The height distribution histogram window is activated by the histogram tool button or from the ProcessingHistogram menu item. The height distribution histogram window is activated by the histogram tool button or from the ProcessingHistogram menu item.
The histogram is an important analytical tool that provides important information about the height distribution and serves as an important tool for the Z-calibration algorithm.
It is a good idea to monitor the histogram while performing slope correction because the histogram is the best indicator for the flatness of the surface. Plane surfaces are characterized by high and narrow histogram peaks.
The context menu (right click) contains more functions dedicated to histogram analysis:
Cursors On
To activate the cursors right click on Cursors On, use the View Pane, or just press "C" on the keyboard. When pressed repeatable the number of curser pairs will shift between 0, 1, and 2.
The cursors can be moved by mouse and for precise positioning by the arrow keys. The Up/Down arrow keys will move the cursor in the direction of a local summit, which is useful for finding local minimum or maximum points. When a cursor is positioned on a slope, it will be indicated by a tilt of the cursor. Summits are indicated by the cursors pointing straight downwards.
Based on the cursor positions you can also determine the area and volume for the range between the markers. There are provided two volume numbers Material Volume (Mat. Vol.) and Void Volume (Void Vol.). All height values below the surface is considered as material while height values above the surface are considered as void. Thus it is possible to calculate the volumes between the height values given by the markers.
The images below illustrate a situation where the void and material volumes are measured at different height ranges by moving the cursor position in the histogram:
Clip Values Outside Markers
It is possible to use the blue and red markers for defining the lower and upper clipping values of the image. To perform the clipping right click and select Clip Values Outside Markers.
Set Values Outside Markers to Void
To define the pixel values outside the z-range given by the markers as void pixels click on Set Values Outside Markers to Void. This function will also define pixels inside the z-range if they are located on a slope between the two z-values and has shown to useful in grain analysis for separating particles at different levels.
Define Image Zero Level by Active Cursor
This function will level the entire image so that height value given by the active cursor will be set to zero. In combination with grain analysis where it is desirable to report z-values relative to a certain surface height you may take advantage of this function, because you may then use the absolute values directly.
Freeze Axes
Right click on Freeze Axes to keep the X and Y scaling fixed. This is very practical when comparing histograms from different images on the same scale. You might for comparison purposes also want to save a duplicate by pressing Ctrl+D.
To define the scaling more specifically enter the property menu, by right clicking on Properties or double clicking
Show Integration
Right click on Show Integration so display the Integration curve of the histogram. The difference between the integration values at the cursor positions reflect the relative surface area having height values between those marked with the cursor pair and will be indicated in the Area% numerical field.
Z-Calibrate (Requires the Calibration Module to be included in the license)
Right click on Z-Calibrate to perform a step height measurement and calibration, see Z-calibration for further details.
Auto Z-Calibrate
Right click on Auto Z-Calibrate to automate Z-Calibration measurements whenever the histogram is changed. This is for example practical when the histogram is linked to a profile of an image, in which case both the profile, the histogram and the Z-Calibration result is updated when moving the cross section line in the image.
Save As
The histogram data can be saved into an ASCII file or the STM-BCR file format or as graphical bitmap, jpeg or tiff file. The ASCII file contains the floating point x, y co-ordinate and can be imported by, for example, spreadsheet programs and the STM-BCR file can be read by SPIP.
Copy
The window can be copied to the clipboard by pressing CTRL+C and pasted into third party programs by pressing CTRL+V.
Duplicate
A duplicate of the window can be create by pressing CTRL+D or right clicking on Duplicate
View Settings and Properties
Different view options can be defined in the View Settings Pane belonging to the histogram. From the Property dialog it is possible to change the number of bins if the origin of the histogram is from an image or curve. The Property dialog is activated by a double click. For histograms produced by grain analysis the number of bins is defined in the Grain Analysis dialog.
