Encoding and decoding of video images with delayed reference picture refresh

A method for predictive encoding a sequence of video images, the encoding method employing motion estimation for determining a motion vector between each of a plurality of image areas of an image to be encoded and image areas of a plurality of reference images, said reference images being previously encoded images of said image sequence, the method comprising the steps of:

• subjecting all images of said image sequence to motion estimation during encoding except predetermined individual images thereof, and
• disabling current reference images from being reference images, wherein said disabling step being performed after lapse of a predetermined delay after encoding of an image of said predetermined individual images not subjected to motion estimation wherein all current reference images except the image not subjected to motion estimation are disabled from being reference images.

An encoder for predictive encoding a sequence of video images, comprising:

• a multi-frame buffer for storing a plurality of reference images, said reference images being previously encoded images of said image sequence,
• a motion estimation unit for determining a motion vector between each of a plurality of image areas of an image to be encoded and image areas of a plurality of said reference images, said motion estimation unit being adapted to subject all images of said image sequence to motion estimation during encoding except predetermined individual images thereof, and
• a buffer controller for disabling current reference images from being reference images, wherein said buffer controller being adapted to disable said reference images after lapse of a predetermined delay after encoding the image of said predetermined individual images not subjected to motion estimation wherein all current reference images except the image not subjected to motion estimation are disabled from being reference images.

A method for decoding a sequence of encoded video images, the decoding method employing motion compensation based on motion vectors for predicting image areas of an image to be decoded from image areas of a plurality of reference images, said reference images being previously decoded images of said image sequence, the method comprising the steps of:

• subjecting all images of said image sequence to motion compensation during decoding except predetermined individual images thereof, and
• disabling current reference images from being reference images, wherein said disabling step being performed after lapse of a predetermined delay after decoding the image of said predetermined individual images not subjected to motion compensation wherein all current reference images except the image not subjected to motion compensation are disabled from being reference images.

A decoder for decoding a sequence of encoded video images, comprising:

• a multi-frame buffer for storing a plurality of reference images, said reference images being previously decoded images of said sequence of encoded video images,
• a motion compensation unit for predicting image areas of an image to be decoded by image areas of a plurality of said reference images, said motion compensation unit being adapted to subject all images of said sequence of encoded images to motion compensation during decoding except predetermined individual images thereof, and
• a buffer controller for disabling current reference images from being reference images wherein said buffer controller being adapted to disable said reference images after lapse of a predetermined delay after decoding the image of said predetermined individual images not subjected to motion compensation wherein all current reference images except the image not subjected to motion compensation are disabled from being reference images.