Gray scale processing of hydrographic maps

This paper investigates how gray scale information can be used in a hydrographic map understanding system to improve the system performance. To process gray scale scanned map images, we have implemented a topographic analysis method and a binary analysis method. In addition, deconvolution of the gray scale map image was used as an optional preprocessing step for both the methods. Both the methods process the input image by extracting binary print components, recognizing long lines, splitting touching digits and recognizing the digits. The topographic analysis extracts the information by computing topographic labels for each pixel, while the binary analysis is based on locally adaptive thresholding of the gray scale image. The performance of each method was evaluated by measuring the recognition performance of the digit recognition module. Experimental results indicate that the computationally intensive deconvolution and topographic analysis does not improve system performance. The same high performance is achieved by binary analysis, provided a high quality locally adaptive binary method is used.