THX Tech Training
My blog is a bit later than usual this week, but I've been pretty busy. Tom Norton and I are taking the newly developed video-technician training course offered by THX at the company's headquarters in San Rafael, California, just north of San Francisco in Marin County. Tuesday was the first of three full days of instruction and hands-on lab work, after which some of us went out to dinner and caught Hugh Masekela's set at Yoshi's, a famous jazz spot in Oakland. After a wrong turn by Laurie Fincham, THX's brilliant but directionally challenged chief scientistthanks for the grand tour of San Francisco, Laurie!I just got back to my room.
Now, you might wonder why Tom and I need to take such a courseafter all, we calibrate and review TVs for a living. In fact, we don't need it; most of the material is very familiar to both of us. But there's always something to learn, even in one's field of expertise. Also, we wanted to see how THX was training those who would then go out and perform calibrations for paying customers.
The curriculum is well-planned, and instructors Gregg Loewen and Michael Chen present the information in a tag-team fashion, which helps keep it fresh even after eight hours. They alternate between PowerPoint slides outlining the basic concepts and procedures for calibrating a video display and hands-on sessions with 13 different flat panels and front projectors located around the room. The pace is fast but relaxed, and questions are encouraged.
One thing I learned is that film has an effective resolution of about 2600x1400, or 3.7 megapixels. This is roughly twice the resolution of 1080p, so film should look much sharper than HD video, right? Wrong. As film is pulled through a projector, it starts and stops 24 times per second and, as a result, it jiggles around quite a bita phenomenon called "judder"which reduces apparent resolution.
Also, when the projector's shutter, or "gate," opens for each frame, the heat of the lamp causes the film to move back and forth, which changes the focus. These factors reduce film's actual effective resolution to something like 1.5 megapixels, which is less than 1080p's 2MP. As a result, Blu-ray and commercial digital presentation can actually look more sharply resolved than film. I've preferred digital cinema over film since I first saw it, and now I have some evidence that it is actually better. Take that, film snobs!
Of course, the amount of detail you see is directly related to your seating distance. The figures I've used here assume a seating distance of 1.5 times the screen height, which is usually about halfway back in a typical commercial cinema.
But back to calibrations. As I've maintained for a long time, the course emphasizes that the single most important thing you can do to optimize any video display's performance is to set the black level correctly. The eye is much more sensitive to small changes in low levels than in high levels.
Next in importance is maximizing the dynamic range (contrast ratio) by setting the white level correctly. The THX spec for peak contrast ratio (full on/full off) is 2000:1, and the ANSI (checkerboard) spec is 200:1, which is better than film can manage. I've seen many digital video displays that meet or exceed these specs, which is another reason I prefer digital video to film.
Speaking of ANSI contrast, I haven't been measuring that in my TV reviews because there is a lot of controversy about the methodology by which a meaningful result can be obtained. Loewen and Chen advocate a straightforward approachsimply measure the light levels in each of the checkerboard squares in a dark environment, average the white and black levels, and divide the white average by the black average. This is exactly how I've done it in the past, so I'm considering adding it to my measurements in the future.
Tuesday was all about setting the basic user controlsbrightness, contrast, color saturation, tint, and sharpness. Wednesday, we'll tackle grayscale calibration, and Thursday will finish up with tweaking a set's color-management system (if it has one). Don't tell our instructors, but Tom and I plan to cut class for a while to visit THX's video-certification lab, a new service that complements the company's long-standing audio-certification program.
I'm glad I made this trip to the Bay Areawhere I lived for four years in the '80s and love to this dayand I look forward to honing my calibration skills further. Anyone who wants a solid grounding in the art and science of video calibration would be well served by enrolling in this course, which THX offers at various locations around the country, including the CEDIA Expo in September. Check the company's website for more info.
And now, to sleepanother early day awaits.
If you have an audio/video question for me, please send it to firstname.lastname@example.org.