Method and apparatus for controlling quantization and buffering for digital signal compression

A method for providing quantization and buffering of a digital signal for use in a digital signal compression system, said digital signal comprising one or more frames, each frame comprising one or more blocks, the system having a default target buffer fullness and a bit budget value for a buffer based on the target buffer fullness, the method comprising:

• establishing a maximum allowable step-size value ("maximum Q-step value"), said maximum Q-step value being selected to insure an acceptable frame quality;
• determining a default Q-step value based on the bit budget value;
• determining if the default Q-step value is greater than the maximum Q-step value;
• if the default Q-step value is greater than the maximum Q-step value, then
• increasing the target buffer fullness,
• updating the bit budget value, and
• updating the default Q-step value to a value based on the bit budget value;
• selecting an actual Q-step value based on the default Q-step value;
• and
• quantizing a frame of an input digital signal based on the actual Q-step value.

An apparatus for compressing and displaying a digital video signal, said video signal comprising a plurality of frames, the apparatus comprising:

• a) a digital video signal source;
• b) an encoder connected to the digital video signal source, the encoder comprising a processor connected to a quantization circuit and a memory for storing a plurality of bit budget values and a corresponding plurality of default Q-step values, the processor operable to
• establish a maximum allowable step-size value ("maximum Q-step value"), said maximum Q-step value being selected to insure an acceptable picture quality;
• determine a first bit budget value for a frame,
• retrieve a default Q-step value from memory, said default Q-step value corresponding to the first bit budget value, and adjust the default Q-step value if the retrieved default quantization size exceeds the maximum Q-step value, and send the adjusted Q-step value to the quantization circuit, wherein said quantization circuit quantizes the frame using the adjusted Q-value.

An apparatus for providing quantization and buffering of a digital signal, the digital signal comprising a plurality of frames, the apparatus comprising:

• a) a quantization circuit having an input for receiving an input digital signal and an output for supplying a quantized digital signal, said quantization circuit operable to quantize a frame of the input digital signal based on a Q-step value;
• b) an encoder buffer connected to the output of the quantization circuit;
• c) a memory connected to the processor, the memory including a table of a plurality of default Q-step values and a corresponding plurality of bit budget values;
• d) a processor connected to each of the quantization circuit, the encoder buffer and the memory, wherein the processor is operable to establish a maximum Q-step value, the maximum Q-step value being selected to insure an acceptable frame quality, determine a first bit budget value for a frame, retrieve from the table a default Q-step value based on the first bit budget values, adjust the default Q-step value if the retrieved default quantization step size exceeds the maximum Q-step value, and provide the adjusted default Q-step value to the quantization circuit.