The Technology of Home Theater Projectors and Systems – A Guide to Assist Buyers

The Screen Door Effect - What is It? When is it an Issue?

The days of talking about Screen Door Effect (SDE) are, thankfully, almost over. OK, not this year, and maybe not next, but soon.

Perhaps I should say, instead, that Screen Door Effect is becoming for most shoppers a very minor issue, whereas it was a major one, just 2-3 years ago.

Let’s start by deciding what screen door effect is. And to do that, let me start with the basics: This conversation is about pixel visibility – that is – can you see the pixel structure that makes up the image on the screen, from where you sit?

What is screen door effect?

Answer: It is (for projectors), having the image you are watching, appear to be distored much as it would be if you were watching through a screen door! (OK, that’s simple enough Obviously, its not something you would prefer to do, rather you want the clearest, cleanest possible image.

Let me say this: Being just barely able to see the pixel structure (on things like credits and large stationary areas of the image), is not the same as screen door effect. Screen door effect is perhaps best described as when you get a moire’ like pattern as the pixel structure visibility meets fine graphics details in the image.

One example of screen door effect might be the interaction of grass on a football field, interacting with the pixel structure, to give you a really muddy, poorly defined grass area, instead of a nice crisp one where blades are clearly visible.

The slight bit of pixel visibility isn’t a problem for most people, as most sit where the structure is just barely visible (again – large stationary bright areas, and credits).

I’m going to bounce around a bit here, to cover everything. Let’s start with the types of projectors and how they stack up, in terms of SDE and pixel visibility.

There are three types of projectors (we won’t mention those rare CRT projectors beause they are not “fixed pixel” and therefore can’t have screen door effect):

1. DLP projectors (relatively less visible pixel structure)

2. LCoS projectors (such as those from JVC, Sony and Canon, although each has its own name for LCoS – SXRD, D-iLA, etc.). LCoS projectors have pixel structures that for the sake of this article, are so fine, as to not be an issue.

3. 3LCD projectors – these have the most visible pixel structure, and therefore are the most susceptable to SDE. There are exceptions, notably the Panasonic home theater projectors which employ what Panasonic calls SmoothScreen Technology, a filtering system that makes their pixel structure no more visible than LCoS.

Considered Next is Projector Resolution!

Let’s put it this way, with 1080p resolution projectors, while pixels are still sometimes visible, even with the most visible technology (3LCD), there really is no screen door effect. The image still looks nice and clear and sharp, but you can faintly make out the pixel structure on things like movie credits, or “signage” such as all the text and graphics they put up for sporting events – scores, stats, etc. With DLP and LCoS, you just can’t make out the pixel structure, let alone any screen door effect, at normal seating distances. Even at my relatively close seating of 12 feet to a 128″ screen, with a typical DLP projector (in this case the Optoma HD71), I really can’t make out individual pixels. With the Epson Home Cinema 1080 UB – a 3LCD projector, the pixels are just a bit more visible than the DLP, and barely visible if looking for them. Still even at my close seating, its not visible enough to impact picture quality.

Editor’s note: Over the last two generations of 3LCD panels, visibility of the pixel structure has dimminshed significantly. Still not as invisible as DLP, and well behind LCoS, 3LCD is now much closer to DLP than ever before, and I would say, the difference between the two technologies in terms of pixel visibility, is now small whereas it was rather dramatic before.

Now, if you aren’t buying a 1080p projector, then you are almost certainly buying a 720p one. 1080p has 2.25 more pixels than 720p, and therefore, 720p pixels are 2.25 larger in area – and therefore more visible.

With 720p projectors many people will sit a bit further back, to avoid both pixel visibility, and if sitting very close, probably some real screen door effect.

Again, DLP has a slight advantage today, over 3LCD. LCoS projectors really aren’t on the market at this resolution.

Lastly comes 480p projectors, which, for the most part, are now just the all-in-one projectors with built in speakers, DVD players, etc., There are a couple few 480p stand alone projectors around, but they are a tiny percent of sales (whereas all-in-ones are a fast growing segment). I should note, that the first 720p all-in-one projector is shipping – the Epson MovieMate 72, which we reviewed, and is rather excellent.

With 480p, again pixel size grows by another 2.25 times. At almost anything remotely resembling normal seating distances, pixels are definitely visible on DLP models, and downright blatant, on 3LCD projectors. On 480p projectors screen door effect is easy to see.

With 480p all-in-ones I tend to favor DLP models over the 3LCD ones, all else considered, because of how bad the pixel visibility and screen door is, on 3LCD models. It’s not good on the DLP’s either but the difference is rather significant!

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