| 摘要 |
PURPOSE:To prevent the scale of the unit from going large, the cost of it from going expensive and the processing time from going long by varying a threshold value at multi-value coding so as to be an optimum threshold value in response to the result of the secondary differentiation at each picture element. CONSTITUTION:An analog picture signal read by a picture input means 1 is applied with A/D conversion and shading correction, the result is outputted to a Laplacian output circuit 2. The secondary differentiation Lap(i,j) is obtained from the signal by the Laplacian circuit 2 and a prescribed value K is added by an adder circuit 3, the result is given to an operation section 7 via an operating section 7 and a reciprocal number calculating ROM17. The operating section 7 calculates a binary-coded threshold value T(i,j), the result is fed to a comparator 8 so as to binary-code a picture signal P(i,j) outputted from a buffer memory 9.
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