Tuesday, November 13, 2007

"Things..." episode 010.

010: More fun with pixels.

You're obviously familiar with television, known these days as "standard-definition television" (SDTV). And you've probably at least heard of high-definition television, or HDTV. But what about enhanced-definition television (EDTV)?

The EDTV format lies between SDTV and HDTV, quality-wise. Though it is seldom referred to as such, the common DVD player is actually an EDTV device. While a DVD player can generate a signal for a standard-def television set, it can also generate a higher-quality signal for a widescreen high-def set.

The actual resolution of this enhanced-def image is the same as the standard-def image I wrote about last week: 720 x 480. But, where the SDTV pixels are interpreted as "skinny," the EDTV pixels are interpreted as "wide." Instead of the boring old 1.33:1 aspect ratio, an EDTV image is displayed in the glorious widescreen aspect ratio of 1.78:1 (16:9, to be exact).

So, what happens when you play these wide pixels on a standard-def television, with its skinny pixels? The DVD player is smart enough to decode this image on the fly and output a "letterboxed" SDTV image, with black bars at the top and bottom of the screen to keep the image at the correct aspect ratio.

Here are a few examples, featuring Mr. Kyle Holman in a shot from Interplanetary...

EDTV image as encoded, 720 x 480 pixels.

EDTV image as displayed on a widescreen television, 854 x 480 pixels.

EDTV image as displayed on a standard television, 640 x 480 pixels.

Since television resolution is all about the "lines" (vertical resolution), the EDTV scheme is pretty clever. It is a way to display a widescreen image and still use all the available vertical pixels. With standard letterboxing, a significant number of lines are basically wasted, displaying only black bars.

I mention all this because many video cameras can record EDTV images. And, if you're shooting film (yay!) and composing for widescreen, you can have it transferred to video in an EDTV format. An ED transfer isn't as sharp as HD, but it is usually a lot cheaper. And, of course, better than letterboxed SD.

I think two posts about pixels are enough for the time being -- I'll move on to something less esoteric next week. But, if you have any pixel questions, email them to me or write them up in a blog comment, and I'll answer them in a future post.

1 comment:

Andrew Bellware said...

I never knew that about DVD players being able to change the pixel aspect ratio. That makes a lot of sense now. I feel much better.
Aren't you supposed to be editing?