Navitar Support

Home Theater: Standard and Wide screen Formats

Standard 4:3 Format

Nearly all of the projector fixed resolutions are in a 4:3 ratio format (horizontal:vertical). That is, the projector's internal panel, onto which the incoming image must be mapped, is a bit wider (by 1.33 times) than it is high. This is the industry standard for most portable home-theater projectors.

This 4:3 ratio/shape is exactly the same as a standard TV signal (NTSC) and picture tube. An incoming standard TV video signal consists of 480 lines of resolution (and is 640 pixels wide). When displaying a standard TV broadcast with an LCD or DLP projector, the incoming image will first be expanded so that it corresponds/maps to the resolution of the projector's internal panel (either exactly 800 pixels wide x 600 pixels/lines in height if SVGA, or 1024 x 768 if XGA). A mathematical algorithm is used to add/interpolate pixels within the expanded image, so that the density of pixels will remain the same as the original signal. The resulting image, when projected, will completely fill the 4:3 ratio screen top-to-bottom and left-to-right, regardless of its size, with a bright, dynamic picture.

Wide screen 16:9 Format

True "Home Theater" signals mimic the shape of a movie theater screen rather than a standard TV. That is, the ratio of width to height is much more exaggerated, in a ratio of 16:9 (1.78 times wider than high) rather than 4:3 (1.33).

For example, high-definition television (HDTV) comes in two different formats, both of which are in a 16:9 ratio: 720p (720 lines of resolution in "Progressive" scan format) and 1080i (1080 lines in "Interlaced" format). There is currently no HDTV standard, and the various broadcasting companies are currently using one or the other system.

How Projectors Interpret Formats

How a 4:3 XGA Projector Handles an Incoming 16:9 Signal
Over the next several years, the current NTSC television standard will likely be replaced with the HDTV standard. A wide-screen video signal (with a 16:9 ratio horiz:vert) cannot be mapped onto a projector's internal panel whose dimensions are in a 4:3 ratio. Nor will the incoming signal's resolution (in terms of lines) exactly match the projector's "fixed" resolution. The following two examples will help explain how these situations are resolved:

Example 1
Suppose you have a projector containing an XGA panel (1024 pixels wide x 768 pixels/lines of resolution, a 4:3 ratio horiz:vert), with an incoming HDTV video signal (1280 pixels wide x 720 pixels/lines of resolution, a 16:9 ratio). When the incoming image is mapped onto the projector's internal panel, it needs to first be "shrunken" by 20% so that the original 1280-pixel-wide HDTV image will fit onto the 1024-pixel-wide XGA panel.

The proportional 20% shrinkage in the vertical dimension will result in an image that no longer contains 768 lines of resolution, but rather 575. This necessary loss of resolution occurs in spite of the fact that an XGA panel has the capacity for 768 lines of resolution, and an HDTV signal consists of "only" 720 lines. But the final picture, when projected onto the big screen, will still look great -- far superior to standard TV's 480 lines.

Also note that because the resulting 575-line image is less than the projector's internal panel's 768-line capacity, only 80% of the panel's vertical dimension will be covered with image, and the rest will be blank. Therefore, when centered and projected onto a 4:3-ratio screen, the resulting picture will have the so-called "letterbox" effect, with dark horizontal bars visible both above and below the image. (Some projectors will project black in the blank area, while others will actually turn off the pixels for darker black area.)

Example 2
Take the same projector with an XGA panel, and an incoming DVD video signal. DVD uses the NTSC standard (640 pixels wide x 480 pixels/lines of resolution, a 4:3 ratio) so that discs can be fully viewed on standard television sets. However, most DVDs are also "enhanced for 16:9," meaning that they contain an additional encoded 16:9 image consisting of the same number of lines of resolution (480) but extending across a full 854 pixels horizontally. Therefore there is no loss of resolution when viewed on an XGA home-theater projector.

When this 16:9 image is mapped onto the XGA projector's internal panel (which can accommodate a line as wide as 1024 pixels), the full image can be accommodated without first having to be "shrunken." (In fact, in this case, it will be "stretched" by about 10% so that the 854-pixel_wide signal will fill the 1024-pixel-wide panel. The corresponding 10% stretch in the vertical dimension increases the image to about 575 lines high, still less than the panel's 768-line capacity, thus resulting in a "letterbox" effect.) Since there is no loss of resolution, the projected picture will be of stunning quality.

Will an SVGA Projector Do as Well as an XGA?
Because of SVGAs much lower-resolution 800 x 600 internal panel (as compared to an XGA projector's 1024 x 768) the final picture will contain even less resolution than a standard NTSC TV signal! This is because, when an incoming 720p or 1080i HDTV wide-screen image is mapped onto the projector's panel, it needs to first be "shrunken" by 37.5% (if 720p) or 41.7% (if 1080i), so that the original 1280-pixel-wide HDTV image (if 720p) or 1920-pixel-wide image (if 1080i) will fit onto the 800-pixel-wide SVGA panel. The proportional percentage shrinkage in the vertical dimension results, in either case, in an image that no longer contains 720 or 1080 lines of resolution, but rather 450, which is less than standard TV's 480 lines!