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In the Black

Joel Brinkley's recent comments on black level issues with the new digital video displays was right on the mark for flat panel displays, but things are looking up, at least a little, with front and rear projection sets. I'm currently working on reviews of two new models, the front projection Sony VPL-VW100 SXRD projector and the Hewlett-Packard md5880n DLP. Both of these are 1080p displays—though only the HP will accept 1080p through its HDMI inputs.

But with all of the hullabaloo about 1080p, the most interesting feature on both displays is their implementation of an auto or dynamic iris. Those who have been following our reviews know what a dynamic iris is, and what it offers, but others may be puzzled by what appears to be a mechanical band-aid for a seemingly intractable problem.

Digital sets, at least to date, have had trouble rendering true black because their light source, unlike a CRT display, is always on whenever the set is in operation. (Technically, of course, there is always some voltage on a CRT when it's powered, but the amount of light this produces on the screen when reproducing black, in a well-designed set, is usually miniscule.) A flat-panel LCD requires a backlight—usually some sort of fluorescent, though LEDs have been researched as a possible replacement, largely because they offer better color. (At least one Sony LCD display with LED backlighting has been marketed in Japan, but not here as yet. And manufacturers are looking into various ways to modulate both fluorescent and LED backlighting for better blacks.) Plasmas need to be kept in a primed state for reliable operation, which results in a low-level glow on the screen even when the video source is a full black field. And projection sets of all descriptions use a projection lamp.

All such displays are able to deflect or block the light source when they display very dark scenes, but they need to do better if they are to render genuinely inky blacks. What is needed is a way to either turn off the light source or block it completely when it's not required.

Rear projection sets using LCD, LCoS, or DLP imaging elements are known in the industry as microdisplays, not because they're tiny in size, but because they use a small imaging chip or chips together with a bright projection lamp. Combine the stray light from that always-on lamp with the high gain screens that rear projector manufacturers use to achieve that searing, showroom brightness they are addicted to, and you have a recipe for mediocre blacks.

Enter the dynamic iris, marketed under various names (Sony calls their version the Advanced Iris, HP uses DynamicBlack, a Texas Instruments trademark you'll see on new rear projection DLPs from many manufacturers). It literally responds to the video source on an instant-by-instant basis. If the scene is bright, it opens up. If it's dark, it closes down to make the blacks even darker.

The automatic iris might seem like the proverbial bumblebee that can't fly (though I recently heard that the scientific community has decided that it can). But it works. While there is some unevenness to the black field in both the sets mentioned here (slightly lighter in some areas than in others—in the case of the HP, this almost certainly comes from internal reflections), this should be solvable at the design end. And even with this limitation, the admirably deep blacks in both sets do produce consistently rich, punchy images from a good source.

Sony's VPL-VW100 SXRD, in particular, now produces deeper blacks and better contrast than the company's upscale Qualia 004. The latter is brighter, so it can drive a larger screen. And it has a number of other unique features like lens options. But it lacks the auto iris feature, and at three times the cost of the new SXRD projector I'd be very surprised if an upgrade isn't in the works to keep it a true flagship.

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