Why is my LCD HDTV flickering based on the contents of the scene?
December 26, 2010 11:32 PM   Subscribe

Why is my LCD TV dimming every time there's a dark scene in a movie?

This is sort of a last ditch question, I feel like I've tried every setting there is with no effect. Next step is to contact Samsung support, I guess.

I have a 40" LCD TV, the Samsung LN40B530. Attached to it is a Toshiba SD7200 upconverting DVD player. The problem is, every time there is a scene in a film where most of the screen is dark, the backlight on the TV will dim enormously, making the normally-bright parts of the scene much dimmer.

This is tremendously annoying. You can see the brightness of the scene's lighter areas tick down hugely. Sometimes if the amount of dark areas in a scene are just right, the damn lighter areas flicker back and forth between brightness levels a few times a second.

There is a setting for "Dynamic Contrast", but setting it to OFF or HIGH have no effect either way.

I cannot stress enough how much this flickering drives me nuts during a film with lots of dark scenes. Has anybody ever experienced something like this?
posted by geodave to Technology (13 answers total) 3 users marked this as a favorite
I would have said "dynamic contrast", but you've covered that! I'll note that, on the C series sets, the setting is per-input - so if you've turned it off while watching TV, it'll still be turned on for the DVD input.

It could also be due to the … umm, I forget the exact terminology, and I'm not in front of one at the moment … the processing mode. IIRC, the higher-processing modes like "movie" also to some degree dynamically alter the black level independent of the contrast setting. Try changing that to "game" (which should equal 'don't touch the signal!' on the B-series) to see what happens.

I'll drop back in later tonight when I'm in front of my gf's C650 and see how things are going…
posted by Pinback at 11:41 PM on December 26, 2010

Response by poster: Wish I could set it to game, but the only modes are "Dynamic", "Standard" and "Movie"
They all suffer from that same automatic dimming. I just can't imagine this is normal behavior, it's so obvious that it distracts you from whatever you're watching.

I do have a friend who has the same model, I think I may have to take a DVD over there and see if it's an issue with my player rather than the TV.
posted by geodave at 11:56 PM on December 26, 2010

Is there an "Eco mode" on the TV you can turn off?
posted by hariya at 12:06 AM on December 27, 2010

I have a Sony TV that does this sometimes. It happens on occasion, but not quite frequently enough for me to figure it out. I'd be interested to hear if you have any progress (for the record, this happens to me on multiple inputs).
posted by jaffacakerhubarb at 12:25 AM on December 27, 2010

Switching to standard plus dynamic contrast off should give you a steady state, which obviously it doesn't. Even if it was supposed to change contrast level it's a damn sight more subtle than that! It certainly is on my similar model samsung.

Definitely test the dvd player just in case but I think it's probably your tv, and it's warranty time. It's really not supposed to do that.
posted by ArkhanJG at 12:58 AM on December 27, 2010

Best answer: Ah yes - "game" mode is in the setup menu, not the picture menu…

On the off-chance, you could try turning off all up-converting and processing in the DVD player (letting the TV handle it) and see what happens.

And after looking at the manual for the LN40B5230, it's sufficiently different from my gf's LA32C650 that I'll bow out, except to say a) as a test, try turning all the assorted picture- and input-processing settings off in the various menus and sub-menus (the complicated menu structure is a failing of Samsung sets in general!), and b) check out the reviews and forums at UK HDTVTest for ideas - when I was looking earlier this year, they had the best coverage of Samsung sets (their equivalent set would be an LE40B5xx).

Afaik, none of the Samsung sets have an ambient light sensor. And the LN series are CCFL backlit, so it's not due to local dimming either.

Final thought: This happens on all discs, right? ISTR reading about picture processing issues (pulsing, flicker) with certain Samsung sets and certain DVD players when playing 50Hz->60Hz (i.e. PAL to NTSC) converted content.

On preview: ArkanGJ is right - dynamic contrast, on the C series at least, is fairly subtle - but it's annoyingly noticeable at night and/or with certain content that seems to hover around a critical level of black. IIRC, on my gf's set I've got it set to "Off" for all sources (except maybe USB?)
posted by Pinback at 1:05 AM on December 27, 2010

Best answer: I'm not sure if this counts as an answer, but it might help get to one: on display devices, contrast is the white level, brightness is the black level. I was always confused by that until I learned it. What they do is to adjust where a signal level maps onto the display device level.

Explanation: imagine for a moment that there are only 100 different levels of brightness that the TV and the DVD can produce. A perfectly adjusted system will have them map one for one- when the DVD says 0, the TV produces as little light as it can. When the DVD says 100, it goes as bright as it can. And the levels match linearly in between. When the DVD says 25, the TV gives 25% brightness, and when it says 75, the TV gives 75% brightness.

So, if you mis-adjust the contrast up too high, for example, all the signals above 85 all display as 100% bright. A snowy scene that should show subtle shadows will just be blown out white. If it is adjusted too low, a 100% bright signal might only be displayed as 85% white on the TV.

Same for brightness- too high, and blacks aren't as black as they can be. Too low, and subtle differences in black are lost- any signal under the level you have set it at will just be black.

So, now that I'm talking about that, I wonder if the TV was designed with "please the masses" picture enhancing image processing. Where even with the contrast enhancing mode off, it still does some of that depending on how the brightness and contrast "knobs" are adjusted. Basically, the TV is trying to out-think you.

So what I'm thinking is to run the DVD to one of those points where you get the effect, pause it, and set the brightness and contrast to make it appear correct. And then run the DVD back and see if the effect is reduced.

(I have an older Sony CRT projection TV, and it does something like this to me. I plug a computer in, open up Paint and create an image that is 100% white. Adjust the settings to where it is as bright as possible. Then I go into the TV's menu system and it will show a white that is significantly brighter. I still don't understand it completely- it is connected via a digital interconnect, so I know I'm not losing signal due to analog messiness. I have given up on it.)

One thing to try is plugging a computer in, or temporarily use a different input for the DVD player and see if it makes a difference. Might help narrow down the subsystem of the TV that is causing the issue.

You can also use the computer to output a test image, something like these.
posted by gjc at 6:15 AM on December 27, 2010 [1 favorite]

Best answer: Don't have time right now to find the solution, but many of the LCD/LED Samsungs have an auto-dimming "feature" that's either listed under Eco-Mode, but more often is found in the service menu and must be disabled that way.

Look in AVSForums. Be warned that futzing around in the service menu can completely bork your TV.

Prior Samsung LCD/LEDs I've owned could only have the auto-dimming option turned off in the service menu. The TV does this during dark scenes to minimize backlighting issues (clouding/flashlighting/etc.), and it's annoying as hell.
posted by herrdoktor at 7:34 AM on December 27, 2010

I had this 'feature' in my Sony LED, and hated it. Research on AVS Forum revealed that it was not something that could be turned off. I returned the TV.
posted by eas98 at 7:34 AM on December 27, 2010

As for test images most THX certified DVD discs have a set of test patterns. ( Finding Nemo is one)
posted by Gungho at 8:17 AM on December 27, 2010

Does it also happen on regular broadcast tv? Have you tried resetting the tv to it's factory state? (I thinks it's one of the bottom menu options)
posted by bonobothegreat at 9:07 AM on December 27, 2010

Response by poster: Although the image remains, these answers are really really informative and the dozens of pages of thread that I've crawled through at AVSForums has led me to believe this is an issue I need to get serviced.
Thanks all for your help!
posted by geodave at 9:12 AM on December 27, 2010

Ok, here goes:

Enter the service menu:
1. Power off TV
2. On remote, press MUTE, 1, 8, 2, POWER ON
3. Find option called "CE Dimming" and toggle it to "off" or "0" or whatever it's not already set at
4. Power off TV.

I had a couple LCD/LED Samsung TVs with the same issue. Just to try to match what you're describing: basically, the TV would dim the backlighting any time there was a dark scene, and then brighten things up when things got brighter. This is 100% reproducible using different DVDs and different inputs, down to the exact time/scene change. It would always seem to lag a bit, and would be annoying as hell. No change in brightness/contrast or the easily-accessible settings would affect this.

AVSForums is a good source for info. Samsung, nor the techs they sent out, would declare it a problem: it was normal behavior for the TV. It's there to basically make any flashlighting/clouding less noticeable.

The only way I was able to fix this was to bite the bullet and go into the service menu. I'm telling you this now: DO NOT DO THIS IF THE IDEA OF VOIDING YOUR WARRANTY AND POSSIBLE TURNING YOUR FANCY TV INTO A TALL, THIN PAPERWEIGHT MAKES YOU FEEL FUNNY "DOWN BELOW."

That being said, it was easy to do: easy to find the CE Dimming option, easy to turn it off, and easy to turn it back on again. The TV will indeed keep track of your entry into service mode (I remember there being a counter somewhere), but I do recall that there's an option somewhere to restore the TV to factor defaults and reset everything, in case you're worried.

Even if you are worried, you'd be lying if you were asked if you futzed around service mode and said "no." I was never asked. I reset everything anyway. I ended up returning a TV to Samsung.

Just make sure that you do not change anything else. No "exploring," no "hmn, what's this setting do," no NOTHING. Unless you've don't care and that funny feeling "down there" is the exhilarating feeling of discovery and experimentation.

The proper answer for me to give you is to let Samsung and their techs guide you through the process of troubleshooting everything. I am quite confident that they will not lead you to the service menu, or find a solution to your problem. You might ask them flatly if they could guide you to turning "CE Dimming" off, and you might score. I did not.

Good luck.
posted by herrdoktor at 2:04 PM on December 27, 2010 [2 favorites]

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