1. A method of motion detection using an adaptive threshold, adaptive for determining whether a plurality of target pixels are moving pixels or not, the method comprising: giving a first threshold for determining whether the target pixels in a current scan line are moving pixels; calculating a number of moving pixels in a previous scan line of the current scan line; determining whether the number of moving pixels is larger than a second threshold; if the number of moving pixels is larger than the second threshold, adjusting the first threshold by a decrement; and determining whether the target pixels in the current scan line are moving pixels by using the adjusted first threshold.