853x480 with 1.1850 or 1.2121?

groovedude wrote on 4/30/2004, 10:04 AM

I'm sorry, I really hate to beat a dead horse but I'm trying to get a good understanding of project setups.

I work with square pixel image sequences going out to 16:9 animorphic Mpg2 DVD. From what I've surmised I'm to create my images at 853x480 (or any 16x9) and squish to 720x480, then set up a 1.2121 project and select 1.2121 on my images property settings. Rendering out as Widescreen 1.2121 with 16:9 selected under video tab.

I assumed I would get the same result doing the above but just using the 853x480 images and selecting 1.000 (sqaure px) in the image property settings. Thinking Vegas interpolates the image saving me from having to run my images through a batch in Photoshop to squish down to 720x480. But in the Preview window I see a sliver of black on each side of the image. Whereas doing the above fills the frame. However, I've found that if I am using a 853x480 sq px images and set the project aspect manually to 1.1850 it will fill frame. And yes, I always have the preview window set to view project aspect. And in both cases the image is set to maintain apect ratio under properties.

Am I in danger of playback errors or DVDA incompatiblity setting the project apsect settings to 1.1850?

Also, I understand for Widescreen we are suppose to use the 1.2121 setting, I just don't understand where that number is coming from.

Comments

planders wrote on 4/30/2004, 1:49 PM

I haven't done anything with widescreen but just completed a big video slideshow presentation. What you're trying to do is ensure that circles stay circular and squares remain square when shown at a non-square aspect ratio.

The factor for non-widescreen images is 0.9091, or 0.9091:1. Thus, pixels are a bit narrower than they are tall (width is ~91% of the height). Multiply 720 by 0.9091 and you get just shy of 655 pixels.

So, for non-widescreen images, the frame size using square pixels is 655x480; when you add that to a DV timeline it automatically is scaled to 720x480 and the aspect ratio is corrected.

In your case, (assuming 853x480 is the correct frame size), you shouldn't have to do anything. Create your image at that resolution and drop it on the timeline.

Interestingly, for my big slideshow I didn't even have to go to that much trouble: Vegas took my square-pixel images and automatically adjusted them correctly, simply by dragging them onto the timeline. I haven't done a project like this recently and can't remember if older versions of Vegas handled this automatically, but it was pretty neat.

The easiest way to create stills now is probably to use Photoshop CS and its DV presets--complete with aspect ratio correction and safe area guides. All you have to do is select the correct (DV) pixel aspect ratio in the event properties in Vegas and it works perfectly.

rmack350 wrote on 5/1/2004, 12:17 AM

GD,

There's "what to do" and then there's "why you do it". Let's start with the first.

Vegas is likely to be dealing with images a little differently than you expect, especially if you've gotten all your info from the manuals of other NLEs. The first thing to know is that with any NLE, if you follow their instructions about dealing with stills then everything will work out in their program.

So here's the deal with Vegas:
1. It's designed to accept pictures with a 1.0 pixel aspect ratio. It'll do all the stretching or squashing.
2. When using the NTSC DV Widescreen project template, Vegas assumes that your uncorrected stills will be some multiple of 872x480. Not 853x480. (There's a good reason for this, it has to do with the way the Vegas programmers are doing their math and, by the way, they're right)
3. If you crop all your stills to a multiple of these dimensions they'll fill the frame. It's all you have to do. Don't bother resizing.
4. If you don't want to crop the images you can just put them into the timeline and then use the pan/crop tool to "match aspect". Look around the forum if you aren't already familiar with this.
5. When you drop images onto the timeline, Vegas sizes them to fit in the frame-not to fill the frame. So if the image isn't the right proportion Vegas will always show black at the short edges.

The "Why" part is a little sticky. I'm a little more comfortable trying to explain it in terms of an SD image but the same ideas apply to wide screen as well.

1.Almost all of the NLEs start with an assumption about the frame size and then base their math on the assumption.
2. The assumption is, for instance, that the standard video frame is a 4:3 image.
3. The assumption is wrong. The real answer is that the viewable image is supposed to be 4:3 but the entire frame is wider. This area is masked by TVs but the area is always there and was included to give TVs enough time to douse the TV line to 0 VDC before moving to the start of the next line and bringing the signal back up. Remember that the standards were designed to work with vacuum tube electronics.
4. If you look at an analog capture of taped footage from a VHS deck you'll probably see a good example of this. The left and right edges should fade to or from black. No sharp edge because the electronics don't have to be good enough or fast enough to capture the image at those edges.
5. To their credit, the Vegas engineers actually looked at the spec for a video signal and did their math properly. (They didn't solve for the expected solution, they solved for the problem. We could use that in our polititians, BTW). The result is that a 1.0 PAR image that fits perfectly in the NTSC video frame is a little wider than you might expect if you've been reading a Premiere or FCP manual.
6. If this is contradicting everything you think you know, relax, let go, read and follow the instructions, and don't overwork the problem.
7. Do tests to satisfy yourself that everything is working okay.

Rob Mack