DPCM image compression with plural quantization table levels

A method of decoding a digital image, the method comprising:

• providing a decoder quantization table including a plurality of levels, each level including a plurality of values;
• receiving level information identifying one of the plurality of levels, the level information being received through an information stream, the level information based on a calculated intra-frame difference between a first sample associated with a first element of a current scan line and a second sample associated with a second element of a previous scan line, the second element located immediately above the first element in a frame;
• wherein the frame comprises a plurality of scan lines and the current scan line and the previous scan line represent a portion of the plurality of scan lines;
• selecting a quantization table level based on the level information;
• receiving guantizer information corresponding to a quantizer, the
• quantizer information previously generated using an encoder quantization table;
• selecting a value from the selected quantization table level, the value generally representing the calculated intra-frame difference between the first sample and the second sample, and
• restricting the encoding to intra-frame differences by repeating the above for each sample in each scan line of the plurality of scan lines until the frame is completely decoded.

A computer system, comprising:

• a processor coupled to a bus;
• a main memory coupled to the bus to store a decoder table;
• and
• an imaging device coupled to the bus, the imaging device having an encoder that includes
• a first encoder quantization table including a plurality of levels, each level including a plurality of quantizers, the encoder designed to:
• calculate an intra-frame difference between a first sample associated with a first element of a current scan line and a second sample associated with a second element of a previous scan line, the second element located immediately above the first
• the first element in a frame, wherein the frame comprises a plurality of scan lines and the current scan line and the previous scan line represent a portion of the plurality of scan lines,
• select one of the plurality of quantization table levels based on the calculated difference between the first sample and the second sample, place information corresponding to the selected quantization table level into the information stream, the information stream delivered over the bus,
• select one of the plurality of levels according to the calculated intra-frame difference between the first sample and the second sample;
• if a level switch occurs, place information identifying the selected level into an information stream,
• select one of the plurality of quantizers from the selected quantization table level according to the calculated intra-frame difference between the first sample and the second sample;
• place information corresponding to the selected quantizer into the information stream, and
• restrict the encoding to intra-frame differences by repeating the above for each sample in each scan line of the plurality of scan lines until the frame is completely encoded.