Thursday, December 21, 2006

A New Bedroom HDTV for Me, Part VI

In A New Bedroom HDTV for Me, Part II through A New Bedroom HDTV for Me, Part V I spent a lot of time kvetching about the problem that my new Sony KDL-40XBR2 1080p LCD TV seems to exhibit: vertical bands that are a little bit darker than their surroundings (and have a slight color tinge). These faint bands show up most prominently in gray full-field test patterns from the Avia calibration DVD, such as the one shown here.

I imagined that this was a case of "mura": "low-contrast imperfections that are larger than a single pixel, and are visible when the display is driven at a constant gray level ... caused by non-uniform distribution or impurities of liquid crystal or mechanical imperfections in the display assembly," according to this PDF. Now I'm not so sure it's mura after all.

Mura is supposed to be a problem with the liquid-crystal display panel, not the whole TV. You replace the panel, you cure the mura. Or you get different mura. You don't get the same exact mura in the second panel.

Yesterday a service technician replaced under warranty the LCD panel in my Sony. The faint vertical bands remained exactly as they were before.

The above photo exaggerates the problem somewhat, I admit. It's not really all that obvious in person. In fact, the service guy couldn't see it at all.

On actual programs it's even less visible. Last night I watched Memoirs of a Geisha on DVD and saw little or none of it. I was watching in the dark, so I turned the TV's Backlight control down to zero and the Picture (contrast) control up to its maximum of 100. I fiddled with the Black Corrector and Advanced C. E. (advanced contrast enhancer) controls in Picture Settings->Advanced Settings to get the deepest, darkest blacks I could. The picture I saw was phenomenal! And as I say, I could detect little, if any, of my "faux mura" problem.

So my problem might best be described as phantom faux mura.

Turning on Clear White in the Advanced Settings, I have found, is also a good idea. It seems to get around the need to fiddle with adjusting the TV's color temperature color-by-color using the White Balance settings. I had originally done the latter as a means of getting rid of non-neutral color tinges in black & white pictures, and it worked well. But it's a pain to do. I now find that Clear White does roughly the same thing, and equally successfully, with just a single button press.

I'm not sure how Clear White really operates or what it does, technically speaking. It doesn't really seem to change the color temperature, which determines how warm-to-cool or reddish-to-bluish the overall picture looks.

Color temperature, in degrees Kelvin or just Kelvins, determines the "color of white"... and of all grays from black to white. It also affects colors per se. It's supposed to be 6504°K — for a fairly warm picture — at every brightness level from white to black. Most TVs prefer a higher, bluer color temperature, which facilitates a brighter image since the light source of most TVs puts out more blue light than red light.

But the Sony, like most modern TVs, gives you several choices of color temperature. I'm using Warm 1.

Turning on Clear White doesn't seem to alter its warmth. The manual says Clear White "emphasizes white and light colors." If by that is meant whites and pastels are boosted in brightness, no, that doesn't seem to be the case. Are they, perhaps, washed out? No, not that either ... not visibly, at least. My best guess is that maybe, just maybe, colors very near to a neutral white or gray (including very dark grays) are moved closer to white/gray, thereby removing faint tinctures of color ... like laundry detergent is supposed to remove grass stains.

Call it video bleach ... except that I cannot tell that it causes any "fading" of the overall picture. Not a bit of it. Colors stay rich and pleasing — in a color picture, of course. In a black & white picture, the picture looks just ... black & white. Not greenish. Not bluish. Not reddish. Just B&W.

For the life of me, I don't see how Clear White does it. It's as if the Sony sees there is no color input signal, just B& ... which in itself is no big mystery. Any TV can do that. But it's also as if the Sony somehow knows it's about to add a false tinge of color to a B&W image, and it resists the temptation of doing that. That's a mystery. How does it know that its internal processing would otherwise result in a smidgen of hue where no hue belongs? How does it know how to correct for it? And if it does know how to correct for it, why doesn't it correct for it all the time?

Now, back to my phantom faux mura. What could be its cause is also something that presently baffles me. The service tech suggested it might be the fault of the DVD player that sends the TV, for instance, a gray-field pattern. But I can tweak the TV into producing the same phantom mura on a blank — hence black — video input, as well as on an inactive cable channel from my TiVo.

There's another mystery associated with that last situation. When I first installed the TV and TiVo, it seems to me that inactive channels put up a gray screen that showed the despised vertical bands fairly easily. Now these channels put up a black screen, the phantom bands are harder to see, and I don't know what happened to account for the difference. With a black screen, I have to maximize Backlight, Brightness, and Picture on the TV to bring out the phantom vertical bands.

But they're definitely there.

At least, my eyes think they're there. I've even begun to wonder if somehow a magnetic field causes them ... but LCDs aren't supposed to respond to magnetism, the way CRTs do. Plus, it doesn't look like a magnetism type of problem. It looks too regular, too ruler-straight, for that.

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