Color Flow-Visualization Photography and Digital Image Processing Techniques

Color flow-visualization photography and digital image processing techniques have been developed for the purpose of flow measurement in the flow field of a circular vessel with recirculation flow. The pathlines of aluminum powder were photographed on a color reversal film by illuminating it in red, white, and green in turn within an exposure time. The pixel values in red, green, and blue for 256 steps prepared by the drum-scanner as the digital image data of the film, the resultant stimulus and trichromatic coordinates of each pixel were evaluated from them. The pixels for pathlines were distinguished from the background by the threshold-level of resultant stimulus, and their colors were determined by using the principal component obtained from combined and standardized residuals for the regression formulas of trichromatic coordinates. The velocity vectors can be derived from both the location and color of pixels, and the time interval of white color illumination.