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
Due in large part to performance limitations owing to their basic structure, I believe CCD image sensors will be relegated to lower-end cameras. They won’t disappear altogether anytime soon, but their higher power consumption and slower data-transfer performance relative to CMOS sensors mean they likely will be seen in fewer and fewer cameras moving forward.
I also believe that CMOS image sensors are here to stay for quite a bit longer, and that their development largely will be evolutionary rather than revolutionary. This may involve changes that seem rather significant, and that greatly improve resolution and image quality. Probably, they will be extensions of what’s currently possible rather than something entirely new. For a start, it’s likely we’ll see an increase in photodiode density across the board. Microlenses will be universal and will cover the full photosite area. Amplification technology will be put to full use to ensure the purest signals possible. Sensors with backside-illumination will become standard. But I think we’ll also see some changes that might be surprising.
I suspect we soon may see image sensors from Canon and Nikon that record a full color value at each photosite, rather than recording one color (red, green or blue) per photosite and using interpolation to calculate the full color value. Sigma digital cameras employ such technology with the Foveon X3 image sensor, so the general concept isn’t entirely new. Still, it holds promise for further advancements from the top manufacturers of digital cameras.
What I know for certain is that no matter what technological advancements occur in digital photography, many photographers (perhaps myself included) will continue to postulate that the end is near and that digital camera development has reached a dead end. But as we’ve seen so many times, just when we think the potential for a particular tool has been maxed out, smart engineers find a way to squeeze a bit more power out of current technology and impress us with new possibilities.
|Has ISO Maxed Out?|
|Back when the world of photography revolved around film, photographers typically were eager to use film with the lowest ISO rating possible. The intent was to ensure the finest grain structure possible, of course, and a higher ISO meant more grain. With digital cameras, the trend has reversed itself. Now photographers seem eager to find cameras with the highest possible ISO setting and the digital camera with best noise performance even at high ISO settings.
The highest ISO rating for commercial photographic film was 3200. In fact, the published charts that outline ISO values max out at around 10,000. And yet the latest digital cameras include much higher ISO setting options, with some even offering a staggering ISO of 102,400.
Of course, a higher ISO setting means more noise, but over time camera manufacturers have been able to improve their noise-reduction technology to the point that noise levels are acceptable even at very high ISO settings. Levels of around 1600 in the latest cameras are generally considered to represent the threshold of acceptable image quality. The question is, how much further can the signal be amplified while still achieving good results?
The reality is that even with advanced technology, a signal only can be amplified so much while still retaining the accuracy that enables low noise and reasonably high dynamic range. That means achieving higher effective ISO with good image quality will require larger photodiodes. That, in turn, will require lower resolution (something photographers aren’t likely to embrace) or larger image sensors (which would require different lenses that project a larger image circle and, thus, a different overall camera system). Also, because there’s a benefit to using the lowest ISO setting possible for a given photographic situation, there’s a practical limit to the ISO settings photographers need.
While I’m sure we’ll see noise levels at the currently available ISO settings come down as sensor technology improves, it’s becoming less likely that will include an ability to achieve images of acceptable quality at ever more extreme ISO settings.
Tim Grey has leveraged the latest technology to ensure maximum signal and minimum noise in his new video training titles in the Learn By Video series, produced by video2brain and published by Adobe Press. Get the latest info at www.timgrey.com.
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