Mailbag

Interesting "editorial" [on ½-inch CCD imagers, see 11/21 edition], but strangely one-sided. And it also doesn't address the issue of progressive vs. interlaced, and that 1080i can only hold about 700 odd lines of measured vertical resolution due to the line pair summation/vertical low pass filtering employed to avoid line twitter that's inherent in interlaced video. I'd argue that any interlaced format should not really be considered "high definition".

Properly done, 720p, being progressive, blows up to 1080i very well, although due to it's interlacing, 1080i is pretty tricky to correctly downsample, hence the problems it has with progressive
displays. Oh, and of course, CRTs, the "interlaced" monitor, are not
made any more. Every display is now inherently progressive. To be
still selling interlaced acquisition is like selling horse carts after the invention of the motor car.

Also, it doesn't look at photosite size, which is a key contributor
to, all other things being equal, noise levels in the image. A
smaller photosite will be noisier than a larger one. A bigger chip
means a bigger photosite for the same resolution, or allow finer
resolution without reduction in photosite size.

Aliasing is an interesting point, and is caused not by the size of
the photosite per se, but by inadequate anti-alias filtering by the
optical low-pass filter.

A smaller, higher resolution sensor sounds nice, but you're now
battling against the evils of noise, and you have to have higher-
quality lenses to take advantage of that finer pixel-pitch.

Of course, the answer is larger chips, not smaller ones, and
progressive, not interlaced, and ultra-high definition, not the
"barely better than SD" that 1080i and 720p are.

Graeme Nattress
Ottawa, Canada