Using Pan/Crop as a digital zoom

[Gregory Lee]

I thought I would try using the pan/crop feature in Vegas as a digital zoom but I found this compromises picture quality even though I'm shooting on 60i 1920x1080 but outputting to 720x480 DVD.

- I imported the video onto the timeline with HD 1920x1080 video properties. I then, cropped the picture to 720x480
- If I render this cropped image to HD or DVD resolution video, I find that the picture quality is poor. Noticeably poorer than video which is not cropped but rendered to DVD resolution. Why is this? I would have thought that starting with HD resolution and cropping to DVD resolution should produce the same image quality as simply rendering as DVD quality without any cropping.

Is there a way to digitally crop HD video and not go below DVD resolution?

[Leslie Wand]

you need sd project properties

[Gregory Lee]

I tried doing the same thing with SD Properties and still the same problem.

[Leslie Wand]

interestingly enough i just asked pretty much the same question over on scs -the reply from one of the guru's there was:

the math says you can zoom sqrt[(1920x1080)/(720x480)] or a linear zoom factor of 2.45x without loss. That's quite a good number.

just tested it out here (pal 1440*1080/50i>720*576) works fine......

exactly how much are you 'zooming' in?

[Gregory Lee]

I'm zooming in about 800x400 (approximately, I don't remember the exact numbers) and I'm maintaining the aspect ratio. So it's weird that I'm seeing such a loss in picture quality.

[Mike Kujbida]

I'm working on an edit where I'm regularly zooming/cropping from NTSC 1440 x 1080/60i to 720 x 540 with no loss at all.
My suspicion is that you've gone past the limit since you said you're at 800 x 400.
Double check that because, if you're keeping your aspect ratio as you said, they don't sound right.
Keep 720 x 480 in mind, don't go smaller than either of these two numbers and you should be ok.

[Gregory Lee]

Here is a videoclip showing the issue I have. The project property settings are NTSC DV widescreen 720x480. Pixel aspect ratio is 1.2121

The imported video was AVCHD 1920x1080 60i, and it was rendered as a NTSC DV 720x480.

The 'digital zoom' is done in Vegas with the crop feature.

http://www.gregorylee.org/temp/Wynnewood/test.mpg

[Gregory Lee]

This time, I cropped to 720x480, but I could not 'lock' the aspect ratio from the original 1920x1080.

Still looks fuzzy.

http://www.gregorylee.org/temp/Wynnewood/test2.mpg

[Mike Kujbida]

Have you done a test with "normal" video instead of a test chart?

I see a few things working against you in these tests.
First of all, you're shooting a test chart that isn't framed exactly square to the camera and doesn't appear to be properly lit.
Second, that particular chart isn't designed to be zoomed in on.
Third, you're rendering to MPEG-2, a compressed format, which means even more quality loss.
Last, make sure that neither number in your cropped video is smaller than 720 or 480.

[Edward Troxel]

Are you sure you're using Pan/Crop and not Track Motion? Pan/Crop will use the full resolution of the image as you zoom in. Track Motion will not.

[Gregory Lee]

Originally Posted by Mike Kujbida

Have you done a test with "normal" video instead of a test chart?

I see a few things working against you in these tests.
First of all, you're shooting a test chart that isn't framed exactly square to the camera and doesn't appear to be properly lit.
Second, that particular chart isn't designed to be zoomed in on.
Third, you're rendering to MPEG-2, a compressed format, which means even more quality loss.
Last, make sure that neither number in your cropped video is smaller than 720 or 480.

I did a lot of experimenting and I used the chart again in better light and framed square to the camera (the first clip is a little crooked, sorry), which I put on a tripod. The camera is a HMC-150 at 21mbps AVCHD. In fact I'm beginning to think my source footage is the problem, so I've uploaded the raw footage here. Both are very short clips shot in 1920x1080, 60i. In the first clip the chart fills the entire frame, in the 2nd clip, the chart fills a smaller part of the frame and you can use Vegas to pan/crop. I know the chart isn't necessarily accurate, but I'm using it more as a point of comparison. If you can try the same thing I did (use pan/crop to zoom in, and compare the two pictures when outputted to SD), I'm curious if you also notice a difference in quality.

http://www.gregorylee.org/temp/Wynnewood/00016.MTS

http://www.gregorylee.org/temp/Wynnewood/00021.MTS

[Leslie Wand]

well, and this is not meant offensively:

a. the sample chart is crap in the first place - not only does your camera obviously lack resolution in the first place, but it's still not lit / squared up correctly.

b. crap in, crap out - but still testing it out i see no 'problems' at all other than those caused by a. above

try some live footage - obviously the problem (if there is one) is at your end since doing as directed (p/c) works perfectly well for the majority of us.

btw. why not simply dl a high res test chart and try experimenting on that?

[Gregory Lee]

I had issues with live footage originally actually. So here it is:

http://www.gregorylee.org/temp/Wynne...utdoortest.wmv

The first few seconds shows the crop/pan at 874x492; then cuts to the unaltered footage.
I outputted to .wmv (3mbps); still compressed but I couldn't find the uncompressed render option.

Here are the two raw files:
http://www.gregorylee.org/temp/Wynnewood/00038.MTS
http://www.gregorylee.org/temp/Wynnewood/00039.MTS

[David Jimerson]

Keep in mind that when you zoom in, it will be apparently lower-resolution than the footage you don't zoom in on. Even if it ends up as bona-fide verifiable SD-resolution footage, it will still look less sharp and lower-quality than the surrounding footage -- even if you render the entire project as 720x480.

[Gregory Lee]

Are you talking about optical zoom? Funny thing is that the optical zoom is sharper than the digital zoom.