Digital image compression and decompression method and apparatus using variable-length coding

An image compression coding method for compressing a supplied digital image signal, performing a discrete cosine transform of the signal, linearly quantizing the signal to provide a quantized coefficient, and performing variable length coding, in order to improve recording efficiency, said method comprising the steps of:

• first extracting an activity by dividing the digital image signal into subframes and then detecting activities of each of the subframes;
• second extracting an activity by accumulatively operating a result extracted in said first activity extracting step and then extracting the activity in units of a frame;
• first bit allocating to allocate a number of bits in units of the subframe by the activities extracted in said first and second activity-extracting steps;
• third extracting an activity to extract activity of a predetermined block by the quantized coefficient;
• and
• second bit allocating to allocate a number of bits corresponding to the block based on the activity of the block extracted in said third activity-extracting step and on the number of bits assigned in said first bit-allocating step.

An image compression apparatus including a discrete cosine/transform unit for performing a discrete cosine transform of a supplied digital image signal to provide a transform coefficient, a quantizing unit for linearly quantizing the transform coefficient generated from the discrete cosine transform unit, and a variable-length coding processor for performing a variable-length coding of the quantized coefficient generated from the quantizing unit, said apparatus for improving the recording efficiency comprising:

• a first activity-extractor for dividing the digital image signal into subframe units and then detecting activity of each subframe unit;
• a second activity-extractor for accumulatively operating a result extracted in said first activity-extractor and then extracting the activity in units of a frame;
• a first bit allocator for allocating a number of bits in units of the subframe by the activities extracted in said first and second activity extractors;
• a third activity-extractor for extracting activity of a predetermined block by the quantized coefficient;
• and
• a second bit allocator for allocating a number of bits corresponding to the block based on the activity of the block extracted in said third activity-extractor and on the number of bits allocated in said first bit allocator.

An image decompressing apparatus for performing variable-length coding of a digital image signal according to, respectively, principle information and remaining information, and decoding the information recorded on separate regions, said apparatus comprising:

• a merging unit for merging the reproduced signal to restore the information allocated and recorded on the separate regions, in units of predetermined blocks according to a number of coded bits of the predetermined block units;
• a variable-length decoder for variable-length decoding according to a merging order in said merging unit;
• and
• a restoring unit for restoring the bits decoded in said variable-length-decoder by inverse-quantizing the restored bits and by performing an inverse discrete cosine transform.