Specifications

248 Appendix C Display Issues
HOT-SPOTS Hot-spots appear as bright areas near the center of front or rear-projected
images. As you move your vantage point across the screen, these bright areas
tend to move with you in relation to the projected image. The only way to solve
such problems is to use another screen material. Suitable low-gain screens for
both front and rear edge-blended projection are available from most profes-
sional screen manufacturers (see also “Rear Projection” on page 245).
CREEPING SHADES When fading an image, you may sometimes see shades or ridges creeping
across or around smooth image areas. These artefacts are somewhat reminis-
cent of the Newton rings sometimes seen with slide projectors. They are gener-
ally caused by lack of resolution, similar to the description under “Banding” on
page 245.
The best way to diagnose these problems is to use a set of test images with hori-
zontal, vertical and radial gradients. Fade such an image slowly and look for
bands or rings moving across the image. Run the same test with a known good
display. The solution for this problem is the same as outlined above under
“Banding” on page 245.