Pixelated rendered video

vectorskink wrote on 1/4/2004, 3:07 PM

I don't know if anybody has experienced the same problem, but last night I rendered an edited holiday video out to a single avi file and found that a part of the video seemed very pixelated. The original footage looked perfect, but after it was rendered to PAL DV avi file using best settings, interlaced, with broadcast colors set to very conservative applied to entire project, there's one scene that is very pixelated. It looks like very low bitrate mpeg2, but it's DV!! The scene is some footage of the Daintree rainforest.
I have noticed this has happened to me a few times now. Is it some anomaly with the Sony DV codec?

Thanks in advance


farss wrote on 1/4/2004, 3:25 PM
just a guess here, are you certain it's not in the original footage?
It sounds like a head clog and the Daintree would be the place to get one. It may not be that noticeable in the original AVI, you might need to check it frame by frame. If it is a head clog you may also get a small glitch in the audio.

If it is what I think it is it's most likely recorded on the tape however it may have happened during playback, give the heads a clean and try again.
PeterWright wrote on 1/4/2004, 3:49 PM
You could try removing the Broadcast filter.
(Unless the camera is well out of whack, it shouldn't be necessary to apply this to DV video - it's more for graphics.)
lhotch wrote on 1/4/2004, 3:51 PM
I noticed the same thing, I had a friend render some video off my Canon GL2. Occassional pixel in replay, first thing I thought of were dirty heads so I cleaned them and recaptured DV and the same thing happened. I then pluged cam into TV inputs and played it back and it was perfect. On my firends system he has a base 80 gig EIDE disk with the OS (win XP) and a dedicated 160gig EIDE/ATA100 7200rpm with 8mb cache on a pentium 2.0ghz with 1 gig of ram so I wouldnt think it would be an issue with the PC itself.
vectorskink wrote on 1/4/2004, 4:33 PM
Thanks for the replies!

I have already checked the original - it's perfect, not a hint of pixelation, even frame by frame.
I have edited some footage in the past that hasn't had any filters applied and has done the same thing. The only thing in common with the current and previous footage is the content. Previous stuff I've filmed was our front garden, which is very rainforesty as well. Maybe the codec has issues with very 'busy' green content???? I'm wildly speculating here!! Has anyone else had issues rendering DV shot in rainforests?

PS. I took a close look at all my other footage shot in the rainforest (after rendering), and there is some very mild pixelation in them. Other rendered footage - perfect. Original footage is perfect - on tape and captured files.
PeterWright wrote on 1/4/2004, 6:58 PM
Did you try without the filter applied?

If you're using DV material and standard DV project settings, you should be able to capture and print back to tape without any change at all - it should just be copying the same information back and forth.
vectorskink wrote on 1/4/2004, 6:59 PM
Hi Guys

Just did some tests while I was at home for lunch....
I also had the HSL adjust plugin added to the main video track to punch the colours a little. When I removed the hsl adjust effect, the pixelation was almost gone! Removing Broadcast colours filter seemed to have no effect. Any ideas? Sony?
farss wrote on 1/4/2004, 7:48 PM
Have you done anything like pan and crop, i.e. adjust the frame size in anyway?

Can you give a clearer idea of what the pixelation looks like (roughly how big and what do they contain, just leading edge of moving things etc)?
I'm assuming you're using a DV camera of some kind and capturing via firewire.

It's just that it's a very odd problem, even stranger that the HSL FX had any effect on it, hmm, what are you monitoring on also?

vectorskink wrote on 1/4/2004, 9:21 PM
Hi farss

No panning/cropping. I have shot the footage on an Canon XM2, captured by firewire. I am monitoring to tv via Canopus ADVC-100. I have rendered to mpeg and burnt to DVD - the pixelation effect is still there.

The pixelation is rather large, just looks like very low bitrate mpeg - blocky. I'll get a screenshot or small sample happening.

I'm pretty disappointed about it. The rest of the video is fine. It just seems to have a problem with the rainforest shots with the HSL FX applied (saturation bumped up to 1.41)

farss wrote on 1/4/2004, 9:50 PM
Is it right through the entire shot or just a few frames?

If you cannot get it up on a web site somewhere you could email it to me at farssAToptusnetDOTcomDOTau, not that I have anyway to put it up anywhere but I'm really curious about this one.

I'll be out until late tonight so it might be a while before I can get back to you.
vectorskink wrote on 1/4/2004, 10:00 PM
Thanks heaps farss

I will send it to you tomorrow morning.
It happens for the whole clip - looks weird. But only on the green leafy rainforesty takes.
JJKizak wrote on 1/5/2004, 5:50 AM
My opinion: I got the same thing when I used SVHS or Digital when shooting "woods" or leafy trees. Problem is the low light in the woods causing the camera to open up everything to get the right amount of exposure and this is even evident on "Monday Night football" on certain low light shots into the stands from ground level. You can see the pixelation in all the dark areas. (This is with 100 grand High Definition cameras).The trick is to have enough light as the MPeg2 codec cannot handle pixelation and noise. Also do not use CBR. Use VBR at default. I have many comercial bought DVD's that have visable pixelation. Example: Magnificent Seven . When you apply the HSL or convolution or brightness and contrast filters you amplify the low light areas even more making it worse. This is evident even on PBS documentary programs on still pictures with the pixelated background which of course I can pick out faster than a New York minute.

lhotch wrote on 1/5/2004, 5:51 AM
Well, I think we got around our pixelation. It turned out that the"windows" screen saver was doing enough processing to mess things up. Friend did a recapture off my Cam last night with screen saver turned off and said captured video was clean. I will check it out after work tonight and see how it looks.
farss wrote on 1/5/2004, 6:09 AM
Great theory, pity the video in question isn't being mpeg encoded.
farss wrote on 1/5/2004, 6:19 AM
CPU speed, RAM, disk size and which phase the moon is in all have no effect on render quality period. They also have no effect on capture quality as there is no quality issues involved in capture. If things are too slow, frames will get dropped, I wouldn't even count that as a quality issue, just a bit of it got lost issue. Even when frames are dropped, what was captured will still be of no lower quality.

Pixelation due to head clog can be very hard to detect. On static shots it is very rare to see any, on shots with motion it's more noticeable. DV does have some error correction which may account for this. Also you need to check everything very carefully, is the device having trouble reading the data off the tape or was it written badly to start with or is it a guide / head alignment problem.
donp wrote on 1/5/2004, 6:48 AM
I have an issue which may not be related to the main line of this thread bit it involves pixelization. I capture via firewire from my TRV-350 into vegas and the capture looks fine. Then I place the captured clips on the time line and what appears in the preview monitor is pixelated at "auto" normal setting but when I set it to Full (720x480) it is clear and then I render to and put it on a DVD, it is clear there too, no pixelization. But the smaller window is really bad, at that point I cannot even reconize peoples faces until they areal close.
The problem just haoe it is presented in Vegas in the preview screen of the timeline. This doesn't cause any problem as the input and out put are fine, I was just wondering what may be causing this in Vegas.
lhotch wrote on 1/5/2004, 7:06 AM
If im not mistaken your problem is directly related to you video cards ability to handle the render.
JJKizak wrote on 1/5/2004, 7:38 AM
Sorry about the Mpeg thing.

vectorskink wrote on 1/5/2004, 1:58 PM
Hi guys

I have posted two clips on my website (2.7MB each). One raw clip and one with the HSL effect on it. I was mucking around some more with it last night and found that putting broadcast colours on it would also increase the artifacting and adding HSL seems to compound the problem.

I have two other short clips that I can email if anyone wants to check it out, just don't have enough room on my website...



The pixelation is best seen on an external monitor.
farss wrote on 1/5/2004, 2:07 PM
The video card has NO effect on the render and very little on how the preview will look. Vegas uses none of the smarts on the video card.
farss wrote on 1/5/2004, 11:28 PM
I've downloaded both clips into a project and cannot not see anything unusual in either of them, either on the internal or external monitor. There are a lot of DV artifacts, these look like marching ants on the upper edges of the branches and tree trunks. I'd expect them as you have a very abrupt shift in levels and diagonals make them really apparent. The total amount of detail in the frame also adds to the load on the encoder.

Maybe I'm looking at the wrong thing here, I've tried a few things to try to make anything else appear with no luck..
The only other thing I did notice is the levels are pretty hot. Wasn't causing me any issues but you could try adding the BC filter, Conservative template, and see if that helps, maybe either the D/A or monitor is being upset by the levels.

It maybe something else entirely, you've got a lot of motion with a lot of detail and close and distant objects in sharp focus, could it be some motion artifact? Do you see the same problem going through the clip frame by frame?
vectorskink wrote on 1/6/2004, 2:44 AM

On the HSL version, the BC filter is applied using very conservative. Yeah my XM2 does produce hot colours but a wanted a lush colourful look so I opted for HSL and then BC to clip the peaks. The non-HSL version is basically straight from the cam.

I'm annoyed that it didn't work for you. You ask if I can see the problem frame by frame, YES! Hard to see in preview window but very apparent on an external TV. Another way I do it is put the clips on separate tracks above and below each other and mute the top track on and off to see the difference on one frame. Either way I find it easy to see the artifacting, unfortunately.

Here are two more examples (same size as the other ones -2.73MB)

Daintree short2.avi

Daintree short2 HSL.avi

Take particular notice of the back of my wife's top where it creases mid back, also the lines of her upper arms. The artifacting is very noticeable there.

Thanks heaps for you time farss, I really appreciate it.
farss wrote on 1/6/2004, 4:30 AM
OK I've bought those two clips in.
I can see what you're talking about, much the same as what I saw in the other ones, at least now I know for certain what you're talking about! Sorry I thought you were talking about something about 30 pixels square.

On the top of the shoulder you've got a combination of things happening. Firstly there are interlace artifacts due to the motion, they'll look worse on the internal than the external monitor due to the internal monitor being progressive scan.
Secondly I'd say there's some typical DV compression artifacts, not much you can do about them. Add to that at one point the angle of the shoulder is almost horizontal, so it drops from one scan line to the next giving a jagged edge. Again that's video.
Thirdly, there's a big energy transition there, from the light reflected off the skin to the background. This will perhaps look much worse on an external monitor than an internal one, particularly if the external one is fed via a composite signal. This can happen even though the levels are within broadcast legal range. You can test this out on your rig, try white text on a black background, apply BC filter just the same and see how really bad it looks!

Getting back though to this clip, it looks like the top edge of the shoulder is still outside BC legal, have a look on the histgrams. This usually isn't too mcuh of a problem but here where you've got a sudden drop from superwhite to a very low level might be screwing things up for you.

What to do?

Try a few things. Firstly color curves, change the curve to just pull the highs back a bit, that'll reduce the level jump without upsetting everything else. Should make the shot look better, even though you've made the colors richer with HSL the eye is being distracted by the hot spots.
Secondly a LITTLE bit of motion blur might be in order. Again that'll smooth things out around the moving edges.
Thirdly. When I run the clip at normal speed it doesn't look THAT bad, even on an external monitor! There are things there that don't help the medium and even with the best cameras money can buy if it was a staged shot a lot of effort would go into getting the lighting levels kinder to the medium.

You can spend a lot of time in this game fretting over things that no one else will notice and missing things everyone else sees straight away.

Having said all that, one last thing to try and this is really way out there. Right click the original clip and tick "reduce interlace flicker" and rerender. I'll be pretty amazed if it makes a shred of difference but I've had it fix some really odd problems although they were real problems, the 30 pixel square kind of problems.

One thing I have noticed with Cannon cameras, they have very good lenses, in these kinds of situations that seems to make DV look a little worse.
vectorskink wrote on 1/6/2004, 1:56 PM
Thanks heaps farss for your reply

Are you saying that the artifacts the I'm getting is caused by the recompression after the application of the FX, and the codec not handling it well?
It must be that as I was mucking around with some beach scenes last night and there's no artifacting at all after the same FX were applied. The codec seems to struggle with rainforesty type shots - high contrast and very 'busy' with leaves etc. I think more care will be needed when shooting future rainforest or similar scenes. Although it seems funny that the artifacting is also happening on the back of my wife's shirt?

What do you think?
Aan wrote on 3/23/2004, 6:43 PM
That is so funny , I have exactly same probplem ,but opposite of your , Mine pixelated at big screen previews and fine when small screen.