UniServe€ Science News: Newsletter of the Science Software Clearinghouse Vol 1, July 1995

OPTRANS - optics of imaging

Robert Minard is a lecturer in the School of Physics at the University of Sydney

Optrans is a numerical simulation of an optical Fourier bench, designed for use in an advanced physics or engineering course in modern optics. In use, one specifies an object, which is then Fourier-transformed to the diffraction plane. Filters may be applied in this plane and the result is Fourier-transformed to produce the image. Using the available features, 3D plots, profile plots and grey-scale displays are available to examine real functions of the data. These include: modulus, phase, imaginary part, etc, in the object, diffraction and image planes. The object may be built up from various arrays of simple geometric objects or can be imported as a subset of a .BMP file. Several standard filters, such as low-pass and high pass, are also available.

The program is for use only on a PC and installs easily from the single floppy provided. The user interface is pre-Windows and consists of a coloured set of menus which is generally negotiated hierarchically. However, at the top level, menus must be used in a forward sequence corresponding to the three planes. There is a manual which is 21 pages long.

The program performs efficiently and could be used in a computer laboratory with students working through a written tutorial. However, the lack of a Windows interface might tend to create a bad impression. It is somewhat unsuited to live lecture demonstrations due to the complexity of the menuing scheme and the screen mode changes. It could however be used to prepare images ahead of time.

There are several limitations which should be noted:

* There is no facility to unwrap the phase display, which makes it difficult illustrate how shifting the object alters the phase of the diffraction pattern.

* PostScript printers are not supported.

* The size of geometric shapes can be specified but not their position angle.

* There is little control over the assign-ment of greyscale to image amplitudes.

* There is no way to have say two diffraction patterns on screen for direct comparison

This reviewer could suggest some modific-ations the author might like to consider:

* The program uses the terminology input stage, diffraction plane, image plane. Either of the alternative terminologies object/diffraction/image or input/diffrac-tion/output might be somewhat clearer.

* An extensive tutorial illustrating all the uses of the program would be very useful. The tutorial content of the manual is limited to one page.

* Allow the brush size to be specified when painting a general filter and improve the keyboard interface to make painting a mode rather than a command.

* Allow the same methods which are used to construct objects, to be used to construct filters.

There were also one or two occasions when the program crashed.

Nevertheless, despite these limitations, Optrans in its current form is a powerful program for illustrating Fourier concepts with 2D images, and should prove a very useful tool in a teaching laboratory.

Robert Minard

Optrans runs on a PC under DOS 5+, it requires at least 540K of memory, and will run more efficiently if 256K of expanded memory is available. Version 6 requires 4MB of RAM (8MB for 512 x 512 pixels) and a VGA card. Version 5 uses any graphics card.

To obtain Optrans contact its developer:
Dr Michael Reich
Dept of Applied Physics
GPO Box 2476V
Melbourne Vic 3001
Tel (03) 9660 2603
email mike_reich@rmit.edu.au

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