JP4454831B2 - Image forming apparatus and image forming method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus and method for forming an image, and a storage medium.
[0002]
[Prior art]
With the widespread use of electronic devices in general and personal computers, peripheral devices have also become popular. One such peripheral device is a printer device.
[0003]
Such a printer device communicates with a device such as a host computer, receives commands, print data, and the like from the host computer side, performs drawing development on a bitmap memory, and performs print output.
[0004]
When the original image data is color gradation data at the time of such drawing development, even if some color information is lost, a satisfactory output result cannot be obtained unless gradation expression is sufficient. For example, in a printing method such as an electrophotographic method, in printed matter, the non-linearity of the boundary between the drawing portion and the non-drawing portion corresponding to the dot gain increases, and it is difficult to express the gradation with a single pixel. Therefore, in such a printing method, image processing such as so-called halftone dots, in which the gradation of each pixel is expressed by the number of dots in a unit area, is performed. In such a process, it is necessary to make the halftone dot area small and make the halftone dot visually inconspicuous. Therefore, when the resolution of the recording mechanism is about 1000 dpi vertically or horizontally, or less than that, a sufficient number of dots for gradation expression cannot be held in the unit area. Therefore, it is necessary to ensure sufficient gradation by combining the method of performing gradation expression of each pixel and the above-described gradation expression by dots per unit area.
[0005]
[Problems to be solved by the invention]
There are several methods for representing the gradation of each pixel. For example, as one of the methods that are relatively easy to adopt in a scanning recording mechanism, each pixel is further divided in the main scanning direction to reduce the resolution in the main scanning direction. There is a way to increase it. To increase the resolution in the sub-scanning direction, it is necessary to redesign the entire printing mechanism. However, the resolution in the main scanning direction has an advantage that can be realized by reviewing the laser driving circuit and the scanning synchronization circuit.
[0006]
However, even if the resolution in the main scanning direction is increased in this way, when rendering is performed with pixels isolated for rendering, it does not contribute to the gradation effectively. As described above, this results in a wide boundary area between the drawing part and the non-drawing part, and produces an unstable printing result lacking in stability and linearity. Therefore, in order to avoid this, it is only necessary to draw the pixels so as to be continuous with the saturated drawing pixels, that is, the pixels drawn over the entire area of the pixels, in the adjacent pixels.
[0007]
However, if such image data with an increased resolution in the main scanning direction is stored as it is, the amount of information becomes enormous especially in the case of a high-resolution device, resulting in an increase in memory capacity and an increase in cost. Become.
[0008]
In the case of print output with an increased resolution in the main scanning direction, the image resolution is certainly advantageous. However, the method of realizing gradation by the ratio of the drawing area is more efficient than the light intensity modulation of the pixel. It is disadvantageous in tonality. For example, when a pixel is subdivided in the main scanning direction with respect to the sub-scanning direction and a resolution of 8 times is given, the gradation expressing power per original pixel is proportionally 8 times, but the light intensity modulation When an information amount of 8 times the amount of information per pixel is given, theoretically, it has 256 gradations.
[0009]
As described above, regarding the gradation, simply increasing the resolution in the main scanning direction is disadvantageous in terms of memory efficiency as compared with the light amount modulation method, and is not practical to be implemented in a low-cost machine. In addition, the laser drive signal with an increased resolution in the main scanning direction includes a high frequency, which makes it difficult to design radiation noise suppression in the transmission path from the image generation unit to the laser drive circuit.
[0010]
The present invention has been made in view of the above problems, and an object of the present invention is to suppress the use capacity of a memory used when image data is formed.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, for example, an image forming apparatus of the present invention comprises the following arrangement.
That is, an image forming apparatus that forms a gradation image based on multi-value image data ,
Means for generating index image data representing pixel values of the multi-value image data in 4 bits ;
First storage means for storing control data corresponding to the positions of pixels formed based on the multi-valued image data;
First reading means for reading control data from the first storage means in synchronization with scanning for image formation;
Second storage means for storing a binary bit string for each combination of 4-bit index values 0 to 15 and control data stored in the first storage means;
Second reading means for reading a binary bit string corresponding to a combination of the control data read by the first reading means and the pixel value of the index image data from the second storage means;
Image forming means for forming an image by scanning laser light emitted according to the binary bit string read by the second reading means ;
The second storage means is
As a binary bit string corresponding to the control data 00 stored in the first storage unit, a binary bit string for growing each pixel formed by the image forming unit from the left side of each pixel in the scanning direction is stored.
As a binary bit string corresponding to the control data 01 stored in the first storage unit, a binary bit string for growing each pixel formed by the image forming unit from the right side of each pixel in the scanning direction is stored.
As a binary bit string corresponding to the control data 10 stored in the first storage unit, a binary bit string for growing each pixel formed by the image forming unit from the center of each pixel in the scanning direction is stored.
As a binary bit string corresponding to the control data 11 stored in the first storage unit, a binary bit string for growing each pixel formed by the image forming unit from both sides of the pixel in the scanning direction is stored.
Any binary bit string stored by the second storage means is a binary bit string that grows pixels more as the index value corresponding to the binary bit string increases.
The image forming means drives the laser beam when the bit in the binary bit string is 1, and turns off the laser beam when the bit is 0 .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0013]
FIG. 1 is a block diagram illustrating a configuration example of an image processing apparatus (laser beam printer) according to the present embodiment. In the figure, reference numeral 100 denotes a recording unit. In the present embodiment, image recording is performed by an electrophotographic method.
[0014]
An optical modulation unit 110 receives the control data 201 sent from the signal generation unit 200 and the index data 202 sent from the image data generation unit 150 and inputs a pixel division pattern for driving the semiconductor laser element 111. It is generated and supplied to the semiconductor laser element 111. The optical modulation unit 110 includes R bit length bit pattern registration registers corresponding to the number of (201 + 202) signals. In this embodiment, 201 is composed of 2 bits, 202 is composed of 4 bits, and since R = 16 is described, 64 16-bit registers are incorporated. The configuration of this register group is shown in FIG.
[0015]
Reference numerals 400 and 401 denote demultiplexers. The demultiplexers 400 and 401 activate one of the 64 registers by inputting the control data 201 and the index data 202, and read the image division pattern stored as the laser light drive pattern from the activated register. I do.
[0016]
The semiconductor laser element 111 is driven by a modulation signal (image division pattern) output from the light modulator 110 to emit laser light, and forms a potential latent image on a photoconductor (not shown).
[0017]
In addition to the index data 202, the light modulation unit 110 receives control data 201 from the signal generation unit 200 as described above. The light modulation unit 110 uses the pixel division pattern supplied to the semiconductor laser element 111 in accordance with the control data 210. Change the bank. The selection of the bit pattern registration register group in the light modulation unit 110 outputs 16 types of bit pattern signals (see FIG. 2) by inputting the 4-bit index data 202 sent from the image data generation unit 150. Then, it is supplied to the semiconductor laser element 111. Further, the bank consisting of 16 registers is switched based on the bank control data 201. In this embodiment, the bit pattern registration register group is configured to use four banks, but the present invention is not limited to this.
[0018]
The recording unit 100 is provided with a scanning system, an optical system, a developing system, and the like for scanning the laser beam from the semiconductor laser element 111, but these are not important for the description of the present embodiment. They are omitted. In FIG. 1, BD indicates the output of a beam detector (BD) that detects the laser beam emitted from the semiconductor laser element 111 and scanned at the scanning end of one line, and scans the laser beam for each scanning of the laser beam. It detects the timing and outputs a horizontal sync signal.
[0019]
Next, the configuration of the image data generation unit 150 that outputs the index data 202 to the recording unit 100 to control image recording will be described. The image data generation unit 150 generates image data to be recorded in accordance with commands and data from an external device.
[0020]
Reference numeral 151 denotes an interface portion (hereinafter referred to as I / F) with an external device such as a host computer. A CPU 152 controls the operation of the entire printer in accordance with a control program stored in the ROM 153. The ROM 153 stores a control program for the CPU 152 and various data. In addition to final bit image development, this control program stores many processing programs such as interpretation and conversion of recording data, control of the recording unit 100, and man-machine interface control. The ROM 153 stores character font data and the like. A main memory (RAM) 154 stores data received from an external device, and stores parameters for calculation. Used as a temporary processing area for intermediate processing data. Therefore, the CPU 152 processes the commands and data received by the interface unit 151 based on the control program stored in the ROM 153 according to the above description of each unit, and finally develops the image data in the page memory 160 as image data.
[0021]
The print data received by the I / F 151 is developed into index data (here, 4 bits / pixel) based on the dither matrix 155 and font data registered in the ROM 153 and stored in the page memory 160. This index data 202 is input data (4 bits) of the light modulation unit 110. Reference numeral 161 denotes a FIFO memory that sequentially holds 4-bit index data 202 read from the page memory 160 and outputs it to the recording unit 100 in first-in first-out.
[0022]
Here, in the page memory 160, two independent memory accesses, that is, the writing of the index data 202 and the data reading based on the reading request of the index data 202 requested from the recording unit 100 occur. If the two memory accesses conflict with each other, the index data 202 is normally read out and not sent to the recording unit 100, and normal recording is not performed. Physically, when the page memory 160 is not a dedicated individual element but is shared with other memories, more memory access occurs due to data processing prior to image processing. It gets even more serious.
[0023]
Therefore, in this embodiment, the index data 202 is temporarily stored in the FIFO 161 so that the index data 202 can be sent to the recording unit 100 in a form that matches the recording timing while avoiding memory access contention to the page memory 160. Yes. In this way, the transfer timing of the index data 202 to the recording unit 100 is shifted by the FIFO 161 so that the index data 202 is reliably output to the recording unit 100 in accordance with the synchronization signal of the pixel and beam scanning.
[0024]
FIG. 2 is a diagram showing each bit pattern specified by the control data 201 and the index data 202 in the bit pattern registration register. Each bit pattern shown in the figure is stored in each bit pattern registration register corresponding to each data 201 and 202.
[0025]
In each stored bit pattern, the laser beam is driven when each bit constituting the bit pattern is 1, and is turned off when it is 0. Then, it is used as a drive signal sequentially from the upper bits, and finally the least significant bit is used.
[0026]
According to the present embodiment, the memory amount required for the 2-bit control data 201 is saved from the page memory 160. The waveform generated by the bit pattern registered in each bank corresponding to the control data 201 is a central growth pulse whose pulse width increases with an increase in the index data value for each of the four banks, and its inverted waveform, Four settings are left-justified waveform and right-justified waveform. Although the waveforms generated here are different, the pulse grows thicker as the input index data 202 increases.
[0027]
In this embodiment, the waveforms on the bit pattern registration register are simply connected and shown as a monotonically increasing pulse waveform registered. However, in order to perform electrophotographic characteristic correction, smoothing, etc., bit patterns that are not actually continuously lit may be registered.
[0028]
In FIG. 2, when the control data 201 is “00”, a left-justified waveform (waveform in which the number of 1 bits increases from the left side) is shown, and when the control data 201 is “01”, a right-justified waveform (1 bit from the right side) When the control data 201 is “10”, it indicates a center growth waveform (a waveform in which the number of 1 bits increases from the center of the pixel), and the control data 201 indicates “ 11 "indicates an inverted waveform of the center growth waveform (a waveform in which the number of 1 bits increases from both sides).
[0029]
FIG. 3 is a block diagram showing a detailed configuration of the signal generator 200 that generates the control data 201. In the figure, reference numerals 210 and 211 denote a main scanning period register and a sub scanning period register, respectively. Here, periods up to a maximum value K and a maximum value M are set, respectively. Here, for example, the period is set in the main scanning period register 210 and the sub-scanning period register 211 in accordance with the period of the halftone processing of the image data generation unit 150. Reference numerals 212 and 213 are both n-ary counters that count the clock input according to the value set to the n-ary input. That is, the pixel clock VDO is input to the clock input of the n-ary counter 212, and a repetition cycle in the main scanning direction is generated. The n-ary counter 213 receives the scanning synchronization signal BD and generates a repetition cycle in the sub-scanning direction. As described above, the scan synchronization signal BD is generated and supplied every time one scan of the laser beam is detected in the recording unit 100. The pixel clock VDO is a pixel synchronization signal for sending the index data 202 from the image data generation unit 150.
[0030]
Each of 214 and 215 is a demultiplexer that selects the row and column of the register of the register group 250 storing the control data 201 in accordance with the output values of the n-ary counter 212 and the n-ary counter 213. In response to the outputs of these demultiplexers 214 and 215, the output of the only register in which both the column and the row are active is selected from the register group 250, and the value stored in this register is the control data output unit. 216 and output to the optical modulator 110 as control data 201. The register group 250 is composed of a total of K × M registers in which control data 201 is set. The register group 250 includes various setting write signal lines in addition to the row and column selection lines and the output line of the control data 201, but these are omitted here for simplicity. . In the present embodiment, since the input of the control data 201 of the optical modulation unit 110 is 2 bits, each register of the register group 250 is a 2-bit register. In the laser beam printer according to the present embodiment, the value of the control data 210 is set in advance in each of the register groups 250 before the recording operation is performed.
[0031]
The n-ary counters 212 and 213 select one register from the K × M register group 250 for each pixel, and the set value of the selected register is output to the optical modulation unit 110 as control data 201. Is done. As a result, the light modulator 110 changes the bank of pulse signals.
[0032]
4A and 4B show an example of correspondence between the halftone dot processing pattern in the image data generation unit 150 and the register value (control data value) set in the register group 250. FIG. According to the present embodiment, the size of the dot processing matrix is set to 4 × 4, and this pattern starts to grow as the density value increases, and the growth of the pixel of the next rank is started when the pattern has grown. This order follows the order of numbers assigned to each element shown in FIG.
[0033]
In the signal generation unit 200 that outputs the control data 201, banks are set in the same cycle as the image data processing, and the bank setting of each pixel corresponding to the dot processing is shown in FIGS. 4A and 4B. It becomes such an arrangement.
[0034]
Since the growth order of the halftone processing shown in the present embodiment is simple, the values of the banks shown in FIG. 4B are in the same numerical order for each scanning row.
[0035]
Further, when the halftone dots are inclined in consideration of human visual characteristics, or when the angle of the halftone dots is changed for each color plate in the color printing process, the arrangement becomes more complicated.
[0036]
By applying the rule that each growth pixel is saturated and the next pixel is grown with the growth order and bank arrangement of the pixels as shown in FIGS. Other than the characteristic correction pattern, the growth does not include an isolated pixel pulse.
[0037]
FIG. 5 is a diagram showing an example of a threshold table for pixel data input in order to satisfy the law that the next pixel is grown after each growth pixel is saturated. The growth pixel in the growth order shown in FIG. 4A has a threshold table as shown in FIG. 5 for each density. By converting the input density value into a pulse width according to this threshold value table, if the same density is input to all of the halftone processing matrix, the halftone dot is generated only by continuous drawing. By drawing in such a form that the drawing area is tightly solidified, drawing with high gradation stability can be performed.
[0038]
The index data 202 generated in the page memory 160 is temporarily stored in the FIFO 161 in units of columns. The update of the pulse width information of the pixel thus stored and the count-up of the bank selection information are executed at the same timing, and are input to the light modulation unit 110 in a synchronized state, and are drawn and output.
[0039]
FIG. 6 is a flowchart showing a control process performed by the CPU 152 of the image data generation unit 150 according to the present embodiment. A program for executing this process is stored in the ROM 153.
[0040]
First, in step S1, print data is input via the interface unit 151. In step S2, the received print data is stored in the reception buffer of the main memory 154. In step S3, a halftone dot pattern for processing the image data of the print data is set, and control data corresponding to the halftone dot pattern is set (stored) in each register of the register group 250 (step S4). ). In this step S4, the control data is set in each register of the register group 250 by selecting each register from the CPU 152 via the demultiplexers 214 and 215 shown in FIG. This is done by writing data through lines and control lines.
[0041]
In step S5, the main scanning and sub-scanning register setting values corresponding to the number of pixels in the main scanning and sub-scanning directions are obtained based on the input print data, and are set in the registers 210 and 211, respectively. . In step S6, the print data stored in the reception buffer is developed into image data and stored in the page memory 160, and the printing operation is started in step S7.
[0042]
Thereafter, 4-bit pixel data is read from the page memory 160 in synchronization with the pixel clock VDO, stored in the FIFO 161, and transferred to the optical modulation unit 110 in synchronization with the pixel clock VDO. . The optical modulation unit 110 drives the semiconductor laser element 111 based on the input 4-bit pixel data and the 2-bit control data 201 supplied from the signal generation unit 200 according to the pixel position. The pixel division pattern is generated to drive the semiconductor laser element 111.
[0043]
Note that the present invention can be applied to a system (for example, a copier, a facsimile machine, etc.) composed of a single device even if it is applied to a system composed of a plurality of devices (for example, a host computer, interface device, reader, printer, etc.). May be.
[0044]
Another object of the present invention is to supply a storage medium (or recording medium) on which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or apparatus, and to perform computer (or CPU or MPU) of the system or apparatus. ) Is also achieved by reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. This includes a case where part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.
[0045]
Further, after the program code read from the storage medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is determined based on the instruction of the program code. The case where the CPU of the expansion card or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing is also included.
[0046]
When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the flowchart described above (shown in FIG. 6).
[0047]
As described above, according to the present embodiment, an increase in the capacity of a page memory that stores pixel data having the number of bits corresponding to the number of gradations is suppressed, and print data including control information such as bank information of the pixel data is stored. Can be generated and stored.
[0048]
As a result, even with the same page memory configuration, the drawing area becomes dense, and drawing processing that improves printing stability is possible, and the image quality of the printed image is improved.
[0049]
【The invention's effect】
As described above, according to the present invention, it is possible to suppress the use capacity of a memory used when forming image data.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration example of an image processing apparatus according to an embodiment of the present invention.
FIG. 2 is a waveform diagram of a pixel division pattern output in accordance with index data and control data in the light modulation unit according to the embodiment of the present invention.
FIG. 3 is a block diagram showing a configuration of a signal generator according to the embodiment of the present invention.
FIG. 4 is a diagram illustrating a correspondence between a halftone dot processing pattern (A) and a register value (B) set in a register unit in the embodiment of the present invention.
FIG. 5 is a diagram showing an example of a threshold table corresponding to pixel values according to the embodiment of the present invention.
FIG. 6 is a flowchart showing a control process by the CPU of the image processing apparatus according to the embodiment of the present invention.
FIG. 7 is a diagram illustrating a bit pattern registration register group.

Claims (2)

An image forming apparatus that forms a gradation image based on multi-value image data ,
Means for generating index image data representing pixel values of the multi-value image data in 4 bits ;
First storage means for storing control data corresponding to the positions of pixels formed based on the multi-value image data;
First reading means for reading control data from the first storage means in synchronization with scanning for image formation;
Second storage means for storing a binary bit string for each combination of 4-bit index values 0 to 15 and control data stored in the first storage means;
Second reading means for reading a binary bit string corresponding to a combination of the control data read by the first reading means and the pixel value of the index image data from the second storage means;
Image forming means for forming an image by scanning laser light emitted according to the binary bit string read by the second reading means ;
The second storage means is
As a binary bit string corresponding to the control data 00 stored in the first storage unit, a binary bit string for growing each pixel formed by the image forming unit from the left side of each pixel in the scanning direction is stored.
As a binary bit string corresponding to the control data 01 stored in the first storage unit, a binary bit string for growing each pixel formed by the image forming unit from the right side of each pixel in the scanning direction is stored.
As a binary bit string corresponding to the control data 10 stored in the first storage unit, a binary bit string for growing each pixel formed by the image forming unit from the center of each pixel in the scanning direction is stored.
As a binary bit string corresponding to the control data 11 stored in the first storage unit, a binary bit string for growing each pixel formed by the image forming unit from both sides of the pixel in the scanning direction is stored.
Any binary bit string stored by the second storage means is a binary bit string that grows pixels more as the index value corresponding to the binary bit string increases.
The image forming apparatus, wherein the image forming means drives the laser beam when the bit in the binary bit string is 1, and turns off the laser beam when the bit is 0 . An image forming method performed by an image forming apparatus that forms a gradation image based on multi-value image data ,
A generating unit included in the image forming apparatus generating index image data expressing pixel values of the multi-valued image data in 4 bits ;
A first storage step in which a first storage unit included in the image forming apparatus stores control data corresponding to a position of a pixel formed based on the multi-value image data;
A first reading step in which a first reading unit included in the image forming apparatus reads control data from the first storage unit in synchronization with scanning for image formation;
The second storage unit included in the image forming apparatus stores a binary bit string for each combination of each of the 4-bit index values 0 to 15 and each control data stored in the first storage unit. A second storage step;
A second reading unit included in the image forming apparatus reads a binary bit string corresponding to a combination of the control data read in the first reading step and the pixel value of the index image data from the second storage unit. A second reading step;
An image forming step in which an image forming unit included in the image forming apparatus scans a laser beam emitted according to the binary bit string read in the second reading step to form an image;
With
The second storage means is
As a binary bit string corresponding to the control data 00 stored in the first storage unit, a binary bit string for growing each pixel formed by the image forming unit from the left side of each pixel in the scanning direction is stored.
As a binary bit string corresponding to the control data 01 stored in the first storage unit, a binary bit string for growing each pixel formed by the image forming unit from the right side of each pixel in the scanning direction is stored.
As a binary bit string corresponding to the control data 10 stored in the first storage unit, a binary bit string for growing each pixel formed by the image forming unit from the center of each pixel in the scanning direction is stored.
As a binary bit string corresponding to the control data 11 stored in the first storage unit, a binary bit string for growing each pixel formed by the image forming unit from both sides of the pixel in the scanning direction is stored.
Any binary bit string stored by the second storage means is a binary bit string that grows pixels more as the index value corresponding to the binary bit string increases.
In the image forming step, the laser beam is driven when the bit in the binary bit string is 1, and the laser beam is turned off when the bit is 0 .

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