nship between pixel value and displayed intensity on devices such as TV monitors). These are 'wanted effects' or required functions. The unwanted effects introduced by the DSP are due to the fact that is has to digitise a complex combination of waveforms that have large variations in signal amplitude (wide dynamic range). When the input bandwidth exceeds the sampling rate, the DSP will produce aliasing effects (difference frequencies/false frequencies). False low frequencies caused by ADC undersampling create Moire effects (the distortion that you see when someone wears a check jacket on television), coarse quantisation causes fringing, ringing and shadowing. Some of these effects ripple up and down the processing chain. For example, a series of flash guns go off at a press conference and put the DSP into compression, prediction errors fill the output buffer and trigger heavy requantisation, which produces tiling effects. If the system drops chroma coefficients in a desperate attempt to recover, then colour disappears (not that User-Centric Software Figure 8.2 Kodak Bayer pattern. 1 Reproduced with permission of Kodak. you will really notice by this stage). These are sometimes described as excess compression effects. This brings us to the final stage of the processing chain, the JPEG and MPEG encoder. 8.2.4 The JPEG Encoder/Decoder Entropy and redundancy are separated in still images by dividing the image into eight-by-eight pixel macroblocks. Each macroblock is coded in terms of its luma and chroma content divided into what are termed as Y, U and V planes in which Y is the luminance and U and V are colour difference channels. Colour difference is a more efficient way of describing the RGB content of each discrete part of the image. The JPEG compression algorithms are based on a discrete cosine transform (DCT) that separates out the luminance and chroma information in the spatial and frequency domain. These are expressed as DCT coefficients. Compression can then be achieved by comparing one macroblock with other 