JP2710831B2 - Image coding device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding apparatus for compressing image data obtained by scanning a document.

[Conventional technology]

When compressing digitized tone image data, it is known that an encoding method using cosine transform is effective. In this transform coding method, an image is represented by N
The block is divided into a plurality of blocks of N pixels, and a two-dimensional discrete cosine transform (hereinafter, referred to as a two-dimensional DCT transform) is performed for each block to obtain a transform coefficient, and quantization is performed for each component. At this time, the number of component quantization levels is determined using the variance of each component.

When the above-described encoding is performed on the image read by the scanner, it is necessary to read out the image information scanned once, twice. In the first readout, after performing a two-dimensional DCT transform, the variance is obtained by taking the statistic of each component, and the number of quantization levels for each component is determined. Next, in the second reading, after the read image is subjected to two-dimensional DCT transform, encoding is performed at the quantization level determined as described above.

Japanese Patent Application Laid-Open No. 63-109662 discloses an apparatus of this type.

[Problems to be solved by the invention]

However, in the above-described conventional technology, since uncompressed image information is stored, a large-capacity storage device is required, and there is a problem that the cost is increased. Therefore, the original is scanned twice, and in the first scan, two-dimensional DCT is performed, and then the variance is obtained by taking the statistics of each component.
The number of quantization levels for each component is determined. In the second scan, after the read image is subjected to two-dimensional DCT transform, encoding is performed at the quantization level determined as described above.

However, this method does not require a storage device for storing an uncompressed image, but the image reading unit needs to perform two reciprocating operations on the original to perform scanning, which lowers the work efficiency. There's a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image encoding apparatus which is capable of performing a compression process without reciprocating two times of scanning of an image reading unit.

[Means for solving the problem]

In order to achieve the above object, the present invention provides an image in which an image of the original is optically read by a scanning optical system which moves relatively to the original, and the read information is subjected to a two-dimensional discrete cosine transform to perform a compression process. An encoding device that performs distributed processing on the basis of the statistical properties of read information obtained by scanning the original document on the outward path, and performs encoding based on the read information obtained by scanning the original document on the return path and the processing result of the distributed processing unit; And encoding processing means for performing the above.

[Action]

According to the above means, two-dimensional discrete cosine transform is performed on the image information read on the outward path of the original scanning, and a variance is obtained from the statistic of each component with respect to the image information. The number of activation levels is determined. Next, two-dimensional discrete cosine transform is similarly performed on the image information read in the backward path of the original scanning, and the result is encoded based on the number of quantization levels obtained on the forward path. Therefore, it is possible to achieve encoding by one round trip scanning.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to FIGS.

FIG. 1 is a block diagram showing an embodiment of an image encoding apparatus according to the present invention, FIG. 2 is a schematic front view showing details of a reading section, and FIG. 3 is a flowchart showing processing of the present invention.

As shown in FIG. 1, an N-line memory 1 is provided to store digitized signals of image information of a document optically read by a reading unit for each N lines. An N × N buffer 2 is connected. The N × N buffer 2 is connected to a two-dimensional DCT conversion unit 3 for performing the above-described two-dimensional DCT conversion, and an N × N buffer 4 is connected to the two-dimensional DCT conversion unit 3.

The N × N buffer 4 is connected to a switch 5 that switches in conjunction with a switch 9 described later. One of its outputs is connected to a distributed processing unit 6 that performs distributed processing, and the other is a quantization unit that performs quantization processing. 7 is connected. Distributed processing unit 6
Is connected to a bit allocation table storage unit 8, and a switch 9 is connected to its output terminal. Switch 9
The output signal of the bit allocation table storage unit 8 is selectively output to an output terminal or the quantization unit 7.

In FIG. 2, a glass table 21 on which a document 22 is placed is disposed on the upper surface of the apparatus, and a scanning optical system 30 forming a reading unit is disposed below the glass table 21. This scanning optical system 30
Reads a document image by reciprocating in the main scanning direction at the lower portion of the glass table 2. The optical system includes a light source 23 that irradiates the original 22,
It comprises a lens array 24 for forming an image of the reflected light from the document surface at a predetermined position, and a photoelectric conversion unit 25 for photoelectrically converting the light from the lens array 24.

The driving mechanism for reciprocating the scanning optical system 30 is a scanning optical system.
The pulleys 27a and 27b for rotatably loading the wires 26, the motor 28 serving as a driving source for rotating the pulleys 27a and 27b, and the pulley 29 mounted on the rotation shaft of the motor 28 And a belt 30 spanned between the pulley 29 and the pulley 27b.

In such a configuration, when a scan start command is issued, the motor 28 rotates, the rotation is transmitted to the pulley 27b, and the wire 26 rotates clockwise. The rotation of the wire 26 causes the scanning optical system 30 to move horizontally in the illustrated B direction. When the scanning optical system 30 reaches the scanning end position, the motor 28 stops rotating and then reversely rotates. Due to this reverse rotation, the wire 26 rotates counterclockwise, and the scanning optical system 30 moves in the illustrated A direction. While the scanning optical system 30 moves, the photoelectric conversion unit 25 reads one pixel at a time in the sub-scanning direction of the image, and outputs the density of each pixel as a multilevel signal. This output signal is input to the N-line memory 1 shown in FIG.

Next, the operation of the embodiment of the present invention will be described with reference to FIG.

The multi-level signal output from the photoelectric conversion unit 25 is stored in the N-line memory 1 every N lines (step 31). The signal stored in the N-line memory 1 is read out to the N × N buffer 2 at a predetermined timing, and is input to the two-dimensional DCT converter 3.

The two-dimensional DCT converter 3 divides the image information into N × N blocks, and performs orthogonal transform by successive two-dimensional CDT for each block (step 32). Here, the two-dimensional DCT transform when the image signal is X _ij , i, j = 0 to N−1 is defined by the following equation.

The conversion output y _uv by the two-dimensional DCT converter 3 is N × N
Stored in the buffer 4.

When the scanning optical system 30 is on the outward path (the direction B in FIG. 2), the switch 5 has selected the dispersion processing unit 6, so that the separation processing is executed (step 33). The distribution processing unit 6 creates a bit allocation table based on the result of the distribution processing (step 34).
Then, this is stored in the bit allocation table storage unit 8. At this time, since the switch 9 has selected the transmission line 10 side,
The contents of the bit allocation table in the bit allocation table storage unit 8 are transmitted to the transmission path 10 as header information.

On the other hand, on the return path of the scanning optical system 30, the switches 5 and 9 select the quantization unit 7. As in the case of the outward route, data is read (step 35), and two-dimensional DCT conversion is performed by the two-dimensional DCT conversion unit 3 (step 3).
6).

Next, the N × N coefficient from the N × N buffer 4 and the bit allocation table read from the bit allocation table storage unit 8 are applied to the quantization unit 7, and the quantization unit 7 performs a quantization process based on these. Is executed (step 37).

The bit assignment of each coefficient is determined from the variance of each component. The variance of each coefficient is expressed by the following equation.

(Where K is the total number of blocks) Further, the number of bits allocated to each coefficient is represented by the following equation.

(However, M is the number of bits allocated to one block.) A coefficient with a large variance is quantized with a large number of bits, and a coefficient with a small variance is quantized with a small number of coefficients. Also, it is possible to obtain an image with little visual deterioration when reproduced. When the encoded data is restored, a process opposite to the encoding may be performed. That is, a coefficient is obtained by inverse quantization, and an image is reproduced by performing two-dimensional DCT inverse transform. The quantized result is sent to the transmission path 10 (step 38).

A receiving unit (not shown) that receives information transmitted from the quantizing unit 7 to the transmission path 10 inversely quantizes the quantized value based on the bit allocation table transmitted first, and quantizes this value. The image is reproduced by performing the two-dimensional DCT inverse transform.

As described above, the image information can be compressed based on the statistical properties of the image only by scanning the document one round trip.

〔The invention's effect〕

As described above, according to the present invention, the image of the document is optically read by the scanning optical system that moves relatively to the document,
An image encoding apparatus that performs a two-dimensional discrete cosine transform on the read information and performs a compression process on the read information. And encoding processing means for performing encoding based on the read information obtained by scanning of the original and the processing result of the distributed processing means, so that encoding can be achieved without making two round trips of the original scanning, such as a page memory. Can be made unnecessary.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an image encoding apparatus according to the present invention, FIG. 2 is a schematic front view showing details of a reading section, and FIG. 3 is a flowchart showing processing of the present invention. 1 ... N line memory, 2 ... N × N buffer, 3 ...
Two-dimensional DCT converter, 4 N × N buffer, 5, 9 Switch, 6 Distributed processor, 7 Quantizer, 8 Bit allocation table storage, 10 Transmission line, 30 ... Scanning optical system.

Claims (1)

(57) [Claims] An image encoding apparatus for optically reading an image of a document by a scanning optical system relatively moving with respect to the document, performing a two-dimensional discrete cosine transform on the read information, and performing a compression process. Distributed processing means for performing distributed processing based on statistical properties obtained from information read by original scanning, and encoding processing for performing encoding based on read information obtained by original scanning at the return path and the processing result of the distributed processing means And an image encoding device.