AVS HD 709 - Blu-ray & MP4 Calibration - Page 96

Some TVs measure identical video levels (% shown on pattern) as similar lightness (Y) regardless of the measurement pattern, such as certain fixed-backlighting LCD models and similar TV technologies. Other TVs are more like your example, and they tend to vary luminance (Y) measurements depending on the average picture level of the pattern. I can't say how many TVs technologies or settings fall into each category, and the point is simply that different TVs do not all operate similarly.

Lightness variation from changing average picture level is not very difficult to observe by eye, or at least personally I tend to notice adjusting light output in a dim room. Misc. Patterns A5, Dynamic Brightness, can be used to generally observe what happens to the on-screen image as average picture level changes. The bars in the lower right of the pattern are always the same video levels, and the changing background gives five different average picture levels to observe. Another pattern for looking at how average picture level can change lightness (Y measurement) for the same video levels is the "Black Level Bars + Steps + Varying Gray" pattern on the Avia II DVD, which also has constant bars in the image and part of the background changes from black to white. Either the Dynamic Brightness pattern or the Avia II video provide a quick way to look at how average picture level may affect the on-screen image differently for various TVs models or settings.

The gamma graph is simply a comparison of gray lightness (Y) measurements. The Y value is basically the brightness of the measurement, and higher Y numbers indicate more light output from the TV. The intent of the gamma graph is just to relate how lightness (Y) changes between the video level for black and the video level for white.

There is not a lot of difference between the APL patterns and typical windows. The center video levels are exactly the same in either series of patterns. The only difference is that the APL patterns include the other levels to be measured, so average picture level remains constant for the series. Typical windows have the center video level surrounded by black, so as the video level changes the average picture level of the image also changes. Higher average picture levels (higher % windows), or brighter images, are more difficult for plasma to display, and your measurements simply indicate that your TV tends to vary Y as average picture level changes.

My personal opinion is that for most applications, I currently don't see a reason to use typical windows for measurements. Since different displays do not adjust similarly with changing average picture levels, and because I have not found a clearly-defined reason for including changing average picture levels in measurements, I think it generally makes sense to use constant APL measurements. This perspective is in line with what theory I can remember reading from Charles Poynton. For example the gamma articles from http://www.poynton.com/GammaFAQ.html and http://www.spectracal.com/simplepage...USCPMUTKGMKZWU generally seem to relate video levels with display gamma, and he never address how measured gamma may be affected by items such as various patterns, displays, or settings. Likewise I haven't ran across any experienced calibrators suggesting that there is a clearly-defined way of calibrating gamma on different display types, even though various display technologies like LCD and plasma can clearly measure gamma differently. So my current personal opinion is that if you only want to measure one series of patterns, go with the Large APL. One series of measurements will never give you complete information about a display, but honestly gamma measurement and calibration is not precisely defined at the level people seem to suppose. At least eliminating average picture level fluctuation, by using constant APL patterns, gets rid of some possibly-detrimental effects that can arise with how certain displays or settings react.

EDIT: One situation where APL patterns may not be appropriate would be if you're using a non-contact meter. When using a non-contact meter with the Large APL patterns it would generally be a good idea to try to check if the levels around the edge of the pattern influence the measurements. For example with the color patterns, contamination from the surrounding levels would likely cause different xy measurements compared to typical window measurements.

Yes, the disc ejects before the verification. It sounds like a drive or media issue, but it's hard to say which from the current information. It may be possible the disc could have burned correctly and the computer just can't read it to verify, but without the md5 it's all just a guess at this point.

Probably the easiest thing to do would be to use another computer with a DVD drive. There is a verify disc option in Imgburn, and if you make the settings change from the first post it will give you an md5 for verification. I tested the AVCHD I had and the verify disc in ImgBurn created the correct md5 after I unchecked the "Verify against image file" option.


It would be ideal to verify the disc on another computer, but if the video plays and you can see near-white flash on chapters 2 and 3 then I'll figure chapter 1 probably also works. One way that you might not be able to see any near-black bars flash is if you sent computer levels to a TV expecting typical video levels. The PS3 settings at http://www.avsforum.com/avs-vb/showt...3#post13955243 should get typical video levels from the player.

If you can see flashing on the other Basic Settings chapters the video is probably fine. Since it's a calibration disc, it's just best to verify that you have a good burn.


Yes, in order to verify the disc, you can do the following:

1) Install ImgBurn
2) Change ImgBurn settings to create an md5, as shown in the first post
3) Choose ImgBurn 'Verify disc' option from the main ImgBurn screen
4) Uncheck 'Verify against image file' and run
5) Compare the md5 from ImgBurn with the hash in the first post


I would do the above test first to see if the md5 matches. If the md5 doesn't match or if there's read errors again, then I might try a new burn on a second computer. Your download is probably good since you used the Wuala software, so if you have a usb memory stick that is big enough to hold the downloaded file you probably wouldn't need to download again.

A matching hash indicates that the disc should be identical to the original. A non-matching hash indicates something probably didn't go exactly as planned in the download, decompression, or burn. A non-matching hash likely comes down to computer troubleshooting.

Did you use the download from the first computer when you burned the disc from the second computer? If so, on second thought, that probably wasn't the best advice. I suppose it's possible the issues on the first computer could have been been from memory or storage, rather than the DVD drive or media like I first guessed. I've seen more than my fair share of computer memory issues, so I've decided to run a thorough memory check like http://www.memtest86.com/download.html whenever I buy a different computer.



A non-matching hash won't necessarily cause issues. For example something like bad memory could throw off the hash, but it would be unlikely to consistently change video levels. Mainly the hash is simply provided as piece of mind that everything worked exactly as intended and you have a disc that's identical to the original. Honestly I doubt most people check the hash.



I don't have experience with a number of the items on the list. Between DVE and Avia, I've always thought Avia had better practical explanations for video adjustments. I haven't used the Spears & Munsil disc, and I don't agree entirely with all their comments I've read, but I do think http://www.spearsandmunsil.com/articles.html is very thorough in regards to practical explinations.

The description in the PDF for using the APL Clipping pattern shouldn't be wildly different from the sort of black level setting that would typically result with the standard DVE pluge instructions. The Black Clipping pattern simply takes some guesswork out of the typical DVE pluge instructions on some displays. It sounds like your setting from the DVE ramp might not correspond with the standard DVE pluge instructions, so one way or another you may have to choose a compromise. Setting brightness lower than suggested by the main patterns here, or the standard DVE pluge, would likely result in a loss of information on darker scenes.

It's possible that black level might fluctuate on some digital displays. If black level does vary it would likely change depending on average picture level. If black level changes depending on average picture level, then any single static image will not give complete information on how the display functions. The Dynamic Brightness pattern here includes 10% bars in the corner, and you can see if the bars tend to adjust relative to each other as the background changes. For example some CRTs vary so much that the 10% bar can blend with black on some scenes. On DVE they included a pluge on all their grayscale windows, and so you could look at the DVE windows to see if the pluge varies from window to window. Avia II has some tests where constant bars are shown and part of the image changes average picture level. My main point is that if your display varies black level, only looking at the ramp/bar test will not show what happens with other average picture level images.