JPH0670171A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device which can compress and restore image data by using the memory of small capacity. CONSTITUTION:This image forming device is characterized by including a first compressing means 1, 2 to compress the inputted picture data, a storage means 3 to store the compressed image data, a second compressing means 4, 5, 6 to restore the image data stored in the storage means 3 and execute prescribed image processing in respect of the restored image data, and afterwards, store the processed picture data in the storage means 3 after compressing it again, and a restoring means 7, 8 to restore again the image data stored in the storage means 3 by the second compressing means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including image data compression means and decompression means.

[0002]

2. Description of the Related Art FIG. 7 shows a hardware configuration of a general image forming apparatus, and FIG. 8 shows a flow of color signals in a hard copy.

FIG. 7 shows an image input unit 96, image memories 97 and 98, image processors 99 and 100, an image output unit 101, etc. connected to the arithmetic control unit 95, and FIG. ) Color separation scanning (106)
Then, sampling and quantization (107) are performed to perform shading correction (108), color system conversion color correction (109), MTF correction (110), logarithmic compression γ correction (111), UCR black generation (112). The image is reproduced (118) through the color correction masking (113), the recording system γ correction (114), the pseudo gradation conversion (115), the dot signal generation (116), and the CMY recording system (117).

As described above, various image forming apparatuses using an image memory as shown in FIG. 7 and FIG. 8 are open to the public, but by storing information in the image memory and restoring the stored information, the image is formed. There is no system for processing data.

It is a general method to store (store) the image information in the memory as it is without compressing it. Alternatively,
Although there is a method of compressing image data and then storing it in a memory after image processing, there is no method of compressing data before image processing and performing image processing after decompression.

[0006]

When the information processing amount of an image is small, for example, when the data of a video camera is targeted, a white / black data of 8 bits per pixel is 400 x 64.
Although the plane data of 0 pixels is 256 KB data, the resolution is 400 DPI, A4 size (297 x 210 mm) 1 page 1 pixel When handling 8-bit data, the amount of information is 16 MB Becomes

Therefore, in terms of memory cost, it is difficult to handle such large-capacity image data as it is.

An object of the present invention is to provide an image forming apparatus capable of compressing and decompressing image data by using a small capacity memory.

[0009]

According to the present invention, there is provided a first compression means for compressing input image data, a storage means for storing the compressed image data, and an image stored in the storage means. A second compression means for restoring the data, performing a predetermined image processing on the restored image data, compressing the image-processed image data again, and storing the compressed image data in the storage means; The image data stored in the storage unit by the compression unit is restored again.

[0010]

The input image data is compressed by the first compression means and stored in the storage means, and the image data stored in the storage means is restored and then subjected to predetermined image processing, and then the second image data is restored. The image data stored in the storage means after being compressed again by the compression means and stored in the storage means.
Since the data is restored by the restoration means, the amount of memory used can be reduced, and the image processing that was performed in two scans can be performed in one scan. By performing this one scan, processing time can be shortened and processing can be performed. The operation can be simplified.

Further, in the embodiment of the present invention, even if the image processing function is limited, high-order image processing can be performed by performing the compression / decompression processing a plurality of times, and the image data to be feature-extracted is reduced in size. It is possible to significantly reduce the processing speed by performing the scaling process and restoring it.

[0012]

Embodiments of an image forming apparatus according to the present invention will be described with reference to the drawings.

FIG. 5 is a sectional view showing the overall construction of a digital copying machine which is an embodiment of an image forming apparatus capable of forming images on both sides according to the present invention.

As shown in FIG. 5, a digital copying machine 30 is provided.
The scanner unit 31, the laser printer unit 32, the multi-stage paper feeding unit 33, and the sorter 34 are provided.

The scanner unit 31 includes a document placing table 35 made of transparent glass and a double-sided automatic document feeder (RDF) 36.
And a scanner unit 40.

The multi-stage paper feeding unit 33 includes the first cassette 5
It has the 1st, 2nd cassette 52, the 3rd cassette 53, and the 4th cassette 55 which can be added by selection.

In the multi-stage paper feeding unit 33, the papers are fed one by one from above the papers stored in the cassettes of the respective stages, and are conveyed toward the laser printer section 32.

The RDF 36 sets a plurality of originals at one time, automatically feeds the originals one by one to the scanner unit 40, and scans one side or both sides of the original according to the operator's selection. It is configured to be read by the unit 40.

The scanner unit 40 includes a lamp reflector assembly 41 for exposing a document, a plurality of reflection mirrors 43 for guiding a reflected light image from the document to a photoelectric conversion element (CCD) 42, and a reflected light image from the document. It includes a lens 44 for forming an image on the CCD 42.

When scanning a document placed on the document placing table 35, the scanner section 31 is configured to read the document image while the scanner unit 40 moves along the lower surface of the document placing table 35. When the RDF 36 is used, the document image is read while the document is conveyed while the scanner unit 40 is stopped at a predetermined position below the RDF 36.

The image data obtained by reading the original image with the scanner unit 40 is sent to the image processing unit and subjected to various processing, and then temporarily stored in the memory of the image processing unit and in response to the output instruction. The image data in the memory is supplied to the laser printer section 32 to form an image on the paper.

The laser printer unit 32 includes a manual document tray 45, a laser writing unit 46, and an electrophotographic process unit 47 for forming an image.

The laser writing unit 46 is a semiconductor laser which emits laser light corresponding to image data from the above-mentioned memory, and a polygon mirror which deflects the laser light at an equal angular velocity.
It has an f-θ lens and the like for correcting the laser light deflected at a constant angular velocity so as to be deflected at a constant velocity on the photosensitive drum 48 of the electrophotographic process section 47.

In the electrophotographic process section 47, a charging device, a developing device, a transfer device, a peeling device, a cleaning device, a static eliminator and a fixing device 49 are arranged around the photosensitive drum 48 in a known manner. ing.

A conveying path 50 is provided on the downstream side of the fixing device 49 in the conveying direction of the sheet on which the image is to be formed. The conveying path 50 is connected to the sorter 34 by a conveying path 57 and a multi-stage sheet feeding unit. It is branched to a conveyance path 58 leading to 33.

The conveying path 58 is branched in the multi-stage paper feeding unit 33, and the reversing conveying path 50 is formed as a conveying path after branching.
a and a double-sided / composite transport path 50b are provided.

The reverse conveyance path 50a is a conveyance path for reversing the front and back sides of a sheet in a double-sided copy mode for copying both sides of a document.

The double-sided / composite conveying path 50b is a double-sided copy mode.
In the single-sided synthetic copy mode, the sheet is conveyed from the reverse conveyance path 50a to the image forming position of the photosensitive drum 48, or the image of different originals or the toner of different colors is formed on one side of the sheet to perform the synthetic copy. A conveyance path for conveying the sheet to the image forming apparatus of the photosensitive drum 48 without reversing the sheet.

The multi-stage sheet feeding unit 33 includes a common conveyance path 56, which is common to the first cassette 51 and the second cassette 51.
The sheets from the cassette 52 and the third cassette 53 are carried out toward the electrophotographic process section 47.

The common conveyance path 56 is the electrophotographic process section 47.
On the way to the transport path, it joins the transport path 59 from the fourth cassette 55 and leads to the transport path 60.

The conveying path 60 is a confluence point 62 of the double-sided / composite conveying path 50b and the conveying path 61 from the manual document tray 45.
And the photoconductor drum 48 of the electrophotographic process unit 47
And a transfer device, and a confluence point 62 of these three conveying paths is provided at a position close to the image forming position.

Therefore, in the laser writing unit 46 and the electrophotographic process section 47, the image data read from the above-mentioned memory is stored in the laser writing unit 46.
The laser beam is scanned by the laser to form an electrostatic latent image on the surface of the photosensitive drum 48, and the toner image visualized by the toner is the toner image of the sheet conveyed from the multi-stage sheet feeding unit 33. It is electrostatically transferred and fixed on the surface. The sheet on which the image is thus formed is sent from the fixing device 49 to the sorter 34 via the carrying paths 50 and 57, or is carried to the reverse carrying path 50a via the carrying paths 50 and 58.

Next, the structure and function of the image processing unit included in the copying machine 30 will be described.

FIG. 6 is a block diagram of the image processing unit included in the copying machine 30 of FIG.

The image processing unit included in the copying machine 30 includes a memory 73 including an image data input section 70, an image processing section 71, an image data output section 72, a RAM (random access memory) and the like. And an image processing central processing unit (CPU) 74.

The image data input section 70 is a CCD section 70a,
It includes a histogram processing unit 70b and an error diffusion processing unit 70c.

The image data input section 70 is the CCD 4 of FIG.
The image data of the original document read from No. 2 is binarized and converted, and while the histogram is taken as a binary digital amount, the image data is processed by the error diffusion method and stored in the memory 7
3 is configured to be stored once.

That is, in the CCD section 70a, after the analog electric signal corresponding to each pixel density of the image data is A / D converted, MTF correction, black and white correction or gamma correction is performed, and 256 gradations (8 (Bit) digital signal is output to the histogram processing unit 70b.

In the histogram processing unit 70b, the digital signal output from the CCD unit 70a is added for each pixel density of 256 gradations to obtain density information (histogram data), and if necessary, the obtained histogram. The data is sent to the image processing CPU 74, and is also sent to the error diffusion processing unit 70c as pixel data.

The error diffusion processing unit 70c uses the error diffusion method which is a kind of pseudo halftone processing, that is, the method of reflecting the binarization error in the binarization judgment of the adjacent pixels.
The 8-bit / pixel digital signal output from the unit 70a is converted into 1-bit (binary), and a redistribution operation for faithfully reproducing the local area density in the original is performed.

The image processing unit 71 includes multi-valued processing units 71a and 71b, a synthesis processing unit 71c, a density conversion processing unit 71d, a scaling processing unit 71e, an image processing unit 71f, an error diffusion processing unit 71g and a compression processing unit 71h. Contains.

The image processing unit 71 is a processing unit for finally converting the input image data into the image data desired by the operator, and the output image data finally converted into the memory 73. It is configured to be processed by this processing unit until it is stored as a data. However, each of the above-mentioned processing units included in the image processing unit 71 functions as necessary and may not function.

That is, in the multi-value quantization processing units 71a and 71b, the data binarized by the error diffusion processing unit 70c is converted again into 256 gradations.

In the synthesizing section 71c, a logical operation for each pixel, that is, a logical sum, a logical product, or an exclusive logical sum is selectively performed. The data which is the object of this calculation is the bit data from the pixel data and the pattern generator (PG) stored in the memory 73.

In the density conversion processing unit 71d, the relationship between the input density and the output density is arbitrarily set for the 256 gradation data signal based on a predetermined gradation conversion table.

In the scaling processing unit 71e, the pixel data (density value) for the scaled target pixel is obtained by performing interpolation processing with known data that is input according to the instructed scaling ratio. The main scanning is scaled after the sub scanning is scaled.

In the image processing section 71f, various image processings may be performed on the input pixel data, and information extraction such as feature extraction may be performed on the data sequence.

The error diffusion processing unit 71g performs the same processing as the error diffusion processing unit 70c of the image data input unit 70.

In the compression processing section 71h, binary data is compressed by the encoding called run length. Also, image data
Regarding the compression of data, the compression works in the final processing loop when the final output image data is completed.

The image data output unit 72 includes a restoration unit 72a, a multi-value quantization processing unit 72b, an error diffusion processing unit 72c, and a laser output unit 72d.

The image data output unit 72 restores the image data stored in the memory 73 in a compressed state and restores the original 2
It is configured so that it is converted into 56 gradations again, error diffusion of 4-valued data that is a smoother halftone expression than 2-valued data is performed, and the data is transferred to the laser output unit 72d. There is.

Immediately, in the decompression unit 72a, the compression processing unit 71h.
The image data compressed by is restored.

In the multi-value processing section 72b, the image processing section 71
Processing similar to that of the multi-value quantization processing units 71a and 71b is performed. In the error diffusion processing unit 72c, the image data processing unit 70
Processing similar to that of the error diffusion processing unit 70c is performed.

In the laser output section 72d, based on the control signal from the printer control CPU 79, the digital pixel data is output.
Data is converted into a laser on / off signal, and the laser is turned on / off.

The image data input section 70 and the image data are input.
The data handled by the data output unit 72 is basically stored in the memory 73 in the form of binary data in order to reduce the capacity of the memory 73, but deterioration of the image data is taken into consideration. It is also possible to process in the form of 4-valued data.

FIG. 1 shows a basic block diagram of an embodiment of the present invention. Image data in which the input circuit unit 1 and the error diffusion unit 2 A / D-convert the input data from the so-called CCD and perform various corrections.
The data is usually multi-valued data of about 8 bits per pixel. The error diffusion unit 2 sets the multivalued data to 1 from the standpoint of image processing.
It is a conversion block that converts to 1 bit or 2 bits / 1 pixel, and this conversion reduces the memory usage to 1/4 (when 2 bits),
It is possible to reduce 1/8 (when 1 bit).

The image data stored in the image memory 3 is restored by the smoothing block 4 to, for example, 8-bit data. As the smoothing block 4, a window function of 3 × 3, 7 × 5, etc. is used to restore the multilevel data. The image processing block 5 includes a high contrast, density conversion for background removal, a calculation circuit for scaling, a feature extraction calculation function for image size recognition and area recognition, and the like.

The data processed by the image processing block 5
The data is processed by the same error diffusion unit 6 as the error diffusion unit 2, and the image data is compressed (8 bits are 2 or 1 bit),
It is stored again in the image memory 3. The stored data is again smoothed by the smoothing block 4, the image processing block 5, and the error diffusion unit 6.
It is also possible to go through the processing loop (hereinafter referred to as the processing loop). The finally processed image data is restored to multi-valued 8 bits by the smoothing filter 7, and the laser drive circuit 7 which is a part of the circuit of the LBP printer which receives the multi-valued data as an input.
The multi-valued data is converted into a pulse width, and the laser diode is driven to print the data.

FIG. 2 is a block diagram showing the details of FIG.

Circuit blocks 11 to 17 in FIG. 2 correspond to the input circuit unit 1 in FIG. 1 and are input correction circuits including various correction circuits.

Reference numeral 11 is a CCD line sensor, which is an analog white /
Outputs black data. Reference numeral 12 is an A / D converter, which is an analog data
Data into a digital value of 8 bits / 1 pixel. Thirteen
Is a shading correction unit in the main scanning direction, and 14 is an MTF correction unit that performs MTF correction as blur correction of the lens optical system. Reference numeral 15 is a γ correction unit for correcting the visibility, 16 is a circuit for extracting and cutting out the effective image data area from the drooping image data, and 17 is a histogram creation block of the image density for the effective area. The data created in the histogram creation block 17 is usually multi-valued data of 1 pixel 8 bits, but when storing it in the image memory, the error diffusion unit 18 uses 1 bit or 2 bits of 1 pixel by the error diffusion method. Convert to data. Next, the outline of the error diffusion method will be described with reference to FIG.

In FIG. 3, assuming that the pixel point of interest is the point A in the two-dimensional data of the image, the image data at the point A is divided into the result + error. The threshold depends on the number of bits of the error diffusion output. The following table shows the relationship between the threshold and the error when the output is 2 bits. The result at the point A becomes the output data of the error diffusion. The remaining error is distributed to peripheral pixels B, C, D and E and added to the image data at each point. Based on this procedure, the same processing is performed at any time while shifting the ordered pixels in the main scanning direction and the sub scanning direction, so that the processing of the entire target area can be completed.

As a result, the image data is compressed from 8 bits to 2 bits, and the image density is preserved in the total target area total.

The data (for example, 2 bits / 1 pixel) of the error diffusion unit 18 is further image-compressed by the compression unit 19. If you use a run length method such as FAX as a compression method, it is usually 1 /
Compressed to about 10. The compressed image is DMA-120
Is stored in the image memory configured by the D-RAM 21.

The smoothing block 4 shown in FIG. 1 is the DMA 23, the restoring unit 24, and the smoothing filter 2 shown in FIG.
Corresponds to 5. The DMA 23 reads data from the image memory 21. The decompression unit 24 corresponding to the control unit is a unit that arithmetically decompresses the data compressed by the run length in the compression unit 19. The image data after restoration has one pixel of 2 bits, but this is restored to 8-bit multivalued data by the smoothing filter 25.

The details of the smoothing block in this embodiment are shown in FIG.
Shown in.

In the 3 × 3 area centering on the pixel of interest, the edge detection unit 90 determines the edge, and if the edge is the edge, the target area is close to the text original. Therefore, the pixel calculated by the 3 × 3 smoothing filter 91. When the data is not an edge, it is regarded as a photographic original, and the pixel data calculated by the 7 × 5 smoothing filter 92 is switched by the selector 93 and output.

As a result, the 8-bit multilevel data is restored. Next, the image processing block 5 in FIG. 1 has the 1/8 reduction unit 26, the binarization unit 27, and the feature extraction unit 2 in FIG.
8 corresponds to the density conversion unit 29 and the scaling unit 80.

For example, the density conversion unit 29 is used for high contrast and background removal, but the internal structure is a LUT formed by RAM. The conversion can be easily performed by connecting the image data output from the smoothing block to the RAM address (for example, 8 bits) and writing the density conversion data in the RAM data. For example, the background threshold level is calculated from the histogram data at the time of reading the image, and in this density conversion table, the data below the threshold is corrected to 0 so that it is not printed because it is in the background. It can be realized by putting it on.

Similarly, high contrast is possible. Further, a feature of the present embodiment is that high contrast and background processing can be performed in one scan.

In a general model, it was mainly performed with two scans. Since histogram data is created in the first scan and then high contrast and other measures are performed in the second scan, the scan takes twice as long and complicated control is required. In this embodiment, the density of one scan can be converted with the minimum memory usage.

The scaling unit 80 carries out a scaling operation for main scanning / sub scanning. Since the main scanning / sub-scanning operations are separately performed, univariable magnification is also possible. A feature of this embodiment is that it is possible to determine the magnification and perform the scaling processing with a minimum amount of memory after the scan is completed in one scan. For example, when the document size of the read image is determined by image processing, the document size cannot be known until after the image processing. Therefore, it is possible only in the present embodiment to auto-magnify the document size on the designated paper.

The 1/8 reduction unit 26 is provided to reduce the document size to 1/8 and shorten the processing time. The binarization unit 27 is based on the fact that feature extraction can be performed only with binary data. The feature extraction unit 28 performs the extraction of the document area, the determination of the shadow of the document, etc., but the feature extraction is performed using the figure reduced by the 1/8 reduction unit 26, and blocks that are not necessary for repeating the feature extraction process are selected. The structure is such that the processing loop can be circulated many times while storing the processing data in the image memory.
The error diffusion unit 81 and the compression unit 82 have the same functions as the error diffusion unit 18 and the compression unit 19.

[0074]

The input image data is compressed by the first compression means and stored in the storage means, and the image data stored in the storage means is restored and then subjected to predetermined image processing. Since the image data stored in the storage means by the second compression means is compressed again and stored in the storage means by the second compression means, the image data stored in the storage means is restored by the decompression means. The image processing performed in step 1 can be performed in one scan, and the processing time can be shortened and the processing operation can be simplified by performing this one scan.

[Brief description of drawings]

FIG. 1 is a basic block diagram of an embodiment of the present invention.

FIG. 2 is a detailed explanatory diagram of the embodiment shown in FIG.

FIG. 3 is a diagram illustrating an outline of an error diffusion method.

FIG. 4 is a diagram illustrating details of a smoothing block.

FIG. 5 is a sectional view showing the overall configuration of a digital copying machine which is an embodiment of the image forming apparatus according to the present invention.

6 is a block configuration diagram of an image processing unit included in the copying machine of FIG.

FIG. 7 is a diagram showing a hardware configuration of a general image forming apparatus.

FIG. 8 is a diagram showing the flow of color signals in hard copy.

[Explanation of symbols]

 1 Input Circuit Section 2, 6 Error Diffusion Section 3 Image Memory 4, 7 Smoothing Block 5 Image Processing Block 8 Laser Driving Circuit 30 Digital Copier 70 Image Data Input Section 71 Image Processing Section 72 Image Data Output Department

Claims (2)

[Claims] 1. A first compression means for compressing input image data, a storage means for storing the compressed image data, and a means for restoring the image data stored in the storage means. Second compression means for performing predetermined image processing on the restored image data and then compressing the image-processed image data again and storing the compressed image data in the storage means; and the storage by the second compression means. An image forming apparatus comprising: a restoring unit that restores the image data stored in the unit again. 2. The first compression means and the second compression means are respectively configured to compress image data by an error diffusion method, and the second compression means and the decompression means are respectively for decompression. The image forming apparatus according to claim 1, further comprising: