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Abstract

An efficient motion estimation technique for an arbitrarily-shaped video object reduces the number of searches for motion estimation for shape coding and texture coding. The technique can be easily employed in an MPEG-4 encoder for coding Video Object Planes (VOPs). In a pixel loop, an m.times.m block traverses a reference video image with the video object, and the alpha plane value of each pixel is examined. If the alpha plane values in a block are not all the same, this indicates the block overlaps the object boundary. Accordingly, a shape coding mask value for the coordinate of a reference pixel in the block, such as the top, left pixel, is set to '1'. As the block traverses the reference video image, a shape coding mask that generally follows the shape of the object boundary is developed to define a shaped reference image search area. A texture coding mask is defined similarly when the blocks overlap or are inside the object. When the same search range is used for both shape and texture motion estimation, the texture coding mask can be defined by ORing the shape coding mask with any blocks inside the object but not already included in the shape coding mask.

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