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Old 09-22-2013, 01:17 PM
 
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Quote:
Originally Posted by 313 TUxedo View Post
Pixelation is a side effect of data rate compression techniques peculiar to digital image (especially television) systems. Images are (oversimplified) cut up into groups of 64 pixels that can appear, disappear or move quickly, and each of the 64 pixels in the group changes far more slowly if your eyes are able to pay attention to the detail.

Were it not for compression, a single high-definition TV service could take up the entire over-the-air TV band, or half of all the bandwidth an RG-6 cable could carry.

Now, if the transmission were to be interrupted or corrupted, you would be missing the data for some of the pixel groups. The imaging hardware and software will show these blocks in the same place, even if the rest of the scene is moving or even if the scene has changed (a jump-cut), and you may see a set of skyscraper windows in the shape of a person's face (for example).

Pixelation can be expected if the signal is too weak to decode, affected by interference, or by multipath (echoing). When TV was analog, these would usually be perceived as snow, wavy lines, or ghosting, respectively.

Problem is, with digital, the difference between a signal that produces a perfect picture and a pixelated mess can be very small, and you can actually have a very poor (unreliable) signal and think it is perfect. In analog, one could see the imperfections easily and could more easily correct the problem causing the poor picture.
Compression, in itself, does not cause pixelation. Pixelation is not a side-effect of digital tv compression.

Quote:
Originally Posted by thecoalman View Post
There is two things that are similar but completely different issues that can cause this. With digital it's all or nothing. You have a bunch of 1's and 0's and if you don't have all of them the video can display large blocks of solid color and would be unrelated to the content. If the sound is missing or corrupt then that is the issue. If it's OTA you need a better antenna, if it's cable it could be a variety of things like a weak signal caused by the cable being split too many times. It's absolutely unwatchable.

Over compression is the other issue but will manifest as something related to the content especially where you have fast moving objects. You can also see this in things like scenes where there is a sky with slightly varying shades or if you have flashes of light like lightning. In the following image this is too compressed, the lights are moving fast so you get macroblocking. If this is cable or OTA you can't fix this becsue it's the source.
Missing data and over compression do not result in pixelation. You are confusing pixelation and artifacting. Pixelation occurs when an image is resampled.
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Old 09-24-2013, 03:58 PM
 
40,197 posts, read 41,799,403 times
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Quote:
Originally Posted by NJBest View Post
Missing data and over compression do not result in pixelation. You are confusing pixelation and artifacting. Pixelation occurs when an image is resampled.
I'm not confusing anything, they are referred to as macroblocks for both video and images as the reason for their creation is the same. A video is just bunch of images strung together but there is a specific way it's done with compressed formats like MPEG, WMV etc. They have what is called a GOP or group of pictures that might be for example 18 frames for DVD, only the first frame or the I-frame is a full image. Since a video like DVD might be running at 30FPS (or 29.976FPS if you want to be absolutely accurate) very little of the content changes over that time which is little more than half a second. . Compression is achieved because subsequent frames only contain the data needed to adjust for what has changed from the I-frame.

When you dont have enough bitrate to allocate to in between frames the encoder basically blows up a single pixel of color to something large enough that the bitrate will allow. This is the exact same thing that happens with compressed image formats like .jpeg when the compression level is too high. The difference with video and the reason you don't see macroblocks in the entire frame like you would with an image is we have the I-frame for reference so you'll only get the macroblocks in areas that have drastically changed. The image I posted previously provides a great example becsue the lights that have caused macroblocking are flashing and moving very fast. The people are not so there is plenty of data from I frame to prevent macroblocking in that part of the frame. It's only when the bitrate gets ridiculously low that you'll get macroblocking though the entire frame in which case the I-frame itself does not have enough bitrate.

FYI I shot that video, you can find other samples and the video itself from this post at Videohelp.com I made back in 2005.

AVI-DV to MPEG vs. MPEG to MPEG

Last edited by thecoalman; 09-24-2013 at 04:59 PM..
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Old 09-24-2013, 08:47 PM
 
24,503 posts, read 35,965,437 times
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Quote:
Originally Posted by thecoalman View Post
I'm not confusing anything, they are referred to as macroblocks for both video and images as the reason for their creation is the same. A video is just bunch of images strung together but there is a specific way it's done with compressed formats like MPEG, WMV etc. They have what is called a GOP or group of pictures that might be for example 18 frames for DVD, only the first frame or the I-frame is a full image. Since a video like DVD might be running at 30FPS (or 29.976FPS if you want to be absolutely accurate) very little of the content changes over that time which is little more than half a second. . Compression is achieved because subsequent frames only contain the data needed to adjust for what has changed from the I-frame.

When you dont have enough bitrate to allocate to in between frames the encoder basically blows up a single pixel of color to something large enough that the bitrate will allow. This is the exact same thing that happens with compressed image formats like .jpeg when the compression level is too high. The difference with video and the reason you don't see macroblocks in the entire frame like you would with an image is we have the I-frame for reference so you'll only get the macroblocks in areas that have drastically changed. The image I posted previously provides a great example becsue the lights that have caused macroblocking are flashing and moving very fast. The people are not so there is plenty of data from I frame to prevent macroblocking in that part of the frame. It's only when the bitrate gets ridiculously low that you'll get macroblocking though the entire frame in which case the I-frame itself does not have enough bitrate.

FYI I shot that video, you can find other samples and the video itself from this post at Videohelp.com I made back in 2005.

AVI-DV to MPEG vs. MPEG to MPEG
From this post, it seems clear that you are confusing macroblocks (a common form of artifacting) with pixelation. This thread is about pixelation.

Here's some detail: http://forums.att.com/t5/Features-an...d/td-p/2137559

It is possible, that like you, the OP is confused between the two.

Hope this helps!

Last edited by NJBest; 09-24-2013 at 09:03 PM..
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Old 09-25-2013, 02:05 AM
 
40,197 posts, read 41,799,403 times
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Quote:
Originally Posted by NJBest View Post
From this post, it seems clear that you are confusing macroblocks (a common form of artifacting) with pixelation. This thread is about pixelation.
You have crystal ball and know what poster is referring too?

As I've already stated there is two separate issues that can be confused, the first is caused by loss of the signal in the case of OTA and cable or a corrupt video file. The article you are using is describing it as pixelation however the technical term is still a macroblock.. The reason they appear is the same which is lack of data, the difference with a non corrupt signal is the decoder has a reference frame.
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Old 07-30-2014, 02:34 AM
 
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I am using TV card and this pixelation happens very frequently.
My platform is win XP SP 3 , Intel celeron 3ghz , 500MB RAM.
Do I have to change my display refresh rate for solving this?
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Old 07-31-2014, 11:27 PM
 
Location: Out there somewhere...a traveling man.
40,069 posts, read 48,962,399 times
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We get pixilation occasionally when interference is caused by an airplane flying overhead.
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Old 08-05-2014, 10:58 AM
 
Location: NYC
13,773 posts, read 9,280,776 times
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If you can cut the cord, do it. I haven't had cable or sat for 2 years now. Enjoy not having to pay $100+ for commercial TV. A lot of sports programs are going Internet option such as NFL, MLB, NBA TV.

Cable signals are still garbage compared to OTA.
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Old 08-05-2014, 07:00 PM
 
Location: Out there somewhere...a traveling man.
40,069 posts, read 48,962,399 times
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Quote:
Originally Posted by vision33r View Post
Cable signals are still garbage compared to OTA.
^^^This is so true, you lose 20-25% of quality/signal using cable-tv vs over the air TV.
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Old 01-12-2016, 02:31 PM
 
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We have an antenna that we can rotate to get a clear picture. We will be receiving a clear picture for perhaps two or three hours and then all of a sudden the picture will pixelate. There usually is no perceptible change in the weather. Our cables are new and well connected. This phenomenon is very frustrating.
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Old 01-12-2016, 05:26 PM
 
10,702 posts, read 9,663,994 times
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Quote:
Originally Posted by vmaxnc View Post
It's almost certainly the TV service, and I've seen it on all of them. Dish, DirectTV, various cable services. I've seen it much less on OTA, when decoded by an ATSC tuner in the TV, but it still happens. Not much you can do about it beyond making sure you're receiving the best possible signal you can.
Same here, it was the cable box. With the 'free' indoor OTA antenna it may happen now and then, but not nearly as often as with the 'expensive' cable box.
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