| 摘要 |
PURPOSE:To detect the lightness change point in a screen on real time, by comparing the vector synthesis of the rate of change of horizontal and vertical lightness with a prescribed threshold value. CONSTITUTION:A differential amplifier 19 obtains difference between a signal VE of a noted picture element in a local matrix 14 and a horizontal picture element signal VF to the noted signal. A differential amplifier 20 obtains a difference between the signal VE and a vertical picture element signal VH to the noted picture element. Outputs lx, ly of the amplifiers 19, 20 are squared at multipliers 21, 22 respectively and summed at an adder 23. A comparator 25 compares the output l<2> of the adder 23 with a prescribed threshold value L<2> and when l<2>>L<2>, a lightness change detection signal (a) is takens as 1. When one of the rate of change of lightness of horizontal or vertical direction is a prescribed value or over, and when it is desirable that the rate of change of lightness of both directions is synthesized as the lightness change point although respective rate is smaller than the specified value, since the signal (a) is 1, then the lightness change point is detected accurately. |
