JP2000280525A - Image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tandem type imaging apparatus in which color shift can be eliminated with small memory capacity by generating the read address of an image memory from corrected main canning address and sub-scanning address, performing skew correction before it is expanded and then expanding the image data of each color read out at the expanding section. SOLUTION: A main scanning adjusting section, 600 dpi skew correction section, and a block truncation coding(GBTC) expanding section 328 correct the writing position in the main scanning direction, converts a single side document position reference into a central sheet position reference, corrects skew in the sub-scanning direction with 600 dpi, and expands a GBTC compression data to an 8 bit (256 gray level) data. In the 600 dpi skew correction is performed roughly for the mechanical fluctuation of apparatus. In the actual implementation, GPTC expansion is performed following to 600 dpi skew connection. In such an arrangement of skew correction/GPTC expanding section 328, memory capacity for positional correction is reduced by a factor of 3 as compared with a conventional one.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to image data processing in a tandem image forming apparatus.

[0002]

2. Description of the Related Art In a tandem-type printer, a photosensitive member for forming a four-color toner image includes one photoconductor along a paper conveying direction.
Placed in a column. In order to control the delay of the image data between the photoconductors, the image data is temporarily compressed and stored in a memory. Then, the compressed data of each color is expanded while performing the delay control between the photoconductors of each color. Next, in order to correct the printing position shift in the exposure head of each color and the skew correction due to the shift in the parallelism of the arrangement of the photoconductor and the LED head, image data for a plurality of lines is stored again in a line memory or the like. Correction and print start position deviation correction are performed. (For example, Japanese Patent Application Laid-Open No. 10-315545)
No.). In the printer, the multi-valued image data is once compressed, for example, into a unit of N * N pixels by a fixed length compression method and stored in an image memory. When printing,
The expanded image data for N lines is output in raster order, but it is necessary to perform skew correction and print start position deviation correction. For this reason, the compressed data for a plurality of lines is read out once every N lines, is decompressed into image data of N * N pixels, and is stored in the line memory for (N-1) lines.

[0003]

In the above-described image data processing, data for a plurality of lines is compressed to reduce the memory capacity. However, in spite of this, it is necessary to store the expanded image data in a line memory for a plurality of lines for skew correction and print start position deviation correction.
Therefore, a large amount of line memory is required for color misregistration correction, which increases the overall cost of the apparatus.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image processing apparatus for eliminating a color shift with a small memory capacity in a tandem image forming apparatus.

[0005]

The image processing apparatus according to the present invention is a tandem type image forming apparatus, wherein the fixed length compressing means comprises main scanning N dots (N is an integer) for each color data.
Fixed-length compression is performed in units of sub-scanning M dots (M is an integer), and the image memory stores fixed-length compressed data. The address generator corrects the main scanning address with respect to a skew amount and a printing start position generated when raster exposure is performed on the photoconductor in accordance with image data of each color, and an image memory is corrected from the corrected main scanning address and sub-scanning address. Generates a read address. Thus, skew correction is performed before expansion. The expansion unit expands the image data of each color read from the image memory at the address generated by the address generation unit. Preferably, the address generation unit includes a buffer memory storing a correction amount of the main scanning address, and calculates data read from the buffer memory to generate an address signal of the image memory. Also,
Preferably, the compression unit writes the data collectively in the data memory once for each of a plurality of lines at the time of compression, and the decoding unit repeats the data by a predetermined number of times in the plurality of lines. From the data memory for decoding. Thus, in the decoding process, the compressed data of the block including the target sub-scanning line is read by the number of sub-scanning lines.

[0006]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same reference symbols indicate the same or equivalent ones. FIG. 1 shows the overall configuration of a color digital copying machine. The copying machine includes an automatic document feeder 100, an image reading unit 200, and an image forming unit 300. Normally, the automatic document feeder 100
The document conveyed to the image reading position by the
0, and reads the read image data into the image forming unit 3.
00 to form an image. The interface 207 enables connection with an external device.

Next, the image reading unit 200 will be described.
The reflected light of the original on 8 is guided to a lens 203 by a group of three mirrors 202 and forms an image on a CCD sensor 204. The exposure lamp 201 can scan the original on the original glass 208 over the entire surface by scanning at a speed corresponding to the magnification by a scanner motor. The reflected light of the document incident on the CCD sensor 204 is converted into an electric signal in the sensor,
Analog processing of an electric signal by the image processing circuit 205, A
After undergoing / D conversion and digital image processing, the image data is sent to the interface unit 207 and the image forming unit 300.

Next, the tandem image forming section 300 will be described. Imaging units 302c, 30
2m, 302y, and 302k are arranged vertically in a line along the sheet conveying direction of the sheet conveying belt 304. The image data sent from the image reading unit 200 or the interface unit 207 is converted into cyan (C), magenta (M), yellow (Y), and black (K) print data, and the control unit of each exposure head. (Not shown). Each exposure head control unit emits a laser in accordance with the electric signal of the image data sent thereto, and the light is one-dimensionally scanned in the main scanning direction by a polygon mirror 301, and each of the imaging units 302c, 302m, 30
The photosensitive member in 2y and 302k is exposed. Inside each imaging unit, elements necessary for performing an electrophotographic process centering on a photoreceptor are arranged. C,
Each image forming process is continuously performed by rotating each of the photoconductors for M, Y, and K clockwise. The latent image on the photoconductor in each imaging unit is developed by each color developing unit. The desired size of paper is
a, 310b, and 310c, the sheet is conveyed to the sheet conveying belt 304 by a sheet feeding roller 312 and a conveying roller pair 313. The toner image on the photoconductor is transferred to a transfer charger 3 installed in the paper transport belt 304 so as to face each of the photoconductors described above.
The sheets 03c, 303m, 303y, and 303k are transferred onto the sheet on the sheet transport belt 304 in a superimposed manner. Here, the sheet conveyance belt 304 is detected by the timing sensor 306.
The upper reference mark is detected, and the transport timing of the transported paper is adjusted. The transferred toner image on the sheet is heated and melted by the fixing roller pair 307 to be fixed on the sheet, and then discharged to the tray 311.

Further, in order to detect the amount of color misregistration, three registration correction sensors 312 are arranged in a row in a direction perpendicular to the conveying direction of the belt 304 (in the main scanning direction) at the most downstream of the imaging unit. You. Paper transport belt 304
When the upper resist pattern is formed, the C, M, Y, and K resist patterns are detected by the sensor and compared with each other to obtain the color of the C, M, Y, and K images in the main and sub scanning directions. The shift amount is detected. As explained later,
By performing the drawing position correction and the image distortion correction in the image data control unit, the color shift of the C, M, Y, and K images on the paper is prevented.

In the image data control unit shown in FIG. 2, image data C, M, Y, and K from the image processing unit or the interface unit 207 of the image reading unit 200 are fixed-length compressed via the image interface unit 320. And variable-length code conversion. Specifically, block truncation coding (GBTC)
Divides the image into blocks of 4 * 4 dots, and compresses the data of each block to 48 bits (see FIG. 10). The data of each block is composed of average value information LA (8 bits), gradation width information LD (8 bits), and 2-bit code data φ _{i, j of} each pixel. The code data φ _{i, j} is
Four levels of gradation data of 256 gradations (MAX =
LA + LD / 2, MH = LA + LD / 6, ML = LA−
LD / 6, MIN = LA-LD / 2). Next, the fixed-length data is converted into 2, 10 or 50 bits using the gradation width information LD of the GBTC code data. Next, the frame memory unit 324 performs delay control in the sub-scanning direction, and corrects an image position corresponding to the distance between the C, M, Y, and K photoconductors. Next, the fixed-length data conversion unit 326
The variable length code data is converted into fixed length data (GBTC compressed data). Conventionally, GBTC decompression has been performed at this stage, but will be performed later in this embodiment.

Next, a main scanning position adjustment unit, a 600 dpi skew correction unit, and a GBTC decompression unit 328 correct the drawing position in the main scanning direction, convert the one-side original position reference to the center paper position reference, and The skew is corrected at 600 dpi, and the GBTC compressed data is expanded to 8-bit (256 gradation) data. In this 600 dpi skew correction,
The skew is roughly corrected for the mechanical variation of each device. Thus, in the present embodiment, 600 dp
After i-skew correction, GBTC decompression is performed. In this image data control unit, a main scanning position adjustment unit 600 that handles the fixed length data obtained by the fixed length data conversion unit 326
The configuration of the dpi skew correction unit / GBTC decompression unit 328 is different from the conventional one. In this configuration, the memory capacity for position correction is reduced to one third of the conventional one.

Next, the tone reproduction section 330 performs 2400 dpi resolution conversion on the skew in the sub-scanning direction, and
The edge smoothing process, the gamma correction, and the screen process by 00 dpi interpolation are performed. Here, 600dp
When it is desired to further reduce the color misregistration of the i-skew-corrected image data, the skew in the sub-scanning direction is subjected to 2400 dpi resolution conversion to increase the resolution and further reduce the color misregistration, but a description thereof will be omitted.
The obtained C, M, Y, K data is sent to the exposure head control unit.

FIG. 3 is a conceptual diagram of skew correction. The upper part of FIG. 3 shows an example of color shift due to skew correction.
Here, since the printing positions of the two colors are different, a color shift occurs. In the 600 dpi skew correction shown in the center of FIG. 3, the displacement is accommodated within one line. In the 2400 dpi skew correction shown in the lower part of FIG. 3, the resolution is quadrupled in the sub-scanning direction.
Further, the color shift is reduced.

FIG. 4 shows a main scanning position adjusting unit 600 dpi.
The skew correction unit / GBTC decompression unit 328 is shown in detail.
The sub-scanning address generator 400 generates a sub-scanning address. As specifically shown in FIG. 5, in the sub-scanning address generation unit 400, the line ring counter 40 is generated based on the horizontal synchronizing signal -HSYNC and the sub-scanning effective area signal -VIAIN.
00 generates the sub-scanning address LCT. The sub-scanning area output signal generating section 4002 generates a sub-scanning area output signal -VIAO based on the sub-scanning effective area signal -VIAIN.
Output UT. FIG. 6 shows the relationship between the skew correction and the sub-scanning area output signal -VIAOUT. As shown on the right side of the figure, the effective image data is read obliquely after the skew correction, and the skew correction amount (the maximum skew correction amount is 44
Line), the sub-scanning effective area output signal -VIAO
The UT is output longer than the sub-scanning effective area signal -VIAIN. This eliminates image defects in the sub-scanning direction.

The main scanning address generator 402 generates a main scanning address based on the horizontal synchronization signal -HSYNC, the dot clock DOTCLK, and the horizontal write enable signal -HWE. The compressed data flows once every four lines by the horizontal write enable signal -HWE. The main scanning position adjustment unit 404 is controlled by the CPU of the image data control unit, and adjusts the main scanning position (44 lines at maximum). As described above, the resist correction sensor 312 detects the C, M, Y, and K resist patterns,
The amount of color misregistration of the C, M, Y, and K images in the main and sub scanning directions is detected. The CPU adjusts this color shift amount for the main scanning line.

More specifically, as shown in FIG. 7, in the main scanning address generation section 402, the write area main scanning dot counter 4020 is based on a horizontal synchronization signal -HSYNC, a dot clock DOTCLK and a horizontal write enable signal -HWE. Generates a main scanning address WHA. The read area main scanning dot counter 4022 generates a main scanning address RHA based on the horizontal synchronization signal -HSYNC, the dot clock DOTCLK, and the horizontal read enable signal -HRE. Horizontal read enable signal-
The HRE is generated from the horizontal synchronization signal -HSYNC and the dot clock DOTCLK as follows. The main scanning dot counter 4024 generates a dot count value CNT from the horizontal synchronization signal -HSYNC and the dot clock DOTCLK, and inputs the dot count value CNT to the read area signal generation unit 4026. On the other hand, the main scanning position adjustment start address DA and the main scanning position adjustment end address DB from the main scanning position adjustment unit 404 are connected to the read area signal generation unit 4026 via the register 4028.
Is input to The read area signal generation unit 4026 generates a horizontal read enable signal -HRE between the main scanning position adjustment start address and the main scanning position adjustment end address, and a signal MPX (fine adjustment of the horizontal read enable signal -HRE). DA1-0). Correction coefficient RAM
A main scanning address D 406 is obtained by taking out any of the 44 lines based on a signal from the CPU of the image data control unit.
A correction coefficient PD7-0 for CT12-2 is output.

As shown in FIG. 8, a write address generator 408 uses a multiplier and an adder to generate a sub-scan address LCT5-2, a line width (7360), and a main-scan address from the sub-scan address generator 400. From the main scanning address WHA12-0 from the unit 402 to the write address WA1.
4-0 is generated and output to the data memory 412. In other words, the two dimensions of the sub-scanning address and the main scanning address
Create a dimensional address WA.

As shown in FIG. 9, the read address generator 410 includes a sub-scanning address LCT5-0 from the sub-scanning address generator 400 and a correction coefficient PDO7- from the correction coefficient RAM 406 for skew correction of the sub-scanning address.
Are added by an adder to generate a sub-scanning address RVA5-0. The sub-scanning address RVA502 (excluding the lower 2 bits) and the main scanning address RHA12-2 (lower 2 bits) from the main scanning address generator 402 are generated. ) To generate the write address RA14-0. In addition, the lower two bits RVA1-0 of the sub-scanning address and the lower two bits of the main scanning address RHA1-0 are output to the decoding unit 414 as VS and HS.

The data memory 412 writes the fixed-length data of C, M, Y, and K from the fixed-length data converter 316 to the write address WA14-0. Also, the fixed length data is read from the read address RA14-0, and the signal BD
Output as O47-0. Data memory capacity is 2
0 kB * 48 bits. FIG. 10 shows the concept of data memory control. The data memory 412 is a RAM of 20 kilowords * 48 bits, and fixed-length compressed data (here, 48-bit data for each block compressed by GBTC) is sequentially written. When the last address is reached, writing is continued by returning to the first address. Thus, the data memory 412 stores the main scanning address VA (0 to 10) and the sub scanning address HA (0 to 18).
39) for each of the 4 * 4 pixel blocks
8-bit data (one word) is stored. Therefore, data of 1840 * 11 words * 48 bits is stored in data memory 412. Since the capacity of this memory stores data before decoding, it can be reduced to 1/3 as compared with the conventional case of storing data after decoding.

The decoding section 414 expands the signal BDO by a known GBTC encoding method. That is, as shown in FIG. 11, the gradation data generation unit 4140 outputs the average value information LA (BD) in the signal BDO for each 4 * 4 pixel block.
O47-40) and gradation width information LD (BDO39-32)
From four levels out of 256 tones (MA
X = LA + LD / 2, MH = LA + LD / 6, ML = L
A-LD / 6, MIN = LA-LD / 2), and the code information selection table 4142 stores the code data φ _{i, j} (BDO31-0), VS, and H for each pixel in the signal BDO.
S outputs the selection data PX1-0. FIG. 12 shows a code information selection table 4142 for generating the selection data PX.
Indicates the contents of The decoded data selection table 4144 selects any one of the four levels according to the selected data PX and outputs it as image data C, M, Y, K57-50. FIG. 13 shows a decoded data selection table.

Next, skew correction will be described with reference to FIG. 14. Data is written to the data memory 412 every four lines. When the data of the latest four lines (the sub-scanning address is LCT / 4) is written to the data memory, if the four lines written first are 0 to 3 lines, the latest 4 lines are 40 to 43 lines.
Here, the skew-correctable lines (41 lines) until the next four lines are written are LCT / 4, LCT / 4 +
1, LCT / 4 + 2 and LCT / 4 + 3 are as shown in the figure. Here, the data for 44 lines to be subjected to skew correction has a two-dimensional distribution determined by the number of lines and the main scanning address. (The data of each block composed of 48-bit fixed-length compressed data is data of four lines continuous in the sub-scanning direction at the same main scanning address.) With respect to these data, data is read in consideration of skew correction. Here, the correction coefficient RAM 406
Outputs the skew correction coefficient PD6-0 for the skew address correction data read address as indicated by the black mark in the figure. As shown on the right side of the figure, the read address of the skew correction data to which the correction coefficient has been added is the sum of the read address of the skew correction data before adding the correction coefficient and the skew correction coefficient, LCT + 4 + PDi (i = 1,
2, ..., 1839). The skew correction coefficients are 39, 38,..., 2 in the illustrated example.

FIG. 15 is a timing chart for skew correction. After performing the skew correction and the printing start position deviation correction, the decoding unit 414 reads out the compressed data in the sub-scanning line cycle by the number of times of the sub-scanning lines, and performs expansion processing. That is, at the time of decoding, compressed data flows once in four lines (-HWE), and data is written to the data memory 412 for the first line N of the four lines by the -HRE signal. That is,
Writing to the data memory 412 is performed once for each of a plurality of lines (N = 4) at the time of compression. In order to output image data after decompression for N lines in a raster order, reading is repeatedly performed a predetermined number of times within a plurality of lines (N lines). On the other hand, for each line, the correction coefficient RAM 40
6, the correction coefficient is read, the data is read from the data memory 412, and the GBTC decoding is performed by the decoding unit 414. In the effective area -HIA, four lines of decoded data DOUT and an interpolation coefficient POUT are output. Conventionally, in decoding, it was necessary to store four lines of decoded data in a line memory. In this embodiment,
In this configuration, a plurality of memory lines for outputting image data of N lines in raster order are unnecessary, and no line memory is used for the decoding unit and the dot-unit main scanning position adjustment unit. Thus, this can reduce costs.

The dot-unit main scanning position adjustment unit 416 uses the table shown in FIG.
When 7-0 is output to the tone reproduction section, MPX (0 to 3) is output.
The main scanning position is adjusted with a delay of (dot). Also,
The signal -HRE from the main scanning address generation unit 402 is output as an effective scanning area signal -HIA, and the correction coefficient RAM4
The lower 2 bits of the signal from 06 are output as a signal POUT.

[0024]

The skew correction and the printing start position deviation correction are performed with a small memory capacity. It is possible to independently control the delay control of the photoconductor of each color and the skew correction due to the shift of the printing start position and the arrangement of the photoconductor in the four exposure heads and the parallelism of the exposure head. The complexity of address control for delay control can be reduced. After performing the skew correction and the printing start position shift correction, in order to output the expanded image data for N lines in the raster order, the compressed data is read by the number of sub-scanning lines in the sub-scanning line cycle, and the expansion process is performed. Therefore, the memory for outputting the image data of N lines in raster order can be reduced, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of the overall configuration of a color digital copying machine.

FIG. 2 is a block diagram of an image data control unit.

FIG. 3 is a diagram showing the concept of skew correction.

FIG. 4 is a block diagram of a main scanning position adjustment unit, a 600 dpi skew correction unit, and a GBTC decompression unit.

FIG. 5 is a block diagram of a sub-scanning address generation unit.

FIG. 6 is a diagram showing a relationship between skew correction and a sub-scanning area output signal.

FIG. 7 is a block diagram of a main scanning address generation unit.

FIG. 8 is a block diagram of a write address generation unit.

FIG. 9 is a block diagram of a read address generation unit.

FIG. 10 is a diagram showing the concept of data memory control.

FIG. 11 is a block diagram of a decoding unit.

FIG. 12 is a diagram of a code information selection table.

FIG. 13 is a diagram of a demodulation data selection table.

FIG. 14 is a diagram for explaining skew correction;

FIG. 15 is a timing chart of skew correction.

FIG. 16 is a diagram of a dot unit main scanning position adjustment table.

[Explanation of symbols]

328 main scanning position adjustment unit, 600 dpi skew correction unit, GBTC decompression unit, 400 sub-scanning address generation unit,
402 main scanning address generator, 406 correction coefficient RAM, 408 write address generator, 41
0 Read address generation unit, 412 data memory, 414 decoding unit.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2C362 BB37 BB46 CA22 CB43 CB55 CB75 DA09 5C073 AA02 AA03 BB07 CC01 CE01 CE09 CE10 5C077 LL02 LL17 MP08 NP05 PP05 PP33 PP38 PP39 PP58 PP59 PQ22 RR21 TT02 TT03 A01 DA06 TT02

Claims (3)

[Claims] 1. A tandem-type image forming apparatus, comprising: fixed-length compression means for performing fixed-length compression in units of main scanning N dots (N is an integer) and sub-scanning M dots (M is an integer) for each color data; An image memory for storing fixed-length compressed data, and a main scanning address corrected for a skew amount and a printing start position generated when raster exposure is performed on a photoconductor in accordance with image data of each color, and the corrected main scanning is performed. An address generation unit that generates a read address of the image memory from an address and a sub-scanning address; and an expansion unit that expands image data of each color read from the image memory with the address generated by the address generation unit. Image processing device. 2. The image processing apparatus according to claim 1, wherein the address generating unit includes a buffer memory storing a correction amount of the main scanning address, and generates an address signal of the image memory by adding the correction amount read from the buffer memory. The image processing device according to claim 1. 3. The image memory according to claim 1, wherein the data is written once for each of a plurality of lines during fixed-length compression, and the decompression unit reads and decodes the data repeatedly a predetermined number of times in the plurality of lines. The image processing device according to claim 1.