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Picking the Proper Projector Part 2: Beyond Brightness

It’s funny how great minds think alike. No sooner had I posted my first blog on picking the proper projector than I received a comment from Aaron Peterson at Mechdyne pointing out that I missed a crucial part of the puzzle, and that is the misleading marketing around projector resolutions.

Projectors

Warning: If you thought the last blog was “tech geek fabulous,” this one is going up a notch.

To start at the beginning, many projectors tout a 4K resolution, however, the components inside the machine are not actually producing a native 4K image. They are utilizing an LCD or DLP engine that is likely either 1080p native resolution or 2560×1600 (WQXGA) native resolution, and then they are “moving” that engine at 180 or 240Hz to create a larger pixel map by double/triple/quadruple flashing the chip for every frame.

In fact, the only two TRUE 4K projector engines I know of are DLP projectors that utilize the 1.38″ DMD with a native 4096 x 2160 resolution (only available in cinema and high end RGB laser projectors) and the Sony or JVC products using the 8.5 million pixel SXRD and D-ILA LCoS variants.

Any of the other LCD and DLP projectors touting 4K are really “Faux K.”

Let me say that at smaller screen sizes and in single projector installations, some of this pixel-shifting or wobulation if your prefer, can be acceptable, especially when viewing PowerPoint or full-motion video.

However, when you start to reach larger screen sizes, need to blend multiple projectors, or need to reproduce very fine detail accurately, pixel shifting and wobulation can be a problem.

There is an upper limit to screen size and detail.

When I was at Barco, we had a client who used one of our projectors to analyze launch data for a space program. As you can imagine, in this use case, the legibility of data was critical. We quickly found that the 4K mode of the projector, which utilized a native 2560 x 1600 chip and moved it around to create a 4K canvas, was a problem. At the scale at which it was being produced, the data was blurry. Luckily, Barco projectors have the option to disable the 4K mode and utilize the native resolution of the chip. Barco also had a product that was native 4K with the 1.38″ DMD, so we were able to offer the first option at no additional cost or the second one for a fee.

Blending while moving is not encouraged.

Another application where pixel shifting and wobulation may be a problem is in applications where you are blending multiple projectors. In a blend, you are overlapping pixel areas of two projectors to feather the images together, and if those two images are moving around, then those feather zones may be soft or very noticeable. There is already an art to creating the right black levels in a blend zone, but add in some movement and your issues potentially increase. I typically advised that the 4K mode be disabled in blending applications, to assure the best chance for a natural blend, even if at a slightly lower total resolution.

Pretty pictures versus data.

I’ll always remember walking into Projection Design’s booth at InfoComm, (prior to their acquisition by Barco in 2013), and seeing something NONE of the other booths were showing. Excel.

Most projector companies utilize beautiful content with vivid, high definition imagery. So why was Projection Design showing excel on one of their screens in the booth? To show off the detail in its WQXGA projector. Sure, a peacock looks great on a lot of projectors, but what about 11-point font?

Even at smaller sizes, content that requires higher detail is best displayed in native resolution. Shifting the pixels in a very small area becomes more noticeable and can have a negative effect.

Proper aspect ratio.

My number one rule is match native resolution and aspect ratio of the content to the playback device if at all possible. This assures what was created will play back as intended.

See related  Picking the Proper Projector

However, many times we may not know what content is going to be played back.  In these cases I typically recommend 16:9 as most content is trending that way. Even most of the new dvLED cabinet based systems are 16:9 aspect ratio now.

Of course many projectors have the option to do different aspect ratios like 16:9, 16:10 and 21:9 now. What you need to understand is that the if you’re doing the math on brightness we talked about in the first blog, that you will need to use the native aspect ratio of the projector when doing that math.

The projector’s light path will be in the native aspect ratio. For instance, let’s go back to the 16′ wide screen we were using in the first blog. A 16:9 image is 16 feet wide and 9 feet tall or 144 square feet. A 15,000-lumen projector would provide 104 lumens/sq foot. If you are doing a 21:9 aspect ratio image with that same projector, the image width is still 16 feet and the height of the image is 6.85 feet. The total image area is 110 square feet. What is the brightness per square foot?

If you divided 15,000 by 110 to get 136 lumens per foot you’d be … wrong.

The brightness is still 104 lumens per foot on a 16′ wide screen. You’re just not utilizing the top and bottom of the light path, as the light path doesn’t change, it’s still 16:9, you’re just cropping content within it. This means you should also be cognizant of the reflectivity of the material above and below, as “video black” still has some brightness to it that may show up on the screen or wall.

Changing aspect ratios.

One of the most challenging projects I ever had was a projection environment that needed to support different aspect ratios at a constant image height. They wanted to support the most common cinema and video aspect ratios being 16:9, 1.85:1, 2.35:1.

However, they didn’t want the image height to change at all and the native aspect ratio of the projector was 16:10.

So how do you accomplish something like this? I think an illustration will help.

 

Constant Height

 

As you can see, the light path is larger than the image area, so that light and those pixels are “thrown away.” Every image is a constant 9′ tall, but at different widths. If you know projectors, you know throw distances are based on image widths, so each of these screens has a different throw distance.

This requires a few things:

  1. A lens with a throw range able to accommodate both extremes of the image widths.
  2. A projector with motorized zoom and the ability to index and save different zoom presets.
  3. Optional: a projector with internal masking to create a physical crop around the image and eliminate the light bleed in the unused areas.
  4. Optional: a motorized masking system for the screen to bring the left and right edges in to create the proper aspect ratio black frame.

Note: Yes, you could also do this with a single zoom setting and use processing to “window” the smaller images into the proper portion of the screen, however those smaller sizes would be at lower resolutions than in the scenario above. They would all be at 1090 pixels tall with differing resolution widths.

That about does it for part 2, and I think I’ve gotten geeky enough today to last a little while.

Will there be a Part 3?

It depends on if another engineer calls me out on LinkedIn or not … LOL. JK Aaron! Thanks for the inspiration and for challenging me to go deeper.

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