ADCT compression with minimum compression ratio

Details ADCT compression with minimum compression ratio ADCT compression with minimum compression ratio

1993-07-19

1994-06-14

Coles, Sr, Edward L.

Facsimile and static presentation processing

Facsimile

Auxiliary signal

358444, 358426, 358445, 348384, H04N 1415

Patent

active

053215222

ABSTRACT:
A method of compressing an original document image in a manner assuring a minimum compression ratio includes the steps: a) storing to a tile memory a portion of the document image; b) from the document image portion stored in tile memory, using the discrete cosine transform a basis function (DCT), forming a frequency space representation of the image at a transformer; c) retrieving a set of stored values referred to as a Q-Table, d) dividing each of the Q-Table values into the DCT value, and returning the integer portion of the value as the quantized DCT value; e) encoding the quantized DCT values using a statistical encoding method; f) determining whether the data block size is larger than desired, and if not, passing the data block to an output; g) otherwise, reducing a least one high frequency component of the frequency space representation of the document image and and repeating steps e)-g) until the size of the data block is acceptable. In accordance with another aspect of the invention, the steps of f and g may be expressed as: f) counting the number of bits representing the compressed tile of image data; g) comparing the count to a reference; h) if the count is less than the reference, passing the compressed tile to an output; i) if the count is greater than the reference, modifying the quantized DCT values, and repeating steps e)-i).

REFERENCES:
patent: 4999705 (1991-03-01), Puri
patent: 5001559 (1991-03-01), Gonzales et al.
patent: 5049991 (1991-09-01), Niihara
patent: 5051840 (1991-09-01), Watanabe et al.
patent: 5220440 (1993-06-01), Hisatake
W. H. Chen & C. H. Smith, "Adaptive Coding of Monochrome and Color Images", IEEE Trans. Comm., vol. Com-25, No. 11, Nov. 1977, pp. 1285-1292.
P. G. Roetling, "Visual Performance and Image Coding", Proceedings of the S.I.D., 17/2, pp. 111-114 (1976).

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