Method of measuring the noise in an active video image and device for implementing the method

An apparatus for reducing noise in an active video signal, comprising:

• means for receiving said video signal and subtracting a previous video signal of a image preceding said active video signal to produce a first signal;
• a movement detector which receives said first signal and outputs a movement signal;
• a noise measurement circuit for measuring noise in said first signal and for outputting a noise signal;
• means for producing a noise-reduction coefficient using said movement signal and said noise signal;
• a multiplier which multiplies said first signal and said noise-reduction coefficient to produce a second signal;
• and
• an adder for adding said second signal and said previous video signal to output a third signal being a noise-reduced video signal;
• wherein said noise circuit measurement circuit comprises:
• an absolute value circuit for taking the absolute value of said first signal and producing an absolute value signal;
• a squaring circuit for squaring said absolute value signal and producing a squared signal;
• an accumulator which adds said squared signal to previously produced squared signals and produces an accumulated signal;
• a counter for counting a number of squared signals accumulated by said accumulator;
• and
• means for comparing said number of squared signals to a predetermined number, outputting said accumulated signal when said number of squared signals is at least equal to said predetermined number, and outputting a previous value of said accumulated signal when said number of squared signals is less than said predetermined number.

A method of reducing noise in an active video image, comprising:

• storing a first video signal of a first image;
• subtracting said first video signal from a second video signal of a second image subsequent to said first image to obtain a subtracted image;
• detecting movement in said subtracted image to obtain stationary pixels in said subtracted image;
• measuring noise in said subtracted image using said stationary pixels;
• determining a noise-reduction coefficient based on said detecting of said movement and said measuring of said noise;
• multiplying said subtracted image by said noise-reduction coefficient to obtain a multiplied signal;
• and
• producing a noise-reduced video signal from said first signal and said multiplied signal;
• wherein said step of measuring noise in said subtracted image comprises:
• determining a first noise-reduction coefficient;
• counting a number of said stationary pixels;
• comparing said number to a predetermined value;
• using said first noise-reduction coefficient when said number is at least equal to said value;
• and
• using a previously determined noise-reduction coefficient when said number is less than said value.

A method of reducing noise in an active video image, comprising:

• storing a first video signal of a first image;
• subtracting said first video signal from a second video signal of a second image subsequent to said first image to obtain a subtracted image;
• detecting movement in said subtracted image to obtain stationary pixels in said subtracted image;
• measuring noise in said subtracted image using said stationary pixels;
• determining a noise-reduction coefficient based on said detecting of said movement and said measuring of said noise;
• multiplying said subtracted image by said noise-reduction coefficient to obtain a multiplied signal;
• and
• producing a noise-reduced video signal from said first signal and said multiplied signal;
• wherein said step of measuring noise in said subtracted image further comprises:
• determining a first noise-reduction coefficient;
• counting a number of said stationary pixels;
• comparing said first noise-reduction coefficient to a previously determined second noise-reduction coefficient;
• if said first noise-reduction coefficient is greater that said second noise-reduction coefficient, comparing said number of said stationary pixels to a first threshold value, using said first noise-reduction coefficient when said number is at least equal to said first threshold, and using said second noise-reduction coefficient otherwise;
• and
• if said first noise-reduction coefficient is no more than said second noise-reduction coefficient, comparing said number of said stationary pixels to a second threshold value, using said first noise-reduction coefficient when said number is at least equal to said second threshold, and using said second noise-reduction coefficient otherwise.