Nasty artifacts with AVI render

Tech Diver wrote on 5/16/2006, 9:53 AM
Until now I have not noticed that Vegas is producing some pretty nasty rendering errors that are best revealed under the following circumstances:

Set your project to NTSC DV. Create some text with the Text Media Generator (font, size, effect does not matter). Make the text one pure color (say blue 255) and the background any other color (try red 255). Now render as an AVI with the NTSC DV setting.

Notice how there are small Vertical lines or tears at various locations of the text. If this same file is rendered as and AVI with the Uncompressed setting, there are no artifacts. However the video image is wider and circles are now oval. This most definitely has to do with 0.9091 multiplier that is applied to the first rendering and is independent of the interlace setting. This artifact problem is also very visible when rendering a circular ring that is either red, blue, or green.

I would be interested to know if others are able to reproduce this, and if so, is there any workaround.

Comments

winrockpost wrote on 5/16/2006, 12:00 PM
i think it is a feature of dv,
5:1 compression
Tech Diver wrote on 5/16/2006, 1:09 PM
Have you actually tried the example I gave? I understand that compression is a lossy proceedure, but these artifacts go far beyond what I believe is acceptable. I'm talking about spikes coming out of the bottom of text stings and not little ones either.
winrockpost wrote on 5/16/2006, 1:14 PM
yeah, its nasty ,its a dv thing with the solid colors,, someone smarter than be me can explain,, not at my edit system ,so I cant preview on an external monitor,, but looks totally horrible on the puter screen.
rs170a wrote on 5/16/2006, 1:21 PM
...is there any workaround.

Stick to proper NTSC (or PAL) maximum levels and things should look a bit better. Using extreme levels (red or blue at 255) is just asking for all kinds of trouble.
If you want to know the levels you should never exceed, throw the colour bar signal up on the Vegas timeline and see what the RGB values for each colour are. You'll be surprised that they are as low as they are.

Mike
Tech Diver wrote on 5/16/2006, 1:28 PM
I'll tone down the color levels a bit and turn up some other channels so its not just R, G, or B alone. Thanks.
rmack350 wrote on 5/16/2006, 2:10 PM
Still, DV is horrible when it comes to titles and graphics. The color is only sampled every fourth pixel. It is averaged for the three pixels in between samples. That is the primary problem you're seeing. Using color values that are too hot just makes it worse. Top the values out at 235.

Don't know what's up with you're uncompressed renders. They should be done at the same PAR.

Rob Mack
John_Cline wrote on 5/16/2006, 2:28 PM
Well, basically any highly saturated color for text on a highly saturated solid color background will give DV fits. Remember, it's 4:1:1, which means that there horizontally there are 720 luminance samples but only 180 samples for color. You might also try adding just a hint of noise to the text and/or the background.

John
rs170a wrote on 5/16/2006, 2:57 PM
And here are two excellent articles about dealing the DV "nasties" and why the format is so bad.

Great Titles with the DV codec.

4:2:2 vs. 4:1:1 vs. 4:2:0.

Mike
johnmeyer wrote on 5/16/2006, 5:17 PM
There have been at least two VERY long threads about this subject in the past eighteen months. I don't have time to do a search now, but you should be able to find it if you search a little.

Bottom line, it is a known issue with DV, and not a problem specific to Vegas. You will only see the really nasty artifacts under fairly extreme circumstance, most likely not occurring in most video.

Tech Diver wrote on 5/16/2006, 5:44 PM
OK, After some reading I now have a much better understanding of the AVI sampling issue with regard to compression. However, there seems to be another issue which may be a genuine bug:

When I render with AVI Uncompressed, the PAR is ALWAYS 1.000 regardless of what setting I enter. The dialog box does accept the value and it remains persistent even if I exit and reopen it, but it completely ignores it.
rmack350 wrote on 5/16/2006, 6:30 PM
I've never seen that happen. That's not to say it isn't happening, just not on my system. My guess is that there's something up with your setup rather than a Vegas bug.

Rob Mack
Marco. wrote on 5/16/2006, 11:33 PM
Take a look at the field order. Render an uncompressed AVI and have it set to lower field first. But the render result is upper field first (at least on PAL systems).

Marco
rmack350 wrote on 5/17/2006, 9:03 AM
Ah. I see that. Both the uncompressed and the Sony YUV formats become upper field first no matter what. It matches the PAL Standard template but it looka like it's impossible to match the PAL DV template.

So which one are the PAL people supposed to be using?

Rob
Tech Diver wrote on 5/17/2006, 12:54 PM
After trying dozens of combinations of project PARs with AVI rendering PARs I have come to realize that my "problem" had to do with whether or not the "Maintain aspect ratio" box was checked in each of the media properties. Since it was not checked, the media was stretched regardless of my render setting.

Before this, I thought I understood how PAR works since everything I worked with was 0.9091 and never bothered measuring the roundness of circles. Now I am confused (as apparently are some other folks based on the number of threads on the topic). If someone has a good explanation somewhere specific to Vegas (or is willing to write one) I'm sure it would be welcomed by quite a few.
farss wrote on 5/17/2006, 2:07 PM
1) Most video with the exception of DV25 is Upper Field First. Just why the video gods made DV25 LFF I don't know.

2) The problem with very nasty vertical tearing is a preview only problem that's way more noticable with PAL than NTSC.
In PAL if you select Simulate Aspect Ratio for the preview window the result is pretty horrid even at Best / Full. If you turn off simulate Aspect Ratio you'll get to see the video without the nasty tearing but at 1.0 PAR. The reverse seems to apply for NTSC. This is a BUG.
However it has no effect on final render and video looks fine when sent to external preview devices including using the second monitor as a preview device.

Nonetheless it should be fixed. Most of the world uses PAL and having clients see video with nasty vertical tearing does little to enhance the image of Vegas. There are situations where running preview out to external or secondary monitors is not practical.

Bob.
Spot|DSE wrote on 5/17/2006, 2:15 PM
Aspect ratio and the field order aren't necessarily related, I didn't read all the thread, but in short, if it's a DV project in Vegas, then graphics should be 655 x 480 in NTSC, and 768 x 576 in PAL.
As Bob mentioned, you can see the square value if you turn off Simultate Device Aspect Ratio.
But in reading the thread, it meanders from 4:1:1 compression artifacts to interlace vs progressive and now aspect ratios. All are very different subjects. Not sure which one keyed in on your problem and either fixed it or frustrated it.
Marco. wrote on 5/17/2006, 2:51 PM
>> 1) Most video with the exception of DV25 is Upper Field First.

That's right. But if I render a video with the render property set to Lower Field it shoulb become Lower Field then, no matter what it normaly is. If I render a DV file with render property Upper Field it will become Upper Field though DV is always Lower Field.
On the other hand - Lower Field First is part of the standard render template given for uncompressed AVIs so I asume this should be correct.
And there are even some kine of DV files - which are Lower Field for sure - of which Vegas says it's Upper Field.

So to me it's likely more kind of a bug if an uncompressed AVI which was definetely rendered to Lower Field is said to be Upper Field later.

Marco
Tech Diver wrote on 5/17/2006, 3:07 PM
Yes, this thread does meander. Sorry about that, but one issue led to another in my search for a solution. As it stands:

1. I now understand that the AVI artifacts were caused by the 4:1:1 sampling method and not related to PAR of 0.9091 vs 1.0000, which I was experimenting with when I rendered AVI uncompressed. Issue closed.

2. I thought that I had a problem with AVI rendering ignoring my PAR values but discovered that I had "Maintain aspect ratio" unchecked in my media and the image always rendered the same. Issue closed.

3. I became confused about PAR when I rendered circular objects and found they were elliptical when I viewed the AVI files. I just validated that when part of a DVD compilation, these elliptical objects appear circular and are therefore correct. Issue closed.

Sorry to have belabored this thread but I did learn and discover issues that were not clear to me before. Thanks to all.