Device and process for coding video images by motion compensation
View Patent ↗A device and a method for coding video images by motion compensation. The device incorporates a coding unit and a filtering unit. A calculation unit for calculating a recursivity coefficient as a function of an estimated noise level and a prediction error, a measurement unit for measuring the intra-image correlation and the inter-image correlation, a selection unit for selecting a type of coding applied to the current input image as a function at least of the measurements of the inter-image correlation and of the measurements of the intra-image correlation and as a function of the estimated noise level, a coding unit for coding the current input image as a function of the type of coding selected.
1. Device for coding video images by motion compensation comprising a coder comprising:
means of storage of at least one input image,
motion estimation means, designed to produce motion vectors and quantities representative of motion-compensated image variations, on the basis of a current input image and of at least said input image stored previously in said means of storage,
means of calculation of a motion-compensated image on the basis of a filtered image and of said motion vectors,
means of calculation of a prediction error, between said current input image and said motion-compensated image,
means of calculation of a recursivity coefficient,
first means of filtering, intended to produce a weighting of said prediction error by a modified recursivity coefficient,
second means of filtering, intended to add the content of said motion-compensated image to the prediction error weighted by said modified recursivity coefficient when said input image is an image coded as intra type, and
means of estimation of at least one noise level as a function of at least said quantities representative of motion-compensated image variations wherein:
said recursivity coefficient is calculated as a function of said noise level and of said prediction error,
said coding device comprises: means of measurement of the intra-image correlation,
means of measurement of the inter-image correlation, and
means of selection of an image coding type applied to said current input image as a function of at least the measurements performed by the means of measurement of the inter-image correlation and the means of measurement of the intra-image correlation and as a function of said estimated noise level,
and the means of filtering and the coder of a motion-compensated image are dependent on said image coding type selected by said means of selection.
2. Device according to claim 1 , wherein said recursivity coefficient is calculated for each pixel of said input image.
3. Device according to claim 1 , wherein it comprises means of detection of change of scene.
4. Device according to claim 3 , wherein said recursivity coefficient takes a zero value for the first image following the change of scene when the means of detection of change of scene detect a change of scene.
5. Device according to claim 3 , wherein said means of selection of an image coding type select the image coding type applied to said current input image as a function of information received from said change of scene detector.
6. Device according to claim 1 , wherein the images are coded as intra, predictive or bi-directional type and the means of selection of the image coding type adjust the sequencing of the image coding types and the choice of the number of successive bi-directional images.
7. Device according to claim 6 , wherein the first image following a detection of change of scene is coded as intra type and the following image is coded as predictive type.
8. Device according to claim 6 , wherein the spacing between two successive images of intra or predictive type is calculated according to the formula
GOPM =Max[ GOPM default −nint[ β*max{( FD d −LD d )/ LD d, 0}],1],
where:
β is preferably equal to “1” and “nint” represents the nearest integer,
FD d =Max(1, FD−σ inf ),
LD d =Max(1, LD−σ inf ),
GOPM default represents the maximum value permitted by the coding device, Max representing the maximum function, FD representing the inter-frame correlation measurement and LD representing the intra-frame correlation measurement.
9. Process for coding video images by motion compensation in which
at least one input image is stored,
motion vectors and quantities representative of motion-compensated image variations are produced on the basis of a current input image and of at least said input image stored previously in said means of storage,
a motion-compensated image is calculated on the basis of a filtered image and of said motion vectors,
a prediction error between said current input image and said motion-compensated image is calculated,
a recursivity coefficient is calculated,
a weighting of said prediction error by a modified recursivity coefficient is produced,
the content of said motion-compensated image is added to the prediction error weighted by said modified recursivity coefficient when said input image is an image coded as intra type,
at least one noise level is estimated as a function of at least said quantities representative of motion-compensated image variations, wherein
said recursivity coefficient is calculated as a function of said estimated noise level and of said prediction error,
the intra-image correlation is measured,
the inter-image correlation is measured,
an image coding type applied to said current input image is selected as a function of at least the measurements of the inter-image correlation and of the measurements of the intra-image correlation and as a function of said estimated noise level,
said current input image is coded as a function of said image coding type selected.