False Colour Image Display

The basis of all interactive data analysis in FIT2D is the false colour image display for 2-D data, or an X/Y Graph plot for 1-D data. The flat image display allows easy and unambiguous interactivity. An example of the false colour image display and a control menu is shown in Figure 3⁷. The whole of the ROI is displayed as an image even if there are less screen pixels than data elements, which is often the case.

Figure 3: Example of False Colour Image Display

For general data analysis the style options are generally not important, with the exception of the intensity or ``z-scaling''. It is necessary to understand the manner in which the data element values are changed into displayed pixel colours, to interpret the display images.

Generally usage is very obvious, but it is necessary to understand the different scaling modes, which may be present. The mode of intensity scaling can be changed by using the Z SCALING command and subsequent sub-menu (see Section 5.3, Page ). This sub-menu may also be obtained simply by clicking on the intensity scale colour bar, in the main menus of the different interfaces.

By default FIT2D uses automatic full range linear scaling of the ROI data values. This means that the minimum value and maximum of the ROI are found and all values in-between are converted to a colour (black, white and grey's are colours) in the current colour table, using linear interpolation.

With automatic range intensity scaling the whole of the range of data values will always be visible, although some images with a very few very extreme intensity values may not appear very interesting. Full range automatic scaling may be selected using the FULLY AUTOMATIC button. As the ROI changes then so do the current minimum and maximum values, and same intensity values may be displayed using different colours. This can be confusing and undesirable in some circumstances.

``Fixed'' range intensity scaling is also available. With completely fixed scaling the minimum and and maximum data values which correspond to the extremes of the colour table are fixed to some values. Thus, as the ROI changes the intensities displayed with particular colours stay fixed. However, if data values outside the defined range are encountered then they are just displayed using the colour corresponding to the minimum or maximum of the range.

The full range of scaling options are (together with linear or logarithmic scaling):

FULLY AUTOMATIC: Automatic full range re-scaling. Every time the ROI or the data is changed the minimum and maximum are found and the scaling is set to cover the whole range. This is often suitable, but when a few very high or low valued pixels exist, the detail may be lost in the image.

WEAK PEAKS: Automatic limited range re-scaling. Every time the ROI of the data is changed, a number of regions are used to calculate averages, and standard deviations. The range is set to hopefully display best weak features in the data.

USER MIN/MAX This uses user entered fixed minimum and maximum values for the displayed intensity range.

USER MINIMUM This uses an user entered fixed minimum value for the displayed intensity range, but the maximum is automatically defined by the ROI data values.

USER MAXIMUM This uses an user entered fixed maximum value for the displayed intensity range, but the minimum is automatically defined by the ROI data values.

If data is input but nothing appears to be displayed, it is likely that the intensity scaling is fixed, and that the data values are not within the range. The Z-scaling mode and range values are remembered between calls to FIT2D (V9.113).

For further information on controlling the intensity scaling see Section 5.3, Page .

Aspects of the false colour diagram style can be changed using the OPTIONS command, which is present in many menus (see Section 5.5, Page ), and other forms of graphical display are available through the DISPLAY command which is also generally available (see Section 5.4, Page ).