| 摘要 |
PURPOSE:To hold always a correct white-level envelope to obtain a stable binary output, by tracking the white-level envelope only when the binary output is all white, in an optical character reader. CONSTITUTION:Video input signal (a) is converted to a-bit digital data through A/D converter 11 and is subjected to logarithmic conversion by ROM12 and is inverted by latch 13 and is input to adding circuit 22. This signal is added to white- level envelope signal (c), which is output from white-level envelope tracking circuit 100, by circuit 22 to black-level signal (d) subjected to shading correction. This signal (d) is supplied to black level tracking circuit 200, and fluctuation quantity data of the slice level is selected, and the binary output is taken out through comparator 30. In this case, the white-level envelope is tracked only when the binary output is all white, so that a correct white-level envelope is always held to obtain the stable binary output. |
