PURPOSE: To extract stably a character area at a high speed without using picture memory by dispersing the degree of a density gradient direction histogram, and comparing at least two types of thresholds, and extracting a character candidate area.
CONSTITUTION: An input picture signal S is converted into a digital picture by an analogue/digital convertor circuit 11. The 1st and the 2nd density gradient detection circuits 12 and 13 scan a differential filter having such shapes as shown in Figures (a) and (b), and a density gradient direction circuit 14 transfers successively output values d1 and d2. According to the output values d1 and d2, the density gradient direction detection circuit 14 calculates the direction of density gradient, and a histogram calculation part 2 calculates a density gradient direction histogram by the obtained value. A variance calculation part 3 calculates the variance of degree of the density gradient direction histogram. On the other hand, a character area extractor 4 extracts the candidate of a character area by using two types of thresholds, and a real character area is extracted based on the extracted result.
GOTOU TOSHIYUKI
IWASE HIROMICHI
