DIGITAL SUBTRACTION SYSTEM

摘要

PURPOSE:To compensate the reduction of a peripheral level and to improve the resolution of a peripheral blood vessel by putting a peripheral level compensating circuit between a TV camera and a D/A converter. CONSTITUTION:The video signal sent from a TV camera 10 passes through an LPF22 to produce an envelope curve and then inverted by an inverse amplifier 20 to be applied to an adder 28 as a signal having its minimum level turned into a pedestal level. While the video signal passed through a delay circuit 26 having a delay amount equal to the time delay produced by an LPF22 and an amplifier 24 is sent to the adder 28 to be added with the video signal sent from the amplifier 20. This output of the addition compensates the reduction of the peripheral level. Furthermore the pedestal level is increased by a pedestal level setting circuit 30 in order to emphasize the picture of the peripheral vessel. Thus the maximum and the minimum levels of the video signal are set at the maximum and the minimum levels of the input voltage of an A/D converter 12 respectively.