Optoma H56 DLP front projector Calibration And Performance

Calibration And Performance

After calibrating the H56 with the Video Essentials test DVD, the AccuPel HDG-2000 test-pattern generator, and DisplayMate for Windows, I managed to pull just under 600 ANSI lumens out of the Optoma H56 with an average ANSI contrast reading of 470:1 (really quite good) and a peak contrast reading of 814:1 (outstanding). Brightness uniformity was 56% (not so good), just above where you'd start to see a hot spot, while white-field uniformity was 5.3% (terrific). The H56's lens had some pincushion distortion when zooming (not so good), but provided very good text sharpness with slight lens flare (good).

The most frustrating controls to use were the H56's RGB Contrast and Brightness settings. At first glance, I thought I could dial in a specific color temperature quite easily with these six adjustments and a calibrated color-temperature meter. Unfortunately, the controls interacted too much with each other.

This problem was compounded by a pronounced green shift when viewing 1920x1080i signals in Y-Pb-Pr (analog component) mode. I would spend several minutes trying to achieve a neutral gray scale with a 480p or 720p signal, then shift the HDG-2000 to 1080i output and watch the entire image go green—not solid green, but a strong tint of "can't dial it out" green.

Further investigation revealed that the problem occurred only with tri-level-sync signals (the ATSC standard for digital TV). Changing to a bilevel-sync format cleaned up the gray scales immediately, as did selecting the RGB analog input for all HDTV sources. Using the H56's RGB input may be a practical solution for some set-top boxes, but older STBs and some current ATSC tuners, such as Samsung's SIR-T151, don't support this output format.

In Color Temperature modes 1 and 2, gray-scale test patterns had a noticeable magenta tint. There was also a certain amount of green-blue that I had problems tuning out. Sure enough, a color-temperature meter with a three-axis indicator showed that while I could adjust the low end of a gray scale to be close to D6500, higher luminance values then shifted greenish-red.

So I set the higher luminance values to a neutral gray value—but then lower values started to swing green. Arrrgggh! In the end, I opted for setting a 50% gray bar to a close match at D6500 and let the other bars fall where they might. An easy brute-force color-correction fix was achieved by using a 20R (red) Wratten color filter over the lens to forcibly "yank" the entire gray scale into a more desirable white balance—but this had the effect of cutting the H56's light output by half.

I got the best white-balance results using 480p/60 and 720p/60 input sources, plus 1024x768 PC sources or video scalers. Here, I managed to achieve a moderately good gray scale, although it varied by as much as 1000 kelvins from top to bottom. RGB mode provided slightly better results, but not nearly as good as some thoroughbred LCD and DLP home-theater projectors. Dang—it looked so easy with those six sliders . . . —PP

TJN Comments: My sample of the Optoma H56 was not the one used for PP's review. My sample's color temperature, as delivered, was most accurate in the "1" setting, the "2" setting ranging between 7100K and 8300K, and "3" between 8500K and 10,600K (my results are shown in the graph). I had better luck than PP with the gray-scale calibration. Using our Photo Research spectroradiometer, the gray scale remained within 311K of 6500K, with coordinates very near to the desired D6500 values.

For the primary color points, red was shifted a bit toward red-orange, green slightly to yellow-green, and blue to greenish-blue. These deviations were no greater than those in most of the other DLP projectors we've tested to date. Apart from the input and sync issues noted in the review, I found the H56's subjective color quality to be good.

I measured a peak contrast reading of 900 on my 80-inch-wide Stewart FireHawk screen, with a maximum (100 IRE, full white field) of 12.6 footlamberts and a minimum (black level) of 0.014fL. To put this in perspective, that peak output is higher than that from most of the more expensive HD2 projectors we've tested (good), but the black level is higher (not so good). The best peak on/off contrast measurements I've obtained from HD2 projectors were in excess of 2000, with black levels as low as 0.004fL. The latter figure is from the Marantz VP-12S2 and the Sharp XV-Z1000. (The Sharp is reviewed in this issue.)

PP uses a different technique to measure contrast, employing a white-and-black checkerboard test pattern. In some ways this is more rigorous than the on/off reading; it certainly produces less impressive numbers. I, too, find the peak on/off readings useful as a basis for comparison, but be careful when comparing the contrast readings in manufacturers' specifications; they almost invariably show only peak contrast. More important, they don't all use the same procedures to measure it.

I use the same technique for all my on/off peak contrast readings: The projector's gray scale is first calibrated, then the video controls are set where they produce the best overall images on a wide variety of film-based program material, and not just to produce the best contrast numbers regardless of picture quality.

I didn't find the Optoma to be as quiet as did PP; it was acceptable, but the NEC HT1000 I reviewed in the July/August issue was far quieter. The NEC also had less stray light leaking out of the case. Both projectors were about equally susceptible to rainbow artifacts; those sensitive to this problem will occasionally see them.—Thomas J. Norton