tourenwagen

There are different flavors of high definition video out there. The two most popular are abbreviated as 720p and 1080i. Of those, I prefer 720p for motorsports video. I’ll talk about why.

Way back during the first part of the 20th century, the National Television System Committee (NTSC) came up with a broadcast standard that carries 60* pictures per second. This was a good choice. The 24 pictures per second rate used in film production is inadequate to convey motion properly. I’d like a rate even higher than 60, but that’s a reasonable number.

The 60 pictures per second of NTSC are a funny kind of picture. They’re field pictures, and have only half the scan lines of the image. Sometimes people describe NTSC as 30 interlaced frames per second. Sure, that’s a perfectly valid way to describe it, but it’s the wrong way to think about it. NTSC is 60 pictures per second — 60 field pictures.

The use of fields was a compromise between spatial resolution, temporal resolution and analog bandwidth. For the same bandwidth, one could transmit 30 frames per second, and have a problem conveying motion. Or one could transmit 60 frames per second at half spatial resolution, and have soft images. Today we have the capability to send 60 (or more) high resolution frames per second, because compression technology has solved the bandwidth issues.

But why not keep interlace with high definition? If we were all watching video on a CRT-based television, I’d say, sure, go ahead, do interlace. But we’re not. Most televisions use progressive display technologies rather than field-friendly CRTs. Most of these progressive televisions have high quality de-interlace technology built in, which greatly mitigates the visual impact of field to frame conversion. But increasingly we’re watching video on computers. And computers don’t know how to deal with fields.

You can take a garden variety LCD display, hook it up to a digital set-top box playing a field-based sequence over HDMI, and it looks pretty good. Take that same LCD display, hook it up the the HDMI port of a graphics card in a PC, decode the same interlaced video sequence on the PC, and the video looks like crap. Graphics cards don’t know how to process fields properly. Maybe some company will solve this, but don’t count on it.

What about 1080p? Well, what kind of 1080p are you talking about? If you mention 1080p to video production people, most of them immediately think of 1080p24 — 1920×1080 @ 24 progressive frames per second. A lot of “film” content is produced in this way. Bits on digital media replace images in emulsion. But 24 pictures per second is inadequate to convey motion. Yeah, 24 Hz is part of the “film look”, but the “film look” of motion is crap. Then there’s 1080p30. Same problem. Thirty pictures per second is inadequate. Then there’s the holy grail of HDTV: 1080p60. I can tell you, it’s awesome. Most high end, and even middle range consumer display devices can handle it. Cameras, recorders, editing and decoding technology — even in the professional arena — are lagging.

So for me, the answer boils down to this: 60 pictures per second, frame pictures not field pictures, and the highest resolution that is technically feasible. Right now, 720p is the best format in the consumer/prosumer space for capture devices that meets those criteria. For web-based video, 720p is a real stretch right now. So whenever I post that format, I’ll also post something more reasonable. A format I’ve called “quarter HD” in an earlier post — 640 x 360 @ 60p, 16:9 — is one possibility. Another possibility is 768 x 432, which has 36% of the pixel count of 720p rather than 25%. It’s higher resolution (by 44%), retains square pixels, and has the advantage of containing an integer number of 16×16 blocks of pixels (48 x 27 macroblocks), which is more compression friendly. And it should be decode-friendly on a late model notebook computer. However, “nine twenty fifths HD” doesn’t quite roll off the tongue. I’ll have to work on that.

*This was later changed to 60/1.001 (approx. 59.94 field pictures per second) with the introduction of composite color in 1953. For the sake of simplicity, I’m going to ignore the 1.001. But since composite is obsolete, the 1.001 should be banished to the kludge pile of history.