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What Controls The Picture Quality of a Digital Camera

The picture quality of a digital camera depends on several factors, including the optical quality of the lens and image-capture chip, compression algorithms, and other components. However, the most important determinant of image quality is the resolution of the CCD. The more elements, the higher the resolution, and thus the greater the detail that can be captured.

In 1997 the typical native resolution of consumer digital cameras was 640×480 pixels. A year later as manufacturing techniques improved and technology progressed the emergence of megapixel cameras meant that the same money could buy a 1024×768 or even a 1280×960 model. By early 1999, resolutions were as high as 1536×1024 and before the middle of that year the two megapixel barrier had been breached, with the arrival of 2.3 million CCDs supporting resolutions of 1800×1200. A year later the unrelenting march of the megapixels saw the three megapixel barrier breached, with the advent of 3.34 megapixel CCDs capable of delivering a maximum image size of 2048×1536 pixels. The first consumer model 4 megapixel camera appeared in mid-2001, boasting a maximum image size of 2240×1680 pixels.

At this level, raw resolution is arguably little more than a numbers game and secondary to a digital camera’s other quality factors. One of these – and almost as important to the quality of the final image as the amount of information the CCD is capable of capturing in the first place – is how cleanly the information is passed to the ADC.

The quality of a CCD’s colour management process is another important factor and one of the prime reasons for differences in the output of cameras with the same pixel count CCD. The process should not be confused with the interpolation method used by some manufacturers to achieve bitmap files with a resolution greater than their true optical resolution (the resolution of their CCD array). This method – more accurately referred to as resampling – adds pixels using information already present, and although it increases the effective resolution, it does so at the cost of a reduction in sharpness and contrast. It works by quantifying pixels and qualifying them according to the common traits they possess. In place of the standard interpolation, in which pixels are copied and pasted to create larger images, Some cameras employ a software enlargement technique which it is claimed produces results better than can be achieved by conventional interpolation. This copies and pastes pixels – according to where the enlargement software thinks they are needed to make lines, shapes, patterns and contours – to create larger images.

Another limiting factor is the image compression routines used by many digital cameras to enable more images to be stored in a given amount of memory. Some digital camera store images in a proprietary format, requiring the manufacturer’s supplied software for access, but most digital cameras compress and save their images in the industry-standard JPEG or FlashPIX formats, readable on almost every graphics package. Both use slightly lossy compression leading to some loss of image quality. However, many cameras have several different compression settings, allowing the user a trade-off between resolution quality and image capacity, including the option to store images in with no compression at all (CCD raw mode) for the very best quality.

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