PAL DV black edges & snapshot questions

jdmh wrote on 4/18/2003, 6:45 PM
A couple of questions:

1) When I capture PAL DV footage from Camcorder, I seem to get black around the edges of the image. It's not particularly noticeable, but I happened to notice it when looking at a clip that had been cropped (colour out to the edge of the display) versus a clip that hadn't (a small black frame - wider at the sides than at the top and bottom). Is this "correct" behaviour? Or is there a problem in Vegas or my Camcorder? I don't have any other capture utilities or camcorders to compare against so haven't been able to test if this is standard behaviour, but it doesn't seem right.

2) When snapshotting PAL DV frames (with the "Best (Full)" video preview setting), I'm getting images that are 786x576 instead of the expected 720x586. So I figured Vegas was doing something with pixel aspect ration so I changed this to 1 instead of 1.0926 in the project properties. When I then did a snapshot I did get the expected 720x586 image size, but there were bands of null pixels at the top and bottom of the image (approx 24 or 25 null lines both at the top and bottom). Can anyone tell me what is going on? I actually want to be able to export a series of frames and reimport them without introducing resampling artifacts (eg. I want to be able to export and reimport frames without changing the data).

Explanations greatly appreciated!

David

Comments

SonyDennis wrote on 4/22/2003, 6:23 PM
1) Many cameras produce black pixels on the left and right edges of the image.

2) You must have had the Video Preview set to "Simulate Device Aspect Ratio" so it stretched the 720x576 to 786x576 so it looked right. If you don't want that, then turn off the switch. Changing media or project pixel aspect ratios isn't the solution. If you place clips on the timeline and just do cuts (no FX, transitions, compositing, etc) and then render, you will get zero loss copies, as you wanted.

///d@
jdmh wrote on 5/26/2003, 4:57 AM
1) Thanks, this is handy to know :-)

2) I've tried turning off the "Simulate Device Aspect Ratio" switch (by right-mousing on the image and selecting the option) but it makes no difference. The snapshotted image is 786x576 in both cases (but I am expecting 720x576). Am I doing something stupid?

(Am using Vegas 4.0c).

Thanks!

David
josaver wrote on 5/26/2003, 5:27 AM
DV is a "pseudo-stretched format". The pixels are not squared. When you make a still without correction you see the still a little stretched , on a graphical software, like photoshop. The correct aspect ratio for stills is 787x576 for PAL.

Non DV PAL formats are squared pixels and the aspect ratio is 768x576.

You see the difference with the simulate aspect ratio on the preview window? Is there where you must switch the aspect ratio. Your project must have the default PAL DV settings to work correctly with PAL DV footage. If not, you have some recompression.

PAL DV is:

-bottom field first,
-25 fps,
-Pixel aspect ratio 1.0926,
-720x576 pixels

Black edges are a "feature" of some cameras. There is not a problem on a normal TV set. Only could be a little problem when you make a PIP. But with Vegas you can make a Pan/crop and the black bars disapear.


Josaver.

Sorrry for my bad, very bad english.
jdmh wrote on 5/26/2003, 6:55 PM
Yes, I can see the difference with "Simulate Device Aspect Ratio" turned on or off, and my project settings seem correct.

The problem is that I want to snapshot a frame at the original (unresampled) 720x576 size. But whenever I take a snapshot and look at it in Paint Shop Pro, the dimensions are 786x576 rather than 720x576 (the size I'd expect for a snapshot of the frame that hasn't had the aspect ratio corrected). This occurs even with "Simulate Device Aspect Ratio" turned off.

The reason I want to do this is so I can export a frame, touch it up, and bring it back into the project without introducing any resampling artifacts.

Any other ideas how I might do this?

Thanks!

David

PS Your english seems pretty good to me :-)