Tuesday, December 12, 2006

A New Bedroom HDTV for Me, Part II

In A New Bedroom HDTV for Me, Part I I crowed about my new 1080p HDTV, the Sony KDL-40XBR2 40" LCD panel.

In a minute I'll talk about a minor problem I've discovered. But first, I again want to state how much better this HDTV's picture is than that of the other two HD sets I have, a 32" Hitachi plasma and a 61" Samsung DLP rear-projection unit, both of them of three-year-old design. Yesterday I tweaked the Sony's picture with the Digital Video Essentials test DVD and found that it basically needed very little tweaking!

I had already adjusted grayscale by eye — the Sony offers user-accessible "white balance" adjustments of bias and gain in each of the three color channels (red, green, blue) that combine to make up white or shades of gray. I had chosen the Warm 2 setting for color temperature and the default setting of Low for gamma. I turned off the lights, setting the Sony's backlight to minimum and picture level to maximum. Then I popped in the test DVD and went through its adjustment procedure. The net result was that I needed to drop the brightness level to 29 and the color level to 30. The hue adjustment remained centered at 0. That was all there was to it!

The result was a stunning picture that displayed color footage exquisitely and handled monochrome test patterns equally well.

But, as I say, a minor problem also showed up. It looks as if the backlight behind the LCD image isn't perfectly even in its illumination. There's an irregular swath, predominantly vertical, sitting slightly to the left of the center of the screen in roughly the top two-thirds of the image. In solid light gray test patterns it's barely visible as a slightly darker gray. It doesn't have a distinct edge or border. It grades very gradually into the lighter shades of gray to either side of it.

It shows up only when the image on the screen is of a certain uniform lightness. Most actual programs' images don't reveal it. Or at least, I haven't noticed it except when the screen is basically a uniform light gray.

Backlight unevenness or "cloudiness" or splotchiness is, I've managed to discover, a much-discussed issue with Sony Bravia KDL-nnXBR HDTV owners. This thread at the AV Science Forum deals with it: the Official Sony 46" XBR LCD Uneven Backlight/Cloudy Thread. It's mostly about KDL-46XBR TVs, not KDL-40XBRs, since the uneven backlighting issue seems to beset larger LCD panels more than smaller. But 40" owners have reported similar, if less pronounced, problems.

Most of the complaints deal with light blotches in dark images. I'm seeing a dark blotch in a light image. Despite the apparent difference in symptoms, I think the underlying cause is the same: uneven backlighting.

At least one poster to the thread has suggested that the unevenness is "the result of thermal induced stresses on the LCD panel: — "warping of the panel due to non uniform expansion in response to the increase in temperature" — and says his 46-in. 1080p Samsung European-model LCD "also presents the same type of clouding on the right hand side (top and bottom)."

Intuitively, I expect this is a correct explanation. It might explain why the newer, larger LCDs are prone to the problem that as far as I know is new to the world of LCD HDTVs: the larger the TV, the more prone it is to the problem.

But it doesn't quite explain why owner scuttlebutt has it that Sonys built before August 2006 seem to be immune. It seems to be only the more recent units that exhibit the problem.

More on my experiences with this otherwise magnificent HDTV in Part III!

No comments: