# Technical Question about picture quality



## Stuart Sweet (Jun 19, 2006)

So I'm hoping an engineer-type can answer this, and then we can talk properly about it, and if it's happened to you...

On some channels -- so far only locals for me, I get a weird phenomenon. It is almost as if the camera lens got very wet for a moment then dries. It's more than pixelation, it's the sort of out-of-focus-ness that you get when you're driving through the rain, then you drive under an overpass and everything's clear, then you get hit with "all that water" and everything blurs for a second before the wipers kick in. 

It lasts maybe 1/10 second and then changes to regular pixelation then resolves to a normal picture. This isn't during heavy motion. 

It's as if the key frame is extremely low quality (far below normal) and it takes a couple frames to get it back to normal quality.

I suspect this is an issue at the originating broadcaster since I see it on OTA as well as satellite feeds. 

What would you call this phenomenon, and have you had it?


----------



## Upstream (Jul 4, 2006)

Stuart:

I had a similar phenomenon on my old R15. When I would change the channel, the picture on the new channel would be out of focus for a second, and then sharpen up. I had assumed that it had something to do with clearing the buffer, or changing the video stream. 

The hard drive on that R15 crapped out, and I haven't seen the issue on my new R15. So maybe it had something to do with a hard disk defect.


----------



## rudeney (May 28, 2007)

I’ve seen this, too, and I believe it’s just motion blur compounded by an anomaly in MPEG4 compression. I tend to notice it when there is a total scene change and the new scene has motion in it. While there would be some level of motion blur in the analog presentation, it would not be noticeable unless you look at an individual frame. When run together in sequence, the subject looks clear. 

Now, bring this into MPEG4. The algorithm is trying to do inter-frame compression, i.e. looking for redundant data among adjacent frames. Since this is a scene change, it finds none, so it has to render the entire frame. However, it is also doing intra-frame compression, and blurry frames tend to actually look more blurry when compressed. So, for a frame or two, the motion blur is exaggerated until the compression algorithm “catches up” again with its inter-frame compression.

I hope that makes sense. I guess there is some technical term for this compression anomaly, but I couldn’t find a name for it. Ironically, this did not exist in the old M-JPEG algorithm because it was not doing any inter-frame compression. While MPEG2 does inter-frame, it handles blurry intra-frame much better than MPEG4. Since the locals are MPEG4, you notice it there more. You also may notice it less on the movie channels where the content was originally in 24fps. When converted to 60fps, MPEG4 can now look at the same frame multiple times when compressing it, and this it does a better job.


----------



## davemayo (Nov 17, 2005)

I see this too. Particularly when the program switches from showing something that is in SD back to HD. For example, I see it when watching the local news (which is in HD), then they show an SD video clip, then switch back to the anchors. The anchors are blurry for a few seconds, then it clears up.


----------



## zobeht (Aug 30, 2007)

I've been seeing this for years. Only on my local channels. It happened with my old RCA receivers on 3 different SD TVs. Since have upgraded to HD. New Dish, wiring and receivers, still see it only on my locals on all TVs. Thought I was the only one.


----------



## armophob (Nov 13, 2006)

In the instances I have seen it is during some sort of live or taped broadcast of an event or news program. I have always chocked it up to simple camera man focus speed and reaction. Yelling "focus you idiot" at the tv usually clears it right up.


----------



## ThomasM (Jul 20, 2007)

This happens rarely on my locals....but it does happen. Lately, what I've seen is a momentary "jump" in the picture/audio like a momentary interruption in the digital stream. At first, I thought it might just be my DVR, but one time when it did it, I happened to be recording the program on all three DVR's, and I went back and jumped to that instant in time and observed the exact same effect on all three.

Since I've never seen this on the national channels, I suspect it's something with the DirecTV receiving station where the locals are picked up and then sent to the DirecTV national operations center. I've noticed a lot of changes in this "pickup" location lately. One by one, the SD feeds of the locals have been upgraded to the HD feeds (even on the local CBS affiliate which still isn't carried by DirecTV in HD). How do I know? It's extremely obvious when the analog anomolies (ghosts, bars in picture, etc.) that I've come to know after seeing them for 7 years suddenly disappear, and graphics become crystal-clear.


----------



## Wisegoat (Aug 17, 2006)

armophob said:


> In the instances I have seen it is during some sort of live or taped broadcast of an event or news program. I have always chocked it up to simple camera man focus speed and reaction. Yelling "focus you idiot" at the tv usually clears it right up.


This is exactly how I see it. I only see this issue when it is live sports. Usually it is when they switch camera angles. I always thought it was them showing it to us in SD for 1/2 a second until the HD version kicked in. The camera men also have to frame everything for 4:3 ration, even when using HD cameras. Gotta apease the SD crowd I guess. There might be something that happens when they switch cameras.


----------



## beavis (Jun 9, 2005)

I get that effect too. I call it tiling.


----------



## rudeney (May 28, 2007)

I don’t doubt that there are live camera focusing issues; those have been around since TV. This issue that I am seeing is definitely a digital compression artifact. Like Stuart described, it’s as if the lens is "watery" and then it takes a few frames to clear. If you watch closely, the transition from blurry to clear is sort of a “reverse pixelization”. You can see a similar effect on some of the photo sharing websites where the initial image is blurry and as it downloads more pixels, it becomes clearer.


----------



## Canis Lupus (Oct 16, 2006)

I noticed this most consistently during the Stanley Cup Finals. Whether it was Versus or NBC OTA made no difference. And the one time it would happen was going into or coming out of graphics, almost as if, as described above, the compression algorithm was having trouble resolving the change from a color-laden graphic to a mostly white sheet of ice. Definitely looks like a compression issue though.


----------



## beavis (Jun 9, 2005)

One thing I notice when watching Wheel of Fortune is when they go to the final spin there's extreme macroblocking. Course, it's on NBC here and NBC's HD is horrible.


----------



## John in Georgia (Sep 24, 2006)

Great description of this, Stuart. 

I always record the Today Show (an HD local) in case they run a story I'm interested in. I see this many times during the program -- for me, it normally appears when coming back to the network HD image from a local or network SD image. 

I've been seeing this for many months and its always seemed as if the compression algorithm takes a second or two to catch up with the new HD video input -- looking "soft" prior to "locking-in" on the new signal. It's definitely not an "out of focus" camera ... it's way too consistent to be an operator error.

John


----------



## Bushwacr (Oct 31, 2007)

Stuart Sweet said:


> So I'm hoping an engineer-type can answer this, and then we can talk properly about it, and if it's happened to you...
> 
> On some channels -- so far only locals for me, I get a weird phenomenon. It is almost as if the camera lens got very wet for a moment then dries. It's more than pixelation, it's the sort of out-of-focus-ness that you get when you're driving through the rain, then you drive under an overpass and everything's clear, then you get hit with "all that water" and everything blurs for a second before the wipers kick in.
> 
> ...


I have created it, but not with D*.

I record OTA using BeyondTV and an attic ant. The native recording is .TP which is an MPEG2 container at 19.2 Mbits/sec. That stream will play flawlessly on the PC or TV and is gorgeous. (It actually impresses the wife)

If I recode to MPEG2 at 8Mbits/sec it will degrade fast motion and rapid/large color changes, but not too badly.

If I recode the original stream to MPEG4, 1 Pass, HD720 it will resolve to about 5 Mbits/sec and will show the effects you are talking about, again in fast motion and rapid color changes. I think it's because the encoder only gets one guess at the pixel characteristics between key frames. FWIW it takes approx 1 hour to recode 1 hour. (This always gets the wife to inquire regarding blur) Sometimes the result approaches SD quality depending on content.

If I recode the original to MPEG4, 2 pass, HD720 the effects lessen because the encoder gets to look at more frames and make better guesses as to transition between key frames. This takes a loonnnnnggggg time on a dual core 2.8 Gz machine. I've never tried 4 pass which claims to be near accurate.

Recoding a lower bitrate MPEG2 to MPEG4 is useless since it's guessing at a guess.

Each process may or may not introduce AV synch issues but these can be fixed later.

I think the problem you see lies in transcoding and playing the stream. These type of issues seem to be common across every HD DVR platform I read about be it HDTivo, BTV, Sage, Mythbuntu. To be honest I'm not sure the technology is there yet to handle the process for any manufacturer. I somewhat base this on watching my cpu usage; recording is easy, transcoding and/or playing a good stream is tough.

If this helps and is OT, cool ..... if not delete it.


----------



## Stuart Sweet (Jun 19, 2006)

Thanks, all!

I should point out, again, that I see this with OTA, even with a direct line into the TV, so it's not a DIRECTV issue. Curt8403 had some suggestions for me, and I'm going to contact the chief engineers on the two worst offending stations.


----------



## groove93 (Jun 10, 2008)

New member here. I have the same issue with my OTA connection. I see it primarily during sports programming on ABC (out of Augusta, GA). For example, Indy 500 and NBA Playoffs, any form of Sports Statistics on screen for the respective programming followed by a camera change will produce a blur that will last 5 seconds or more. This is on my Sony Bravia 46 inch LCD. Recently I've been able to receive another ABC affiliate out of Savannah GA and this phenomena does not occur.

On the other Local HD stations I receive, the blurr happens for a split second. I would've not noticed it at first but now I can see it as a result of watching it on the ABC Augusta Affilate.

I have an HR21 HD DVR being shipped tomorrow but without an AM21 Tuner so I'm wondering if you guys with the Tuner are getting the same Blur effect.


----------



## Stuart Sweet (Jun 19, 2006)

Of course, I should know better... I'm moving this to the Broadcast/HDTV forum. Bad moderator! Bad! Bad!


----------



## Kansas Zephyr (Jun 30, 2007)

Do the stations you see this on have sub-channels?

If so, it may be the statmux dynamically changing the bit budget to support multiple streams.

It's also possible that reception/transmission issues between the network and local station can starve the bit rate.


----------



## gfrang (Aug 30, 2007)

What type tv's that everybody have that are having problems? 
Are the lcd if so what speed processor do they have 60 or 120 hz.
2 what back light to they have? florescent led?
3 What lighting conditions are you viewing the tv incandescent, florescent or natural?


----------



## Stuart Sweet (Jun 19, 2006)

One station has one subchannel (KABC) one has none (KTTV). 
The TV in which it is most noticeable is a Philips LCD, definitely not 120hz, most likely 60. Backlighting is surely fluorescent for what I paid for it. 

Lighting condtions vary from incandescent to CFL to natural.


----------



## gfrang (Aug 30, 2007)

Stuart Sweet said:


> One station has one subchannel (KABC) one has none (KTTV).
> The TV in which it is most noticeable is a Philips LCD, definitely not 120hz, most likely 60. Backlighting is surely fluorescent for what I paid for it.
> 
> Lighting condtions vary from incandescent to CFL to natural.


Ok rules that out.
How is tv hooked up Hdmi or Component?
Native or set to the resolution of the tv?


----------



## Stuart Sweet (Jun 19, 2006)

The problem occurs even when using a direct cable connection between the antenna and TV, but for the record my DVR is hooked up HDMI and is generally locked at 1080i, although I've seen the problem with native on as well. 

It's a funny thing, I have a 720p TV but in general the picture quality is still better with 1080i sources.


----------



## gfrang (Aug 30, 2007)

Does it happen when the channel changes resolution like if you are viewing a 720p 
and switch to a 1080i or vise versa?


----------



## gfrang (Aug 30, 2007)

Just checked both my tv's the only thing is i have noticed is with the back light sensor turned on and when i change channels i see it go from dark to lighter. I checked ota and Directv channels and asked Barb to see if she sees any thing i can't.


----------



## Stuart Sweet (Jun 19, 2006)

Cool. I really appreciate it. I suspect it's an issue at the broadcast end. KABC and KTTV were pretty early adopters of digital broadcasting and I wonder if their encoders are either aging poorly or just worse than the newer ones used by satcasters.


----------



## Tower Guy (Jul 27, 2005)

I see a similar issue on our local NBC station. The picture is soft for a fraction of a second whenever there is a scene change. The other stations are normal. 

I suspect that they have an MPEG preprocessor that intentionally softens the picture during scene changes or rapid motion. Such content would normally cause macroblocking (tiling). By softening the picture, the macroblocking never occurs, only the fleeting soft picture.

The station has two subchannels and is not using statistical multiplexing.


----------



## Scott in FL (Mar 18, 2008)

Not sure my comments will add anything, but here goes... I watch my locals OTA and via DTV and I have never noticed this. I used to work at the local CBS affiliate (up until 6 months ago) and was there when they went HD and through the period when they were ironing out all the bugs. I don't know what you are seeing, but it's odd that it affects some channels and not others.

Also, someone mentioned that OTA signals are not compressed. They are. During local origination (as in local news) the HD signal is compressed at the studio and sent to the transmitter to be transmitted over the air. You have to compress to get an HD signal in a 6 MHz slot.

The CBS network is received via satellite, and this feed is also compressed. So during network programming you have cascaded compression systems which can cause artifacts.

But again, I've never seen them on our local stations.


----------



## Jim5506 (Jun 7, 2004)

I have seen it especially on the Tonight Show when the whole scene changes and on The NBC Nightly News when the whole scene chenges, there is a very short time where the picture is slightly blocky then it sharpens.

I have chocked it up to the amount of time it takes for all the screen info to be downloaded and deciphered in the digital picture. this station runs 1080i and a second sub-channel at 480i.

One of thise little peeves with digital transmission that cannot be helped, I guess.


----------



## n3ntj (Dec 18, 2006)

Stuart Sweet said:


> So I'm hoping an engineer-type can answer this, and then we can talk properly about it, and if it's happened to you...
> 
> On some channels -- so far only locals for me, I get a weird phenomenon. It is almost as if the camera lens got very wet for a moment then dries. It's more than pixelation, it's the sort of out-of-focus-ness that you get when you're driving through the rain, then you drive under an overpass and everything's clear, then you get hit with "all that water" and everything blurs for a second before the wipers kick in.
> 
> ...


I can't say I've seen this phenomenon with my HR20-700. The only time I see anything like this is when watching Yankees games on MY9 (WWOR) as part of MLB EI, sometimes the top 'Fox Box' scoring box gets blurry for a few seconds. Very weird. It happens at least 3 or 4 times for each MY9 Yankees game. Doesn't happen with YES games.


----------



## Davenlr (Sep 16, 2006)

I just check out one of these using step frame on local NBC 1080i Olympic trials, Diver on the board after a moving NBC graphic scene transition. Took 4 frames after the pixellated graphic was completely off screen for the static picture of the diver to clear from fuzzy with random macroblocks to HD sharpness.

My guess: They are using variable bitrate compression at NBC (or the station), and #1, the peak bitrate is to low for fast moving scenes, and the processor takes 4 frames to lock on to the new scene. In any case, its very noticable on NBC sports, no subchannels. Not so much on CBS, one 480 subchannel, or Fox (no subchannels) here. I think if the source used enough bitrate, we would not see this.


----------

