Cropping causes interlacing

Angus wrote on 11/15/2003, 2:26 PM
I have Vegas 4.0d. I have this uncompressed AVI. I'm trying to crop the bottom 3 or 4 lines, and output another uncompressed AVI, but when I do, it interlaces. I can't image why. All I'm doing is using the Event Pan/Crop tool. I'm not resizing the image, that is, the height of the output is however many lines less of what I'm cropping. I was hoping to have the exact same output as the input, minus the lower few lines. Why can't I do that?
BTW, when I playback nothing is being streteched or anything. The input doesn't interlace at all. Why does the output?

Comments

farss wrote on 11/15/2003, 3:20 PM
Can you provide a bit more infomation?
I don't understand what you mean by 'the input doesn't interlace' as pretty much all video is interlaced.
When you say you are trying to remove the bottom few lines do you still want to end up with the same number of lines in the output i.e. replace the bottom few lines with say black or do you wish to remove a few lines and strecth the remaining ones into the same size frame.
SonyEPM wrote on 11/15/2003, 3:31 PM
Try unchecking "stretch to fill frame" in the pan/crop window.
Angus wrote on 11/15/2003, 4:28 PM
I'm looking in the window, and I don't see any such check box.
Angus wrote on 11/15/2003, 4:31 PM
When I playback the original, I don't see the interlacing during fast motion. This is an effect that only exists in the cropped outputs Vegas produces. I've tried saving w/out cropping, and it doesn't interlace.
When I say I want to remove the bottom few lines, I don't mean I want them replaced, I mean I want them gone. That's why I said the height of the output should be less those number of lines.
JL wrote on 11/15/2003, 5:40 PM
Look a little harder for the 'Stretch to fill frame' check box in the Event Pan/Crop window and uncheck as SonyEPM suggests. This should give you the output height you want.

Try pre-rendering one of the cropped sections to see if the "interlacing" problem goes away. The playback frame rate typically drops below 29.97 frames per second during preview of sections with video effects added which lowers the preview quality. Pre-rendering will allow the preview to playback at the full rate.
farss wrote on 11/15/2003, 5:45 PM
Angus,
do I understand you right?
You want to take say 720x576 and end up with 720x572 frame size?
Just curious as to why.
Angus wrote on 11/15/2003, 7:16 PM
I don't know what to tell you, I just don't see it. Are we talking about Tools|Video|Video Event Pan/Crop...? In Vegas 4.0d? I see a number of unlabeled buttons on the bottom and left, with popup tips. None of these popups say anything close to "Stretch to fill frame". I know I've seen that string, however, I just don't remember where.
And to answer Farss's question, he's quite right. To be precise I'm trying to crop the bottom few lines off of 320x240. I'm doing this because the analogue equipment I captured from produced this line of flickering garbage at the bottom of the image. I want to get rid of it.
bowman01 wrote on 11/15/2003, 7:19 PM
Try using the super-sampling, check the help file to learn how to use it, i've had this problem before and used this and seems to help. Takes longer to render this bit though.
JL wrote on 11/15/2003, 7:30 PM
You might have to expand the Event Pan/Crop window to be able to see the two check boxes under 'Source'. It's there. Really.
Angus wrote on 11/15/2003, 7:53 PM
How right you are. I dragged the window bigger, and it revealed the stretch checkbox and the aspect ratio checkbox. I unchecked them both. That didn't work, so I 2nd guessed my decision to uncheck the maintain aspect ratio. That didn't work either. It doesn't seem to clear up the problem at all.
JL wrote on 11/15/2003, 8:03 PM
I guess I don't understand which problem you are referring to as not being cleared up. Have you actually cropped the image to remove the offending bottom lines? You might want to check to see that the effect is keyframed over the portion of video you intended to be cropped.
TimmyRaa wrote on 11/15/2003, 8:20 PM
I've had a similar sounding problem I think; I've got some 4:3 camera output, that I'm cropping down to 16:9 widescreen, and when it plays back, I get horrendous horizontal lines during motion, that look like interlacing problems. I should also note that I don't get this problem on the original 16:9 camera footage, that I had during the same shoot.

See here for screenshot of the problem - http://www.timspence.co.uk/weddingjerkyness.jpg

Is it the same as your problem?
Angus wrote on 11/15/2003, 8:35 PM
Yes, I've cropped the image, whose size was 320x240, and it is now, 320x237. The centre moved up to 118. The offending lines have disappeared, but the new interlace lines persist. As far as the keyframe goes, that isn't it. Anyway, if this cropping didn't affect the whole movie, the unaffected parts wouldn't be interlacing, since removing the cropping removes the interlacing.

Timmy: yes, that sounds exactly like my problem.
TheHappyFriar wrote on 11/15/2003, 8:56 PM
The checkbox is in the render window. It's under the filetype box.

well, it SHOULD be. :)
JL wrote on 11/15/2003, 9:35 PM
Just a thought - if you will be viewing the final production on a TV set (rather than computer monitor), some of the bottom lines (as well as top and sides) will be cut off anyway and the offending lines may not show even with no cropping. You could check this if you are able to preview to an external monitor, or you could also check 'safe areas'.
Angus wrote on 11/15/2003, 10:15 PM
Some TV Out drivers cut off portions and others don't. Either way, I want to have to good on any display. Does this mean you are out of ideas?
BillyBoy wrote on 11/15/2003, 10:29 PM
A few assumptions...

If you have noise at the bottom of the frame, it more than likely will fall in the overscan area and not be visible when viewed on a TV. If it still does or your final output isn't TV, a quick fix is click on Pan/Crop.

IN THE WORK AREA of Pan/Crop begin by clicking the first icon and changing zoom to 50% or greater so you can see what you're doing better. It has no effect on the frame size.

Now right click on the image within the work area. Pick match output aspect. The image should jump to fill the frame. That by itself may get rid of the few troublesome lines at the bottom. If not, drag a corner handle in towards the center. That will zoom in. Just a nudge is all you need for this kind of problem.
Angus wrote on 11/16/2003, 1:52 PM
It did get rid of the lines at the bottom, but it still caused the same problem as it always has, which is the interlacing. Not only that, it cut out parts of the sides, which were never a problem.
This problem is too weird. How hard can it be to render an uncompressed movie w/the bottom few lines removed, and the rest exactly the same?
JL wrote on 11/16/2003, 5:44 PM
Angus – sorry but I have not encountered what you are describing; but then I normally edit in NTSC DV. I tried unsuccessfully to recreate your problem using 320x240 template and media. Your media is progressive scan (non-interlaced) 15fps right? Did you confirm that it’s a problem in the rendered video and is not just a preview anomaly? Just out of curiosity, did you use Vegas for video capture?

As far as using pan/crop, if you de-select the lock aspect ratio button (left side - middle in the pan/crop window) you can just grab the lower edge of the frame and push it up to shorten the frame height without changing the frame width - if I'm understanding what you are trying to do.
Angus wrote on 11/16/2003, 5:51 PM
Actually I solved the problem by changing the "field order" from "lower field" to "none (progressive scan)" whatever that means. I was just coming back to report the good news. The image looks pretty good so far, but I'm wondering just how pure the output is. As I mentioned, I wanted the output to be exactly the same as the input, minus the bottom 3 lines. If the 237 lines are purely identical to those in the input, then I would expect the rendering to go much faster (it seems to take about 130% the time to render as it does to playback) and the CPU usage is very high.

JL wrote on 11/16/2003, 6:04 PM
Rendering could take longer if Pan/crop causes Vegas to re-render each frame that it is applied to, similar to adding video effects, velocity envelope or changing opacity level. Render speed is related to CPU horsepower.

Update: A quick test on my computer showed the same render times for a clip with 320x240 frames and the same clip cropped to 320x237 (render time was 35 seconds for each 1.5 minute clip - uncompressed, 15fps progressive). Also, the rendered file size was exactly the same for each. So yes, there must be something else going on in your case.
Angus wrote on 11/16/2003, 7:57 PM
But there must be other effects being applied. The output file (remember, we are dealing w/uncompressed input and output) is 50% larger than the input. Some of that increase is due to the increase in keyframes, however only 1% of the frames in the input are delta frames.
TimmyRaa wrote on 11/17/2003, 5:46 AM
After your suggestions, I tried rendering to MPEG2, but also changed it to progressive scan rather than interlaced. My issue has also disappeared.

My original basis was on rendered PAL DV video output, which I'm guessing probably isn't interlaced by default, and this looked fine. Whenever I try rendering to something other than DV, it interlaced it, and I let it - as my final output will be viewed on PAL TVs. Now I'm rendering to MPEG2 for a DVD, but in progressive scan, I'm hoping this will still look okay on TVs. Can anyone advise on this??
farss wrote on 11/17/2003, 7:26 AM
Well TVs are pretty well always interlaced.

Seems to me something is seriously amiss here.

If source material is interlaced and is displayed on a progressvie device you will get interlace artifacts, that's just the way it is. PCs display progressive so you'll always get interlace artifacts with interalced sources. There are ways to convert to progessive buy something has to give, usually your going to loose resolution. The very smart boxes and / or software may use motion tracking to minimise the artifacts or else merge the fields where there is no motion and ditch every second one where there is and build new lines by interpolation.

Anyway I can't see what your original issue was, don't really know what your source was either so I'm kind of stabbing in the dark a bit .

But in summary. PAL and NTSC DV or anything else is always interlaced.
It may not have been shot interlaced ie it was progrssive, say from film, but it still gets interlaced, no choice. If you want to print to tape it must be interlaced again no choice. Also though if its kept progressive through the whole chain the interlacing just doesn't matter really.