Another Techno-Rant! Whee!

Observant readers may wish to call me out on the seemingly impossible quality improvement estimation from Malex's Thoughts in this week's Malex Minute episode. So, I present my logic here:

First, we establish that a full 1080-line HD wide-screen (16:9) image captured at 30F or 24F (progressive) will be 1920 pixels wide and 1080 pixels tall. For a total of 2,073,600 pixels.

That was simple enough. But from here comparison becomes difficult, because (for the purposes of this comparison) SD images are based on the analog NTSC (National Television Standards Committee) standard, which has no direct digital equivalent.

A regular NTSC signal has 525 scanlines between frames. Each of these scanlines may have as many "pixels" of vertical information as you have bandwidth to transmit. Most of these scanlines are actually invisible, as they occur outside the television's normal scan range, and they are often used to encode other information. (Such as closed captions.) To further confuse the situation, NTSC (Never Twice the Same Color) signals are usually interlaced at a rate of 60 half-frames per second. (Each interlaced frame contains information from two different moments in time, encoded as half-frames which are "interlaced" together by alternating lines.) Note: If this sounds confusing, there are two possible reasons: 1) I don't understand it, so my explanation is flawed. 2) It's confusing as all screamin' reality.

There may have been a reason for all of this at one time, but nobody has been able to sufficiently explain that part to me.

Anyway, so the practical upshot of all this is that, if you want to pull out a single moment of time, you have to discard half of the lines in your original image.

Now, we enter the digital realm. Standard definition digital video, such as the video you'll find on a DVD or in a DV stream, appears to pretty universally be 720 pixels wide and 480 pixels tall. (Remember how a number of the 525 scanlines in NTSC occur outside the television's scan range? That's one reason why there are only 480 lines in standard-definition digital video.)

Usually, that image is then compressed in the horizontal dimension to achieve a 4:3 "full-screen" image. Unless you're talking about a wide-screen DVD. Then the horizontal dimension is stretched slightly to achieve a 16:9 wide-screen image. That wide-screen image may then be displayed on a wide-screen monitor without any modifications, or displayed on an old television with the addition of black bars at the top and bottom.

Does that all still seem reasonable? It's about to get even more convoluted.

Enter the really crappy consumer digital camcorders from the past 15 years. Some of these came with a "wide-screen" shooting mode, which would result in exactly what you would expect from the output. Specifically, wide-screen video squeezed into a 720x480 pixel format.

The only problem with this? The camera's sensor is the wrong physical shape! It can't capture wide-screen video natively, so it chops off the top and bottom of the image. The result of which is that instead of using the 480 lines of resolution it's able to natively capture, we're only getting closer to 405 lines. (Or 360, depending on how you calculate it.) Then the camera silently and awkwardly scales that information up to fit the 480 line output requirement. (The reason it's impossible to be sure how many lines of resolution it's actually capturing is because this horrible scaling operation occurs inside the black box of how the camera operates. The details are completely hidden from view.)

Now, if you thought 405 lines of resolution was bad enough, you've got a surprise coming.

These consumer-quality SD camcorders force you to record interlaced video. You have no choice. Thus, if you want a single frame (which, if you'll recall, is what we're comparing) you've gotta discard exactly half of the lines you get from the camera.

So when you're in wide-screen mode, each moment in time is only represented by approximately 202.5 lines of resolution.

You couldn't even print that on a postage stamp without obvious image quality problems! Nevertheless, that image is regularly scaled up to a 30-inch television screen. Ick.

So when you follow that logic to its bitter, bitter conclusion, each moment in time is represented by an image whose total density is 720x202.5 pixels, which is a grand total of 145,800 pixels.

145,800 pixels compared to 2,073,600 pixels. That's 14.22 times more information.

So there you have how I came up with that number. And you have a rant.

Hope it makes some sense.

ttyl!

--Alex Markley