Consumers buying HDTV sets are looking for pictures that are both bigger and better than the pictures they’re used to with standard-definition television (SDTV). But meeting this double-barreled expectation sets a limit to how much bigger an HDTV screen can be, since the number of lines of resolution in a TV picture is fixed by its format.
Purchasing a bigger set doesn’t buy more lines of resolution; it just causes the fixed number of lines in the given format to be spread more widely apart.
Suppose you’re used to a 24-inch SDTV set. That set offers 480 lines of vertical resolution in a picture frame, which means you’re used to pictures with 33.33 lines of resolution per vertical inch.
When you replace that old SDTV set with a new HDTV set, you definitely don’t want worse picture quality. But it will get worse—unless you’re careful about the size of your new HDTV. For a new 720p HDTV, the break-even point—the screen offering about the same 33.33 lines of vertical resolution per inch you’re used to from your old 24-inch set—is around 40 inches.
This means that replacing an old 24-inch SDTV with a 36-inch (30.5- x 19.1-inch) HDTV provides a double win: a picture that’s over twice as big with about 13% better resolution (over 37 lines of resolution per vertical inch). But buying a 50-inch (42.4- x 26.5-inch) HDTV may be disappointing. Although the picture is four times larger than a 24-inch SDTV picture, its relative quality drops by over 20% (with resolution of under 28 lines per vertical inch). The drop in image quality gets worse with still bigger screens.
Of course, there’s also HDTV 1080i. But this format only raises the break-even point (in our example) to about 60 inches. That won’t do. When still-bigger screens become widely affordable, consumers will want them.
The Digital Cinema Initiative has recommended a new so-called 4K standard for the motion-picture industry. And with increasingly bigger screens moving into distance-limited homes, the 4K standard will migrate there. So although the in-home IMAX may be a ways down the road, it is not too early to start imagining it.