## Chapter 15 – Colours ### An introduction to colour on the ZX Spectrum Next Up until this point, we haven't really touched the subject of graphics manipulation on the ZX Spectrum Next and that's because the subject –mainly due to its original models' history– can be rather daunting to a beginner. As we've seen in *Chapters 1* and *14* where we really started to get into the more intricate details of the graphics system, the ZX Spectrum Next has some very interesting graphics capabilities that set it apart from its predecessors. The first capability which we will examine in depth is colour. ### Basics of computer colour The first thing we need to remember, and that is important as it explains many of the design choices of the ZX Spectrum Next, is that at its heart beats an 8-bit[^p95-1] processor. This means that it is at its best when manipulating integer numbers up to 255 which are represented as 2 *to the power of* 8 – or properly written: 2⁸. Now taking a step back from that information we should concentrate on how colour can be represented. In reality there are many methods but the most common for a computer – and the one used by the ZX Spectrum Next – is to break colour into three components: Red, Green and Blue (or RGB) and to represent intensities of each of these components as numbers from 0 (for no intensity, or dark) to whatever maximum value a computer can store easily. In the ZX Spectrum Next's case each colour component can have 8 intensities making a total of 512 combined intensities which translates to 512 colours in total. Now from basic maths, we know that to represent the number 8 in binary form (which is what computers understand) we can rewrite it as 2³ – or a binary number of 3 bits of length. To represent the total combination of colours when we combine the colour components, we can rewrite 512 as (2³)³ which in turn can be rewritten as 2⁹. This, given what we just said about the 8-bit nature of the ZX Spectrum Next is presenting a problem as the number of colours we have is represented by a 9-bit number while the computer can best manipulate efficiently 8 bits at a time. Keep this in mind for the moment and lets discuss how a colour could be represented in binary form. ### Colour organisation and representation RGB colour has many ways of being stored in memory and it's usually denoted by the order of the bits. For example the BGR way stores first the bits for the Blue component, then the bits for the Green component and finally the bits for the Red component. As a matter of course, we usually add a number after every component (designated by a letter) to denote the number of bits (ergo also the number of intensities) or a single number at the end of the organisational acronym to denote that all components have equal number of intensities. For example R2G3B3 would mean an 8-bit colour organised as RGB with 2 bits (4 levels of intensity) on the Red component and 3 bits (8 levels of intensity) on the Green and Blue components. The ZX Spectrum Next uses the GRB (for compatibility modes) and RGB methods of organisation and can store colour in three ways: G1R1B1, G3R3B2, R3G3B3 (or RGB3) and R3G3B2. The latter is really a shortcut for an 8-bit subset of the RGB3 way as we will see later but for now, let's assume it can manipulate 3-bit, 8-bit *and* 9-bit colours. ### Spatial vs Colour Resolution Thus far, you've seen references about *resolution* when it comes to graphics but what does the word really mean? In short it means how much graphical information we can fit in a finite space. This doesn't actually mean how many dots we can fit in our screen (to make [^p95-1]: Bit is an acronym for BInary digiT and is a term used to describe the tiniest amount of information that a computer can hold, which is a single binary digit. Microprocessors are classified according to their ability to manipulate binary numbers of a certain order in one go. For example the Z80N CPU which is inside the ZX Spectrum Next can manipulate a number consisting of an 8 bit order in one go, so it is called an 8-bit microprocessor. By contrast the CPU inside the ZX Spectrum Next's "big brother", the Sinclair QL is a 32bit microprocessor as it can manipulate numbers consisting of 32-bits in one go.