AVI: NTSC DV vs. "Uncompressed"

gogiants wrote on 9/26/2003, 5:14 PM
In playing around with different options for rendering to AVI, I came across something that made me curious.

In the "Make Movie - Render Settings" dialog, if one chooses Video for Windows (*.avi), you can then choose from different templates.

One template is NTSC DV, which shows a resolution of 720x480, which I understand. But another choice is "Default Template (Uncompressed)". This shows a resolution of 720x480x32. The predicted file size for the "Uncompressed" template is huge, some 10+ times as big as NTSC DV.

So, my questions:

1) I thought .avi for NTSC DV was uncompressed. It is, right?
2) What, then, is the "uncompressed" flavor of AVI? In particular, what does a resolution of 720x480x32 (especially the x32 part) mean? Are there 3D holographic TVs out there that I'm missing out on? What would the "uncompressed" AVI format ever be used for?

Thanks!

Comments

rdwhitehill wrote on 9/26/2003, 8:03 PM
Hi,
Having worked with VF with school students and staff for about 2 years, I note that there is a slight but noticable difference in the video quality of compressed vs. uncompressed AVI files when viewed on a computer monitor via Win Media Player or some other viewer.
However, when printing to DV tape via FireWire, I note absolutely no visible difference whatsoever. Both look fantastic on tape.
Back to the computer video monitor/LCD porjector viewing... I have found that performance settings in WMP, the quality of the monitor/projector and speed/memory/design of the graphics adapter have more to do with the image quality than whether or not one uses uncompressed AVI.
Bottom line: If one needs *perfect* video, then Vegas and a hot PC should be used instead, period. If one is choosing to use a good general-purpose PC and VF/MovieStudio, then NTSC (aka compressed) AVI is just fine. When printing to tape, then it doesn't seem to matter.
Hope this helps.
Doug Whitehill
Ted_H wrote on 9/26/2003, 8:46 PM
Technically, NTSC DV AVI is compressed. However, it's hard to tell just by looking at it. Uncompressed AVI is about five times the size of NTSC DV, and your video has to be NTSC DV in order for a DV camera to recognize it. BTW - Windows Media Player previews DV compressed video at half-size by default which might explain why you were able to notice a difference. There's a preference somewhere in Windows Media Player that allows you to change this.

Ted
JohnnyRoy wrote on 9/26/2003, 9:32 PM
Bill,

As others have suggested NTSC DV is compressed at about a ration of 5:1. The resolution is 720x480x24. Uncompressed AVI is mostly needed when you need to carry an alpha channel which is 720x480x32. This extra 8 bits carries the alpha information which determines the transparency of the background. You might also want to use uncompressed video when exporting to another program for processing and don’t want to recompress the video more than once.

For example: if you were to create a spinning graphic title in Ulead Cool 3D and wanted to save it with the background being transparent, you would save it as uncompressed in 32 bit depth so the alpha information is preserved. Then when you bring it into MovieStudio and drop it on an overlay track, the background would disappear and the graphic would float on top of the video below it.

I would not recommend using uncompressed video for a whole project to get higher quality because you’re eyes will not see the difference between that and DV at 5:1 compression. By comparison, most digital cameras use 10:1 compression on their images. So 5:1 is very light compression and the Sony DV codec re-compresses with amazing quality.

~jr