TPT - Twin Cities Public Television

HDTV vs. DTV vs. NTSC

A lot has been said about the new TV standards but how does the average viewer get to see what the new pictures will look like? Even broadcasters don't get to see much -- there is very little hardware out there, and most of that is various prototype units.

TPT's Bruce Jacobs (former Chair of the PBS Engineering Committee) has prepared some stills that can give you some idea of what kind of quality will be possible from DTV. They will only be an approximation, since there are some aspects of the standard we can't easily display on a Web browser ... such as how motion looks on interlace vs. progressive scan pictures.

So let's forget about motion; even the stills presented here may put quite a load on your computer. Your computer will need a lot of memory to display the pictures. If you have a 'millions of colors' setting for your display please take the time to switch to that mode (which may require rebooting your machine).

The pictures below will all look pretty much the same (except for the aspect ratio). That's because they are thumbnails for 1920 x 1080 pixel stills. Each thumbnail is a hot link to the full-size image. Folks with 28.8 or slower modem connections may well want to skip trying to view the full size images ... they'll take a long time to load. Unless you're an extremely lucky nerd with a 25" high resolution display you'll need to scroll around to see the entire picture.

Simulated TV stills in various resolutions
	Click and wait to see: 1920 x 1080 wide screen Displayed as: 1920 x 1080 16.7 Million colors Detail below
	Click and wait to see: 720 x 480 wide screen Displayed as: 1920 x 1080 16.7 Million colors Detail below
	Click and wait to see: ~640 x 480 (interlaced) 4 : 3 Displayed as: 1440 x 1080 16.7 Million colors Detail below
	Click and wait to see: ~640 x 480 (interlaced) w/ simulated noise 4 : 3 Displayed as: 1440 x 1080 16.7 Million colors Detail below

Full scale details of the above pictures

Now let's take a look at a tiny corner of these pictures at their full size. The first picture shows a section of the 1920 x 1080 line still. This picture shows the potential of the 1080i ATSC format; the highest quality available in the ATSC set of formats. It does not show the effects of interlace vs. progressive scanning. This still comes from a high-quality image from a photo CD, cropped to 1920 x 1080. Adobe Photoshop was used to add the text. Jacobs chose an intense shade of blue for the "Public Television Nurtures The Mind" caption - this color choice looks great in digital but will give NTSC problems...

1920 x 1080 resolution

fragment

Looks pretty good, doesn't it? Jacobs took the 1920 x 1080 picture, shrunk it to 720 x 480, and expanded it back to the original size. This simulates how a still in the 720 x 480 standard would look a top-of-the-line 1920 x 1080 display. There is some loss of detail in the girl's hair, and the text is ever-so-slightly less crisp. The vertical line just to the left of the 'b' shows how much of the left and right sides of a wide-screen format picture would be cropped off when shown on an NTSC display. From the broadcaster's viewpoint a distinct advantage of 720 x 480 is that much present-day television broadcast equipment may be used to produce programs in this format. Programs in the 720 x 480 format can even be delivered to member stations over the Digicipher satellite system presently in use in the PBS system.

720 x 480 resolution fragment

The picture was now transferred to Betacam tape (a popular broadcast-quality recording format), copied to another Betacam, and transferred back to the computer. This image shows what is about the best level of quality achievable inside an NTSC TV station. We have of course lost the edges of the picture in the cropping process. There is even more loss of detail in the picture, and as predicted the intense blue color didn't do very well -- it lost quite a bit of saturation, and the area around the text picked up a lot of checkerboardish artifacts. You can see this effect at the edges of any intensely-colored area on your present television. The full-size picture also shows another NTSC artifact: rainbow hues in fine detail areas such as the girl's hair.

The television picture still needs to get from the station into your home, in the process it usually picks up noise (snow!). The last picture shows what a small area of the NTSC TV still would look like with good -- ghost-free, but slightly noisy -- reception.