HC720 SDE and Rainbow Effect, Pixel Visibility

Posted on October 5, 2008 by Art Feierman

As a 3LCD projector (3 separate LCD panels), the Epson HC720 does not have a color wheel, and therefore cannot cause the rainbow effect. SDE, or screen door effect, on the other hand, is getting a finely distorted image, caused with the pixel structure of the projector interacts with fine details of the image, giving a pattern similar to looking through a screen door. The less visible and smaller (smaller as in higher resolution - as with higher resolution projectors), the less likely that it is detectable. The solution normally is to sit far enough back so that the pixel structure of the projector becomes completely invisible. Most, though sit just far enough back that the pixel structure is really only visible on signage - things like white text credits, and the kind of overlays you see with scores, and info on sporting events). While 720p LCD projectors, LCD panels have improved over the years, allowing you to sit closer. Let's say that if you have a 100" screen, that limited visibility is going to be there if you sit closer than about 1.5 times screen width (that would be about 130 inches on a 100" diagonal screen, which is 87" wide).

I have been viewing the Epson much closer than that - 12.5 feet back filling my entire 128" screen, which is approximately 110" wide. Theoretically, that would be just over 15 feet. I found the viewing to be fine. I never noticed any screen door effect watching football and other content - and football grass is definitely one place where you usually can spot it. At my distance, I could, however make out the pixel structure in those credits and other signage, and even in large stationary white areas, such as a large cloud, but you really have to be looking for it, to see it in all but the signage. Bottom line, a typical good 3LCD projector in this regard. If you never want to see pixel structure and not sit 1.5 times width or further back, look to DLP projectors, or the Panasonic PT-AX200U, which uses their Smooth Screen technology, but produces a softer looking image (which some will say is also more film like).

Click on the thumbnail image here, for a large version of this highly cropped dts logo. The width of the cropped image is roughly 15% of the fully uncropped image. In the large image, you can see the pixel structure that I describe. Finding the same image on a 720p DLP (or that Panasonic PT-AX200U), will show less visible pixel structure, and if you compare with any 1080p projector, it will be even less visible on those.