Video Projectors

As we've noted before, a video display's contrast can be measured in several ways, each of which results in very different values. Using the Stewart StudioTek 130 screen and test patterns from the Video Essentials test DVD, I measured the InFocus Screenplay 110's contrast three different ways: full-on/full-off, 16-square checkerboard, and 100 IRE (maximum brightness) window. In full-on/full-off, the flat field (full-screen) 100 IRE output was compared with the full-screen black field resulting from an open input (VE, chapter 18-14). The result was a contrast ratio of 311. In the checkerboard test (VE 17-28), each of the 16 squares was measured, the high and low values thrown out, and the resulting average high and low values compared. This resulted in a contrast ratio of 65. And with the 100 IRE white-window method, comparing the output from a 100 IRE window (VE 17-10 or 17-32) with an averaged reading from the black border surrounding it and discarding the low value, the result was a contrast ratio of 173. (The last method is designed to simulate a display's performance with typical video material.)

Using the only gray-scale adjustments available—the overall R, G, and B controls in the user menu—I calibrated the gray scale and got the results shown in the figure. The measured color points are a little off from the absolutely correct value of D6500, tending a little toward the blue (a shortage of green) at brighter average picture levels. But without separate controls available to adjust both ends of the brightness range, any attempt to compensate for this caused the lowlights to shift toward green—the most visibly distracting color shift and one best avoided. While the factory-standard 6500K setting was actually very good, it shifted more strongly toward green at low levels than the result shown here.

Calibration with the Stewart 248 FireHawk screen
The first thing I noticed about the FireHawk screen was that, using the assumed 1.3 gain of the StudioTek as a reference, its gain was approximately 1.08. A light level of 23.6ft-L on the StudioTek dropped to 19.6ft-L on the FireHawk with no change in the projector settings or location. The measured gray scale, however, didn't change—an excellent result. The full-on/full-off contrast was almost identical to that on the StudioTek, at 316. But the contrast measured on the checkerboard pattern improved to 97 and the contrast using the 100 IRE window relative to its black border to 248. Clearly, something positive was going on. The FireHawk improved both the subjective black level and the color quality.

While the correct settings for any projector will depend on many factors, including unit-to-unit variation in various samples, here are the final settings I used with the InFocus projecting onto my FireHawk screen: Brightness, 58; Contrast, 57; Tint, 53; Color, 70; Sharpness, Soft or Medium Soft; Degamma, Film. The color-temperature settings were: red, 60; green, 40; blue, 56. The Kenwood Sovereign DV-5700 DVD player was set as follows: Contrast, -1; Gamma, -2; DNR, 0 or +1; Sharpness, 0 or -1.—;TJN