Some Images may contain "void pixels", which are pixels that could not be measured by the instrument. This is often true for interference microscope images, which need a proper reflectance in order to measure the height values. This may also be true for objects with holes for examples rings. Void pixels can be handled as invisible when drawing in 2D or 3D or they can be shown by other inserted values. For visualization purposes you may want to enhance a certain feature making its surroundings invisible by turning it into void pixels (see 3D example)
For randomly located void pixels it might be desirable to show their interpolated values while structures with real holes is better shown with the void pixels invisible or for example with the minimum value of the valid pixels. You can define how to handle void pixels by right clicking Void Pixels:
The selected option will also have effect on the calculation of histograms and the simplest 1st order statistical roughness parameters. If "Show as Invisible" is set they will not be included in these calculations and they will simply be ignored when calculating plane correction parameters. More complex roughness parameters depending on Fourier analysis will make use of the inserted values. New values can be inserted by selecting one of the choices for the menu. The new values may be accepted by the "Accept" button, meaning that there will be no more void pixels contained in the image.
The number of void pixels contained in the image is shown in the upper part of the Image Property Menu.
You may also find it convenient to use the View Settings for setting the visibility of the Void Pixels:
Pixels exceeding the value boundaries defined by the color clip markers can be defined as void pixels by right clicking on Void PixelsàSet Values Ouside Marker to Void.
The AOI tools can in combination with the right click menu item Void PixelsàDefine Outside AOI’s as Void Pixels..
Defining a region of pixels as void pixels can also be done by combining the Zoom box with the Delete button, working as an eraser tool; likewise regions can be redefined as valid pixels by combining the Insert key with movement of the Zoom box.
Defining void pixels can be appropriate in combination with for example tip characterization where the most outer pixels can have a high uncertainty and therefore better shown as invisible.