Join Chris Meyer for an in-depth discussion in this video New Pixel Aspect Ratios, part of After Effects CS4 New Creative Techniques.
The biggest gotcha in CS4 has got to be the change in pixel aspect ratios for a variety of video formats. Now as it turns out, for all of these years most video applications, After Effects included, have been using a slightly wrong number for pixel aspect ratios for these formats. They made the assumptions that the entire frame is supposed to be visible image and therefore they based their math off of that. In reality there are these two different sizes out there. There's the production aperture, which is the entire image area of the captured file, and then a slightly smaller area known as the clean aperture. That has the true aspect ratio of the final image and sits inside the production aperture just a little bit.
Programs like After Effects have been looking into production aperture to decide PAR when they should have been looking at the clean aperture. Okay, that's a bunch technical stuff. Let's get down to what this means for you. If I have something like a normal like D1 NTSC file and open its Interpret Footage dialog, I'll now see that the PAR is very slightly different. It's 0.91 rather than a 0.9. The true pixel aspect ratio for NTSC image, DV or D1, is actually the ratio 10/11, not the ratio of 9/10 the programs when using for ages.
There's similar small changes in the PAL, and in the widescreen formats as well. The HDV stuff and the DVCPRO HD have not changed. Okay fair enough. Let's say I wanted to make a square pixel D1 composition to work in. I do Command or Ctrl+N, select my preset for NTSC D1 Square Pixel. But notice it is no longer 720x540; it's 720x534. That takes the new pixel aspect ratio D1 into account. I'll name this square pixels. Click OK, drag my footage into it, hit Scale and you'll see that I scale up by an equal amount on X and Y, 110%, remember the 10/11th ratio I have mentioned just a second ago. The inverse is 11/10, 110%.
You'll see that the image fits perfectly. Okay, so far so good. Different numbers, but it still works out. Let us make another comp. Let's go ahead and make a D1 non- square pixel. NTSC D1, 720x486, which I'm familiar with. The new ratio of 0.91 and I will give it a name, non-square, click OK. I'll drag my strange 720x534 comp into my non-square comp, Scale, pull it down and edges fit cleanly all way around. 91%. That's the 10/11 ratio.
So once again even if the numbers are different as long as you let After Effects take care of the math, things will work out. Here is the one difference. What if you are creating web video? Now you need to deal with the extra pixels left over by the production aperture. I'll do Command or Ctrl+N, select the preset for Web Video 320x240, click OK. I'll nest either one of these, just go ahead and just bring the non-square comp into my web video comp. Start scaling it down. You will see that I either going to have a little bit of extra trim on the top and bottom. I'm going to crop off a little bit of stuff on the left and the right. The side effect of this new PARs is when you bring an non-square source into a small square pixel comp such as a web video, you might need to crop or pad to make it fill out the entire image. That's because there are some additional pixels in the production aperture, the captured frame, which you don't want to see on the web.
Now, this is going to really throw some people off initially, they are not going to know what to do, but in truth you shouldn't be seeing this pixels around the edges anyway. We will go back to one of our prior comps, toggle the Action and Title Safe grids and remember a person watching on television is not supposed to see anything beyond the Action Safe area anyway. So why are you showing them that area on the web? You should be cropping this off anyway when you make web video. So I will go back to my web comp, name it Web so I keep track of it, and scale it up slightly so that I am indeed cropping off what would have been the action safe in the full video so that my web video experience matches my broadcast video experience.
So, two things about the PARs. One, in some cases between formats you are going to need to do a little padding or little bit of trimming to make them work right. Second thing is when you are making web video, you really should be cropping all stuff around the edges anyway so that you get rid of the junk that's normally not seen on the television set.
Motion graphics artist Chris Meyer, who has used After Effects since version 1, created After Effects CS4 New Creative Techniques to highlight some of the most exciting features in the latest release. These include several new effects; integration with Photoshop 3D layers; and independent control and keyframing of the X, Y, and Z position parameters. The new composition manager and mini-flowchart are big improvements, as are the Flash export features. Enhanced integration with Adobe Device Central greatly eases authoring for mobile devices. Other interesting changes Chris discusses include the newly bundled Mocha tracking and stabilization program, Wiggle transformations for shape layers, and Pixel Bender integration.
- Implementing the new Cartoon, Bilateral Blur, and Turbulent Noise effects Finding assets in a project or the Timeline with QuickSearch Understanding the new pixel aspect ratios (PARs) Working with XMP metadata Using the new splash screen and interface additions