Recognition of Digits in Hydrographic Maps: Binary vs. Topographic Analysis

This paper compares the performance of topographic analysis and binary analysis for recognition of digits in hydrographic maps. Each of the methods processed the input image by extracting binary print components, recognizing long lines, splitting touching digits, and, finally, recognizing individual symbol candidates. The topographic analysis extracted the information by computing topographic labels for each pixel, while the binary analysis was based on a locally adaptive thresholding of the gray scale image. The performance of each method was measured by the correct classification rate of the final symbol recognition step when processing a complete hydrographic map of size 0.45× 0.6m with about 35,000 digits. The experimental results indicated that binary analysis had a better performance than topographic analysis. Overall, the performance of the binary analysis was acceptable. Deconvolution of the gray scale hydrographic image did not improve the performance of any of the two methods. Keywords— Binary analysis, Topographic analysis, Locally adaptive binarization, Symbol recognition, Data capture.