Home audio & video forum: Pixelation in HD content: The signal or the television?

Question for you:

Do you get your HD through the air broadcast signal or was it through a digital cable box?

My TV is plugged in directly to the cable (no digital cable box) and the HD channels I pick up are the regural air broadcast HD, using the reciever built in to the TV.

In addition, I don't have a dedicated antenna plugged in, it just uses the cable itself as an antenna (hope this makes sense) and I actually don't even pick up all the HD availible in the area because of that.

What's your connectivity like?

I have noticed since I have had three majot boards replaced that I would see a delay in pixel refresh on my plasma hdtv. what could be causing this, is it the signal coming in or something going on with myh hdtv

Pixelation is sometimes referred to as blocking, I believe. Screen door effect is something entirely different and is present (really) only on rear projection HDTVs.

My brother owns a Rear Projection LCD and I have an LCD HDTV. Now I know what people are talking about exactly when they say screen door effect. It's a percieved texture of a rear projection LCD screen (maybe DLP as well) which makes it look like you're watching a TV through a barely visible mosquito net, because the space between pixels is more apperent than on other technologies.

It's not nearly as bad as some people see it but it is a matter of perception.

A good example of a pixelation, on the other hand, would be a low resolution DivX movie, where you see the image starts to look like a jigsaw puzzle in fast motion.

What I have seen on my HDTV, is no where near as pronounced as on a low quality digital video. What is important to me, however, is a clear understanding on whether this is a limitation of a television set or a problem with the signal quality.

If you're a streaming a video through internet connection and some packets are lost, you will likely experience blocking of the image until the stream quality is restored.

I have seen opinions on the web claiming that this is a limitation of the video compression combined with a signal quality while other claim it's the TV.

Is this is a signal quality issue, it's not a problem as it will be improved as the TV world moves towards digital and HDTV. If this is a TV problem and I will see the pixelation even when watching Blue Ray, well that really sucks.

Technical knowledge on this anyone?

Since my purchase of LCD HDTV I've read quiet a bit of stuff, some technical and some not.

In my understanding, that most of the HDTVs including Plasma and LCD have a refresh rate of 60Hz (except the new 120Hz LCDs). Please correct me if I am wrong.

My LCD is actually 120Hz (Sony XBR4), which means it actually refreshes twice as fast as other HDTVs on the market be it plasma or regular LCD, so I do not believe the refresh rate is an issue here.

I've also seen posts when people said that pixelation is a signal issue and can be seen on both Plasma and LCD.

Once again, I don't know if that's true or not that's why I am hoping for more accounts and maybe a more professional explanation of why pixelation maybe seen.

There was this really good post (too bad I didn't bookmark it) about the whole 120Hz and response times, but I understood. Here's a quote from the PDF you sent:

Many of today's larger LCD screens spec out at respose times that sometimes exceed 25ms - long enough to smear motion. Any response longer than 16 2/3 ms will smear TV's 60 fields-per-second video.

This only proves that response times of current LCDs are sufficient for the video signal and the math is consistent with the post I read. So 8ms response time is way plenty for a 60Hz refresh rate, actually twice faster than the required minimum of 16 2/3.

For 120Hz the required time would half of that which is 16.66666/2 is approx 8.33 which comes very close to the 8ms response time but is still sufficient.

So your argument is incorrect. And by the way, plasmas do suffer from phosphor lag, which has been reported by many video gamers. But let's not get into the whole Plasma VS LCD. I am just intersted in the pixelation side of things.

By the way, pixelation is not the same as motion blur.

Math gives me a head ache.

Im not sure what causes the pixelation, It could be signal and/or TV processing, maybe it has something to do with digital all together.

Here is what I have seen, any TV that is 100% digital, meaning the signal passes all the way to the image in digital form, I can always see some type of pixelation this is mostly on LCD, DLP, and micro projections sets.

as for any phosphor based TV like CRT, Plasma, and CRT projo, I dont see it in most cases.
and on my HD CRT tv I almost never see any pixalation, I would try getting an DVE calibration disc, and go through the moving test paterns to see if you get any pixelation, that should answer this tuff question.

I once heard that most phospher based TV's turn the digital HD signal back to analog RGB internally before processing and displaying the image, if this is true this could be the answer, but I dont know how much of this is true or not.

but it makes sence, its like a reciever taking a dolby digital sound track and tranfering the digital to analog using a DAC, this works very well for sound, why not video too.

P.S. if you find out if its the TV or the Signal please let me know.
gabe

I meant to say, "As far as I know, no commercially available television has a refresh rate faster than 120 Hz (not ms).

Which digital point and shoot camera, preferably one of the small ones that fit in purse and has a large LCD screen has the shortest shutter lag (at least i think that's what you call it for the hesitant time between pressing the button to snap picture and when it actually captures it. This delay is frustrating when you have a young child or animal in your viewfinder and by the time the pic has snapped they have looked away. I tried the Casio EX-Z77 and it seemes to have a rapid response????????? got any other suggestions. the other important factor is how long the batteries last?

texasgal

Pixellation occurs when the bandwidth cannot keep up with the amount of data it is expected to carry. This is most frequently a signal compression issue rather than a television problem. I first began to notice it on my old ANALOG TV when my cable provider changed over to digital signals.

You may have noticed it most severely in that fashion show because of all the flash photography. Most scenes, even those containing fairly rapid motion, have large areas that don't change as the picture goes from frame to frame. The areas that keep the same color and luminosity are amenable to high compression ratios. When you get a lot of flashbulbs popping, however, you need to rapidly refresh EVERY SINGLE PIXEL on the whole screen, and this requires much more data to be transmitted, more than the system can handle. So they deal with this by making the "pixels" bigger, and thus the pixellation.

You have a Sony XBR4 -- so do I. It is NOT your TV. I don't get any such effect even under extreme conditions on HD content played on either my Blu-Ray or HD-DVD player, which are connected via HDMI cables. I have enough bandwidth there.

Thanks Dr. Planarian. Your feedback especially considering that you have the XBR4 and Blue Ray/HD DVD is possibly the best prove that it is not the TV.

I also read a number of online posts that mentioned compression as one of the culprits and it makes perfect sense. I was really hoping for some feedback from someone who uses Blue Ray with HDTV LCD.

In addition, I never see any pixelation on my upconverting 1080p DVD player, but of course it is not the same as a true 1080i/p content.

I am going to get a Comcast digital box soon and see if experience any blocking on their HD On Demand content.

Dr Planarium has it exactly correct. Modern video compression is "temporal", meaning that it mostly only transmits the differences between each frame, and occasionally sends a whole frame (the "keyframe"). When the whole picture is changing (for instance, if you see a shot of ripples on a body of water), the transmitter is basically sending continuous keyframes, and has to resort to "spacial" compression (removing image data frame-by-frame) to try to keep the bitrate down. The transmitter might also drop frames, making the motion jerkier.

If you have low signal strength, these periods of high bitrate can look worse. Do us a favour and use your TV's settings to check the signal strength. If it's under 60%, you should upgrade your aerial; but before you do that, simply change the RF cables from the wall to the TV. Often when people buy a new digital TV, they just keep using the worn-out, brittle, corroded RF cables that they used for 15 years, and you can imagine what that does to the signal. Replace the cabling and see if that makes an improvement.

If it does, then you've fixed the problem. If it doesn't, then upgrade the aerial and put some sort of filtering device in the signal path. Many surge protector boards from electrical retailers have RF plugs to protect against surges, and these can also resolve interference problems (if you have high signal strength).

Those are classic symptoms of a weak signal. How far away are the stations from you? What kind of antenna are you using?

Best,
Ben

I have been dealing with this pixelation problem since Feb 07 and after having my HD set replaced and then dealing with Comcast for 6 months I then switched to Direct TV only to find that Comcast was telling the truth. Comcast acknowledged that it was a problem and could not believe that so few people were complaining about it. They gave me a video credit back to Feb 07 but said they could not do anymore for me because it was not in the cable system but the incoming feed to them. My conclusion...everything is routed through satellites and I believe there is too much being compressed as they are required to also transmit analog signals until Feb 09. For those of you who did not have an HDTV until after 06 you would not know what true HD is supposed to look like. You will not read about this in the news paper as it would slow down HDTV sales.
Rick

I disagree. I set my Sony to lower than vivid settings and the pixelation still causes an out of focus picture from a distance. A plasma or lcd hides it well but still does not have the HD detail it should have. The Comcast techs could clearly see the problem from their office on a 15 inch Panasonic lcd. In 2006 my Sony could be set on vivid with a WOW effect...true hd with no pixelation. I now have a Sony 55A2020 and the only fault this set has is the ability to show 6.2 million pixels and thereby show a corrupted signal that much easier. Turning off CineMotion, Adv Iris or decreasing sharpness is of no help. Something happened to the main signal feeds between the end of 06 and the beginning of 07. Comcast, Direct TV and all the rest are left to sell HD that is nowhere near 1080 quality.
Rick