Device and process for estimating noise level, noise reduction system and coding system comprising such a device
View Patent ↗The present invention relates to a device and a process for estimating the noise level of video images before coding. The device comprises in particular means of storage of at least one input image, a blockwise motion estimation module, designed to produce, blockwise, first quantities representative of motion-compensated image variations, on the basis of a current input image and of at least one input image stored previously in the said means of storage, means of estimation of a global noise level for each image as a function of at least certain of the said quantities representative of motion-compensated image variations, The said device comprises means of estimation of a local noise level for each block of the image as a function of second quantities representative of motion-compensated image variations and of the global noise level.
1. A process for estimating the noise level of video images before coding in which:
at least one current input image is stored;
a blockwise motion estimation is performed so as to produce, blockwise, quantities representative of motion-compensated image variations, on the basis of a current input image and of at least one input image stored previously; and
a global noise level is determined for each image as a function of at least certain of the quantities representative of motion-compensated image variations, called first quantities, wherein
a local noise level is determined for each block of the image as a function of the difference between a mean displaced frame difference and a local displaced frame difference, both calculated during blockwise motion estimation, and as a function of the ratio of said difference to the mean displaced frame difference, wherein the local noise level is determined:
by decreasing the value of said global noise level, if said difference is positive, and,
by increasing the value of said global noise level, if said difference is negative; and
wherein, if said difference is positive, the local noise level is determined by:
subtracting from said global noise level the product of said ratio and a first predefined parameter if said difference is below a first predefined threshold, and
subtracting from said global noise level half the value of said first predefined parameter otherwise.
2. A process for estimating the noise level of video images before coding in which:
at least one current input image is stored;
a blockwise motion estimation is performed so as to produce, blockwise, quantities representative of motion-compensated image variations, on the basis of a current input image and of at least one input image stored previously; and
a global noise level is determined for each image as a function of at least certain of the quantities representative of motion-compensated image variations, called first quantities, wherein
a local noise level is determined for each block of the image as a function of the difference between a mean displaced frame difference and a local displaced frame difference, both calculated during blockwise motion estimation, and as a function of the ratio of said difference to the mean displaced frame difference, wherein the local noise level is determined:
by decreasing the value of said global noise level, if said difference is positive, and,
by increasing the value of said global noise level, if said difference is negative; and
wherein, if said difference is negative, the local noise level is determined by:
adding to said global noise level half the value of a second predefined parameter if said difference is below a second predefined threshold and if the displacement vector is above a third predefined threshold, and
subtracting from said global noise level the product of said ratio and said second predefined parameter otherwise.