ABL effects measured for comparison - Page 3

What size are the smallest ones on the GCD disk? 1%?

I have no clue my friend, it there is a source out there please enlighten me

I just checked. The GCD disk has:

1% APL
10% APL
10% standard
Full field

Okay had my hopes up for a minute there thanks

The Duo supports full Triplet and any size window and unlike the DPG, has full external control (not IR) and isn't limited to RGB.

For value for your money in regards to professional level full triplet pattern generators IMO:

1. Duo (if purchased <$1000)
2. Accupel 5000
3. VideoForge (CalMAN only)
4. Quantum Data 780

or

1. <$1000 - Duo
2. <$2000 - Accupel 5000
3. <$3000 - VideoForge (CalMAN only)
4. >$3000 - Quantum Data 780 (has been offered for less than <$3000)

Edited by turbe - 1/1/13 at 8:43pm

Chad,

I thought there are no window size options for the qd780 in calman? I guess its available for the 8xx series quantum data generators?

Sent from my GT-I9100 using Tapatalk 2

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.

Steve

With Plasmas the thing you have to keep in mind is that the patch size will calibrate the display just for that level of stimulus...

If the 'normal' image you then display (DVD film) has different average contrast content the calibration will be invalid.

This is why finding a way to set the 'best' average contrast, and hence patch size, is important.

With plasmas it is actually valid to have different calibrations for different average content - dark moody films; bright lively films, etc...

What you can never have is an accurately calibrated plasmas for all inputs -it's impossible

Steve

Related topic Here http://www.avsforum.com/t/1414313/better-to-have-2-2-gamma-or-stable-2-3-gamma-on-a-plasma

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

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

Any idea why I have serious problems getting a stable result at 90% white on a Panny GT50? Using Calman and an i1D3.

While all consumer display types have some sort of idiosyncrasies, fixed backlight LCDs don't tend to exhibit the sort of small variation in on-screen gamma and grayscale, which depends on the image displayed, shown for the plasma in the first post.

Not to interfere with rhe discussion, but you only quoted a very small portion of Toms post. I am curious what your reaction to the rest would be?

Unfortunately the points mentioned above are rather tainted with confusion over the inbuilt colour management of many displays, which can be turned off in most LCD displays, compared to ABL, which can't be turned off...

My home Sony Bravia LCD is very poor out of the box, with appalling internal colour management.

But, turn it all off, and then calibrate, and the results are way superior.

This is as shown here: http://www.lightillusion.com/idiots_guide.html

And RGB Separation is a very critical component of accurate calibration - more critical than RGB Balance in many ways.
It shows that the primary colours match the expected grey scale, and if they don't the results will always be very, very wrong. especially for the critical memory colours.
It's actually difficult to over state just how important that is!

To prove how bad ABL is profile a plasma with different size patches... the results will vary enormously.
And that makes accurate calibration impossible to achieve.

Steve

Nope, ABL is an electronic limiting circuit that has never been used in any CRT.

Phosphor limiting is a roll-off when the contrast is over cranked.
Plasmas will suffer this to, to a degree, but that is not associated with ABL.
And to a 'degree' due to the Pulse Modulation of plasmas, compared to CRT steady electron beam stimulation.

ABL and phosphor roll-off are very, very different things!!!

Steve

Who needs fancy ABL circuits when you can just let the power supply sag on demand!

There are a number of display technologies that tend to adjust light output depending on the overall image displayed. CRT, plasma, a varying-backlight, or an adjustable-iris are all capable of changing light output while displaying a constant video level in the measurement area. It seems you're basically saying that the only common consumer displays capable of "accurate calibration" would use either a fixed-backlight or a fixed-iris. Sure displays that use a constant light source are typically easy to interpret what most measurements represent, since the measurement is tied clearly to the video level displayed in the measurement area, yet such displays also tend to have their own comparative shortcomings and often offer a dynamic backlight or iris option.

CRTs do not use any technology to adjust light output depending on the image displayed - the phosphor will just saturate if the contrast is set too high - a very different thing.
Set contrast/brightness correctly and CRTs calibrate very well.

But, yep, any dynamic display function will kill accurate calibration stone dead...

We are talking 'accurate calibration' here, not making a display look pretty!

Steve

I'm thinking of putting a CRT next to the plasma just to see whats happening with abl on different shows.

The rear projection CRT my parents own, set according to Avia instructions or Digital Video Essentials explanations or by white measurements, measures more like what TomHuffman was describing when looking at the sorts of various inputs mentioned in the first post, so I'll assume your definition of "correct" means a very low white level.

Considering the number of displays that can potentially fail your definition of "accurate calibration", personally I still think a relevant topic of discussion is to look at whether or not people are likely moving nearer to or farther from an intended target as they attempt to "calibrate" their imperfect displays.
Edited by alluringreality - 1/8/13 at 5:50am

I think it's pretty obvious his position is an extreme one, offered without any defensible measurements against recognized standards, and with many counter-examples throughout this forum.

Yes - this is the information I am hoping to find by following this thread. If one has all the measurements presented in the first post for a given display, how is the optimal pattern type/size determined?
Edited by djams - 1/8/13 at 9:22am

Not really - we just spend our time calibration professional displays that are used for grading the films you then watch at home...
My goal at home is to have the display match as accurately as possible the display that was used when grading, so what I see at home matches the original grading intent.

Simples - there is plenty of defensible measurement for that!

And ABL prevents such calibration!
(as does dynamic iris on projection)

Nothing extreme about that, is there?

Steve

Older CRTs can generate very high levels of brightness without roll-off or flare - it's a well known problem/limitation.
But, if the display is set up to levels below this, the results are very linear indeed, with very, very good RGB Separation.

As for your second point, I would agree totally.
A lot of the information being used for 'calibration' will indeed move a display away from what would be considered accurate calibration...
But, for a lot of users, that is what they desire - and who are we to argue with that?

Steve

There are a couple of posts in other Plasma threads on the use of a 'grey ramp' image to define the optimum patch size for displays with ABL.
This is the approach we use for all plasmas.

A quick search should find one of the posts.

Steve

If you only want to measure one series of patterns to use for setting grayscale, it would probably need to represent some sort of middle-ground in the gamma and RGB balance variation exhibited by the display with the video content you expect to watch, and ideally to really compare your measurement data against other displays you would need to choose a pattern that doesn't vary significantly due to differences in how the compared displays operate. Personally I'm not convinced such a thing is necessarily possible, but mainly I'm just leery of possible operation differences between various displays and settings. Some display settings can make observable changes in the on-screen image that are barely reflected in certain measurements. Of course with calibration software it's not necessarily imperative that we reduce the amount of measured data, but unfortunately I doubt most current software goes much beyond a single reference measurement series for setting grayscale. From a minimalist perspective I might be willing to settle on checking maybe just a couple measurement runs, but personally I still suggest it's probably a poor idea to screw around with a video processor or 10 point gamma control while relying only on measurements that vary overall screen brightness (Windows, Fields, % APL, GCD).

I think a lot of the discussion that crosses this forum assumes that window patterns measured on any type of display tends to reflect display operation similar to a reference environment. I'm not convinced that's the case, but there are only a limited number of consumer displays or settings that strictly operate in the manner you were describing, so it does go against general assumptions. Personally I cannot figure out where a number of the seemingly inherent assumptions from this forum come from, but I'm well aware that certain fixed-iris or fixed-backlight measurements do not necessarily agree with other display measurements. Anyway, I think if I expressed my general opinion of the home calibration industry it would be considered rather extreme too.