JP2001309185A - Data compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image data compressor that enhances a compression rate of multi-value image data through the compression employing a reversible coding system. SOLUTION: The data compressor is provided with a bit stream rearrangement circuit 4 that rearranges a bit stream of multi-value image data into a bit stream obtained by applying sequential bit arrangement of bits of the same bit position by each of a prescribed number of pixel data to each bit position before reversible compression of the multi-value image data by a compression circuit 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a data compression apparatus for reversibly compressing multi-valued image data.

[0002]

2. Description of the Related Art For example, in a PC scanner or a digital camera, when image data read by a sensor is transmitted to another device such as a personal computer,
In order to reduce the amount of image data and reduce the time required for transmission, image data was compressed.However, as the amount of data continues to increase, further data compression is required. It was supposed to be.

[0003]

Here, when the compressed data is decompressed, the reversible compression (also referred to as lossless compression) in which the data before compression is always restored to the original state,
Normally, the compression ratio improves as the probability that the same bit continues in the bit string of the data before compression is increased. On the other hand, in a bit string of multi-valued image data, the probability that the same bit continues is low, and thus, the compression ratio of multi-valued image data by reversible compression has not been so good conventionally.

Accordingly, an object of the present invention is to provide an image data compression apparatus in which the compression ratio of multivalued image data by reversible compression is improved.

[0005]

In order to achieve the above object, in an image data compression apparatus according to the present invention, in a data compression apparatus for performing reversible compression of multivalued image data, a multivalued image data is compressed before compression. The bit sequence of the image data is rearranged so as to be adapted to a reversible compression algorithm and to increase the compression ratio.

For example, before performing compression, a bit sequence of multi-valued image data is rearranged into a bit sequence obtained by sequentially arranging the bits of the same bit position for every predetermined number of pixel data for each bit position. What should I do? With this configuration, after rearranging the bit strings so that the probability that the same bits are continuous increases, lossless compression of multi-valued image data is performed.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. One embodiment of the present invention, P
As shown in the block diagram of FIG. 1, the C scanner 100 includes an image reading sensor 1, a sensor control circuit 2, a correction processing circuit 3, a bit string rearrangement circuit 4, a compression circuit 5, and an interface circuit 6.

An image reading sensor 1 divides an image into a plurality of pixels under the control of a sensor control circuit 2 and converts multi-valued image data by converting optical information of each pixel into a digital electric signal. Generate. The correction processing circuit 3 performs shading correction processing and gamma correction processing on the multi-valued image data generated by the image reading sensor 1.

The bit sequence rearranging circuit 4 rearranges the bit sequence of the multivalued image data which has been subjected to the correction processing by the correction processing circuit 3. The compression circuit 5 includes, for example, MH, MR, M
By using coding methods such as MR and JBIG,
The multi-valued image data in which the bit sequence is rearranged by the bit sequence arranging circuit 4 is reversibly compressed. The multi-valued image data compressed by the compression circuit 5 is transmitted to the personal computer 200 via the interface circuit 6.

The rearrangement of bit strings performed in the bit string rearrangement circuit 4 will be described. The bit sequence rearranging circuit 4 rearranges the bit sequence of the multi-valued image data into a bit sequence obtained by sequentially performing the operation of sequentially arranging the same bit for every predetermined number of pixel data for each bit position.

That is, when the number of bits of each pixel data is n and the bit string rearranging circuit 4 rearranges the bit string for every k pixel data, the bit string of the data input to the bit string rearranging circuit 4 is b (1, n-
1), b (1, n-2),..., B (1, 0), b (2,
n-1), b (2, n-2),..., b (2, 0), b
(K, n-1), b (k, n-2), ..., b (k,
0),..., The bit strings of the data output from the bit string rearranging circuit 4 are b (1, n−1), b
(2, n-1), ..., b (k, n-1), b (1, n-
2), b (2, n-2), ..., b (k, n-2), ...,
b (1,0), b (2,0),..., b (k, 0),.

As described above, by performing the reordering by the bit string reordering circuit 4, the probability that the same bit continues in the bit string of the multi-valued image data is increased. This is because, in a normal image, since the correlation between adjacent pixels is strong, even if the image data is multi-valued, the probability that the bit at the same bit position is the same among a plurality of pixel data is 1
This is because there is a higher probability that adjacent bits in one pixel data are the same. The higher the bit position, the higher the probability that the bits are the same among a plurality of pixel data.

For example, each pixel data is 8 bits,
The data values are A0, A3, A5, A in hexadecimal notation.
Looking at eight pieces of pixel data which gradually increase to 7, A9, AA, AC, and AE, the bit string is shown in FIG.
2 is obtained by scanning the X direction as the main scanning direction and the Y direction as the sub scanning direction. The bit sequence obtained by performing the rearrangement performed by the bit sequence rearranging circuit 4 is the Y line shown in FIG. In the main scanning direction and the X direction in the sub-scanning direction. The rearrangement performed by the bit sequence rearranging circuit 4 increases the probability that the same bit continues in the bit sequence. .

In summary, in the present embodiment, after reordering the bit strings so that the probability of the same bits continuing is high, lossless compression of multi-valued image data is performed, so that the compression ratio is improved. . Specifically, depending on the type of the image, it is expected that the image is compressed to 1/2 to 1/10. By improving the compression ratio of the multi-valued image data by the reversible compression, the time required for transmitting the multi-valued image data to the personal computer without deteriorating the image is reduced.

[0015]

As described above, according to the present invention,
After rearranging the bit strings so that the probability that the same bits are continuous increases, lossless compression of the multi-valued image data is performed, so that the compression ratio is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a PC scanner according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a relationship between a bit string input to a bit string reordering circuit and a bit string output.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image reading sensor 2 Sensor control circuit 3 Correction processing circuit 4 Bit string rearrangement circuit 5 Compression circuit 6 Interface circuit 100 PC scanner 200 Personal computer

Claims (1)

[Claims] 1. A data compression apparatus for performing reversible compression of multi-valued image data, wherein a bit string of the multi-valued image data is adapted to a reversible compression algorithm before compression.
A data compression device, wherein the data is rearranged so as to increase the compression ratio.