AVS HD 709 - Blu-ray & MP4 Calibration - Page 100

It depends how you want to try to make an approximation. Just averaging the video levels doesn't make sense, because a white window clearly puts a lot more strain on plasma or CRT than a field of the same average. What I mean is that a 100% gray (reference white) window at 15% area would average to 15% gray, and I don't think many would argue that a white window is more difficult for plasma or CRT to produce than a 15% gray field. Probably a more reasonable thing to do is to gamma-adjust video levels before averaging, since in effect that's what the TV has to do with the light output. The 15% area white window would still have a gamma-adjusted average of 15%, but the matching field after a 2.2 gamma adjustment would be around a 42% gray field (.42^2.2~15%).

If I put a single-point curve adjustment on the image to approximate 2.2 gamma, here are the results:

Small APL -> gamma-adjusted average around 4.7%, which would be similar to a 25% gray field (.25^2.2~4.7%)

Large APL -> gamma-adjusted average around 24.7%, which would be similar to a 53% gray field (.53^2.2~24.7%)


As examples of random somewhat bright images (white in uniforms), here was the current headline from NFL.com http://www.nfl.com/news/story/09000d...P11_cp#photo=1

If I convert the images to black and white and then follow the same procedure, here are the results:

Image 1 -> gamma-adjusted average around 17.6%
Image 2 -> gamma-adjusted average around 23.5%
Image 3 -> gamma-adjusted average around 21.6%
Image 4 -> gamma-adjusted average around 12.9%

For examples of random movie images, the Blu-ray posts from the Star Wars http://www.avsforum.com/avs-vb/showt...6#post20965206

Post #3 -> gamma-adjusted average around 15.7%
Post #4 -> gamma-adjusted average around 21.6%
Posts #5 & #6 -> gamma-adjusted average around 2.4%

No one has reported chapter issues, so I will guess computer problems. Maybe bad memory or storage could alter the playlist file. I would suggest downloading and burning from a different computer. Otherwise if you don't think the problem is from the computer that created the disc, you can also check if the md5 matches. ImgBurn can create an md5 if you check the settings shown under "EXAMPLE FOR WINDOWS COMPUTERS" item 4 and run the verify disc option.

The pictures I used were entirely random. During the week I had watched Star Wars and an NFL game. Except for the last two Star Wars images, the results were similar to other images I had looked at previously.


I was just talking about the sort of power draw likely required to produce different images. I had assumed a perfect power supply, and hadn't including anything like power limiting. I have a tendency to think that a real-world measurement of power draw on plasma is not likely to be similar when showing a 15% area white window and a 15% gray field. I could be entirely wrong, but your measurements don't seem to indicate that a 15% gray field introduces power limiting in the same way that a 15% area white can on plasma.


From what I've read about plasma, I agree that how long the pixel is running (duty cycle) appears to be the primary way to produce different on-screen brightness levels.


If I take this entirely at face value, I will agree.

In order to put it more into context:

• If white is represented by the pixel running 100% of the time, how long does the pixel need to run to produce light that measures about 1.5% of the brightness of white? (15% gray at 2.2 gamma)
• How long does the pixel need to run to produce light that measures about 15% of the brightness of white? (42% gray at 2.2 gamma)

I may have been wrong for lumping CRT with plasma. Since CRT tends to have a natural non-linear relationship between the input and light output, I suppose it's possible a simple average might be a better comparison for similar images on CRT.

If the "power draw in both cases is identical" then I figure that something like a Kill-A-Watt meter would report similar numbers for a plasma TV when displaying either the white window or the 15% field from this project. If I still lived in Denver, where the public library rents power meters, I would probably test the idea myself. Off hand I can't think of a way to reconcile such behavior with light measurements that seem to indicate power limiting on the white window pattern, unless somehow the 15% field is also power limited.

If an an average is all that's needed, here are approximate averages for the APL patterns.

Small APL about 7% gray
Large APL about 36% gray

Here are averages for the Star Wars Blu-ray images that I used before http://www.avsforum.com/avs-vb/showt...6#post20965206

Post #3 about 33% gray
Post #4 about 41% gray
Post #5 about 9% gray
Post #6 about 13% gray

Considering the averages for #5 & #6, I would tend to think that most video I watch likely has a higher overall average than the statement "Television program material is said to have a 15% APL over a long period of time" from http://www.videoessentials.com/glossary.php I also question the statement "The Window patterns used for setting gray scale in all three titles have a 16% APL so that they will closely represent normal program material in their current drain on the high voltage power supply.", unless they meant to only refer to the white window with 16%.