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

Claim 1

Method of adjusting a noise-reduction coefficient K in an active video image, characterised by the following steps: during a given processing period, detecting movement and measuring noise in the video image in parallel, a measurement of the noise being obtained for each pixel of the video image considered to be stationary, using a movement detector processing successive images, by calculating a difference f d between an unprocessed video signal corresponding to this pixel, and a video signal processed with a noise-reduction coefficient K corresponding to the pixel at a same spatial position in a preceding video image; calculating the square of the absolute value of the difference so as to obtain a value |f d | 2 ; adding the value |f d | 2 to other values |f d | 2 already obtained for the pixels defined as stationary, so as to form a sum value Σ|f d | 2 ; recommencing the above operations until a number of pixels processed is equal to a first threshold value N 0 , or until the end of the processing period; at the end of the above operations, when the number of pixels processed is at least equal to the first threshold value, using the sum value Σ|f d | 2 to determine a value of a reference point corresponding to the movement as a function of the noise, this value giving as a function of a transfer curve in which the noise-reduction coefficient is a function of the values at the output of the movement detector, a new value for the noise-reduction coefficient K, otherwise a former value of the noise-reduction coefficient K is kept; and using the value determined as the noise-reduction coefficient K to reduce noise in the unprocessed video image to produce a noise-reduced video image.

Claim 8

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.

Claim 9

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.

Claim 12

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.

Claim 13

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.

Claim 14

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.

Claim 15

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.