Recently, Apple announced the new iPhone and several of the hardware changes were directed at the camera. Thanks to the infamous lost iPhone fiasco, we were expecting the 5-megapixel camera and flash, but Jobs announced that the camera had illumination on the back. That left us stumped, so we did some research on camera chips.
What is back lighting?
Stop laughing first… Okay… I admit I think they could have come up with a better name. Some of the jokes I saw on Twitter seemed to be especially crude about this feature. Backlighting is a trick to getting better digital photos by getting more available light where you measure.
Digital Camera First Year Overview
The key part of all digital cameras is a chip called a CCD (charge coupled device) that detects light falling on its surface. Light affects the charge of a network of millions of tiny capacitors created on the silicon when the chip is fabricated (making chips is called fabrication and involves a lot of etching and deposition of thin layers and different materials in a precisely controlled way). For simplicity, think of black and white CCDs where the array of capacitors corresponds to the array of pixels that make up a digital image (color sometimes uses a lot more tricks). The chip has additional circuitry that measures the charge on all the capacitors, which is basically how light levels are read from the image. In order to read all of these capacitors, there are minuscule thin wires that extend across the top. These aren’t actually wires, but a thin layer of aluminum or copper that is effectively sprayed onto the chip and then carefully eaten away with acids to leave connection traces, which are practically metal wires attached to the chip.
Why rear lighting?
All of those wires and other capacitor parts sit on top of a square tile of silicone (called a matrix) with the capacitors on the bottom. The circuitry and cables don’t obstruct it too much while it’s working, but it blocks some light and scatters it onto the surrounding capacitors, reducing the quality of the captured image, especially in limited lighting. Let’s go back to that square silicone tile. Silicon is the main ingredient in normal glass (also known as silicon dioxide), but the material used to make chips is a transparent, superpure silicon crystal. With back lighting, the problems with traditional CCDs from the capacitors at the bottom are literally reversed and it now illuminates the image on what was the bottom of the silicon tile and lets light shine through the silicon onto the capacitors. . In this way you avoid all the cables and more light reaches the capacitors.
With this new camera chip, Apple has shown some beautiful images, but the key area of ​​performance will be low light. Capture scenes like the last light of a fading sunset. Earlier iPhones (Original and 3G) had very basic fixed-focus 2-megapixel cameras that struggled in low light. The 3GS brought autofocus and auto white balance which improved performance, but still struggled with such scenes, often distorting colors. Now, with the new camera chip, the iPhone should take much improved photos, along with the built-in flash to handle low lighting indoors.
