• 
• 

Tuesday, October 5, 2010

Megapixels And ISO: Have We Reached The Limit?

Although there’s no question that the pace of increase has slowed, noise-reduction advancements are poised to fuel continued resolution boosts

This Article Features Photo Zoom

By comparing noise levels in an exposure to a completely dark frame, the camera is able to determine dead pixels and noise through pixel mapping. Performing noise reduction at the chip level also helps to maintain image sharpness.

Microlenses certainly help, but a perhaps better solution for getting more light to the photodiodes on a CMOS image sensor is to get the supporting circuitry out of the way. This variation on an image sensor is referred to as a backside-illuminated sensor, and such sensors are already in use in a variety of digital cameras. For now, backside-illuminated sensors are only used in consumer point-and-shoot cameras. As the cost of producing these sensors is reduced and additional technological and manufacturing hurdles are overcome, we’ll almost certainly see this technology appearing in digital SLRs.

Increasing the ISO setting on a digital camera doesn’t change the actual sensitivity of the image sensor, rather it results in increased signal amplification. However, even at the lowest ISO setting, there’s still some amplification of the signal recorded by the image sensor. Even under the best circumstances, amplification of a signal will lead to some noise, and there actually are several varieties of amplification used within an image sensor at various stages of the capture and processing cycle, which provides multiple entry points for noise. Advancements in amplifier technology, as well as clever engineering and sensor design, help minimize the noise caused by signal amplification.

Despite stringent manufacturing processes and highly advanced technology, imaging sensors don’t always do a consistent and perfect job of recording a signal with complete precision. This behavior varies not only from one image sensor to the next, but also from shot to shot for a given image sensor due to the electrical charge not being completely released from each photodiode, excessive heat and other issues. Many digital cameras now employ a technique whereby a “blank” image is captured immediately before the actual capture in order to record the current noise signature for the image sensor, which then can be subtracted from the subsequent capture.
On The Horizon
It seems we’re all looking for some earth-shattering news of a major technological development that will take digital photography by storm and greatly improve the level of detail and quality we’re able to achieve in our images. And yet it seems the greatest potential, at least in the near term, comes from variations on solutions that already have been tried.

It’s obviously incredibly difficult (and perhaps even foolhardy) to attempt to predict what the future may hold in terms of technological development. However, I can reasonably predict a few things.