| 摘要 |
PURPOSE:To prevent refusal of reading and misreading of characters by detecting the whitest value in each small area on the surface of a document, setting up a binary threshold from the detected output and converting a multilevel digital signal corresponding to the brightness of the surface of the document into a binary signal on the basis of the threshold. CONSTITUTION:A scanning part 40 photoelectrically converts characters and codes scanned on the document 10 to form a picture signal having multi-level density consisting of 16 levels. The formed picture signal is guided to a temporary storage part 60. Shift registers 61-65 in the storage part 60 shift the inputted picture signal and output the shifted signals to shift registers 71-75 in a mask part 70. Picture signals from respective registers 71-75 are inputted to a whitest value detecting part 80, which detects a value close to the whitest value and sends the detected value to a threshold determining part 90. The determination part 90 determines the threshold on the basis of the whitest value and sends the threshold to a binary-coding circuit 100. The circuit 100 compares a center picture element 733 in the mask part 70 with the threshold, encodes the compared value into a binary signal and outputs the binary picture signal to the external.
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