Sign & Digital Graphics

September '14

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ELECTRIC SIGNAGE 82 • September 2014 • S I G N & D I G I T A L G R A P H I C S duced by a display are simply combina- tions of those three colors. EMC Color Control In an LED display, colors are dictated by the EMC's control system, which is the part of the display responsible for controlling the content shown on the screen. An E M C , being an electronic device, communicates in bits (binary digits). These are the 1s and 0s that we hear about so much—and they represent the smallest unit of data within an elec- tronic device. A bit can be a 1 or a 0. Therefore there are two options. When we're talk- ing EMC's and their control systems, that means two brightness levels. What if we have four bits? In that case each bit can be a 1 or a 0, giving us two options but we have four of them. Therefore, we have 2 x 2 x 2 x 2 options or 2 4 = 16 bright- ness levels. Let's bring it back to displays. Most control systems today will support around 16 bits of color per channel. When we say channel, we are refer- ring to the red, blue and green color within each pixel. 2 16 = 65,536 shades. That seems like a lot, but it's just one channel. Those color levels get to mix with each other. With three channels, the total number of colors that a 16-bit system can display ends up being 65,536 x 65,536 x 65,536 = 281 trillion colors. Okay, 281 trillion colors sounds like as many colors as you could possibly commonly used file format for images is JPEG. JPEGs are limited to 8 bits. Let's look at those numbers. An 8 bit JPEG file would have 28 shades per channel. That's 256 total shades. With three channels we have 256 x 256 x 256 = 16.8 million pos- sible colors in our image. If a 16 bit dis- play can show 281 trillion colors, a num- ber that is exponentially larger (I mean that it is literally exponentially larger. It is exactly 16.8 million ^2) than the number of colors that can be contained in the most common file format, what benefit could be garnered from adding even more colors? Not much. Let's step back and make that number real by equating all those colors in terms of distance. If the number of colors that a 16 bit display is capable of showing were represented by the distance from the earth to the moon, the number of colors that a JPEG could display would be equivalent to about ¾ of the length of a basketball court. Calling that excess capacity is a bit of an understatement. Think about it. Have you ever looked at a JPEG photo on your computer and thought to yourself, "I really wish I could get a few quintillion more colors out of this thing?" Why would your EMC be any different? Human Perception It can be quite revealing to illustrate the capabilities of the images being displayed on an EMC. Let's go deeper though. EMC's are an effective advertis- ing medium. The fundamental goal in need. Go back to your display quota- tion though. Odds are you're looking at a figure much higher than that. Many vendors will boast numbers you've probably never heard of—numbers in the quadrillions and quintillions of colors. The natural questions that come to mind are; should you care? Or, will this mean that my customer will have a better per- forming product? In today's market, the resounding answer is no, as long as we're meeting a minimum number of colors. I'll show you why. Excess Capacity First and foremost, let's think about how one uses an LED display. Through software, one of the most common uses is to load and display photo images on the display. Like any digital file, photos must adhere to units of data as well so 1s and 0s are being used again. The most A bit can be a 1 or a 0 (two options). A four- bit channel offers 16 brightness levels.

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