The defocus method is known as a method which can measure three dimensional coordinates of particles by one camera, and it is especially suitable for the 3D-PTV measurement of micro-flows. Although the color defocus method has solved some problems of the conventional defocus method, light absorption by color filters caused new difficult problems of insufficient light intensity. This paper proposes two new techniques which can take pictures more clearly than the existing color defocus method. By employing light-color filters, the serious problem of light absorption can be resolved. As a result, the combined use of those filters and HSI color analysis allows wider selection of filter colors. The introduction of laser illumination brings wider applications of the color defocus method, which enforces measurement precision of the method. Some measurement examples are shown here.
