AVS Forum banner
Status
Not open for further replies.
1 - 9 of 9 Posts

· Registered
Joined
·
167 Posts
Discussion Starter · #1 ·
I found that the brightness of the "black" bars during Avia calibration is not even from bottom to top when right side of the screen is white. It seems that both bars are brighter at the top and become darker to the middle of the screen. E.g., I still can see both bars at the top of the screen but only brighter one at the middle. It only happens when the right side of the screen is white. When the screen is all black (using another Avia test pattern), the "black" bars have perfectly even brightness from bottom to top. The same with color filed - the screen is perfectly even. Is something wrong with my TV (TH-42PA25)? I have never noticed any brightness problems during normal play (DVD or cable).
 

· Read the FAQ!
Joined
·
37,689 Posts
Check to see if your display has an automatic display brightness adjustment that causes the display to change light levels based on what's being displayed. It's probably called something like Automatic Gain Control or AGC in the picture adjustment settings. If you find it, turn it off and see if that fixes things for you. I would recommend you leave any such "feature" turned off.

--Bob
 

· Registered
Joined
·
167 Posts
Discussion Starter · #3 ·
Does anybody know if Panasonic plasmas have AGC? I have not seen how to turn it off. Indeed, when during DVE test pattern play the bright white arrow shows up on the top of the dark screen with black bars, I can see brightness change in the top area...
 

· Registered
Joined
·
167 Posts
Discussion Starter · #4 ·
OK, this is weird. I have found that when I use DVI input (from Denon 1910), the black bars are always even. When I go back to component, the bars are not even (when right half of the screen is bright as I described above). I believe lots of ppl on this forum used Avia and Panny ED is very common set. Have anybody seen anything like this? Is my TV defective?
 

· Registered
Joined
·
549 Posts
Quote:
Originally posted by Maxim5
Does anybody know if Panasonic plasmas have AGC? (...)
Panasonic TH-42PWD6UY has it. Picture->Advanced Settings->AGC (On/Off)
 

· Registered
Joined
·
1,173 Posts
the 7uy has it on the advanced settings menu portion of the picture menu.
 

· Registered
Joined
·
167 Posts
Discussion Starter · #7 ·
I checked and it seems that consumer model (42PA25) does not have AGP control settings in menu. I don't think it makes "real" picture worser, just want to be sure that my TV operates properly. So, I hope it is normal for consumer model to show not even (from top to bottom) black bars brightness in Avia test with half black/half white screen when use component input...
 

· Read the FAQ!
Joined
·
37,689 Posts
Maxim5,

Well it's certainly not desirable for it to work that way from an image perfection point of view. But it may not be an issue for you depending upon what you like to watch.


I suspect it's not a defect in the set -- just the way this particular display was designed to work. Someone else who actually has one of these might be able to confirm.


--------------------------------------------------------


Since you don't see the problem when connected via DVI you might want to reserve the DVI input for the source that you intend to view most critically. This could be your DVD player or, perhaps, an HDTV receiver. Or if all your sources offer DVI, you might want to invest in a DVI switch designed for home theater use. Both Gefen and Dtronics make these for instance and there are a pair of threads in the Power Buys forum discussing the successes and problems people have had with each.


As for setting black levels for the Component input, the purpose of the gray half screen in the Avia test screen for setting black levels is SPECIFICALLY to trigger any AGC that might be active in the display. Now usually you would expect the effect of AGC to apply uniformly across the screen but since that's not what's happening in your display the odds are you'll be better served by calibrating based on the darker portion of the moving bars you are getting towards the middle of the set.


If you go to the advanced tests on Avia for whites blacks and grays you'll find several different versions of this moving black bar test screen. One has the half screen gray used in the basic setup, another has a full black screen except for the moving bars, and another has a half screen at full white intensity. Because your eye will be more sensitive the less light the screen is putting out, the black bars would naturally be more distinct in the black screen, and less distinct in the white half screen. The gray half screen is thus a good compromise from that point of view as well.


But since you are seeing unusual effects, apparently from the AGC, you might want to check the range of Brightness settings you would get if you re-did the setting using each of those three screens and then try a compromise setting between them as a starting point. You will probably have to experiment with some Brightness settings while watching movies to see which really works best for you since the set is fighting you a bit.


Just be sure to double check that your Contrast setting is correct for each Brightness setting you try. When comparing while watching movies, change the PAIR of Contrast/Brightness values to give each setting the best chance of looking good.


----------------------------------------------------------


Another thought: It's possible that the degree of apparent AGC effect you are seeing may vary according to your Contrast setting. You might try an experiment with a significantly lower and/or higher Contrast setting to see if the degree of unevenness you are seeing between the top/bottom and middle of the moving black bars changes in any useful way. If it does, then that may help in your selection of the best Contrast setting.

--Bob
 

· Registered
Joined
·
167 Posts
Discussion Starter · #9 ·
Bob, thanks for nice explanation!


Indeed, it seems to be consumer Panasonic plasma design feature. Today I stop by CC and play with 42" HD Panny (PX25U). With DVE disk it showed black bars which were not uniform from top to middle/bottom. At the brightness level when the bar almost disappeared, it was still visible at the top and completely disappeared in the middle to bottom part of the screen. It was slightly less obvious than with my set; the difference could be a result of the lower contrast of HD set (vs ED) and much higher brightness in the CC showroom. I am very picky about picture quality and I definitely don't see any negative effects of this "feature" on the PQ...
 
1 - 9 of 9 Posts
Status
Not open for further replies.
Top