JPH01202069A - Compression system for binary document image data - Google Patents

Abstract

PURPOSE:To highly efficiently compress image data obtained by compressing a binary image with 8 dots/mm horizontal scanning line density to (1/an integer) times and binary document image data with (1/an integer) times the 8 dots/mm horizontal scanning line density by providing a magnification multiplication part to the prestage of a modified Huffman coded table. CONSTITUTION:The magnification multiplication part 3 is provided to the prestage of the modified Huffman coded table part 4 and the compression system is constituted of a while run/black run detecting part 2, the magnification multiplication part 3, the modified Huffman coded table part 4, and an whole encoder control part 6. Consequently, image data obtained by compressing a binary image with 8 dots/mm horizontal scanning line density to (1/an integer) times and binary document image data with (1/an integer) times the 8 dots/mm horizontal scanning line density are highly accurately compressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a compression method for binary document image data.

[Conventional technology]

Conventionally, as a compression method for this type of binary document image data, there is a modified Huffman method.

This method uses 8 CCITT facsimile test charts at 8 dots/mm in the horizontal direction and 7 dots/mm in the vertical direction.
．． Targeting digitized data at 7 dots/mm,
A Huffman code is constructed based on the probability of occurrence of each run by taking statistics on black and white run lengths.

[Problem to be solved by the invention]

In the Modified Huffman method of the conventional binary document image data compression method described above, the run-length code is configured to maximize the compression efficiency for a binary document image with a specific scanning line density. For binary document image data with scanning line density or reduced binary document image data even with the same scanning line density, the probability of occurrence of white runs and black spots is estimated using the modified Huffman method. Since the probability of occurrence of white runs and black runs is different, there is a problem that compression efficiency decreases.

[Means to solve the problem]

The compression force/formula for binary document image data of the present invention has a magnification multiplier in the front stage of the modified Huffman encoding table, and has a horizontal scanning line density of 8 dots/(1/integer) of the binary document image data of seagull. ) times reduced image data and binary document image data with a horizontal scanning line density of 8 dots) and (1/integer) times the scanning line density of /rm.

[Effect]

In the present invention, by providing a magnification multiplication section before the modified Huffman encoding table, image data obtained by reducing a binary image with a horizontal scanning line density of 8 dots/fi to (1/integer) times and a horizontal scanning direction Binary document image data with a scanning line density of (1/integer) times 8 dots/plot is compressed with high efficiency using a modified Huffman encoding table.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

The figure is a block diagram showing one embodiment of the present invention.

In the figure, 1 is an input buffer unit that receives binary document image data 101, 2 is a white run/black run detection unit that receives binary document image data 102 from input buffer unit 1, and 3 is a white run/black run detection unit that receives binary document image data 102 from input buffer unit 1. Occurrence probability of white run/black run in a binary document image reduced by inputting the white run/young run data 103 from the run/black run detection unit 2 or in a binary document image with a scanning line density different from the modified Huffman method 4 is a modified Huffman encoding table unit which inputs the white run/black run encoded data 104 from the magnification multiplication unit 3; Reference numeral 5 denotes a transmission buffer section for receiving the white run/black run encoded data 105 & input from the modified Huffman encoding table section 4, and 6 is an overall encoder control section that controls each of these sections, which constitute the encoder section 7. ing. In addition, 1
06 indicates the white run/black run encoded data, and 107 indicates the entire encoder control signal.

A magnification multiplication section 3 is provided before the modified Huffman encoding table section 4, and a white run/black run detection section 2, a magnification multiplication section 3, a modified Huffman encoding table section 4, and an overall encoder control section 6 are provided. , reduced image data with a horizontal scanning line density of 8 dots/(1/integer) times the binary document image data of gourd, and horizontal scanning line density of 8 dots/(1/!I number) times the proverbial scanning line density. This constitutes means for compressing binary document image data with high efficiency.

Reference numeral 8 denotes a reception buffer section which inputs the white run/black run encoded data 108 from the transmission buffer 5 in the encoder section 7, and 9 receives the white run/black run encoded data 109 from the reception buffer section 8. There is a defined Huffman decoding table section, 10 is a white run/black run detection section which receives the decoded binary document image data 110 from the modified Huffman decoding table section 9, and 11 is a white run/black run detection section. A magnification correction section receives the restored binary document image data 111 from the detection section 10, and 12 is a decoder overall control section that controls each of these sections, and these constitute a decoder section 13. Note that 112 indicates binary document image data, and 113 indicates a decoder overall control signal.

Next, the operation of the embodiment shown in this figure will be explained.

Here, as image data to be encoded, data digitized at 8 dots/mm in the horizontal direction and 7.7 dots/mm in the vertical direction, and reduced by a factor of 1 in both the vertical and horizontal directions will be described.

First, binary document image data 101, which is image data to be encoded, input to the input buffer section 1 of the encoder section 70 is divided into white runs and black runs by the white run/black run detection section 2. Then, in the magnification multiplication unit 3, in order to bring the probability of occurrence of white runs and black runs in the reduced image data closer to the probability of occurrence of white runs and black runs in the modified Huffman code,
The lengths of the white run and black run are each doubled to obtain white run and black run encoded data 104. This white run/black run encoded data 104 is encoded in the modified Huffman encoding table unit 4 and transmitted to the reception buffer unit 8 of the decoder unit 13 via the transmission buffer unit 5. Here, the encoder overall control section 6 has a function of performing overall control of each functional block inside the encoder.

Next, the decoder unit 13 has a function of restoring the image data encoded by the encoder unit T to the original binary document image data 101.

The white run/black run encoded data 106 (10B) sent from the encoder section 7 is temporarily stored in the reception buffer section 8, and after being input to the modified Huffman decoding table section 9 according to instructions from the decoder overall control section 12. It is decoded and becomes decoded binary document image data 110. Then, this decoded binary document image data 110 is divided into white runs and black runs by the white run/black run detection unit 10, and is multiplied by the magnification correction unit 11, so that the binary document image data 1
Restored to 12.

The decoder overall control section 12 has a function of performing overall control of each functional block within the decoder section 13.

Note that although the document image data reduced by a factor of W has been described here, the present invention is not limited to this, and the present method involves changing the magnification of the magnification multiplication section 3 and the magnification correction section 110. It is also applicable to binary document image data with a horizontal scanning line density of 8 dots/- that has been reduced by an integral number.

Furthermore, the horizontal scanning line density is 8 dots/k integer
It is also applicable to binary document image data with double the scanning line density.

〔Effect of the invention〕

As explained above, the present invention provides a magnification multiplier before the modified Huffman encoding table to convert a binary image of a horizontal scanning line density of 8 dots/tsuru to (1/
A modified Huffman encoding table is used to highly efficiently compress image data that has been reduced to 1/integer) times the image data and binary document image data that has a scanning line density of 8 dots/mm in the horizontal scanning direction (1/integer) times. There is an effect that can be done.

[Brief explanation of the drawing]

The figure is a block diagram showing one embodiment of the present invention. 2... White run/black run detection section, 3... Magnification multiplication section, 4... Modified Huffman encoding table section, 6... Encoder overall control section.

Claims (1)

[Claims] In a compression method for binary document image data, a magnification multiplication unit is provided before the modified Huffman encoding table,
Reduced image data that is (1/integer) times the binary document image data with a horizontal scanning line density of 8 dots/mm and binary document image data that is (1/integer) times the horizontal scanning line density of 8 dots/mm. A compression method for binary document image data, characterized by comprising means for compressing document image data with high efficiency.