| 摘要 |
PROBLEM TO BE SOLVED: To synthesize an HDTV signal and an HD graphics signal without using a very high speed digital element. SOLUTION: The image synthesis circuit 10 is provided with input terminals 1, 4, an NTSC/HDTV discrimination part 18, 1st to 3rd switches SW1 to SW3, a format conversion part 2A, a frame synchronization part 3, and a synthetic part 5. An NTSC signal or an HDTV signal is inputted to the 1st input terminal 1, whether the input signal is the NTSC signal or the HDTV signal is discriminated by the discrimination part 18 and the 1st to 3rd switches SW1 to SW3 and a switch part 23 in the conversion part 2A are switched to the (a) side or (b) side in accordance with the discriminated result. When an NTSC signal is inputted to the input terminal 1, respective switches are switched to the (a) side and the input signal is converted into an HDSC format by the conversion part 2A, synchronized with an HD graphics signal, returned to an analog signal, and then synthesized with the HD graphics signal. When an HDTV signal is inputted to the input terminal 1, respective switches are switched to the (b) side, only the digital conversion of the input signal is executed by the conversion part 2A and the digital signal is synchronized with the frame synchronization part 3 and returned to an analog signal, which is synthesized with the HDTV signal.
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