Method for determining to skip macroblocks in encoding video

An apparatus for encoding video pictures, each encoded picture being divided into non overlapping macroblocks, each macroblock comprising one or more luminance blocks and one or more chrominance blocks, each block comprising an n×m array of pixel data, said method comprising the steps of:

• (a) means for obtaining a sequence of video pictures,
• (b) means for designating certain ones of the pictures of the sequence for predictive encoding and designating one or more of the pictures of the sequence as reference pictures for each picture designated for predictive encoding,
• (c) dividing a picture designated for predictive encoding into macroblocks,
• (d) means for iterating the following steps (e)-(n) once for each ith macroblock:
• (e) motion estimating the ith macroblock, using only the luminance blocks of the ith macroblock, to obtain a motion vector, indicating the temporal and spatial offset from the ith macroblock to a prediction macroblock in a designated reference picture, and the mean absolute difference of the luminance blocks of the ith macroblock and the luminance pixels of the prediction macroblock, the mean absolute difference being computed by evaluating:
• ∑ x = l j ⁢ ⁢ ∑ y = l k ⁢ ⁢ [LeftBracketingBar] P i Y ⁡ [ x , y ] - MB i Y ⁡ [ x , y ] [RightBracketingBar]
• where PYi is the luminance pixel data of the prediction macroblock for the ith macroblock, MBYi is the luminance pixel data of the ith macroblock and j and k are the number of rows and columns of luminance pixel data in a macroblock, respectively,
• (f) if the motion vector is zero and the mean absolute difference is below a first threshold, performing steps (g) and (h) for the ith macroblock, and for otherwise, performing steps (j), (k), (l), (m) and (n),
• (g) generating the chrominance mean absolute difference between the chrominance blocks of the ith macroblock and the prediction macroblock, by evaluating:
• ∑ x = l a ⁢ ⁢ ∑ y = l b ⁢ ⁢ [LeftBracketingBar] P i Cr ⁡ [ x , y ] - MB i Cr ⁡ [ x , y ] [RightBracketingBar] + ∑ x = l a ⁢ ⁢ ∑ y = l b ⁢ ⁢ [LeftBracketingBar] P i Cb ⁡ [ x , y ] - MB i Cb ⁡ [ x , y ] [RightBracketingBar]
• where PCri is the red chrominance pixel data of the prediction macroblock for the ith macroblock, MBCri is the red chrominance pixel data of the ith macroblock, PCbi is the blue chrominance pixel data of the prediction macroblock for the ith macroblock, MBCbi is the blue chrominance pixel data of the ith macroblock and a and b are the number of rows and columns of red and blue chrominance pixel data in a macroblock, respectively,
• (h) if the chrominance mean absolute difference is less than a second threshold, then performing step (i), and for otherwise performing steps (j), (k), (m) and (n),
• (i) inserting an indication into the bitstream indicating that the ith macroblock is skipped, and refraining from performing steps (j), (k), (l), (m) and (n) for the ith macroblock,
• (j) subtracting the luminance and chrominance blocks of the ith macroblock from the prediction macroblock to form the prediction error macroblock for the ith macroblock,
• (k) orthogonally transforming each block of the prediction error macroblock for the ith macroblock,
• (l) quantizing each transformed block of the prediction error macroblock for the ith macroblock,
• (m) entropy encoding each quantized block of the prediction error macroblock and the motion vector for the ith macroblock, and
• (n) inserting the entropy encoded blocks of the prediction error macroblock and motion vector for the ith macroblock into the encoded bitstream,
• wherein said means for iterating refrains from performing steps (j), (k), (l), (m) and (n) for each ith macroblock for which step (i) is performed.

A method for temporally and spatially encoding each picture of a sequence of moving pictures comprising iterating, for each ith macroblock of a temporally encoded picture, in sequence, the steps of:

• (a) motion estimating the ith macroblock, using only the luminance blocks of the ith macroblock, to obtain a motion vector, indicating the temporal and spatial offset from the ith macroblock to a prediction macroblock in a designated reference picture, and the mean absolute difference of the luminance blocks of the ith macroblock and the luminance pixels of the prediction macroblock, the mean absolute difference being computed by evaluating:
• ∑ x = l j ⁢ ⁢ ∑ y = l k ⁢ ⁢ [LeftBracketingBar] P i Y ⁡ [ x , y ] - MB i Y ⁡ [ x , y ] [RightBracketingBar]
• where PY1 is the luminance pixel data of the prediction macroblock for the ith macroblock, MBYi is the luminance pixel data of the ith macroblock and j and k are the number of rows and columns of luminance pixel data in a macroblock, respectively,
• (b) if the motion vector is zero and the mean absolute difference is below a first threshold then performing steps (c) and (d) for the ith macroblock, otherwise, performing step (f),
• (c) generating the chrominance mean absolute difference between the chrominance blocks of the ith macroblock and the prediction macroblock, by evaluating:
• ∑ x = l a ⁢ ⁢ ∑ y = l b ⁢ ⁢ [LeftBracketingBar] P i Cr ⁡ [ x , y ] - MB i Cr ⁡ [ x , y ] [RightBracketingBar] + ∑ x = l a ⁢ ⁢ ∑ y = l b ⁢ ⁢ [LeftBracketingBar] P i Cb ⁡ [ x , y ] - MB i Cb ⁡ [ x , y ] [RightBracketingBar]
• where PCri is the red chrominance pixel data of the prediction macroblock for the ith macroblock, MBCri is the red chrominance pixel data of the ith macroblock, PCbi is the blue chrominance pixel data of the prediction macroblock for the ith macroblock, MBCbi is the blue chrominance pixel data of the ith macroblock and a and b are the number of rows and columns of red and blue chrominance pixel data in a macroblock, respectively,
• (d) if the chrominance mean absolute difference is less than a second threshold, then performing step (e), otherwise performing step (f),
• (e) inserting an indication into the bitstream indicating that the ith macroblock is skipped, and refraining from performing step (f) for the ith macroblock, and
• (f) spatially encoding a prediction error macroblock formed from the prediction macroblock and the ith macroblock,
• wherein step (f) is not performed for the ith macroblock if step (c) is performed for the ith macroblock.