Notes on demonstration images provided with Image SXM

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'Demo 3d Plot' is an STM image of magnetite taken by Neil Condon at the University of Liverpool. 'Demo 3d+axes' is an STM image of gadolinium islands grown on a tungsten surface, and shows the optional xyz axes.  ( Omicron STM )

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'Demo Unsharp Mask' is Si(111)-(7x7), showing two terraces separated by a step. The Unsharp Mask (in the Process menu) suppresses the large-scale terrace structure and enhances the small-scale atomic contrast.  ( WA Technology STM )

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'Demo WATech IV' is a montage of IV spectra. When individual IV spectra are plotted, the Info window displays the IV values of the cursor position. ( WA Technology STM )

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'Demo Compensation' shows the effect of the various modes of compensation for sample tilt, curvature, or artefacts.  ( TopoMetrix SPM )

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'Demo Tip Change' shows the effect of line-by-line quadratic compensation on an AFM image. Note the two abrupt jumps caused by tip changes during the scan. Because a least-squares fit is applied individually to each line of the scan, such artefacts can be virtually eliminated.  ( Digital Instruments NanoScope III AFM )

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'Demo Distortion Correction' shows how geometric distortion of an image can be corrected. To exaggerate the effect in this demo, the image was deliberately distorted prior to applying the correction.  ( Park Scientific Instruments SPM )

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'Demo Hough transform' shows how a HT can be used to detect in an image circles of a specific size (radius 8 pixels in this demo). By thresholding the HT (middle image) at a threshold level of 52, the maxima of the HT can be seen to correspond to the positions of circles of that size in the original image. Plotting circles centred at these positions gives the bottom image. Using the 'Size Distribution' menu item, a series of HTs are calculated and thresholded for a range of circle radii to produce a size distribution. To work effectively, careful consideration must be given to the value of the threshold used. The optimum value will depend on the appearance of the circles in the image - whether they overlap, have incomplete or irregular outlines, and whether or not there are non-circular artefacts in the image.

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'Demo Focus' shows two images of limited depth of field (top and middle) that have been combined to produce a composite image (bottom). The relative weighting of each of the original images in the composite image is determined, pixel-by-pixel, by how well each image is focussed.

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Steve Barrett    August 1997

