Abstract: MATLAB image processing together with professional photo software is employed to extract tidal level data by analyzing tidal level images. Firstly, tide level image was pre-processed by PHOTOSHOP such as image rotation, pixel increment, levels operation, key-point plotting and bitmapping. Then the image was read by MATLAB and the location of key-points could be obtained by program. The tide level data number was obtained by the relative location of tide level key-points and horizontal and vertical coordinates key-points. In addition, different approaches were specified for point-curve image and continue curve image. This method was applied to the acquirement of tidal level data at a tide-gauge station. Application results indicate that the digitized value was very close to the measured value and the mean error was less than 1.0%。This method could be extended to image data acquirement in similar fields.

Key words: MATLAB, image processing, bitmapped, tide level, digitizing, PHOTOSHOP