On the relationship between the illumination of bubble in water and the CCD Gary pattern

Getting clear photographs of bubbles in water and extracting bubbles in the image of aerated water flows are the basis to analyze the characteristics of water flows by image measurement. Because the bubbles in water are colorless, transparent and deforming continuously, furthermore, they reflect and refract light at their boundaries. Up to now, almost all the image processing of bubbles extraction in the images of aerated water flows have problems of miss-extraction or deformity of bubbles which caused by un-uniformity of bubbles' boundary resulted from the un-balance illumination of the image. In order to eliminate the noises in the background and identify the blurry boundaries, based on the systematic analysis of the optical properties of bubbles in water, a set of formulas calculating the relationship between image gray and bubble luminance are deduced in this paper which are applicable to different illumination settings and different CCD. A new method is developed to forecast CCD gay pattern based upon illumination variable and bubble shape, which was demonstrated by the experiments. The proposed method is expected to be used to design experimental scheme of image measurement, and can help to enhance the accuracy of image analysis.