Device and method for estimating the noise of a video signal

1. Device for estimating a noise level of a video signal representing image sequences comprising

movement compensated interpolation means generating a movement compensated output signal,

a recursive filter designed to receive on a first input the movement compensated output signal and on a second input the video signal, said recursive filter generating a video output signal, the video output signal being compensated by the movement compensated interpolation means to produce the movement compensated output signal,

means of calculating a difference between the video signal and the movement compensated output signal,

means of estimating the noise level of the video signal according to the calculated difference and a maximum threshold delimiting the calculated difference, wherein the means of estimating includes:

a comparator for comparing each calculated difference to the maximum threshold; and

an accumulator for accumulating the calculated differences that are less than the maximum threshold to produce an accumulated sum of differences used to estimate the noise level of the video signal according to the calculated difference and the maximum threshold.

2. Device according to claim 1 wherein said comparator further includes means of comparing, for each pixel of an image in the video signal, the difference between said pixel value and said pixel value after movement compensated recursive filtering, at said maximum threshold.

3. Device according to claim 1 further comprising:

means of defining for each image a working window composed of a number of pixels centered on the image, and wherein

the means of calculating the difference being calculated for each pixel in the working window as the difference between the pixel value and the pixel value after movement compensated recursive filtering, and

the means of estimating further includes circuitry for calculating an average noise level by dividing the accumulated sum of differences by a number of accumulated differences.

4. Device according to claim 3 wherein the means of estimating the noise level of the video signal further includes:

means of measuring the inter-image and intra-frame correlations of each image,

means of calculating an overall noise level for each frame according to the average noise level and the inter-image and intra-frame correlations,

means of calculating a local noise level for each pixel of said frame according to the overall noise level of said frame and the luminance of said pixel.

5. Device according to claim 1 wherein said maximum threshold is linked to filtering parameters of said recursive filter.

6. Method for estimating a noise level of a video signal representing image sequences comprising the following steps:

movement compensated interpolation generating a movement compensated output signal,

receiving on a first input of a recursive filter the movement compensated output signal and on a second input of the recursive filter the video signal,

generating a video output signal, the video output signal being compensated by the movement compensated interpolation to produce the movement compensated output signal,

calculation of a difference between the video signal and the movement compensated output signal, and

estimating the noise level of the video signal according to the calculated difference and a maximum threshold delimiting the calculated difference, wherein the step of estimating includes:

comparing each calculated difference to the maximum threshold; and

accumulating the calculated differences that are less than the maximum threshold to estimate the noise level of the video signal according to the calculated differences and the maximum threshold.

7. Device for reducing the noise of a video signal comprising a noise level estimation device according to claim 1 .