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| Using LCDs for HD Monitors |
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By Wayne Cole, June 10, 2006
LCD prices have plummeted to the point that some might think "LCD" stands for "Low-Cost Display." And these low prices have not escaped the eye of those trying to make the jump to HD production on a budget.
HDV and DVCPRO HD camcorders, editing systems and decks for the budget-minded are readily available, while few displays purposed for HD video have yet to follow suit. However, with SXGA and WXGA LCD computer displays supporting HD scan rates and picture aspect ratios, many videographers have opted to use them as HD video monitors.
While cost savings are considerable, using a computer display for video has its pitfalls. With the rare exception, LCDs don't support the full HD raster. Consequently, image scaling has to be done that can compromise both resolution and visible picture area. These problems are even worse if the monitor also has to double as an SD video monitor. Additionally, LCDs with slower response times can create smearing when objects in the video move rapidly.
Compared to HD plasma, DLP and CRT displays, LCDs are woefully lacking in contrast ratio and color gamut. For example, a high-end LCD might be capable of a 700:1 contrast ratio and 16.7 million colors, compared to plasma's 2500:1 contrast ratio and 18.5 billion color capacity. These factors can create some unpleasant surprises when the final video is viewed on a native video display. Contrast, color saturation and even hue can look totally different.
The final hurdle involves physically getting the HD video to the LCD. Computer LCDs often sport video-unfriendly connectors or input standards that may require physical adapters and signal format conversion boxes. These accommodations begin to cut into cost savings.
One LCD that has quietly become a favorite in a number of studios is the HP L2335, a 23-inch widescreen LCD. The L2335 solves some of the problems associated with the use of "normal" computer displays for video while coming in at a street price of about $1,000, well below most other HD monitoring solutions.
For starters, its native resolution is 1920x1200, which will support the full 1080 or 720 HD raster. In addition to its computer-oriented analog VGA and analog/digital DVI-I connections, a removable panel at the side reveals composite and S-Video terminals for SD video input, as well as a triple-RCA terminal for HD analog component input, which could eliminate some adaptation costs.
The L2335 uses a video-friendly 2.2 gamma
. Operated with a 6500K color temperature, the white point and red and green chromaticity coordinates are very close to values for HD, while blue is closer to NTSC 1953 coordinates, meaning a smaller range of possible blue shades can be displayed. The 500:1 contrast ratio is about average for LCDs.
Using the composite or S-VHS inputs in "no zoom" mode, the L2335 will truncate a standard 720x486 picture to 675x456. The truncation occurs outside the safe action boundaries, so it shouldn't be a problem for applications that don't need edge-to-edge monitoring.
The composite input is slightly noisier than the S-Video input. The noise appears mainly in static graphics with highly saturated colors as a slight vertical hum pattern. But both SD inputs produced a picture that is softer and appears slightly out of focus compared to the same video displayed on a CRT.
The overall hue is good and compares closely with that displayed on a CRT. As is the case with virtually all LCDs, however, the blacks are dark gray and bright areas tend to look washed out.
Using the component input for HD display provided much better results. Feeding either 720p or 1080i HD, the L2335 showed the full HD raster in 16:9 aspect ratio with black bars above and below the picture. If the letterboxing bothers you, the zoom control can be used to fill the screen completely, with slight vertical distortion.
HD video appeared crisp, showing no signs of the softening that was evident with SD video. While the low contrast ratio and color saturation common to any LCD was apparent here, the high-resolution picture made those problems less noticeable. The color range and contrast was no match for my 42-inch Pioneer plasma display, but the L2335's HD picture did compare favorably in resolution.
Some smearing was apparent for moderately fast moving objects; there was no discernable difference between 1080i and 720p. The smearing was slightly worse for horizontal motion than for vertical motion. In both directions, the effect was to make the moving object appear softer and less focused, but without the "trails" that some other LCDs exhibit.
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