Quantizer control method and apparatus

A method for transmitting a selected number of bits for representing an encoded image, the number of bits being transmitted being a function of a quantizer step size, said image being comprised of a plurality of sectors, each sector being comprised of a plurality of blocks, said method comprising the steps of

• determining a desired number of bits to be allocated to each sector,
• transmitting said sectors in a selected sequence, and
• associating a quantizer step size with each sector,
• said associating step comprising setting the quantizer step size for a sector as a function of the difference in number of bits actually transmitted for all previous sectors of the image and the desired number of bits to be transmitted for all previous sectors of the image.

A method for transmitting a selected number of bits for representing an encoded image, the number of bits being transmitted being a function of a quantizer step size, said image being comprised of a plurality of sectors, each sector being comprised of a plurality of blocks, said apparatus comprising the step of

• allocating available bits to blocks of the image to be encoded according to the relationship
• B(n)=B.sub.d (n)/N(n)+1/2Log.sub.2 (E(n)/E.sub.TOT (n))
• where
• B(n) is the number of bits allocated to block B for frame n;
• N(n) is the number of blocks of frame n actually coded;
• B.sub.d (n) is the desired number of bits allocated to code frame n;
• E(n) is the prediction error energy for block B of frame n (wherein the DC component is omitted for intrablocks);
• and
• E.sub.TOT (n) is the geometric mean of energy for all blocks (N) actually to be coded for frame n.

An apparatus for transmitting a selected number of bits for representing an encoded image, the number of bits being transmitted being a function of a quantizer step size, said image being comprised of a plurality of sectors, each sector being comprised of a plurality of blocks, said apparatus comprising

• means for determining a desired number of bits to be allocated to each sector,
• means for transmitting said sectors in a selected sequence, and
• means for associating a quantizer step size with each sector,
• said associating means comprising means for setting the quantizer step size for a sector as a function of the difference in number of bits actually transmitted for all previous sectors of the image and the desired number of bits to be transmitted for all previous sectors of the image.

An apparatus for transmitting a selected number of bits for representing an encoded image, the number of bits being transmitted being a function of a quantizer step size, said image being comprised of a plurality of sectors, each sector being comprised of a plurality of blocks, said apparatus comprising means for allocating available bits to blocks of the image to be encoded according to the relationship

• B(n)=B.sub.d (n)/N(n)+1/2Log.sub.2 (E(n)/E.sub.TOT (n))
• where
• B(n) is the number of bits allocated to block B for frame n;
• N(n) is the number of blocks of frame n actually coded;
• B.sub.d (n) is the desired number of bits allocated to code frame n;
• E(n) is the prediction error energy for block B of frame n (wherein the DC component is omitted for intrablocks);
• and
• E.sub.TOT (n) is the geometric mean of energy for all blocks (N) actually to be coded for frame n.