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BY ZIV HAPARNAS

Digital camera megapixel madness is very similar to the personal computer MHz madness back in the 90s. The number of pixels a camera uses to produce a digital photo is just one element in determining photo quality. Another (usually forgotten) is the sensor size. Here is why.

Digital cameras use an electronic sensor (also known as a CCD) to capture a digital photo. This sensor replaces film used by traditional cameras. The electronic sensor is built from small light sensors, also known as pixels. When you take a photo, the camera opens the shutter for a certain amount of time. During that time, light hits each individual pixel. The amount of light that hits each pixel determines its intensity (also known as the pixel value). A digital photo is comprised of many pixels, each with its own pixel value.

There is a direct relationship between the size of the camera’s CCD, the number of megapixels it supports and the size of each pixel. For a fixed CCD size, the more pixels the CCD supports the smaller each pixel is. On the other hand, for a CCD with a fixed number of pixels, the larger the CCD the bigger each pixel is.

So why should you care about the pixel size? Many reasons; it plays an important role in the overall quality of your digital photos.

One reason that is very easy to understand is sensitivity to light. Assume that you are taking a photo with the shutter open for a fixed amount of time. During that time, light hits each pixel. The larger a pixel is, the more light energy it accumulates during that period of time. The result is that with larger pixels, you could take photos in darker scenarios than with smaller pixels. Also, with larger pixels, the amount of noise in each pixel value is reduced.

If you have two digital cameras with the same number of pixels, but one uses a larger CCD sensor, the camera with the larger CCD will be able to take digital photos that are sharper and with less noise. It will also be able to take digital photos in scenes that are too dark for the other camera. Higher light sensitivity also allows more flexibility with both shutter speed and aperture settings.

High end cameras like digital SLRs use a larger CCD than point and shoot digital pocket cameras. Why is that? The main reason is simple: cost. It costs more to manufacture a larger CCD (for reasons such as yield and other specific manufacturing process issues). The CCD size also influences other optical attributes of the camera — for instance, the aperture needed in a specific scene changes as the CCD size changes, and depth of field is directly influenced by such aperture changes.

So, when buying a digital camera, always remember not to get fixated on the number of pixels. Although this number is important, it is not a standalone feature. If you plan to take digital photos in extreme conditions, if you do care about depth of field, aperture settings, shutter speeds and light sensitivity, then you should also check the size of the CCD the camera uses among other optical parameters of the camera.

Ziv Haparnas is a technology veteran and writes about practical technology and science issues. He write for printRates, a site dedicated to photo printing, where you can find more information about photo album printing and photography in general.