Dynamic pre-filter control with subjective noise detector for video compression
First Claim
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1. A method of filtering a digital video signal comprising the steps of:
- applying a low pass filter with an adjustable cut-off frequency to the digital video signal;
encoding the output of the said filter;
generating a locally decoded video image as part of the encoding process;
applying a subjective noise detector to the locally generated video image wherein said detector consists of one or more noise filters, and calculates the sum of the absolute differences between the locally generated video image and the output of the said filters;
applying a pre filter controller to the output of the subjective noise detector wherein said controller compares the output of the subjective noise detector with a predetermined threshold with the difference being an error signal employed to adjust the cut-off frequency of the adjustable low pass filter.
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Abstract
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.
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Citations
12 Claims
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1. A method of filtering a digital video signal comprising the steps of:
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applying a low pass filter with an adjustable cut-off frequency to the digital video signal;
encoding the output of the said filter;
generating a locally decoded video image as part of the encoding process;
applying a subjective noise detector to the locally generated video image wherein said detector consists of one or more noise filters, and calculates the sum of the absolute differences between the locally generated video image and the output of the said filters;
applying a pre filter controller to the output of the subjective noise detector wherein said controller compares the output of the subjective noise detector with a predetermined threshold with the difference being an error signal employed to adjust the cut-off frequency of the adjustable low pass filter. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A digital video apparatus comprising:
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A source of a digital video signal;
A digital signal processor connected to said source of a digital video signal programmed to perform filtering on the digital video signal by applying a low pass filter with an adjustable cut-off frequency to the digital video signal;
encoding the output of the said filter;
generating a locally decoded video image as part of the encoding process;
applying a subjective noise detector to the locally generated video image wherein said detector consists of one or more noise filters, and calculates the sum of the absolute differences between the locally generated video image and the output of the said filters;
applying a pre filter controller to the output of the subjective noise decoder wherein said controller compares the output of the subjective noise detector with a predetermined threshold with the difference being an error signal employed to adjust the cut-off frequency of the adjustable low pass filter; and
an output device connected to the digital signal processor for outputting the filtered digital video signal. - View Dependent Claims (8, 9, 10, 11, 12)
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Specification