JP2001358943A - Image processing method and image processing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing unit that can obtain a recording image with high quality by a high-speed processing. SOLUTION: In the case of converting quaternary image data with a data resolution of 600 dpi into binary image data with an engine resolution of 1,200 dpi, 4-stages of thresholds are set to one pixel because of a relation of (1,200 dpi/600 dpi)×(1,200 dpi/600 dpi)=4. That is, one pixel with a resolution of 600 dpi is divided into 2×2 areas with a resolution of 1,200 dpi and number of recorded pixels is decided depending on a gray scale level to more finely express the gray scale.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image processing method and an image processing apparatus for performing binarization.

[0002]

2. Description of the Related Art Conventionally, as this kind of image processing method, a method using an image processing apparatus as shown in FIG. 11 is generally used.

FIG. 11 shows a print controller 1101.
And a dot matrix type printer 1100 such as a laser beam printer or an ink jet printer including a print engine 1102. In such a page printer, from the host computer 1103,
Inputting vector data such as figures and characters,
In step 04, the data is converted into raster data composed of a set of pixels (dots), and is expanded in the page memory 1105 for one page. Then, printing is performed by attaching toner or ink to the recording material based on the raster data.

[0004]

However, the above-mentioned prior art has the following problems. (1) By increasing the resolution of the image data input from the host computer, or by inputting the image data having the increased resolution in the host computer,
Even if an attempt is made to improve the image quality, the higher the resolution, the longer the processing time for developing the image data in the page memory. (2) To reduce the processing time, a method of simply binarizing multi-valued data having an intermediate density can be considered. For example,
As shown in FIG. 12, a resolution of 600 dp as shown in FIG.
The original quaternary image of i is converted to a density value 0 as shown in FIG.
1 is set as a threshold, and 0 is set when the density of a certain pixel is 01 or less, and 1 is set when the density is larger than 01. As a result, the converted image is as shown in FIG. In other words, what is expressed in N gradations by one pixel is converted into binary data of one pixel, so that the gradation information becomes (N / 2), and the print quality is remarkably deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art. It is an object of the present invention to provide an image processing method and an image processing apparatus capable of performing high-speed processing and obtaining a high-quality recorded image. To provide.

[0006]

In order to achieve the above object, a method according to the present invention comprises the steps of: inputting multi-valued image data having a first resolution and developing the data into storage means; Reading the multi-valued image data and changing to binary image data having a second resolution larger than the first resolution and outputting the binary image data to the print engine, wherein the binarizing step includes: The multi-valued image data of one pixel is converted into binary data of a plurality of pixels, and the gradation of the multi-valued image is expressed by the number of recording pixels in the plurality of pixels.

[0007] The binarizing step is characterized in that quaternary image data of one pixel is converted into binary image data of 2 × 2 pixels.

The binarization step is characterized in that one-pixel quaternary image data is converted into binary image data of four pixels in the main scanning direction and one pixel in the sub-scanning direction.

In order to achieve the above object, a storage medium according to the present invention comprises: a multi-valued image data having a first resolution; A computer-readable program storing an image processing program including: reading image data; and changing the binary image data into binary image data having a second resolution greater than the first resolution and outputting the binary image data to a print engine. In the memory, the binarizing step converts multi-valued image data of one pixel into binary data of a plurality of pixels, and expresses the gradation of the multi-valued image by the number of recording pixels in the plurality of pixels. It is characterized by the following.

[0010] The binarizing step is characterized in that one-pixel quaternary image data is converted into 2x2 pixel binary image data.

The binarization step is characterized in that one-pixel quaternary image data is converted into four-pixel binary image data in the main scanning direction and one pixel in the sub-scanning direction.

In order to achieve the above object, an apparatus according to the present invention comprises a storage means for expanding and storing multi-valued image data having a first resolution, and reading the multi-valued image data from the storage means. Binary output means for outputting binary image data of a second resolution which is greater than one resolution and outputting the binary image data on a recording material based on the binary image data output from the binary output means. And a print engine for recording an image in the plurality of pixels, wherein the binarization output means converts multi-valued image data of one pixel into binary data of a plurality of pixels, and converts the number of pixels according to the number of recording pixels in the plurality of pixels. It is characterized by expressing the gradation of a multi-valued image.

The binarized output means converts one pixel of quaternary image data into 2 × 2 pixel binary image data.

The binarized output means converts one pixel of quaternary image data into binary image data of four pixels in the main scanning direction and one pixel in the sub-scanning direction.

[0015]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the relative arrangement of components described in this embodiment, formulas, numerical values, etc., unless otherwise specified,
It is not intended to limit the scope of the present invention only to them.

(First Embodiment) First, a printer as a first embodiment of an image processing apparatus according to the present invention will be described with reference to FIGS.

FIG. 1 is a block diagram showing a schematic configuration of a printer according to the present embodiment. The printer 100
Print controller 101 and print engine 102
And from the host computer 103,
The input vector data such as figures and characters are converted into raster data composed of a set of pixels (dots), and are developed in the page memory 105 for one page. When the raster data is output from the page memory 105, the conversion unit 104 converts the raster data into high-resolution binary data, and the print engine 102 prints toner or ink on a recording material based on the converted binary data. Printing is performed by attaching.

FIG. 2 is a diagram showing the binarization processing of the multi-valued image in the conversion unit.

In this embodiment, as an example, quaternary image data with a data resolution of 600 dpi is converted to an engine resolution of 1
A process of converting the image data into binary image data of 200 dpi is shown.

The print engine of this apparatus can print up to an engine resolution of 1200 dpi. Therefore, when binarizing a quaternary image with a resolution of 600 dpi, (1200
dpi / 600 dpi) x (1200 dpi / 600d)
With pi) = 4, four levels of threshold values can be set for one pixel. That is, one pixel of 600 dpi is set to 1
By dividing into 2 × 2 areas of 200 dpi and determining the number of recording pixels according to the density level, it is possible to express the density more finely.

Hereinafter, the algorithm of the resolution conversion processing will be described with reference to the flowcharts shown in FIGS.

First, when print data is received from the host computer in step S11, the print data is analyzed by a drawing processing unit (not shown) in the apparatus, and rasterized into raster data. This data is used in step S13 for RAS_source [x] [y]
To be stored. (X indicates the pixel number in the main scanning direction, and y indicates the pixel number in the sub-scanning direction.) Next, in step S14, the resolution of the print data is obtained.
Store in D_rsl. In step S15, the resolution that the engine can take is acquired and stored in P_rSl [K] (K is the number of possible values, and the data is stored in ascending order). Then, step S
In step 16, the variable n is initialized, and in step S17, the engine resolution P_rsl [n] is compared with the data resolution D_rsl. If the data resolution is larger, the variable n is incremented in step S19 to retrieve the next possible resolution, and the process returns to step S17. If the possible engine resolution is equal to or higher than the data resolution in step S17, the engine resolution E_rsl is determined in step S18.
Set to. Further, in step S20, the width (Ras_wd) and the height (Ras_ht) of the raster data being developed are acquired.

In step S21 of FIG. 4, the number of gradations of the original raster data is obtained and set to Ras_bpp. In step S22, a coordinate enlargement ratio is obtained from the engine resolution and the data resolution, and is set as Ext_cnt. Step S23
Then, the number of divisions of the original pixel (the number of thresholds used in binarization) is obtained and set as Level_cnt. In steps S24 to S27, Level_cnt threshold values for the original density are obtained. In a step S24, a variable n is initialized, and in a step S25, a threshold is calculated from the lower density. That is, a range obtained by dividing the original gradation number Ras_bpp by the division number Level_cnt is set as a range, and a value obtained by adding this value to the immediately preceding threshold value is set as the next threshold value. This is repeated for the threshold number, and each value is Leve
Store in l_shd [n]. When all the thresholds have been obtained, in step S28 the engine transmission buffer RAS_d_es
get t. The size is (number of main scanning lines after resolution conversion) x (enlargement ratio in the sub-scanning direction), and the processing result for one main scanning of the original raster data is stored here.

Next, the process proceeds to step S29 in FIG. 5, in which a variable v (sub-scanning direction) used for specifying the pixel position of the raster data and h (main scanning direction) are initialized in step S30.

In step S31, v is compared with the height of the original raster data to determine whether or not it is the last line of the sub-scan. When the processing of the last line is completed, the processing ends. Next, in step S32, h is compared with the width of the original raster data to determine whether or not it is the last pixel in the main scanning. If it is the last pixel, the converted pixel stored in RAS_dest is sent to the engine in step S33, and the sub-scanning of the original raster data is incremented in step S34, and the process proceeds to step S30.
Return to If it is not the last pixel, a variable 1cnt for counting the number of evaluations of the threshold is initialized in step S35,
Buffer RAS_ for storing the converted pixel in step S36
A variable xcnt indicating the position of dest in the main scanning direction is initialized, and y indicating the position in the sub-scanning direction is similarly set in step S37.
Initialize cnt.

In step S38, the density of the original raster data at the coordinate position (hv) is compared with the lcnt-th threshold Level_shd [kcnt] of a predetermined threshold group. [xcnt] and [ycnt] are set to 1 (ON), and 0 (OFF) if they are the same or lower.

In step S41, 1cnt is set to the threshold number Level_
When the comparison with all the thresholds is completed, the position of the original raster data in the main scanning direction is incremented in step S42, and the process returns to step S32. If there is still a threshold to be compared, the threshold count is incremented in step S43, and it is determined in step S44 whether or not the last line of the buffer. In the case of the last line, xcnt is incremented in step S46 to increment the buffer. The position in the main scanning direction is increased by 1, and the process returns to step S37.
If it is not the last line, ycnt is incremented and the process returns to step S38.

With the above processing, high resolution conversion is performed for each pixel of the original raster data, sent to the engine one main scan at a time, and the conversion is completed when all the lines have been converted.

By performing the above processing, the four-valued original print data is expanded in the page memory as the four-valued data, and is transmitted to the print engine as a video signal.
One value pixel is converted into 2 × 2 binary pixels. As a result, it is possible to minimize a decrease in print quality due to the binarization processing of multi-value data while avoiding an increase in data processing time due to an increase in resolution of the original data.

(Second Embodiment) Next, FIGS.
The second embodiment of the present invention will be described with reference to FIG.

For example, in a laser beam printer, print data sent from a host computer is developed by a print controller into raster data which is a set of pixel data. A video signal is generated based on the raster data, and is converted into a drive signal for controlling ON / OFF of the laser beam. A laser beam emitted based on the laser drive signal (video signal) is applied to a photosensitive drum that has been charged in advance with negative charges.

First, a laser beam is scanned over the photosensitive drum in a direction parallel to the drum (main scanning). When scanning of this line is completed, the next line is scanned.
The start position of the main scanning is shifted in a direction perpendicular to the drum by rotating the photosensitive drum (sub-scanning). When the laser beam scans over the charged photosensitive drum, the electric charge in the portion irradiated with the laser beam disappears, so that a potential difference is generated between the portion not irradiated with the laser beam and a latent image having the same shape as the raster data is formed. .

Further, a visible image is formed by depositing a toner having a positive charge on the drum having the latent image, and the image recording is completed by transferring the visible image to a recording material. .

The number of pixels that can be expressed per unit area on the drum is called "engine resolution". The engine resolution in the main scanning direction is determined by the interval at which the laser light is turned on / off, and the engine resolution in the sub-scanning direction is determined by the unit rotation angle of the photosensitive drum.

Normally, in a color printing apparatus, it is possible to process a plurality of bits of image information (multi-valued information) for one pixel, that is, to change the density of a pixel according to the level of the image information. . At this time, as the density expression, a method of expressing the density by changing the intensity of the laser light, and changing the irradiation time while keeping the intensity of the laser light constant, changing the density by changing the toner adhesion area of each pixel. There is a way to express.

In normal printing, optimal print quality is maintained when output is performed at an engine resolution that matches the data resolution. In the case of a monochrome printing apparatus that cannot perform printing at an intermediate density in pixel units, it is necessary to increase both the data resolution and the engine resolution in order to improve the printing quality.
At this time, the resolution in the main scanning direction is ON / OFF of the laser beam.
The effect on the engine speed can be said to be relatively small because it can be electrically changed by controlling the interval.However, when increasing the resolution in the sub-scanning direction, the drum rotation angle becomes smaller, so the engine speed becomes slower and the printing time becomes shorter. It has a significant effect. Therefore, in a printing apparatus capable of printing at different resolutions in the main scanning direction and the sub-scanning direction, when performing high-resolution conversion, increase the resolution in a direction that does not affect the engine speed, and do not change the resolution in the scanning direction that affects the engine speed. Each pixel is arranged.

Specifically, in the present embodiment, in a device capable of having different engine resolutions in the main scanning direction and the sub-scanning direction, as shown in FIG. A conversion process is performed in which the resolution in the scanning direction is 600 dpi, which is the same as the original data, and the resolution in the main scanning direction is 2,400 dpi.

The algorithm of the resolution conversion processing according to the present embodiment will be described with reference to the flowcharts of FIGS. Steps for performing the same processing as in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In step S55 of FIG. 7, an engine resolution group P_rslX that can be set in the main scanning direction is acquired. In step S56, a variable n is initialized, and in step S17, the engine resolution P_rslX [n] and the data resolution D_rsl
Compare. If the data resolution is larger, the variable n is incremented in step S59 to return to the next possible resolution, and the process returns to step S57. Step S57
In step S58, the engine resolution in the main scanning direction is set to E_rslX in step S58 if the possible engine resolution is found to be equal to or higher than the data resolution.

Next, the process proceeds to step S60 in FIG. 8, and it is determined whether or not a resolution different from the main scanning direction can be set in the sub-scanning direction. If the resolution cannot be set, the same value as the resolution in the main scanning direction is set as the resolution in the sub-scanning direction in step S61, and the process proceeds to step S66. If it can be set in step S60, the variable n is initialized in step S62,
The engine resolution P_rslY [n] that can be set in 63 is compared with (data resolution / double printing speed value), that is, (D_rsl / SPCntl).

If the data resolution is larger, the variable n is incremented in step S64 to retrieve the next possible resolution, and the process returns to step S63. Step S23
In step S65, the engine resolution in the sub-scanning direction is set to E_rslY in the case where the engine resolution that can be obtained in step S5 is equal to or higher than (data resolution / printing speed double speed value). In step S66, the width (Ras_wd) and the height (Ras_ht) of the raster data developed are acquired.

Further, the process proceeds to step S67 in FIG. 9, and the number of gradations of the original raster data is obtained and set to Ras_bpp. In steps S68 and S69, the coordinate enlargement ratio in each direction is determined from the engine resolution and the data resolution, and is set as Ext_cntX and Ext_cntY. In step S70, the number of divisions of the original pixel (the number of thresholds used in binarization) is obtained and set as Level_cnt. Step S71 to step S7
In step 4, Level_cnt thresholds for the original density are obtained. In step S71, a variable n is initialized, and in step S7
In step 2, the threshold is calculated from the lower density. That is, a range obtained by dividing the original gradation number Ras_bpp by the division number Level_cnt is set as a range, and a value obtained by adding this value to the immediately preceding threshold value is set as the next threshold value. Repeat this for the number of thresholds and set each value to Level_sh
Stored in d [n]. When all thresholds have been obtained, an engine transmission buffer RAS_dest is obtained in step S75. The size is (number of main scanning lines after resolution conversion) x
(Enlargement ratio in the sub-scanning direction) stores the conversion processing result for one main scan of the original raster data.

Proceeding to FIG. 10, the processes of steps S36 to S53 are performed as in the first embodiment, except that step S50 is followed by step S76.
To determine whether the current line is the last line of the buffer RAS_dest by comparing the coordinate expansion rate Ext_cntY in the sub-scanning direction with ycnt.

With the above processing, high resolution conversion is performed only in the main scanning direction for each pixel of the original raster data, sent to the engine one main scanning at a time, and the processing is terminated when all the lines have been converted.

As described above, in a device capable of printing at different resolutions in the main scanning direction and the sub-scanning direction, when performing high-resolution conversion, the resolution in a direction that does not affect the engine speed is increased, and the resolution in the scanning direction that affects the engine speed is increased. By arranging the pixels so as not to change the printing speed, it is possible to avoid a decrease in printing speed due to an increase in resolution at the time of output.

(Other Embodiments) Even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus including one device (For example, a copying machine, a facsimile machine, etc.).

Further, an object of the present invention is to supply a storage medium (or a recording medium) in which program codes of software for realizing the functions of the above-described embodiments are recorded to a system or an apparatus, and to provide a computer (a computer) of the system or the apparatus. It is needless to say that the present invention can also be achieved by a CPU or an MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. Also,
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also the operating system (OS) running on the computer based on the instructions of the program code.
It goes without saying that a case where the functions of the above-described embodiments are implemented by performing some or all of the actual processing, and the processing performs the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the program code is read based on the instruction of the program code. Needless to say, the CPU included in the function expansion card or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

When the present invention is applied to the above-mentioned storage medium, the storage medium described above (FIGS. 3 to 5 and //
Alternatively, a program code corresponding to the flowchart (shown in FIGS. 7 to 10) is stored.

[0050]

As described above, according to the present invention,
It is possible to provide an image processing method and an image processing apparatus that can perform high-speed processing and obtain a high-quality recorded image.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a printer according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating data conversion according to the first embodiment of the present invention.

FIG. 3 is a flowchart illustrating an algorithm of a data conversion process according to the first embodiment of the present invention.

FIG. 4 is a flowchart illustrating an algorithm of a data conversion process according to the first embodiment of the present invention.

FIG. 5 is a flowchart illustrating an algorithm of a data conversion process according to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating data conversion according to a second embodiment of the present invention.

FIG. 7 is a flowchart illustrating an algorithm of a data conversion process according to the second embodiment of the present invention.

FIG. 8 is a flowchart illustrating an algorithm of a data conversion process according to the second embodiment of the present invention.

FIG. 9 is a flowchart illustrating an algorithm of a data conversion process according to the second embodiment of the present invention.

FIG. 10 is a flowchart illustrating an algorithm of a data conversion process according to the second embodiment of the present invention.

FIG. 11 is a block diagram illustrating a schematic configuration of a conventional printer.

FIG. 12 is a diagram illustrating an example of conventional data conversion.

Claims (9)

[Claims] 1. A storage step of inputting multi-value image data having a first resolution and developing the same in a storage means, reading the multi-value image data from the storage means, and providing a second resolution which is larger than the first resolution. And a binarizing step of outputting to the print engine while changing the binary image data to the binary image data. The binarizing step converts multi-valued image data of one pixel into binary data of a plurality of pixels, An image processing method, wherein the gradation of the multi-valued image is expressed by the number of recording pixels in the plurality of pixels. 2. The image processing method according to claim 1, wherein the binarizing step converts the quaternary image data of one pixel into binary image data of 2 × 2 pixels. 3. The method according to claim 1, wherein the binarizing step converts the quaternary image data of one pixel into binary image data of four pixels in the main scanning direction and one pixel in the sub-scanning direction. Image processing method. 4. A program code for a storage step of inputting multi-valued image data having a first resolution and developing the same in a storage means, reading the multi-valued image data from the storage means, and providing more than the first resolution. A computer readable memory storing an image processing program including: a program code of a binarization process for outputting to a print engine while changing to binary image data of a second resolution; A computer-readable memory that converts multi-valued image data of pixels into binary data of a plurality of pixels, and expresses the gradation of the multi-valued image by the number of recording pixels in the plurality of pixels. 5. The computer readable memory according to claim 4, wherein said binarizing step converts one pixel of quaternary image data into 2 × 2 pixel binary image data. 6. The method according to claim 4, wherein the binarizing step converts the quaternary image data of one pixel into binary image data of four pixels in the main scanning direction and one pixel in the sub-scanning direction. Computer readable memory. 7. A storage means for expanding and storing multi-valued image data having a first resolution, and reading the multi-valued image data from the storage means, and storing binary data of a second resolution which is larger than the first resolution. A binary output means for outputting while changing to image data; and a print engine for recording an image on a recording material based on the binary image data output from the binary output means. The binary output means converts multi-valued image data of one pixel into binary data of a plurality of pixels, and expresses the gradation of the multi-valued image by the number of recording pixels in the plurality of pixels. Image processing apparatus. 8. An image processing apparatus according to claim 7, wherein said binarization output means converts one-pixel quaternary image data into 2 × 2 pixel binary image data. 9. The apparatus according to claim 7, wherein said binarization output means converts the quaternary image data of one pixel into binary image data of four pixels in the main scanning direction and one pixel in the sub-scanning direction. The image processing apparatus according to any one of the preceding claims.