Compression and expansion methods and apparatus
First Claim
1. A method of compressing image data for transmission from a first device to a second device which is physically separate from but connected to the first device, the second device having a limited memory capacity, comprising the steps of:
- (a) querying said second device, thereby determining an available memory capacity of said second device;
(b) encoding and storing said image data to obtain first encoded data;
(c) comparing an amount of said first encoded data with said available memory capacity;
(d) transmitting said first encoded data to said second device if the amount of said first encoded data does not exceed said available memory capacity;
(e) compressing said image data with a certain compression ratio to obtain compressed data, if the amount of said first encoded data exceeds said available memory capacity;
(f) encoding said compressed data to obtain second encoded data;
(g) comparing the amount of said second encoded data with said available memory capacity;
(h) transmitting said second encoded data to said second device if the amount of said second encoded data does not exceed said available memory capacity; and
(i) repeating said steps (e), (f), (g), and (h), with successively increasing compression ratios in said step (e), if the amount of said second encoded data exceeds said available memory capacity, until the amount of second encoded data does not exceed said available memory capacity.
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Abstract
A compression and encoding system for bi-level image data determines the available memory capacity of a receiving device, then compresses and encodes the image data with successively increasing compression ratios until encoded data not exceeding the memory capacity of the receiving device are obtained. Preferably, the image is divided into rectangular blocks, and successive bit planes are generated on the basis of the number of dark picture elements in each block, and on the basis of adjacency relationships among like-valued picture elements in each block. Feedback may be employed to adjust the darkness of certain compressed blocks according to the darkness of the preceding block.
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Citations
28 Claims
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1. A method of compressing image data for transmission from a first device to a second device which is physically separate from but connected to the first device, the second device having a limited memory capacity, comprising the steps of:
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(a) querying said second device, thereby determining an available memory capacity of said second device; (b) encoding and storing said image data to obtain first encoded data; (c) comparing an amount of said first encoded data with said available memory capacity; (d) transmitting said first encoded data to said second device if the amount of said first encoded data does not exceed said available memory capacity; (e) compressing said image data with a certain compression ratio to obtain compressed data, if the amount of said first encoded data exceeds said available memory capacity; (f) encoding said compressed data to obtain second encoded data; (g) comparing the amount of said second encoded data with said available memory capacity; (h) transmitting said second encoded data to said second device if the amount of said second encoded data does not exceed said available memory capacity; and (i) repeating said steps (e), (f), (g), and (h), with successively increasing compression ratios in said step (e), if the amount of said second encoded data exceeds said available memory capacity, until the amount of second encoded data does not exceed said available memory capacity. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A compression and encoding apparatus for preparing image data for transmission from a sending device to a receiving device which is physically separate from but connected to the sending device, the receiving device having a limited memory capacity, comprising:
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a plurality of data compressors, for compressing said image data with different compression ratios, thereby generating compressed data; a selector coupled to said data compressors, for selecting the compressed data generated by one of said data compressors, responsive to a control signal; an encoder coupled to said selector, for encoding the compressed data selected by said selector, thereby generating encoded data; an encoded data memory coupled to said coder, for storing said encoded data; and a memory checker coupled to said encoded data memory, for comparing the amount of said encoded data with an available memory capacity in said receiving device, and generating said control signal, thereby causing said selector to select compressed data that have been compressed with successively increasing compression ratios, until the amount of said encoded data does not exceed said available memory capacity. - View Dependent Claims (9, 10)
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11. A data compressor for compressing bi-level image data, comprising:
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a block formatter for arranging said bi-level image data into two-by-two blocks; a counter coupled to said block formatter, for counting said bits having a certain value, thereby determining a weight of each said block; an adjacency detector coupled to said block formatter, for detecting horizontal, vertical, and diagonal adjacency relationships among like-valued bits in the two-by-two image area represented by each said block; a compressed pattern generator coupled to said counter, for generating, from each said block, at least one bit with a value responsive to the weight of said block, and for generating, from blocks having a certain weight, at least one subsequent bit having a value responsive to said adjacency relationships; and a bit selector coupled to said compressed pattern generator, for selecting, as compressed image data, at least one bit generated by said compressed pattern generator for each said block. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A compression and encoding apparatus for preparing bi-level image data for transmission from a sending device to a receiving device which is physically separate from but connected to the sending device, the receiving device having a limited memory capacity, comprising:
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a data compressor, for compressing said bi-level image data with different compression ratios, responsive to a control signal, thereby generating compressed data; an encoder coupled to said data compressor, for encoding said compressed data, thereby generating encoded data; an encoded data memory in said sending device coupled to said encoder, for storing said encoded data; and a memory checker coupled to said encoded data memory, for comparing the amount of said encoded data with an available memory capacity in said receiving device, and generating said control signal, thereby causing said data compressor to generate compressed data that have been compressed with successively increasing compression ratios, until the amount of said encoded data does not exceed said available memory capacity;
wherein said data compressor comprises;a block formatter for arranging said bi-level image data into two-by-two blocks, each block representing a two-by-two image area; a counter for counting bits having a certain value, thereby determining a weight of each said block; an adjacency detector for detecting horizontal, vertical, and diagonal adjacency relationships among like-valued bits in the image area represented by each said block; a compressed pattern generator for generating, from each said block at least one bit with a value responsive to the weight of said block, and for generating, from blocks having a certain weight, at least one subsequent bit having a value responsive to said adjacency relationships; and a bit selector for selecting, as compressed image data, at least one bit generated by said compressed pattern generator for each said block. - View Dependent Claims (24)
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25. A decoding and expanding apparatus for decoding and expanding compressively coded image data, comprising:
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an interface unit for receiving said compressively coded image data and receiving information specifying a compression ratio from a device physically separate from but connected to said decoding and expanding apparatus; a receiving memory coupled to said interface unit, for storing said compressively coded image data; a decoder coupled to said receiving memory, for decoding said compressively coded image data, thereby generating decoded data; a plurality of data expanders coupled to said decoder, for expanding said decoded data with different expansion ratios, thereby generating expanded image data; a selector coupled to said data expanders, for selecting the expanded image data generated by one of said data expanders, responsive to said compression ratio; and an output unit coupled to said selector, for outputting the expanded image data selected by said selector. - View Dependent Claims (26, 27, 28)
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Specification