Digital Cameras in Focus
Although attributed to NASA (National Aeronautics and Space Administration), it took Kodak to develop the first commercial digital camera for photojournalists, then Apple to spark public imagination with its mass-market, attainable Quick Take 100, and by 1997 a rash of both consumer and professional digital cameras were on offer from the mainstay of the 35mm film manufacturers along with relatively unknown photographic upstarts from the electronics industry like Hitachi and Sony.
The initial driving force was increased sensor size, in an attempt to generate better image quality. The first CCDs (charge coupled devices) measured 100 x 100 pixels and produced grainy, indistinct monochrome images. Resolutions soon grew and decent colour emerged once various imaging technologies began to mature and soon the term megapixel (million pixel) was coined as the measure of image size and (not necessarily correctly) image quality.
Yet it took one more aspect beyond the gratification of immediate photographic results to encourage mass consumer uptake of the digital phenomenon: print quality. Kodak were prompt to react with a photo-CD service processing a variety of storage media and returning an indexed CD of images ready to view through TV or computer plus hard-copy prints. It wasn’t until the advent of home ‘processing’ and the ever evolving resolution of ink-jet printers that consumers bought in droves and printed their own shots on high quality – though then expensive – ink-jet photo-quality paper. So, in the late-‘90s, began the digital revolution.
Digital Image Quality
CCD and CMOS (complimentary metal-oxide semiconductor) are the two main image sensor technologies within digital cameras, although for reasons of fabrication efficiency, compactness, technological convenience, power consumption and cost CMOS now commands the consumer digital camera market – especially with recent advances made in sensitivity by Canon which have largely overcome the deficiencies of earlier designs.
This is not to say that CCDs are out of favour. They are employed in areas of science, industry and business where image quality is of paramount importance since their design delivers superior image performance, being far more sensitive to light variations – and where the cost equation is largely an irrelevance to image fidelity.
Image sensors of whichever type respond solely to the intensity of light falling on them. They do not distinguish colour. For that to happen filters or CFAs (colour filter arrays) for the electromagnetic primary colours – red, green, and blue – are overlaid on each sensor to produce the pixel (picture element) responsible for filtering out the colour value. This sounds simple in principle; in fact a lot of additional work is required if either technology, CCD and CMOS, is to generate accurate imaging. Refinements in layout techniques and micro lenses which cover the pixel element have led to significant gains in sharpness and colour purity, notably in CMOS circuitry, where the working at the atomic level presents considerable challenges.
Other designs of CFA exist for reproducing colour but the premise remains identical: split the light falling on a sensor array pixel into its three constituent primary colour light channels with their respective levels of intensity then recombine them to produce a single point of light.
Digital Camera Resolution
For today’s consumer, digital cameras are commonly measured and advertised in megapixels, leading to the false assumption that the higher the count, the better the image quality. Not true. It’s the image sensor itself, commonly the size of the individual pixel photo element, and the attendant digital circuitry that determines image quality.
Put simply, 99% of consumers are not photographers; they are people who have been given the opportunity to take pictures and, through other apparatus, process the results almost instantly. Their knowledge extends only as far as what they are told in commercial retail outlets, whose sales staff are often as poorly educated as their customers when it comes to the whys and wherefores of digital (or, for that matter, film) photography. And why should the public be expected to understand the working of a consumer product. Does it work? and How well? are the only questions a mass-produced digital camera should answer. And that can be determined only in use.
Contemporary resolution levels (as of summer 2006) for a general purpose, medium specification consumer camera lay between the 5 and 8 megapixel range. Cameras offered in the ‘90s tied their formats closely to PC screen dimensions – 320 x 200, 640 x 480, 1024 x 768 – whereas contemporary layouts now have little to do with viewing screen sizes, with some seemingly random dimensions like 2952 x 1944 or similar on offer. This is partly due to differing CMOS sensor size and implementation but mostly down to the irrelevance to PC screen size since modern digital cameras produce far higher resolution images than can be displayed in full on the average user’s screen. Moreover, manufacturers now offer photo editing software as part of the camera retail bundle, permitting users to either manipulate their images on-screen and reduce them to the desired screen resolution or output them directly to printer.