HD Today: How H is Your HD?
Posted Sep 23, 2005

Back in the day, we watched broadcast TV that was shot on smeary tube cameras and recorded our favorite shows at home on VHS tapes that delivered some 360 lines of resolution. That was fine for many years. But as broadcasters raised their standards across the board, and better TVs filled our homes, we saw a difference between prime-time broadcast TV and VHS recordings. VHS clearly wasn't as good.

Then DVD arrived and opened our eyes to the incredible clarity and resolution of so-called "standard definition": NTSC's 30 interlaced frames of 720x480 video. Actually, because it is interlaced, we only get that full resolution when nothing moves. If you look at each field, you have to cut the vertical resolution in half. Each field offers us about 720x240 pixels. (I won't get into phosphors, LCD refresh rate, or the argued persistence of vision here.)

Standard definition (SD) may look good, but when I talk to my clients about the advantages of high definition (HD), they don't really understand until I make it clear how low resolution SD really is. The best way to do this, I've found, is to talk about digital photography.

Most people have at least become aware of digital photography in the past few years. People who don't even own a digital camera know the key term: megapixels (MP). Not too long ago, 3MP was a big number for a point-and-shoot, and 5MP demarcated "pro" photography. Nowadays, even some 7 and 8MP cameras have entered the consumer realm. By the time you read this, we may even be talking double-digits.

If you do the math, our 720x480 standard definition video is 0.3MP. That's very, very small. With interlaced video, it's 0.17MP per field. Most people are surprised it is so low--especially when they want to print out a frame of video.

You'd think that a DVD with this low-resolution (and heavily compressed) image would look bad. But flicker those images smoothly on a screen, and make us care about what's in the frame, and you'll satisfy vast majority of people.

Now comes the push for HD. The two different flavors, 1080i and 720p, have their supporters. Before you buy into them, do the math again. 1080i is still only 2MP (1MP per interlaced field), and 720p is only 0.9MP. The HDV spec records only 1440x1080, which is 1.5MP.

But the main difference between the HD formats may lie in our perception of the images. For instance, feature films are still far higher resolution than HD video. They are shot at 24fps progressive. Each frame is a complete still image. NTSC, on the other hand, is interlaced. There are 60 half-frames (fields) shown to us every second. But many display systems cannot eradicate the previous half frame so we see continuous smooth motion. This helps to explain why film looks like film, and video does not.

The key difference between the two current HDV formats, 1080i and 720p, is the frame rate. As of this writing, prosumer 720p is limited to 30fps. The 1080i version is also 30fps, but remember, it is interlaced, so the field rate is 60. It offers twice as much temporal resolution—2X more resolution over time. Couple that with the higher spatial (pixel) resolution, and I'll place my chips on the 1080i side of the table.

In the professional world, the Panasonic Varicam shoots DVCPRO HD at up to 60p (it always records 60p on tape). The Sony CineAlta shoots 1080i at fixed settings including 24p, 30p, and 60i. If you are shooting with either of these, you are making some very pretty pictures. The rest of us are looking at HDV.

Both 1080i/60 and 720p/60 offer the same temporal resolution. But if you dig into Sony's specs, you'll realize that the Z1U is limited by its 1440x1080 chip resolution. Without counting the effects of pixel offset technology, the actual 960x1080 resolution creates spatial resolution figures that are a lot closer to 720p; 0.92 versus 1.0MP, respectively. Then you have to assess the value of the 720p's chips offering actual resolution without any interpolation. Lastly, the JVC allows you to put some high-quality glass on the front. So when you look at everything, it becomes pretty evident that a good 720p60 camcorder easily wins this comparison.

But don't think that these cameras are the be-all and end-all of HD. ARRI has entered the digital fray with the D-20, a digital film camera sporting a 6MP single CMOS sensor. It's designed to handle frame rates up to 150fps. At 5Mb/frame (based on still camera RAW image file sizes), that is potentially 700Mbps! Thomson offers the Viper Filmstream camera, which touts three 9.2-million pixel Frame Transfer CCDs enabling 4:4:4 color space during acquisition. Not to be outdone, Panavision offers their Genesis Digital camera with a 12.4MP, true RGB sensor and dual link 4:4:4 HD-SDI outputs.

So we are at the dawn of a new era in video production. Sony's FX1 will likely become as "venerable" a camcorder as the VX1000 has, and help to usher in HDV in as the new recording format of choice, just as the VX1000 established DV. But when talking HD to your clients, remember to keep the big picture in mind--from NTSC to Digital Cinema--and where you fit in the mix.

Anthony Burokas (eventdv@ieba.com) of IEBA Communications, a self-confessed "gadget guy," has been an event videographer for more than 15 years. Has has shot award-winning video internationally and is technical director for the PBS series Flavors of America.