Different brightness with different calibration DVDs? - AVS Forum
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post #1 of 9 Old 01-16-2009, 06:33 AM - Thread Starter
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I've searched, and haven't been able to find a good answer yet.

I'm trying to calibrate my new plasma (Panasonic 42PX80U), and so far have used three calibration DVDs: DVE HD Basics, AVCHD, and rudimentary THX calibration at the beginning of Wall-E. The problem is, on the brightness adjustment I'm getting different values for each one. DVE is coming in the lowest at 57, then AVCHD at 63, and finally THX at 68.

My TV isn't the best, I know, but I figured at least the brightness calibration would be consistent throughout. Can anyone explain to me why this is happening, and how I can compensate for it? Even as it is, at a brightness of 57 my blacks are a little too gray for me.
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post #2 of 9 Old 01-16-2009, 07:16 AM
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There could be a lot of reasons. One possible explanation is that the patterns are designed differently. I know that AVSHD will give you a different setting in most cases than AVIA, simply because AVSHD has a more fine pattern to look at.

The second explanation is that your TV (and possibly eyes too) are reacting to a change in the Average Picture Level (APL).

Try using AVSHD to set the black level using the flashing black bars. Then check the next pattern (the APL pattern) and see if your calibration holds. If it doesn't, then your TV is reacting to the change in APL and you will have to make some compromises.

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post #3 of 9 Old 01-16-2009, 07:54 AM
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Greetings

Once you make the BTB go away ,.. you should try taking it all the way down to see how much blacker the real video black of the TV gets. It should not get any blacker ... stuff just disappears as it gets crushed.

At which point ... if you don't like the blacks ... you either bought the wrong TV or you need to add a bias light to improve the black levels.

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post #4 of 9 Old 01-16-2009, 09:08 PM
 
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Part of this has to do with the APL of the pattern.

For instance there are on AviaII, several black level patterns with black bars on a completely back background, to a half gray, to a half full-white background. The higher APL scenes with the bright white parts of the pattern will serve to obscure the visibility of the black bars, leading you to set black level higher than you would with the full black background with nothing but the black bars on the screen. The levels of the black bars that are encoded in these patterns are exactly identical, but their visibility varies depending on the ANSI-contrast performance of your system and what else is on the screen simultaneously. This is why the same pattern elements used in different patterns may yield different results.

Setting black level, thus, is somewhat elusive because you may want to set it lower for lower absolute black (use a pattern with little or no bright elements in it), or you may want to bias it towards maintaining shadow detail even in the brightest and most difficult scenes (use a pattern that is bright, such as colorbars or another very bright pattern that also contains black bars.).

Choosing a pattern and reaching the subjective compromise you prefer in your system is about understanding the tradeoff between best absolute black, and best shadow detail.
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post #5 of 9 Old 01-16-2009, 09:25 PM
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Quote:
Originally Posted by Zoltank View Post

I've searched, and haven't been able to find a good answer yet.

I'm trying to calibrate my new plasma (Panasonic 42PX80U), and so far have used three calibration DVDs: DVE HD Basics, AVCHD, and rudimentary THX calibration at the beginning of Wall-E. The problem is, on the brightness adjustment I'm getting different values for each one. DVE is coming in the lowest at 57, then AVCHD at 63, and finally THX at 68.

My TV isn't the best, I know, but I figured at least the brightness calibration would be consistent throughout. Can anyone explain to me why this is happening, and how I can compensate for it? Even as it is, at a brightness of 57 my blacks are a little too gray for me.

The 42PX80U is pretty damn good, actually (take it from me...and CNET's editor's choice). I also have the tv, and my brightness setting is +55 (in Cinema mode) and works somewhat with contrast. If I put my contrast higher (it's now at +79), then my brightness goes down.

But on the DVE, when I bring the brightness down until I no longer see any of the darkest bar, it's usually anywhere from 53-55.
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post #6 of 9 Old 01-17-2009, 06:15 AM
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Quote:
Originally Posted by Voyeur View Post

The 42PX80U is pretty damn good, actually (take it from me...and CNET's editor's choice).

Aside from the incorrect color gamut...

Lee Gallagher
Imaging Science Professional
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post #7 of 9 Old 01-17-2009, 06:30 AM
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Originally Posted by Lee Gallagher View Post

Aside from the incorrect color gamut...

I used to have a Sony 34XBR970, and was able to correct its color decoder within the service menu. So I have a pretty good idea what correct color on the TV should look like. The color on this set may not be perfect (very few come out that way from the manufacturer) but I've got mine looking quite comparable to that Sony...and way better than the color I've seen on other sets.
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post #8 of 9 Old 01-17-2009, 06:41 AM
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Glad to hear you're happy with your panel.

I calibrated one for a mastering house not too long ago. They ended up returning it and getting the 800U because the colors could not be rendered accurately on the 80U.

Lee Gallagher
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THX Certified Professional

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www.advancedaudiovisual.tv
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post #9 of 9 Old 01-17-2009, 07:42 AM
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Quote:
Originally Posted by Zoltank View Post

Can anyone explain to me why this is happening

How technical do you want to get? I'm not going to discuss the THX patterns, but I'll compare our comments against DVE. Light in the room and APL of the pattern will affect perception, but to try to keep things simple I'll assume a dim or dark room and a low-APL pattern.

The middle bar on the DVE pluge is reported as 2% above black, which is 20 or 21 for how we label bars. So if you set brightness low enough so that the 2% bar on the main DVE pattern is just barely visible (your 57 setting) then it's likely that the Black Clipping Pattern from our disk will begin flashing nearer to 20 or 21. If on the other hand you set brightness so that 17 just begins flashing on our pattern (63 setting) then the above black bars on the DVE pattern will be brighter.

On many digital displays the actual brightness of black will likely remain the same regardless if the lower (DVE 57) or the higher (AVS 63) setting is chosen. There are basically just two things that are likely to change - clipping and gamma. Clipping is indicated by the AVS Black Clipping Pattern, so using the lower setting you will be losing a bit of information near black for very dark scenes. By clipping higher than black, like the lower DVE setting indicates, then that will raise gamma near black. A higher gamma near black just means that dark shades near black will be darker.

So to sum things up so far, the lowest brightness setting possible with either disc will likely cause the following on many digital displays:
DVE - Some clipping above black with darker shades near black.
AVS - No clipping above black, but shades near black will be brighter than if you lowered brightness and clipped levels above black.

On a few displays it would be possible to account for both clipping and gamma and arrive at about the same brightness setting for either the DVE or AVS patterns. To do this though you will likely need to be able to adjust gamma, because brightness on many displays is mainly just a clipping control. A majority of displays do not have a way to adjust gamma, and for the ones that do it's probably best to use measurements to get an idea of what is going on with gamma.

Quote:


how I can compensate for it? Even as it is, at a brightness of 57 my blacks are a little too gray for me.

I'm not familiar with your TV, so I can't comment if it might have any other controls that would affect light output near black. Generally if the TV is set as dark as possible and a full field of black is not dark enough for you, then like Michael TLV commented all you can really do is to use more light in the room or buy a different display.
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