and two peaks of red), which when interpreted by the brain are combined to produce the range of color we can see.

Most calibration devices are colorimiters, and while for any particular screen they will generally produce fairly consistent results, they are not guaranteed to always calibrate exactly the same, and will not necessarily calibrate each device the same. This is generally not a problem, as they work within the bounds of human perception (and in the same way as human perception...hence their slightly subjective results). Their slight variation is rarely detectable except when recalibrating and comparing before/after results. Combined with different kinds of back-lighting such as fluorescent tubes (which tend to oscillate at a multiple of the frequency of their power supply), and you have a system with a few variables that can cause different calibration results for different devices/different times. Some calibration systems, such as the Spyder3Elite v4.0, allow you to synchronize the calibration of multiple devices by creating a shareable profile that may be used to normalize the calibration of multiple, disparate devices to a common baseline.

Higher end (and usually more expensive) calibration devices are often spectrophotometers (usually in the form of a spectrocolorimiter.) A spectrophotometers is a truly scientific device, and is able to generate consistently accurate measurements at all times. Spectrophotometers can still be susceptible to lighting oscillations of fluorescent tubes, however most calibration devices that use spectrophotometry (and even most colorimiters these days) take that into account and are still able to produce consistent results. Spectrophotometers use mathematics to convert their light measurements into estimated tristimulus values. Since the final calibration results are estimated via mathematics, rather than directly measured, while calibration results may be scientifically true to the measured light, they often have a slight, but consistent, deviation from what you would expect. Again, these deviations are usually not detectable by the human eye when not comparing images from before/after calibration.

If you suspect that your calibration results either being skewed by the backlight oscillations of your screen, or by inaccuracies of the calibration device, you might want to look into a system that is designed to calibrate multiple devices to a consistent baseline. The DataColor Spyter3Elite with the v4.0 software offers this capability. It is able to generate a sharable calibration target that can be used to calibrate any number of devices, of varying types (LCD, CRT, TV, laptops, projectors, etc.) to produce consistent output. Calibration will obviously take longer when calibrating multiple devices, and you may need to do a couple re-calibrations of each device to get perfect normalization, but if you do regular multimonitor work and need accurate calibration across all of your displays, the investment in a system that can calibrate them all is worth it.

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Thanks for the extra details on hardware, I forgot to ask for suggestions on how the problem might be solved. Good info on the Spyder 3. –  Shizam Nov 23 '10 at 1:57
    
Spyder 3 OTW, puttin' it to the test. –  Shizam Nov 23 '10 at 3:15
    
Make sure it is the Elite. I am not sure that the Spyder3Pro comes with the new v4.0 software, where as I am pretty certain the Spyder3Elite does. It is the v4.0 software you really want, more than the device, since it is the software that offers all the multi-device profile synchronization. –  jrista Nov 23 '10 at 3:44
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That's an amazingly well-informed answer. My head is reeling! +1 –  AJ Finch Nov 23 '10 at 10:51
    
Yup, I confirmed the that the purchase was for the Elite version and that 4.0 comes with any newly purchased device. –  Shizam Nov 23 '10 at 18:09

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