What do Windows' display colour options mean?

Helpline Q&A Directory

In Control Panel, Display, Settings there are different colour options: true colour (24bit), high colour (16bit), 256 colour and 16 colour. What are the differences between these and what are their practical effects? Next to this is a slider giving a choice of 640x480, 800x600 or 1,024x768, showing less for the smaller numbers and more for the bigger numbers. But it seems that the bigger the numbers, the smaller the image on the screen. Where is the logic in this?

The colour options control the number of different colours that can be displayed simultaneously. When computers purely displayed text, 16bit colour was used. It's now an obsolete standard that Windows supports because all graphics adapters can display this mode without needing special drivers. It can only be used in Safe Mode, when Windows has the wrong drivers (or none at all).

Until recently a more popular mode was 256bit, but it gives a less-than-perfect display of graphical images. This is because only 256 different colours are available for use on the whole screen. So images that use more colours than that must be converted to use those that are available. If you have several graphics files on screen at the same time, there may not be enough different colours to display them all very well.

High colour (16bit) and true colour (24bit and 32bit) give good results with photographs and other images. In theory, the more bits the better, although you probably won't be able to tell the difference between high colour and true colour mode.

The main difference is in performance. True colour only uses 24bits, but computers and most modern graphics cards have a 32bit architecture, which means they can move 32bit data around faster. This makes 32bit the best option in most cases, if it is available. The exception is if your computer or graphics card doesn't have much memory. True colour 32bit mode uses twice as much memory as high colour 16bit mode. So, if your computer runs slow and there is a lot of hard disk activity when working with graphics files, try switching to high colour mode.

The desktop size settings represent the number of dots or pixels that are used, horizontally and vertically, to fill the screen. They are like the dimensions of a real desktop: the larger they are, the smaller anything on the desktop will seem, given that you only have the same amount of space (the screen) in which to display it. You can make text more readable at higher resolutions by clicking the Advanced button next to the settings slider and choosing 'Large Fonts'. However, this defeats the object of using a higher resolution in the first place: the best solution is to buy a bigger screen!