Thursday, August 16, 2007

Contrast beyond measurement

Part of the challenge of taking pictures outside is that the world has a lot of dynamic range, and our ability to capture that dynamic range is fundamentally limited by the flare in the lenses that we use. So, I've been working on reducing flare in my lenses for a few months.

It turns out there are some guys, Paul Boynton and Edward Kelley, at NIST who had a similar problem (here's the link). They were trying to measure the contrast of LCD displays. It turns out that customers demand higher contrast from their displays than a standard camera can directly measure, because of limitations of veiling flare in the camera. To reduce flare from air/glass interfaces, they built a camera with no air/glass interfaces by filling it with liquid. Totally cool. But also very geeky, not the kind of thing you'd expect to bump into in the day-to-day world.

This morning the DJ on the radio was reading an ad for a Pioneer LCD TV, and claimed that it had "contrast beyond measurement". The person writing that ad probably doesn't know what that means, but I wonder who he heard it from. I find it funny to think about that phrase working it's way from one of the few thousand people who actually care, through executives and ad campaigns and broadcast radio, to me, one of the other few thousand who actually know something of the back story.

Random disorganized blog thread: The high-contrast LCD TV thing raises two leading questions: how are broadcasters producing those high-contrast signals in the first place, if cameras can't capture that much dynamic range, and how is it that customers can discern contrast levels that cameras cannot?

I think the answer to the first question is that broadcasters are stretching image contrast before display, probably to make up for veiling glare on the air/glass interface at the front of the LCD.

The answer to the second is that the human eye probably has less veiling flare than a camera, because it has just one air/liquid interface. I wonder if the human eye has dichroic antireflection coatings/layers on the exterior air/solid interface? I know we've not yet evolved correction for longitudinal or lateral chromatic shift (achromatic and apochromatic lenses), which I think is odd, given the sharpness benefits.