PURPOSE: To avoid the effect due to the variation of picture density by binary coding the picture data with plural threshold values to count the binary coded density sum, calculating the threshold value from the counted density sum so that this sum is set at a constant and binary coding pictures with the calculated threshold value.
CONSTITUTION: A control part 17 actuates a scanner 11 to give a scan to an original in the forward direction and sends pictures 21 fed successively to binary coding circuits 12 and 13. These circuits 12 and 13 binary codes the pictures 21 with threshold values θ1 and θ2. The outputs of the circuits 12 and 13 are counted by counters 14 and 15 to calculate the binary coded density sums (number of picture elements having density equal to "1") T1 and T2. When the forward scan is over, the part 17 reads out the contents of counters 14 and 15 as well as a register 18 to which a constant S is set and calculates the new threshold value θ with which the binary coded density sum is equal to the constant S to set the new value θ to the circuit 12. Then the part 17 actuates the scanner 11 to scan the original in the reverse direction. The pictures 21 fed successively are sent to the circuit 12 and binary coded with the new value θ. The output of the circuit 12 is sent to an interface 16, and a picture 26 of high accuracy is sent to an external device.
TAKEDA HARUO
MINAMI TADASHI
TAKIGUCHI AKIHIKO
