What is the new backlight on the new iPhone?

Apple recently announced new iPhones and made several hardware changes targeting the camera. Thanks to the lost iPhone fiasco, we expected a 5-megapixel camera and flash, but Jobs announced that the camera was backlit. This baffled us so we did some research on the camera chipset.

What is the backlight?

First stop laughing... Hmm... I'll admit I think they could have come up with a better name. Some of the jokes I've seen on Twitter seem particularly crude about this feature. Backlighting is a technique for obtaining better digital images by having more light available where the measurement is being taken.


		Find 26 AbeBooks coupons and free shipping coupon codes for January on RetailMeNot. Today's top AbeBooks coupon: Free Shipping.

First an overview of digital cameras

At the heart of all digital cameras is a chip called a CCD (charge-coupled device) that senses light falling on its surface. When a chip is manufactured, light affects a charge on a grid of millions of tiny silicon capacitors (making a chip is called fabrication and involves many punches, thin layers, and deposits of various materials in a precisely controlled manner).

For simplicity's sake, just think of a black and white CCD where arrays of capacitors correspond to arrays of pixels that make up a digital image (color sometimes uses a lot of tricks). The chip contains an additional circuit that measures the charge on all capacitors, which is basically how you read the light levels in an image. To be able to read all of these capacitors, the fine micro wires are facing up. These aren't actually wires, but rather a thin layer of aluminum or copper that's effectively sprayed onto the chip and then carefully etched with acid to leave traces of the interconnect, which are the metal wires attached to the chip.

Why backlight?

All of these wires and other parts of the capacitors sit on top of a square silicone plate (called a die) with the capacitors underneath. The circuits and cables don't get in the way as much as they work but they block some of the light and scatter some of it into the surrounding condensers which reduces the quality of the images taken especially with limited lighting.

Back to the square silicone tiles. Silicon is the main ingredient in regular glass (also known as silicon dioxide) but the material used to make the chips is an ultra-pure, transparent silicon crystal. With backlighting, the traditional CCD problems under capacitors are literally reversed, and now you can shine the image onto the underside of the silicon tiles and let the light shine through the silicon onto the capacitors. This way you can avoid all the wires and get more light on the capacitors.

Apple showed off some nice photos with this new camera chip, but its key performance area will be in low light. Catching scenes like the last light of a blurring nightfall.. Previous iPhones (the original and the 3G) had very basic fixed focus 2MP cameras that struggled in low light. The 3GS brought auto focus and auto white balance which improved performance but still suffered from scenes like this, often with color distortion. Now with the new camera chip, the iPhone should take vastly improved photos, along with the built-in flash for low light on the inside.

Built-in LED flash for iPhone camera

YOU MUST READ THIS