ABSTRACT
Colour is of ever-increasing importance in photography and digital imaging, and we are given more and more information about the colours we use in digital systems. Digital camera outputs are described by red, green and blue (RGB) values. The output of computer software in graphics and imaging applications is also described by RGB pixel values and, frequently, in terms of Lab, HCL or HSL values. This chapter seeks to clarify what these descriptors mean and why they are of importance. In each case the quantities are parts of systems of colour description or specification, so that is where we shall start. (A full and rigorous survey is beyond the scope of this chapter and the reader is referred to the Bibliography section for further details.)
We may think in terms of three methods of specifying colour. The first is very familiar and of great practical significance – specification by sample. We have already encountered the second – physical specification – and the third – specification by synthesis –- may not be at all familiar to most readers but is the basis of most of the numbers which we encounter in the description of colour in imaging.
