| 摘要 |
PURPOSE:To detect robbery or a trespasser optically by utilizing the phenomenon that the distribution of respective frequency components in a video signal vary with an object to be photographed. CONSTITUTION:When the video signal obtained by photographing a standstill object is processed by a warning signal generating circuit 5, the integral value of its high and low frequency components is unchanged. Therefore, the ratio output of a dividing circuit 15 is constant, so a warning generator 17 does not operates. If, however, a change is caused in a photographic screen by the removal of a body from the screen or entry of a body, the distribution of frequency components in the video signal varies. Outputs of integrating circuits 11 and 12 vary according to the variation of the distribution and the ratio output of the dividing circuit 15 varies, which is detected by a variation rate detecting circuit 16 to put the warning generator 17 in operation. When the brightness of the screen varies with out any change in the screen, the high and low frequency components in the video signal both vary, so the warning generator 17 does not operate. |
