Data representation

For visual representation of your acquired data several methods and modes are at hand.

Default is a two dimensional grayscaled image. The following modes are available for display via the Channelselector->View.

no: There is no no window open, data can be acquired anyway. Saves space and performance.
Grey 2D: Standard grayshade image. Several functions to modify.
Surface 3D: 3D surface-rendering, uses MESA GL, Hardware accelleration is recommended. Several functions and options via popup menus.
Profile 1D: Display of horizontal lineprofiles. Use popup menu to browse through them.

Displaymodes

Quick, Direct, Logarith., Horizontal Diff, Periodic

In Direct mode are displayed 'as is'. Only contrast and brightness are regarded (see )

In scanning probe microscopy two sorts of artefacts are common, which prohibit the use of the direct mode. First of all, the sample is commonly slightly tilted with respect to the scan head; secondly, from line to line small 'jumps' may occure. To meet this shortcomiings, the Quick Modus was introduced. Only for display a line regression for any line profile is carried out. The source data are not modified.

Horizontal shifts the lines, so that their average is zero.

Diff. displays the lines first derivation. Calculated through:

$\begin{displaymath}H(x=0) = 0, H(x, \text{for} x=1,2,3,\dots N-1) = H(x)-H(x-1)\end{displaymath}$

Logarithmic Scale

Logarithmic scaling is chosen by the Logarith Button in the main window. It's purpose is the correct (appropriate) representation of 2D-SPA-LEED data. The translation happens in the following way:

$\begin{displaymath} Grey \propto \log \left( 1 + \left\vert Data - Min \right\vert \times Contrast + Bright \right) \mbox{,} \end{displaymath}$

with

being the smallest value.

Display

Helligkeit und Kontrast

The parameters Bright and Contrast control the conversion of the data in grayshade- or color-values:

$\begin{displaymath} Grey = Data \times Contrast + Bright \end{displaymath}$

SPA-LEED: CPS High - Low

In SPA-LEED mode the scaling of CPS-High/Low can be set.

Gamma Korrektur

Die Gammakorrektur wird nicht online verwendet, sonder funktioniert wie ein Filter (Background-Gamma). Dabei werden the Z-Werte nach folgender Rechnung transformiert:

$\begin{displaymath}Z_{new} = (Z_{hi}-Z_{lo}) \frac{(Z_{hi}-Z_{lo})^\gamma}{(Z-Z_{lo})^\gamma} \end{displaymath}$

Color mode, Xxsm only

Xxsm offers to display a color image of your data, using a mapping algorithm, which maps the data onto a part of the color circle. You can also use a new color palette.

Falschfarbendarstellung

Choose View-Use Color HUE (Xxsm only) to activate the color mode. Use Autodisp to initialize the display.

The slice of the color circle you wish to map can be chosen through HUE Start-Winkel to Ende-Winkel.

Start at black ...HUE-Start ...HUE-Ende ...white.

Use Display-Contrast und Display-Bright you can select a distint portion of the generated palette.

Own palettes

The color palette is simply a one dimensional PNM-bitmap file, that can be selected through an entry in the resources, or in the Preferences. Click View-Use Palette to apply it. Check Autodisp again

Here a short description of the PNM file format:

P3
# CREATOR: The GIMP's PNM Filter Version 1.0
1024 1
255
R
G
B
R
G
B
...

The file is expected to have 1024 RGB-entries (R, G, B values in the range 0 ...255) just following the header. Use gimp to generate this conveniently.

Gxsm can load a new palette at any time. Choose a new one in Settings/Preferences/User/Palette and press AutoDisp.

Next: Programming via Remote-Control Up: Gxsm and Xxsm User/Referenz Previous: Monitor - Eventlogging Contents

Percy Zahl 2002-05-08