A semi-automatic technique is presented for obtaining the density field from interferograms provided by a Mach-Zehnder setup in infinite fringe width adjustment using short exposure times. The algorithm relies on extracting the fringe edges from the original image and then numbering the resulting polygons according to their order of interference using a graphical editor. The density field is then interpolated between the polygons by calculating its value from the intensity in the original interferogram. This results in highly accurate, high resolution scalar data fields. The results may then be presented in a quasi three-dimensional form using a shading model

An optical method for the discrimination between slow and fast tracer particles convected within a flow is proposed. It is based on the dependence of the brightness of a trace on the velocity of the corresponding tracer. The images of the traces are captured by a CCD-camera and processed on-line. A practical application of this technique to the visualization of the low velocity streamlines in a rotating duct is presented. The possibilities to develop this technique into a quantitative tool for velocity measurements is discussed.therefore be related to providing rules of thumb for practical results.As an appropriate recording medium for the capture of the particle tracks CCD-cameras seem to be suited best. Their advantage over conventional photographic recording film is mainly due to the linear response of a CCD to the incoming light. In combination with a frame grabber one gets the immediate availability of the images for further computer aided signal conditioning and analysis.