The GUI MASK Command

The MASK command is available in a number of interfaces, and will gradually be generalised. At present it is used to mask out ``bad'' or contaminated data pixels from regions to be integrated, or fitted.

Allowing elements to be arbitrarily included or excluded from fitting and other operations is a very powerful facility which allows much flexibility in the data analysis process. ``Bad'' data points can be excluded from operations. Optimum non-rectangular data regions can be selected reducing calculations for fitting and other calculation intensive operations.

The ``mask'' is a 2-D area of the same size as the current data and memory arrays. Each data element may be ``masked'' or not. By default no elements are masked.

``masked-off'' areas can be defined graphically for small blemishes, or for large regions, or from the data values themselves by using the THRESHOLD MASK command. This allows a threshold value to be defined and all data elements with values above, or below (as required), this value are defined as ``masked-off''

The current ROI is displayed as a 2-D pixel image together with the graphical menu giving a choice of commands allowing the masking and un-masking of regions of the data. ``Masked-off'' pixels are displayed using a single colour. An example of this display and menu are given in Figure 20.

Figure 20: Example of the MASK Sub-Menu

The available choices are:

• EXIT: Exit from MASK sub-menu and return to calling menu.

• ?: Display list of commands with a short description.

• CLEAR MASK: Set all elements in the ROI to be un-masked.

• ZOOM IN: Graphical region definition.

• UN-ZOOM: Make region displayed bigger.

• FULL UN-ZOOM: View whole of data image.

• MASK PEAKS (5): Mask out peaks (Diameter 5 pixels). The user is prompted to select graphically the centre of each peak to be masked out with a circle of diameter 5 pixels. When finished click within the graphical prompt box. The display is updated with the maksed out pixels being dispalyed in the masking colour (red by default).

• MASK PEAKS (9): Mask out peaks (Diameter 9 pixels). Works in the same manner as MASK PEAKS (5).

• MASK PEAKS (15): Mask out peaks (Diameter 15 pixels) Works in the same manner as MASK PEAKS (5).

• MASK PEAKS (27): Mask out peaks (Diameter 27 pixels) Works in the same manner as MASK PEAKS (5).

• MASK POLYGON: Coordinate definition of region to mask off The user clicks on the corners of an arbitrary polygon region. When finished click within the graphical prompt box. The polygon is closed by a line going from the last entered coordinate to the first. Normally this should be a simple convex shape.

• UN-MASK POLYGON: Coordinate definition of region to un-mask. Works in the same manner as MASK POLYGON.

• UPDATE DISPLAY: Re-draw image, including masked regions

• MASK ARC: Define an arc region to be masked-off. If the arc is made large enough a circular region can be masked. .

• THRESHOLD MASK: Allows pixels within the ROI to be masked if they are less than an entered minimum threshold value, or alternatively if they are greater than a maximum threshold value. First the user is prompted for LESS THAN COMPARISON. If NO is selected a greater than comparison with be used. Then the DECISION THRESHOLD DATA VALUE is entered. The masked off pixels are added to any existing masked pixels, and the display is updated.