JPH08139938A - Image processing device - Google Patents

Abstract

(57) [Summary] [Purpose] To select an appropriate compression method according to the characteristics of the input image. A separation means (42) for separating an input image into constituent elements, and a selection means (44) for selecting one of a plurality of compression methods in at least one frame unit according to a separation result by the separation means. ) And compression means (4) for compressing the input image according to the selection result by the selection means.
5) is included.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for separating an input image for each constituent element and selecting a compression method based on the separation result.

[0002]

2. Description of the Related Art Generally, in an image processing apparatus, a document is read by an image input section and converted into an electric signal, and the signal is image-processed by the image processing section and then recorded as an image by an output section such as a laser printer. It is known to be done. By providing an image storage unit in the image processing unit, an image formed by forming a plurality of images by outputting a document read by the image input unit once from the image storage unit to the laser printer a plurality of times. There is a processing device.

In such an image processing device, an image compression unit and an image decompression unit are installed before and after the image storage unit to make the image storage unit efficient.

On the other hand, as high-efficiency compression, although the image after compression / expansion is slightly different from the image before compression, many irreversible compression methods that can dramatically improve the compression rate have been proposed and put into practical use. There is.

[0005]

However, conventionally, an effective selection method for separating an input image for each component and selecting an appropriate compression method according to the separation result has not been sufficiently studied.

Therefore, an object of the present invention is to provide an image processing apparatus capable of selecting an appropriate compression method according to the characteristics of an input image.

[0007]

In order to solve the above-mentioned problems, the image processing apparatus of the present invention provides a separation means for separating an input image for each constituent element, and a separation result by the separation means. It is characterized in that it has a selecting means for selecting one of a plurality of compression methods in units of at least one frame, and a compressing means for compressing the input image according to the selection result by the selecting means.

[0008]

【Example】

(Embodiment 1) FIG. 1 is a sectional view of an image copying apparatus according to a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a document feeder, which feeds placed documents one by one or continuously to a predetermined position on a document table glass surface 2. Reference numeral 4 denotes a scanner unit including a lamp 3, a scanning mirror 5 and the like. When a document is placed on the platen glass surface 2 by the document feeding device 1, the document is reciprocally scanned in a predetermined direction to scan the reflected light of the document. Mirror 5
7 to 7, an image sensor unit 9 including a three-line sensor having an RGB color separation filter via a lens 8.
Image on.

Reference numeral 10 denotes an exposure control section composed of a laser scanner, which is an image signal control section 1 of the controller section CONT.
The photoconductor 11 is irradiated with the laser beam modulated based on the image data output from 023 (see FIG. 2).
Reference numerals 12 and 13 denote developing devices that visualize the electrostatic latent image formed on the photoconductor 11 with a developer (toner) of a predetermined color (for example, black and red). Reference numerals 14 and 15 denote transfer paper stacking units, which store and store fixed-size recording media, and are fed to the registration position by the driving of the feeding roller, and the image leading edge alignment timing with the image formed on the photoconductor 11. The paper is re-fed in the state where it has been taken.

Reference numeral 16 denotes a transfer separation charger, which transfers the toner image developed on the photoconductor 11 to a transfer paper and then the photoconductor 11
It is further separated and conveyed by a conveyor belt, and is fixed by the fixing unit 17. A paper discharge roller 18 stacks and discharges the transfer-receiving paper on which the image formation is completed on the tray 20. Reference numeral 19 is a direction flapper for switching the carrying direction of the transferred paper on which image formation has been completed to either the paper exit or the internal carrying path direction to prepare for the multiplex / double-sided image forming process.

Image formation on a recording medium will be described below. The image signal input to the image sensor unit 9, that is, the input signal from the image reader control unit 1022 described later is subjected to predetermined image processing by the image signal control unit 1023 controlled by the CPU circuit unit 1025, and the printer control unit. It is transmitted to 1024. Printer control unit 1
The image signal input to 024 is converted into an optical signal by the exposure control unit 10 to irradiate the photoconductor 11. The latent image formed on the photoconductor 11 by the irradiation light is developed by the developing device 12 or the developing device 13. The transfer sheet is conveyed from the transfer sheet stacking unit 14 or the transfer stacking unit 15 at the latent image timing, and the developed image is transferred to the transfer unit 16. The transferred image is fixed on the transfer paper by the fixing unit 17, and then discharged from the paper output unit 18 to the outside of the apparatus.

During double-sided recording, after the transfer target paper passes through the paper ejection sensor 19, the paper ejection unit roller 18 is rotated in the direction opposite to the paper ejection direction. At the same time, the flapper 21
Is moved up and the copied transfer paper is stored in the intermediate tray 24 via the transport paths 22 and 23. Next, the transfer paper stored in the intermediate tray 24 is fed at the time of back side recording,
The back side is transferred.

Further, at the time of multiple recording, the flapper 21 is raised and the copied transfer paper is stored in the intermediate tray 24 via the conveyance paths 22 and 23. During the next multiplex recording, the transfer paper stored in the intermediate tray 24 is fed and multiplex transfer is performed.

FIG. 2 shows the controller unit CO shown in FIG.
It is a block diagram explaining the structure of NT, 1025 is C
The PU circuit unit incorporates the ROM 1026 and the RAM 1027, and collectively controls each unit based on the control program stored in the ROM 1026.

Reference numeral 1021 denotes an automatic document feeder control unit which controls the feeding of placed originals one by one, or continuously feeding two originals to a predetermined position on the surface of the original glass 2.

Reference numeral 1022 includes an image reader control unit, the image sensor unit 9 and the like, and R (not shown).
RG color-separated by the GB separation filter and photoelectrically converted
The B analog image signal is output to the image control unit 1023.

A printer controller 1024 drives the exposure controller 10 based on the video signal output from the image signal controller 1023 to irradiate the photoconductor 11 with a light beam. An operation panel 1028 is provided with an operation panel having keys, a display and the like for setting a mode required for image formation.

FIG. 3 shows the image signal control unit 1023 of the present invention.
3 is a block diagram showing the details of the configuration of FIG.

In FIG. 3, the RGB analog image signal output by the image reader unit 1022 is converted by the A / D converter 30 into 8-bit digital signals of R, G, and B respectively.

Next, after the black level / white level correction unit 31 performs the black level correction and the white level correction (shading correction), the RGB signals are input to the ND signal generation unit 32.

In the ND signal generator 32, the RGB signals are added and divided into 1/3 to output the luminance signal Dout.

Dout = (Rin + Gin + Bin) / 3 The luminance signal Dout is input to the image processing unit 35.

The image processing unit 35 performs a scaling process for enlarging / reducing an image, an image area separation process for separating each element constituting an input document image such as characters and photos, and a halftone process for character / photograph parts. , Compression selection processing, compression processing, storage processing, decompression processing, etc. are performed.

Thereafter, the density correction unit 36 performs luminance-density conversion and density correction in the printer, and sends the result to the printer control unit 1024 of the laser printer.

The operation of the image processing section 35 will be described with reference to FIG.

First, the input signal Dou from the ND signal reproducing section
In response to an instruction from the operation unit 1028, the scaling unit 41 scales the image signal for t.

Next, the image data is input to the image area separation unit 42, and the image area is separated into a portion having a large luminance change (character portion) like a character and a portion having a small luminance change like a photograph (photograph portion). . The result of image area separation is output as a 1-bit determination signal in this embodiment.

In accordance with the determination signal from the image area separation unit 42, the halftone processing unit 43 performs binarization processing with a simple threshold value on the data of the character portion in order to preserve the edge information. Pseudo halftone processing (for example, error diffusion method) is applied to the data of the photograph portion.

The compression unit 45 compresses the data after binarization or pseudo halftone processing by the simple threshold value according to the selection signal from the compression selection unit 44. In this case, data indicating which compression method is applied is added to the head of the compressed data as header information.

The compression selection section 44 counts the determination signals from the image area separation section 42 to obtain the ratio of the elements forming the document image. In addition, the compression selection unit 44 is the same as the compression unit 45.
A typical error of one compression method (difference between the image before compression and the image after compression / expansion) is stored in advance. Based on the ratio obtained here and the stored error, a compression method that minimizes the error due to compression is selected and output as a selection signal.

The output from the compression unit 45 is stored in the storage unit 46.

The decompressor 47 examines the header information,
Recognizing which compression method was used for decompression, decompression is performed by the decompression method corresponding to that compression method.

In the present embodiment, the header information for identifying the compression method is added before the compression information. However, if the selection signal is directly transmitted from the compression selection section 44 to the compression section 45 and the decompression section 47, it is possible. , No header information is needed.

Further, in the present embodiment, the variable power unit is provided before the image area separation unit, but the variable power unit may be provided after the expansion unit.

The operation of the compression selection unit 44, which is the main part of this embodiment, will be described in detail below.

The compression selecting section 44 counts the image area separation determination results from the image area separating section 42, and
The area ratio in one screen of the photograph part is calculated.

Further, the compression selecting section 44 stores a typical error of two compressions possessed by the compressing section 45 as a table. FIG. 5 shows an example of this table. The compression A is an irreversible compression effective for a photograph part (for example, so-called JPEG ADCT method), and the compression B is an irreversible compression effective for a character part (for example, vector quantization method). Each error when applied (mean square error ave between the image before compression and the image after compression / decompression; see the following expression (1)) is shown. Kij is x = before compression
The pixel value of the pixel located at i, y = j, K'ij is compressed /
It is the pixel value of the pixel located at x = i, y = j after decompression. X and Y are maximum values of x and y (for example, X = Y = 8 in the case of compression in pixel block units of 8 × 8).

[0039]

[Outside 1]

Although the error is the mean square error here, other errors (for example, absolute value of difference) may be used.

Using the above ratio and the above table, it is calculated which compression is applied to reduce the error.

When the compression A is applied, the error at that time is: error A = (ratio of photograph portion) * (error when compression A is applied to photographic image) + (ratio of character portion) * (compression A is Error when applied to a character image).

Similarly, if the compression B is applied, the error at that time is: error B = (ratio of photograph portion) * (error when compression B is applied to a photographic image) + (ratio of character portion) * (compression) The error when B is applied to the character image) can be calculated.

By comparing these, the compression method with the smallest error is selected. If the ratio of the photo part to the character part is 0.2 to 0.8, assuming that the entire document is 1, from FIG. 5, A = 0.2 * 0.05 + 0.8 * 0.10 = 0.01 +
0.08 = 0.09 B = 0.2 * 0.20 + 0.8 * 0.01 = 0.04 +
It becomes 0.008 = 0.048.

When compressing such an image, compression B,
That is, if compression effective for the character portion is used for the entire image, it is expected that the configuration will be simple and the error will be reduced.

According to the present embodiment, the most effective compression method is selected from the result of the image area separation means and the error of the compression means stored in advance, and the compression is switched to apply it to the image. Since it is not necessary to have information for this, the device scale can be reduced.

Although the elements constituting the image are divided into the character portion and the photograph portion in the description, they may be divided into other elements such as the CG portion (computer graphic portion). Also,
There may be three or more compression methods.

Furthermore, the lossy encoding method is not limited to the so-called JPEG ADCT method and vector quantization method, and three or more other methods such as a method of performing orthogonal transformation and quantization may be selectively used. Good.

(Embodiment 2) The first embodiment relates to the method of selecting the compression method based on the error caused by the compression, but the compression method can be selected according to the compression rate.

The operation of the compression selection unit 44, which is the main part of this embodiment, will be described in detail below. Other parts are the same as those in the above-mentioned embodiment. In the compression selection unit 44, the above-mentioned image area separation unit 4
By counting the image area separation determination results from 2
Obtain the area ratio of the character part / photograph part.

The compression selection section 44 also stores typical compression rates of the two compressions that the compression section 45 has as a table. FIG. 5 shows an example of this table. Compression A
Is a compression effective for the photo part (for example, JPEG ADCT method), and compression B is an effective compression for the character part (for example, JBI).
G is an arithmetic coding method) and each compression rate (data amount after compression / data amount before compression) when this is applied to a photographic image and a character image is shown.

Using the above ratio and the above table, it is calculated which of the compressions should be applied to reduce the compression ratio.

Assuming that the compression A is applied, the compression rate at that time is: compression rate A = (ratio of photograph part) * (compression rate when compression A is applied to a photographic image) + (ratio of character part) * ( The compression rate when the compression A is applied to the character image) can be calculated.

Assuming that the compression B is applied, the compression rate at that time is: compression rate B = (ratio of photograph portion) * (compression ratio when compression B is applied to a photographic image) + (ratio of character portion) * ( The compression rate when the compression B is applied to the character image) can be calculated.

This is compared and the smaller compression method is selected. If the ratio of the photo part to the character part is 0.2 to 0.8 when the entire document is set to 1, according to FIG. 6, A = 0.2 * 0.2 + 0.8 * 0.4 = 0.04 + 0.
32 = 0.36 B = 0.2 * 0.5 + 0.8 * 0.1 = 0.10 + 0.
It becomes 08 = 0.18.

When compressing such an image, compression B,
That is, effective compression is used for the character part.

As described above, according to this embodiment, the most effective compression method is selected from the result of the image area separation means and the compression ratio of the compression means, and the compression is switched to apply it to the image. Since it is not necessary to have information for this, the device scale can be reduced.

(Embodiment 3) An apparatus can be constructed by combining the above-mentioned first and second embodiments.

In the present embodiment, as in the first embodiment, the image quality-oriented compression method is selected so that the error is reduced when the lossy compression is performed according to the characteristics of the input image. It is possible to manually switch between the image quality priority mode and the compression rate priority mode in which the compression method is selected so as to increase the compression rate according to the characteristics of the input image, as in the second embodiment. ing.

FIG. 7 is a view showing the operation panel of the operation unit 1028 in this embodiment.

In FIG. 7, reference numeral 701 is a ten-key for designating the number of copies, 702 is a start key for instructing the start of copying, and 703 is a stop key for instructing to stop copying.

Reference numeral 704 denotes a liquid crystal touch panel display. In this embodiment, a soft key 705 for designating the image quality priority mode and a soft key 706 for designating the compression ratio priority mode are displayed. The mode setting is performed by specifying or. According to this mode setting, in the image quality priority mode, the calculation for selection using the table of FIG. 5 according to the first embodiment is performed, and in the compression rate priority mode, the calculation according to the second embodiment of FIG. The calculation for selection using the table is performed.

In the above-described embodiment, the compressed image data is stored in the storage unit 46, but the contents are transferred to an image file composed of a magneto-optical disk or the like, or other contents are transmitted through a communication line. It may be transferred as compressed data to the image forming apparatus. In that case, if the information indicating which compression method is selected is added as identification information for each frame, decoding in the decoding unit becomes possible.

Further, in the above-described embodiment, selection is made in units of one frame, but selection may be made in units of at least one frame. For example, the above method is used in units of a plurality of frames (a plurality of images). You may make it select.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of an image processing apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a controller unit shown in FIG.

FIG. 3 is a detailed view of the image signal control unit in FIG.

FIG. 4 is a detailed view of the image processing unit in FIG.

FIG. 5 is a diagram showing a table of errors.

FIG. 6 is a diagram showing a compression rate table.

FIG. 7 is a diagram showing an operation panel.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinori Abe 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yasuhiro Takiyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Co., Ltd. (72) Inventor Hiroshi Kabuki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Atsushi Matsumoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (7)

[Claims] 1. A separation unit that separates an input image for each constituent element; a selection unit that selects one of a plurality of compression methods in at least one frame unit according to a separation result by the separation unit; An image processing apparatus comprising: a compression unit that compresses the input image according to a selection result of the selection unit. 2. The image processing apparatus according to claim 1, wherein the component is an image type. 3. The plurality of compression methods are lossy compression methods, and the selection means selects a compression method according to an occupied area of the constituent element and an error due to the lossy compression method. 4. The image processing apparatus according to claim 1, wherein the selection unit selects a compression method according to an occupied area of the constituent element and a compression rate of the compression method. 5. The image processing apparatus according to claim 1, wherein the selection unit performs selection by selectively using an error or a compression rate of the compression method. 6. The image processing apparatus according to claim 1, further comprising setting means for setting a selection mode by the selection means. 7. The image processing apparatus according to claim 6, wherein the selection mode is an image quality priority mode or a compression ratio priority mode.