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NitWit Blog

Av Designers – Why Your Tool Box Should Include Optical Screens

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Here are some real world examples from our Race to Black series. Let’s use a room with an ambient light level of 30fc and the screen with 10fc of light on it. Using a typical projection screen, which has an ambient reflected value of 35%, the best black level possible would be 10 x .35 = 3.5fc. To get a 20:1 contrast ratio you would have to have a projector that would enable the white point to be 3.5x20 = 70fc. That is achievable, but very bright and uncomfortable to look at. Realistically, you would have to have a projector achieve 30fc and no more to be comfortable, and the max contrast would be 30 / 3.5 = 8.57:1. Viewable, but poor at best.

Using an optical screen with an ALR value of just 5% the same room would have a black level of 10 x 0.05 = 0.5. So, to hit a contrast level of 20:1 the projector would only need to be able to hit a white point of 0.5x20 = 10fc. Now that would be very easily done, but the white level should be between 75% and 150% of the room ambient with 1:1 being perfect. So if you were to use a projector that could hit just 30fc on screen, then it would be very comfortable and offer an outstanding contrast ratio of 30fc / 0.5fc = 60:1. 

At the end of the day, it’s easy to see based on the example above that an optical screen can make a huge difference in image quality. The room was barely capable of supporting projection originally, but with an optical screen it was capable of achieving great contrast and image quality. So where prior a good designer would have only used a light emitting technology such as a flat panel or direct view LED, now a projection system could be used. Combine that with the fact that it really is a race to black, optical screens are a must have in every designer’s tool set. 

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Double the Power, Double the Contrast

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Let’s examine the Race to Black theory a bit more starting with Table B, Black vs Contrast. This chart shows what happens when the black level is reduced while a white level remains constant  similar to what happens with an optical projection screen.  That technology has the ability to reduce ambient light at a different factor than projection light; effectively removing only ambient light, and lowering the black level, while leaving the projection light. In Table B the projection light level used is 400 nits at all times.  ONLY the black level changes. The black level starts out at 50 then decreases to 1 by increments of 1. So, its change is 50/1 = 50; or stated another way, it is just 1/50 times less light than where the black level started. As it does this, the contrast changes as well.  It starts at a value of 0.16 but then increases to 400. In total, the contrast change is 400/0.16 = 2500. So, the contrast went up 2500 times when the black level only changed by a factor of 50 times. What this shows is that a change in black level for an image is not proportional to the change contrast.   

A change in Table A can also be seen but let’s explore this idea further to see how this breaks down. This chart is shows the contrast level change as white is increased from 50 to 1000 nits, in increments of 5 nits. So, 1000/50 = 20 times higher at the highest point than the lowest. The black level stays constant at 50. Through this the contrast increases from a level of 1 up to 20. So, the contrast change by adding white is 20/1 = 20; the same as the light increase.  This shows that the increase in white and contrast is proportional when the black level remains the same. In effect, if a system uses double the power, then you get double the contrast. This is similar to what is done with traditional screens. The ambient light cannot be removed so all you can do is add more projection power. 

When combined, these two tables illustrate that the key to success is a race to zero and not a race to more power. In an industry where designers are running with their hair on fire to add more and more power to overcome a room’s brightness, that’s a bold and confrontational statement. Yet, the reality is that at the end of the day the numbers speak for themselves. So, if you are a designer, stop, turn around and go the opposite direction. Get as black as possible and then work on the power level to get a proper white point. Once that is in place, you can indeed use projection in areas that you could not use before. Stay tuned for our next blog post regarding The Race to Black          

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Contrast is KING!

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When it comes to display technologies, projection systems have been around a very long time.  There have been many improvements in the technology, but nearly all of them apply to the projector.  There have been variations in projector imaging systems, such as three gun CRT, LCD, DLP engines; as well as light engine improvements from electron gun to UHP and Xenon bulbs. So as a system projection grew, but the screens stayed similar being some form of coated vinyl, particulate bead, or a mix of both.  Around 2004, screen technologies that factored in ambient light rejection started to emerge in the market, and that enabled projection to really progress. This is because optical projection screens remove ambient light without removing the projected light. Projection systems can now be used in areas where only light emitting technologies were capable of being used.

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