D isplaying D ata

There axe three different ways in which d ata can be displayed on the m onitor. In IM A G E mode, d a ta is displayed as a 2-dimensional array of pixels, where th e d a ta associated with each pixel is represented by a colour. The colour is related to the d a ta value by a colour bar placed across the top of the screen, whose colour scale is defined w ithin the colour lookup table. Up to four images can be displayed on the m onitor at any one time. The num ber of displayed pixel rows and columns are placed around each image together with a label representing its associated window num ber.

In B U I L D U P mode, cross sections through th e 2-dimensional image can be displayed as a 1-dimensional histogram . Up to six buildups can be displayed on the m onitor a t any one tim e and each one has a set of axes, these being the channel num ber and the number of counts in th a t channel.

In 3D mode small areas of an image can be displayed in a 3-dimensional form at. Half the m onitor is used to display the 2-dimensional representation of the image while the other half is used to display the same area of d a ta but in 3-dimensions.

Many of the most simple commands associated w ith th e image display have been mentioned above, bu t there are many more display features th a t enable the user to view and interpret his data. All the commands as well as their function are listed for each of the three display modes.

1. Image Mode

• I M A G E . Used to set the display to image mode.

• D IS P L A Y . Allows the user to display up to 4 images on th e m onitor at any one time.

• M O S A IC . Used to unscramble and display images larger th a n 1024 x 1024 pixels. The display is updated one quarter at a time.

• R O W S . Defines the first and last row to be displayed. • S T A R T . Defines the first column to be displayed

• L E N G T H . Defines the num ber of columns to be displayed. • S C A L E . Rescales the colour lookup table.

• IM -A V E R A G E . If the d ata is scrunched (due to the acquisition form at being larger th an the display resolution), then only the average d a ta value from the scrunched pixels is displayed.

• IM JS U M . If the d a ta is scrunched, then th e sum of all the d a ta values from the scrunched pixels is displayed.

• I M -M A X . If the d a ta is scrunched, then only the m axim um d a ta value from all the scrunched pixels is displayed.

• G R E Y . Changes the display lookup up table to a grey scale. • R A I N B O W . Changes the display lookup table to a colour scale,

• S Q U A R E . Optimizes the image size on the m onitor to m aintain th e aspect ratio.

• P I C K . Displays a cross hair cursor whose row, column and d a ta value are displayed. A separate colour plane is used for the cursor.

• R E D R A W . Redraws the image w ith a different colour lookup table in order to clear the colour plane used for cursors. If REDRAW is typed again then the image is redrawn using all the colour planes.

• 2 C O M P A R E . Displays the top two images on the image stack. • C L E A R . Clears the display as well as any overlay cursors.

• A S P E C T R U M . Creates a box cursor which can be used to create autom atic buildups or define an area in which a statistical analysis of d a ta w ithin the box can be carried out.

• S H O W . Displays an image on the m onitor using the display param eters defined above.

F ig S.8 shows how data is displayed in Image Mode.

Fig 3.8. D ata displayed in image mode

2. Buildup Mode

• R E S E T . Used to set the display to buildup mode.

• B U IL D U P n. Used to define a buildup along the x (column) axis. The start row and the number of rows to be co-added have then to be entered, n is the buildup number.

• Y B U IL D U P n. Used to define a buildup along the y (row) axis. The start column and the number of columns to be co-added have then to be entered, n is the buildup number.

• T O T A L S . Shows the total number of counts displayed in the buildup. • R O W S . Defines the first and last row displayed using a ybuildup. • S T A R T . Defines the first column displayed when displaying a buildup.

• L E N G T H . Defines the number of columns displayed when displaying a buildup. • S C A L E . Sets the maximum d ata value for the display of any buildup.

• B IA S . Sets the minimum d ata value for the display of any buildup. • B L O C K . Smooths through d ata defined in a buildup.

• L IN E S . D ata is displayed by connecting each d ata point with a straight line. • D E L A Y . Sets the delay time between updating the display when an integration

is in progress.

• P I C K . Displays a cross hair cursor whose channel number and d ata value is displayed.

• S A V E n. Saves d ata in the last displayed buildup on the monitor, n defines the colour plane in which the d ata is saved. D ata from a previous exposure but defined by the same buildup can be displayed on the screen in parallel with the current d ata set. This allows comparison of one exposure with another. This feature is mostly used when focussing the detector.

• U P a ,6, c,d. Allows up to four buildups (where a ,6,c and d are the buildup numbers) to be displayed across the upper half of the display.

• LO a, 6, c, d. Allows up to four buildups to be displayed across the lower half of the display.

• S H O W . Displays buildups on the monitor using the display param eters defined above.

F ig 3.9 shows how data is displayed in Buildup Mode.

3. 3d Mode

• 3d. The program 3D is a 3-Dimensional plotting program, which allows the user to display a small section of an image in 3D form. It is useful mostly for examining single or multiple event profiles captured in a SNAP frame, or a point source image profile. The image must be one which is already on the d ata stack in an unscrambled form. The user selects the image area to be displayed (up to 25x25 pixels), which is then drawn in 2D form, on the right hand side of the screen, and in 3D form on the left hand side of the screen. The d ata can be viewed in one of four viewing modes, each having a different orientation about the Z-axis.

F ig 3.10 shows how d ata is displayed in 3 D ' Mode.

Fig 3.10. D ata displayed in 3D m ode

3 .4 .2 A n a ly s in g T h e D a t a

Although the online d ata processing is limited (as most of the d ata is analysed using STARLINK software), the following facilities do exist:

• A D D . Adds two images of the same size together.

• DIV.

Divides one image by another.

• MULT.

Multiplies one image by another.

• CADD.

Adds a constant value to all d a ta in an image.

• CMULT.

M ultiplies all image d a ta by a constant.

• XFWHM.

Analyses spectroscopic d a ta stored in a ID d a ta file, by finding each line FW HM and its centroid position.

•

IFILL.

Floods an image with a single value. This is used to either clear all the d a ta w ithin an image slot, or to test w hether the com puter can w rite to th e VME memory correctly.

•

STATS.

Produces a statistical analysis on d a ta confined to an area of th e image specified by the user. The program

STATS

produces the to ta l count in th e area, the mean count/pixel, the maximum count in any one pixel, the lowest count in any one pixel, and the standard count deviation.

•

PUSH.

Push an image onto the stack.

• POP.

Pop an image from the stack.

• SWAP.

Exchange the top two stack images.

In document Characterization of the MIC photon counting detector (Page 97-102)