Shading correcting circuit and method for correcting an image de

Details Shading correcting circuit and method for correcting an image de Shading correcting circuit and method for correcting an image de

1990-03-06

1997-08-19

Kulik, Paul V.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

348251, H04N 100

Patent

active

056594887

ABSTRACT:
The shading correction is performed with respect to a signal "A" indicative of the image density read by an optical read device in accordance with a reference signal "B". Both the signals "A" and "B" consist of n bits. An inputted signal having an initial value "A" is doubled by a multiplier when A=B and B.noteq.0. A subtracter subtracts the reference signal "B" from a signal "X" outputted from the multiplier and discriminates whether or not a signal "X-B" is negative. An S/P conversion register doubles an integrated value "S" having an initial value "0" and changes the integrated value from "S" to "2S" when the signal "X-B" is negative. In contrast, when the signal "X-B" is not negative the S/P conversion register adds "1" to "2S" and changes the integrated value from "S" to "2S+1". The signal "X" outputted from the multiplier is again inputted into the multiplier when the signal "X-B" is negative. Alternatively, the multiplier receives the signal "X-B" outputted from the subtracter when the signal "X-B" is not negative. The, above procedure is repeated n times. The last integrated value outputted from the S/P conversion register is equal to or approximately equal to a value obtained by an expression "S=A(2.sup.n -1)/B", and therefore, the former can be regarded as a shading correction signal.

REFERENCES:
patent: 4523229 (1985-06-01), Kanmoto
patent: 4879598 (1989-11-01), Seto
patent: 4945405 (1990-07-01), Hirota

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