In case you’ve ever tried to arrange a projector you will be aware of the wrestle of getting a superbly rectangular picture on the wall. It’s because the lens of projector needs to be perpendicular to the display screen. If any nook of the projector is nearer to the display screen than its reverse, you will get some form of trapezoid as an alternative of a pleasant rectangle. 

This is not a brand new drawback, and for many years projectors have had a “function” to counter this problem. Referred to as keystone correction, or keystone adjustment, it’ll technically make a rectangle out of your trapezoid… so to talk. In case you care in any respect about image high quality, do not use it. This is why.

The issue with not being perpendicular

Projectors are a two-piece system: the projector and the display screen. Even when you’re utilizing a wall or the aspect of your own home as an alternative of a display screen, that also counts. All projectors use rectangular imaging chips to create a picture, and it is essential that the picture despatched by the chip is precisely perpendicular to the display screen. Each nook must be the identical distance to the display screen as its reverse nook and if that does not occur, the form will get distorted.

Even when you’ve by no means used a projector, you have in all probability seen this impact in motion. Ever used a flashlight? Level it straight on the wall and you have a circle. Level it on the bottom forward of you, and it is an oval. Identical idea. 

Some projectors have a function referred to as lens shift, which mechanically adjusts how the imaging chips, lens and display screen line up. Lens shift enables you to transfer the picture barely on the wall with out hurting picture high quality, however its adjustment vary is restricted. In case you’re past how far the lens shift can alter, or the projector haven’t got lens shift in any respect, misplacement will trigger the picture to go askew. 

Most screens have black borders so you do not want actual placement to the picometer, but it surely’d be a disgrace to spend cash on a projector, and time on putting in it, solely to be irritated on the seen edges whenever you’re utilizing it.

Which is why each projector has keystone correction. That does not imply it is good. 

Keystone: Not even as soon as

Keystone correction goals to unravel electronically what’s inherently an optical drawback. The projector will digitally alter the picture in the wrong way to offset the trapezoid. So if the picture is, say, smaller on the left than the precise, the projector can scale back the dimensions of the precise aspect so it seems rectangular once more. Intelligent, proper? Form of. Sadly there ain’t no such factor as a free lunch.

All trendy projectors use one in every of three applied sciences, DLP, LCD, or LCOS. All of them have a hard and fast variety of pixels, or image components, used to create a picture. There is not any solution to change the variety of pixels on one in every of these chips. These imaging chips are typically mounted in place as effectively. 

What keystone correction does is scale the picture smaller, after which additional course of it to kind the form required to “look” rectangular. Or to place it one other means, it is drawing a trapezoid inside a rectangle, however as a result of the projector and picture itself is skewed, that trapezoid now seems to be rectangular.

Each of this stuff scale back picture high quality. Scaling, on this case, reduces the variety of pixels used to create the picture. You are solely utilizing a portion of the imaging chip to create the brand new picture form. The extra you alter the keystone, the less pixels are used, additional softening the picture. 

Most projectors haven’t got a lot processing energy, so this scaling would possibly additional soften the picture, or it’d introduce different noticeable artifacts. Altering the form of the picture is an additional processing problem and may add further artifacts.

And if that weren’t sufficient, it is inconceivable to show “off” the pixels you are not utilizing. So there’s nonetheless going to be mild projected on the display screen from these unused pixels, which seems contained in the trapezoid form you have been attempting to keep away from. In an excessive scenario, you possibly can have a noticeable grey picture past the display screen space. Inelegant at greatest, distracting at worst.

The answer? Place the projector correctly

There is not any higher answer than not having the issue to start with. Correct projector placement placates potential image perils. Or to cite the traditional adage from prehistory: measure twice, reduce as soon as. 

In case you’re mounting your projector completely, double- and triple-check the mount is within the appropriate place in your projector. That is essential. Most projectors, particularly these primarily based on DLP, have their lenses offset from the middle of the projector. Ideally, your mount may have some adjustment “wiggle room,” but it surely won’t. 

Normally you possibly can obtain a mounting template and different information from the producer’s web site. 

Additionally think about that almost all projectors, once more particularly these primarily based on DLP, have an “upward throw.” Which is to say, they create a picture a number of inches above the highest of the projector (or under, if it is mounted on the ceiling). You’ll be able to’t tilt the projector down since that, too, creates a trapezoid. Once more, this information is on the corporate’s web site.

So yeah, when you completely have to make use of keystone correction, go for it. Nevertheless it ought to solely be used as a final resort in conditions the place you bodily cannot place the projector in its correct place. In case you’re mounting it, it is best to spend the time and get it proper the primary time and never depend on image-reducing digital trickery to repair a nasty set up.  

In addition to overlaying TV and different show tech, Geoff does picture excursions of cool museums and places world wide, together with nuclear submarines, large plane carriers, medieval castles, epic 10,000-mile street journeys and extra. Take a look at Tech Treks for all his excursions and adventures.

He wrote a bestselling sci-fi novel about city-size submarines, together with a sequel. You’ll be able to observe his adventures on Instagram and on his YouTube channel.

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