Patent ID: 7817207

Claim:
An image signal processing device for processing an external input horizontal synchronizing signal with a copy guard signal, comprising: a horizontal synchronizing signal detector, for receiving the external input horizontal synchronizing signal and an operating clock, detecting the external input horizontal synchronizing signal, and outputting an internal reference horizontal synchronizing signal, wherein the horizontal synchronizing signal detector comprises a horizontal synchronizing signal period counter for receiving the operating clock and the external input horizontal synchronizing signal for counting each period of horizontal synchronizing signals from the external input horizontal synchronizing signal according to the operating clock, a horizontal synchronizing signal extraction unit electrically connected to the horizontal synchronizing signal period counter, and a horizontal synchronizing signal reference output generator electrically connected to the horizontal synchronizing signal extraction unit; and a horizontal synchronizing signal output controller, which is electrically connected to the horizontal synchronizing signal detector, for receiving the operating clock, the external input horizontal synchronizing signal and the internal reference horizontal synchronizing signal to thus filter an original horizontal synchronizing signal out of the externally input horizontal synchronizing signal according to the frequency of internal reference horizontal synchronizing signal.