 True, they may have cannibalised the low end of the digital camera market but as we shall see later in this chapter the higher-end digital camera market is alive and well and may well have benefited from people using camera phones wanting to upgrade to something that took better pictures and was easier to use. This is a microscale effect with a macroscale impact. But back to technology. 8.2.3 The Colour Filter Array Colour images are a mix of red (400 nm), green (510 nm) and blue (700 nm). A pixel will have a red, blue or green filter and the readings from 3 pixels (a red, blue and green pixel) are combined together to produce the chroma information. This is why colour sensors are three times less sensitive than black and white sensors. This part of the component chain is known as the colour filter array. Human eyes are less sensitive to green than they are to red or blue. The colour filters are therefore arranged in a Bayer pattern, originally invented and patented by Kodak. The Bayer 'checkerboard' has red and green in one row and blue and green in the next. This is shown in glorious black and white in Figure 8.2. The Bayer pattern means that interpolation algorithms have to be used. The unwanted effects of interpolation include optical crosstalk (rays of light taking an oblique route through a red or blue pixel before landing on a green pixel) and blooming caused by charge overflows into neighbouring pixels. Antialiasing filters reduce these effects but the filters blur the image and obscure detail. Using edge-sharpening algorithms (known as high-frequency component gain algorithms) can put this detail back but these algorithms amplify noise in the flat regions of the image. This can be avoided by using edge-recognition algorithms. The sensor array and colour filter array provide the information needed for the DSP and microcontroller to perform a number of system functions including autoexposure, stray-light compensation, autofocus, autowhite balance and gamma balancing (correcting for the nonlin- ear relatio