Display Technology

Certain features used with HDTVs are native to the content and display formats rather than the technology used to create the picture. That doesn't mean all HDTVs must have these features, but rather that similar features can be added regardless of display type. The technology described here may present on an HDTV or HD-ready display, but is usually handled by other devices like a DVD/HD DVD/Blu-ray player or HTPC before a signal is sent to the TV. Some functionaliry in this section is available on som HDTVs as well, although a TV generally isn't as good as other devices at video processing. Other technology listed here is integral either to certain HDTVs.

IVTC and Deinterlacing

Although IVTC and deinterlacing are both used on interlaced video, IVTC specifically refers to recovering progressive frames from 24p film sources, while deinterlacing is used to create progressive frames from footage that's natively interlaced like TV shows originally recorded on video tape.

IVTC

Although HDTV doesn't used distinctions like NTSC and PAL, broadcasters also have to think about analog television owners who will soon have to use converter boxes to display digital signals. That means in areas that currently use NTSC film content will still need to be converted to 29.97fps from 24fps. The traditional way to do this in the analog world, telecine, can also be used before digitizing, resulting in a 29.97i signal. Alternatively, the actual film frames can be captured, and pulldown flags used to repeat fields, creating the same pattern of duplicated fields as a telecine machine. Depending on the equipment used to deliver the picture to your HDTV, you may be able to perform IVTC, or Inverse Telecine, on the video, allowing you to display the original film frames instead of combinations of fields from different frames being displayed together.

There are two basic types of IVTC output, either of which should playback correctly on any HDTV. The first involves the initial stage of IVTC, field matching, and delivers 29.97fps (or 30fps) video with entire frames duplicated in a pattern similar to telecine but with no interlacing, resulting in 3 unique frames and a fourth that has a duplicate.

Deinterlacing

When displaying interlaced content on a progressive display, it's necessary to deinterlace to get rid of interlacing artifacts, which mostly manifest in the form of ghosting and edges that don't line up properly. There are many ways for hardware to handle this, ranging from dropping one field and interpolating it from the remaining one to creating a separate frame from each field and interpolating the missing information. When properly done, this arguably results in the best quality, but will create a doubled framerate that's not supported at all resolutions.

Fixed Pixel Displays

Aside from CRT displays, all HDTVs are fixed pixel displays. Instead of displaying a decoded analog line, fixed pixel displays show the actual samples (pixels) from the source. The number and position of pixels can't be changed, meaning any signal not already at that resolution will have to be resized. For example, if a 720p fixed pixel display receives a 1080p frame, it downsamples to 720p for display.

Projection vs. Direct View

Although all HDTV images are essentially made of projected light, In some displays that light is generated aiming in a different direction than the screen. Images generated this way may come from the same direction as the viewer and reflected off a screen similar to what a movie theater uses. These are called front projectors, or just projectors. Other times the projector is built into a cabinet that also houses the HDTV screen, and the image is either reflected (using mirrors) and refracted (re-focused using lenses) to the screen. This is referred to as a rear projector, rear projection TV, or RPTV. Displays where the image is projected directly toward the screen or viewer are called direct view displays. All flat panels and smaller CRTs are direct view.

RPTV Viewing Angles

One side effect of RPTV technology is a smaller viewing angle than other displays. Although there has been a lot of progress in this area, all RPTVs still have a more limited viewing arc than a direct view display.

Connections

Unlike SDTV, which uses purely analog and interlaced signals, HDTVs may accept either analog or digital signals that are either progressive or interlaced. Unlike SDTV, S-Video and composite video cables have insufficient bandwidth to deliver all the detail necessary for HDTV, so the only analog option for HDTV resolutions is component video. Supported digital connections vary from one HDTV to another. Some have only analog, while others may include DVI, some version of HDMI, and even Firewire.