DPP Home Gear Imaging Tech Megapixels: How Much Is Enough?

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




image sensors
image sensors
The Canon EOS-1Ds Mark III (TOP) and the Nikon D3 (ABOVE) are two of the most popular full-frame, 35mm-type D-SLRs for professionals today. These technological marvels have the most state-of-the-art, on-board image-processing systems available, as well as the most advanced sensors. It’s widely accepted that new, higher-resolution models are on the way, but the images coming out of both of these cameras are outstanding and capable of radical enlargement.
To combat this noise, camera manufacturers have developed a variety of solutions. That includes doing everything possible to keep the size of the individual photodetectors as large as possible (an uphill battle, to be sure), as well as applying sophisticated noise-reduction processing to the data gathered by the imaging sensor.

The size of photodetectors also has an impact on the amount of noise present in a digital photo. Noise results from a variety of factors, but it represents errors in the measurement of pixel values. In effect, noise results when the camera has to guess at the value of a pixel it isn’t able to see very well.

Maximizing the signal level recorded by the sensor in order to minimize noise also will improve final image quality in a variety of other ways, so it’s important to understand some of the ways manufacturers work to ensure as much information is recorded by the sensor as possible (and that the information isn’t lost as it’s processed by the camera while creating the file stored on the digital media card).

To start with, actually getting the light to the sensor is critical. The photodetectors that get so much attention in discussions of imaging sensors are only one of a variety of components working together to record a digital image. The photodetectors aren’t squeezed up against each other, but rather have space between them where wire and electronics are placed. What that means is that a considerable portion of the surface of the imaging sensor is taken up by electronics that—while critically important—aren’t actually recording any light. If you think that means light is potentially wasted, you’re absolutely right. And that can be a problem when it comes to ultimate image detail.

The situation can be improved if you can get the individual photodetectors closer together. This is no small feat, but through meticulous engineering, the various other components can be made smaller, positioned more efficiently and otherwise optimized to provide the maximum area for the photodetectors and minimal area for everything else. By minimizing the distance between each photodetector, you’re minimizing the amount of light that’s disregarded in the capture.

Of course, no amount of engineering will do away with the fact that components other than the photodetectors are necessary in an imaging sensor, so there always will be a certain amount of light lost in the process. But just as a lens on your camera focuses the light from the scene before you onto the imaging sensor as a whole, lenses are used to focus the light for every single photodetector, so that as much light as possible is focused where it’s being recorded and as little light as possible goes to waste. As you can imagine, these lenses are very small. These microlenses play an important role in maximizing the amount of accurate information recorded by each photodetector and thus impact the amount and quality of detail in the final image.

The size of photodetectors also has an impact on the amount of noise present in a digital photo. Noise results from a variety of factors, but it represents errors in the measurement of pixel values. In effect, noise results when the camera has to guess at the value of a pixel it isn’t able to see very well.




 

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