Monday, September 1, 2008
Megapixels: How Much Is Enough?
Pixel count certainly plays a key role in photography, but we’re approaching a point of diminishing returns and potentially reduced image quality as more pixels are packed onto a sensor
It’s nothing short of amazing that technology has continued to advance at such a rapid rate as to enable ever-increasing numbers of megapixels while improving overall image quality. However, as the number of megapixels goes ever higher for a given image-sensor size, overcoming the inherent limitations of smaller photodetector sizes will become increasingly difficult and, ultimately, we’ll run into barriers we can’t avoid. That will require either accepting a limitation on how many megapixels we can have ultimately or using a larger-format image sensor to enable larger photodiodes at a given megapixel count. Even before we reach whatever limits the laws of physics might impose upon camera manufacturers, we’ll likely see some reduction in the performance of new digital cameras. For example, because of smaller photodetectors, the dynamic range will be reduced, causing a loss of highlight or shadow detail in many images.
There’s no question that more megapixels lead to digital photos with improved detail and image quality. However, it has long received too much focus as a measure of the advancements in digital camera technology. What matters most, ultimately, is the quality of the final image. It’s important to appreciate that there’s much more at play here than how many megapixels are packed into the sensor. Perhaps in the future you’ll hear fewer photographers ask, “How many megapixels are in your camera?”, and more ask, “What’s the full-well limit of the photodetectors in your camera?” and “How small is the inter-pixel spacing on your sensor?” Or perhaps photographers will learn to appreciate that the technology in their digital cameras is incredibly advanced and beyond the ability of most photographers to truly understand, so they can go back to focusing on what really matters to photographers: the final image. Isn’t that what it’s all about?
| LEFT: This illustration shows how dust and stray light are eliminated and filtered out in front of the sensor. RIGHT: You can see graphically the relative size differences between sensor types. |
Tim Grey has written more than a dozen books on digital imaging for photographers. He publishes the Digital Darkroom Questions e-mail newsletter and Digital Darkroom Quarterly print newsletter. For more information, go to www.timgrey.com.
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