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Filed under: Motion Graphics •Post Production •

The Hi-Def Checklist

Frame Size Issues

Just as there are a wide variety of legal frame rates in hi-def, there are a variety of sizes to contend with as well. The standard hi-def sizes are 1920x1080 pixels and 1280x720 pixels. The larger size is far more common, but again, ask to be sure, and don’t assume all of your source files are going to come in the same size.

Additionally, some hybrid “production” sizes have emerged. A 1920x1080 hi-def frame has nearly six times more pixels than a typical 720x486 pixel standard-def frame, which can mean it takes up to six times as long to render (although it’s not always that bad; if your project is at 23.976 fps, you have to render only 40% as many frames as you would with a 29.97 fps interlaced project). That large of a frame is also difficult to display comfortably on most monitors, plus results in more bytes to store and move around a network. Some stations have started using a “half HD” size of 960x540 pixels, which they then scale down slightly for their standard-def broadcasts, and double for their hi-def feed. Don’t be shocked if you receive a request to supply graphics at this size, or even the square pixel widescreen standard-def sizes of 864x486 (NTSC) or 1024x576 (PAL).

But wait – there’s more. The one silver lining in the ATSC specification was that all of the higher-resolution formats used square pixels. Alas, that last refuge has been taken away from us by the HDV and DVCPRO HD formats. In HDV, a “1920x1080” frame is actually captured at a size of 1440x1080; the pixels must be stretched horizontally by a factor of 1.333 to become square again. DVCPRO HD uses the same size for PAL frame rate projects (25 frames per second, interlaced), but a different size – 1280x1080, with a pixel aspect ratio of 1.5 – for NTSC frame rate projects. When a 1280x720 frame is called for, DVCPRO HD captures it at 960x720 pixels, also requiring a horizontal stretch of 1.333 to make the pixels square. Some software – such as Apple Motion 2 (see below) – support these sizes and manages them automatically, but not all do as of the time this was written (late 2005). Be aware that you may need to perform these stretches manually in the short term.

Newer programs, such as Apple Motion 2 and later, After Effects CS3 and later, etc., have templates for the numerous non-square-pixel HDV and DVCPRO HD formats. With other programs, you may need to stretch the pixels square yourself.

There are other size implications beyond pixels. Along with larger dimensions, hi-def projects are usually captured and rendered at greater bit depths. Whereas a 10-bit YUV capture and output was often considered a luxury in standard-def video, it is common in hi-def, with some systems supporting 12-bit YUV. Ask the client what bit depth they expect delivery at: Anything over 8-bit means you need to be working in at least 16-bit RGB to render these greater bit depth files. Yes, that means another render hit (and more disk space, and…); on the plus side, working at this greater depth often cures many issues with colors banding and posterizing.

You will need higher-resolution sources to fill these larger frames, requiring you to capture and scan at a larger size than you have before. But what if that crucial shot or photo is not available at a higher resolution? Scale it up – but carefully. If After Effects has an Achilles’ Heel, it is in scaling up objects; sharp edges can start to look jagged once you get past 125% or so. I’ve previously used the ReSizer plug-in from Digital Anarchy, but was disappointed when the second version dropped some of the different algorithms the user could choose to determine which worked best on each shot. There are other solutions now available, such as Instant HD from Red Giant Software.

If you are re-creating or re-rendering images to use in hi-def, don’t just make them larger; consider adding it a bit more fine detail as well. The ability to see fine details is the reason consumers are buying hi-def sets (aside from bragging rights); deliver it in your content by increasing the detail in your 3D texture maps and other elements of your design.

sidebar: Repurposing Footage

If you have stock footage – or have already created 3D elements or other pre-renders – at a frame that is different than what your hi-def project demands, and the resolution is high enough, it may be tempting to use it as-is. However, if you do so, you will end up with motion artifacts that will manifest themselves as a subtle staggering in the final output.

For example, soft clouds are an element you can often get away with resizing from standard-def to hi-def. If the footage came as a 29.97 fps movie, it’s all too easy to place this into a 23.976 fps composition, scale it up, and render that out as a hi-def element. However, a funny thing will happen on the way to output: Frames of the source material will be missing. Four frames will pass directly from input to output, but then to resolve the difference in frame rates, every fifth frame will be skipped. To test how sensitive your eyes are to motion, drag a 29.97 fps clip into a 23.976 fps comp or sequence, and RAM Preview it – notice anything funny? If not, step through it a frame at a time, and notice how the movement jumps every fifth frame.

If the precise peed of the footage is not that important, re-interpret its speed to that of your final output. In After Effects, you would do this by selecting the footage, choosing File > Interpret Footage > Main, making sure “Assume this frame rate” is enabled, and entering the desired number, such as 23.976 just as we showed back on the first page for frame sequences. If the speed is important, and if you have access to the original project that created the footage, re-render it at the new, desired rate (again, making sure any the source footage used is also conformed to this rate). If the speed is important and you don’t have access to the project, then – at a minimum – enable frame blending, causing your software to interpolate intermediate frames at the new rate. Better would be using a plug-in such as RE:Vision Effects’ Twixtor or some other optical flow technology to get more accurate interpolation; be prepared to spend a little time optimizing parameters to reduce artifacts to a minimum.

next page: widescreen aspect issues

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