pre filtering is commonly used in video encoding to remove undesirable noise from video sources . without a pre filter , the noise degrades the performance of a video encoder by wasting a number of bits to represent the noise itself , and by introducing encoding artifacts such as blocking and ringing noise . however , excess use of pre filtering will degrade subjective visual quality . this invention employs an automatic pre filter control using a subjective noise detector capable of measuring noise that strongly correlates to subjective video quality .