| 摘要 |
<p>PURPOSE:To obtain the small scale and low-priced picture synthesizer by providing a comparator to generate a key signal by extracting the direct current component of a first picture signal and comparing the level with a reference level, and a changeover switch to select any one of picture signals corresponding to the level of the key signal. CONSTITUTION:A picture signal S1 outputted from an inverse quantizer 6 is supplied to a contact A of a changeover switch 9, and a picture signal S2 outputted from an inverse quantizer circuit 7 is supplied to a contact B of the changeover switch 9. The picture signal S1 outputted from the inverse quantizer circuit 6 is supplied to a comparator 8 as well and in the comparator 8, the transformation coefficient of the direct current component is extracted for each block of the picture signal S1 so as to form a key signal C by comparing those levels with a reference value V0. When the value of the transformation coefficient of the direct current component is defined as D, the picture signal S1 is selected by the changeover switch 9 in the case of D>V0 and the picture signal S2 is selected by the changeover switch 9 in the case of DHV0 respectively. Thus, this device can be composed of only circuits, and device scale can be considerably reduced.</p> |
