Originally Posted by Light Illusion
No, that is very different.... Plasma ABL is active from the get-go,as any good RGB Separation display (graph) will show.
(And there are post of such data on this forum already).
That is very different from CRTs with contrast set too high, which is what your data shows.
Plasma and CRT display technologies are, unlike LCD, phosphor-based. Both face the same limitations. The light output for phosphor is directly related to the current from the power supply. The difficulty and cost of building high voltage power supplies goes up rapidly with the amount of current they must provide. It would be prohibitely expensive to build power supplies that are capable of adequately driving ALL of the phosphors in plasma and CRT displays up to full power (100% stimulus) and threaten prematurely aging the phosphors. Since real-world content involves relatively low APL images in any case, this is not really a problem for actual program material. However, the limitation is easily seen on full field test patterns. LCDs require much less power and thus do not need any brightness limiting.
The "contrast set too high" statement (115 cd/m2) is true only for the EBU standard, which is 80 cd/m2. The SMPTE standard is 120 cd/m2. In N. America 115 cd/m2 does NOT indicate an excessive contrast setting. Of course, you can get a CRT to measure nicely with full field test patterns. All you have to do is lower the contrast control. On this particular Sony I had to lower it to 70 cd/m2 peak output to resolve the gamma drop off at the high end.
However, the same is also true of plasmas. Lower the contrast enough, and full fields will measure nicely, just like CRT. Plasmas are more power hungry than CRTs, partly because of size (Plasmas are generally 50-60-inches, while CRTs are 25-35 inches.), so you will have to lower the contrast even more. On this Panasonic, the output had to go down to 48 cd/m2 to resolve the drop-off in high-end the gamma response.
You keep stating over and over that plasmas cannot be calibrated. The only evidence you offer for this is that they fail the RGB separation test. There are several problems with this.
First, you offer an idiosyncratic definition of calibration as the ability to pass one test only. In fact, display calibration involves the adjustment of many parameters, not the ability to pass one single test. Your elevation of the RGB separation test seems to be the result of some in house decision. It is certainly not supported by any internationally recognized organization that I am aware of--not CIE, not EBU, and not SMPTE. The SMPTE standards for digital cinema (RP 431), which are the ones I am most familiar with, focus on light output, uniformity, color and grayscale accuracy (graded by dE), gamma response, and contrast.
Second, even if this single test had the importance you place on it, you don't seem to take it very seriously as a test. Any performance test has standards of acceptance and levels of tolerance, none of which you have ever specified to my knowledge. Just what, exactly, constitutes passing or failing this test?
Third, as part of your insistence that plasmas cannot be calibrated--because plasmas fail the RGB separation test and the passing the RGB separation test is necessary for calibration--you attribute that failure to plasma brightness limiting. I decided to conduct a RGB separation test on a plasma I have on hand, a Panasonic ST30, and compare to results I got from an LCD I have here as well, the Sony Bravia KDL-32EX700, a display technology you seem to endorse
. I used your own account
of this test, namely that
In a display with good RGB Separation, the X, Y, Z components of each primary colour measurement patch should be equal to the corresponding grey/white patch:
Xw = Xr + Xg + Xb
Yw = Yr + Yg + Yb
Zw = Zr + Zg + Zb
If this is not true, then the display has poor RGB Separation.
I found that the plasma display actually performed significantly better
in this respect than the LCD.
Fourth, what does seem to be true is that plasma display technology is not suitable for professional broadcast monitors. All such devices I am aware of are the now-discontinued CRTs or LCDs, including LCDs made by Panasonic. I am not familiar enough with the requirements of broadcast monitors to know why this is the case, but whatever it is it doesn't seem relevant for consumer displays. I cannot think of a single area of display performance--other than low power requirements and resistance to image retention--in which LCDs are superior to the best plasma displays.
In short, the RGB separation test is vague and does not have anywhere near the importance that you claim for it. Furthermore, even if it did, I see no evidence that plasma displays do any worse on this test than LCDs. (I tested another LCD--a Samsung model--and it also performed worse than the Panasonic.) Because of this, I also see no evidence that ABL plays a significant role in a display's ability to pass this test in any case.
ColorSeparation.xls 71k .xls file