Study On Optical Wavelet Filter Realized By Film

Optical wavelet transform is a real-time signal processing method which has developed in recent years. It combines the advantage of both wavelet transform and optical information. It is an effective approach to realize image data compression with the characteristic of parallelism and high-speed. It plays a significant role in some application fields which need to transmit abundant image data; for example, sunspace remote sensing and forest fireproofing. By now, it has got achievement on pattern recognition and texture segmentation. Because image data compression makes special demands on precision of the whole optical system, the reports on this field are rare. Placing a filter on the Fourier plane in an optical 4f system is a typical way to implement optical wavelet transform. Grating, spatial light modulator, computer- generated hologram and film can be used as the filter. This thesis focused on the research of the filter made of film. The whole thesis mainly consists of the following contents:Comparing with laser printer and dye-sublimation printer, film recorder of converting digital image into film was determined judging by the need of this project. Considering inaccuracy brought in by man-made factors or hardware devices in the facture of optical filter, it is necessary to measure the error of it. A feasible experiment scheme for measuring the error was provided.For the error, it is impractical to compensate after fabrication. In order to get relative accurate gray level on films, this paper borrowed ideas from predistortion applied to modify original image according to the nonlinear effects in manufacturing process. Therefore, a primary task of the paper is to set up the error model through artificial neural network, and then compensate the error in the system.It is verified by lots of experiments that based on color images of 24 bits. The relation between original image gray level and the one made by film is non-linear, and gray levels of film image varies with different grey level combination of R,G,B channel. Meanwhile, the precision of each channel is different. The performance of R channel is the best, and B channels'is the worst. By polynomial curve fitting, the PSNR of film will increase 10~20dB.Finally, the author made a conclusion and pointed out the problems that need to be explored further and the future research emphasis.