eidschun
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Sep 12, 2008, 8:55 PM
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Problems calibrating displays
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I would like to describe my experience in calibrating displays using Hal Landen's procedure (http://www.videouniversity.com/tvbars2.htm), and ask for explanations as to why I had problems.
I recently calibrated four displays in total: my LCD computer monitor, my NTSC television, and two flat screen TVs. None had a "blue only" switch, and so I had to use gels, and indeed had to double them up in order to see only blue. Here's what happened:
1. LCD computer display -- Lots of fiddling around; very haphazard procedure, requiring lots of experimenting in fiddling with software controls for gamma, lumma and color temperature, as well as having to try different knob settings on the monitor itself for brightness, contrast and color temperature.
2. Flat screen TV, Sony Bravia manufactured in 2006 -- Worked like a charm; was indeed able to adjust the 3.5-unit and 7.5-unit bars to exactly the same level of blackness, leaving the 11.5 unit bar just barely visible.
3. Flat screen TV, Sony Bravia manufactured in 2007 -- I was able to get neither the 3.5-unit, the 7.5 unit nor the 11.5 to display at all, regardless of the brightness and contrast settings that I choose; the only thing I could do was get the general area containing those bars to go from deep black to gray.
4. NTSC TV -- Same as 3., but after removing the gels and watching several TV stations as well as a DVD, it was clear that everything was much too red. I reduced the "color" setting to tone down the red and get things looking normal, according to my eyes. By the way, that TV was manufactured in 1986, i.e. 22 years ago.
I don't understand why the TV mentioned in 2. was unable to display any of the bars that I mentioned. I also don't understand why my NTSC monitor looked way too red after calibration. One thing I should mention though is that in using the gels, I wasn't able to get all four blue bars to look quite the same on any of the displays, as it was as if they were slightly different shades of blue. This, of course, made judging "equal brightness" quite difficult.
If anyone could please enlighten me on why I had problems, and in general on what is going on during calibration, I would be most grateful. Thanks.
Finally, I should say that I would think that the only reliable way to calibrate a monitor, or any light source for that matter, would be to measure its spectral content, i.e. frequency versus amplitude, then compare that with some reference spectrum. I would then alter the frequencies and amplitudes of the display to match those of the reference. However, I realize that in general, displays do not have the necessary adjustments to allow this.
Robert
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