COLOUR TABLE allows the type of false colour table used to represent intensity values of 2-D images to be changed. A choice of a number of different colour schemes is available to the user18. The different available colour schemes are referred by a name e.g. TEMPERATURE, GREY-SCALE, GEOGRAPHICAL. As with entering menu commands the shortest non-ambiguous letter sequence may be entered, and a question mark (?) may be entered to obtain a list all available choices.
Users are recommended to try out the different colour tables, as different data and different aspects of of data may be highlighted by different colour tables. The choice includes grey scales. Generally colour allows most detail to be seen in a single image, but colour can sometimes be confusing and grey scales may be useful to allow the brains natural image processing to spot features or trends in the data.
In addition to the variety of colour tables, the user has control on the range of colour indices used on the workstation or X-terminal to display the image and on the number of separate colour levels used to display the image.
Since windowing systems allow several different windows to have their own colour tables it is possible to have more defined colours than the physical possibilities of the hardware (normally 256 colours for ESRF workstations). If this happens then when a user clicks in a different window the colours of other windows may well change (this effect is known as ``flash''). To try to avoid ``flash'' FIT2D does not by default use all of the colour table. MINIMUM INDEX and MAXIMUM INDEX control the range of colour table indices that FIT2D uses for setting colours and displaying images. (Because the precise number of colours used by other windows can vary it is possible that ``flash'' occurs even using the default settings.) If these values are changed the colour table indices affected will be altered as part of this command, but the indices used to display the image will not be changed, so it is necessary to use the PLOT DATA command to re-display the data as desired.
By displaying a very limited number of different colours it is possible to obtain a kind of colour contour plot. Whilst not perfect this is far ``cheaper'' in terms of calculation than a true colour contour plot. NUMBER OF LEVELS allows the number of separate displayed colours to be changed.