JP2002103683A - Apparatus and method for forming image as well as storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method for forming an image capable of obtaining a recording agent mounting amount reducing effect of a toner or the like without impairing a given image quality even in any output level range corresponding to a density level of a pixel in a recording agent saving mode and a storage medium. SOLUTION: In a conventional recording agent saving mode, an output level corresponding to a density level of each pixel is simply suppressed to a predetermined rate. The method for forming the image comprises the steps of calculating an expecting density value obtained by multiplying an effective density level obtained in a normal mode by a descending rate discnt at each density level (step S33), and calculating the output level corresponding to the expecting density value from an inverse function of a device density characteristic function (step S34). Thus, the output level is suppressed along the device density characteristic function, and the recording agent mounting amount reducing effect is obtained in a total output level range.

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 such as a printer, an image forming method, and a storage medium, and more particularly to a technique for effectively saving a recording agent such as toner and ink.

[0002]

2. Description of the Related Art In a dot matrix type page printer such as a so-called laser beam printer or ink jet printer, vector data such as figures and characters are converted into raster data composed of a set of pixels (dots), and one page of data is converted. Expand to internal memory space. Then, the raster data is printed by attaching a recording agent such as toner or ink to a specific position on a recording medium (for example, recording paper).

A more specific description will be given by taking a laser beam printer as an example.

[0004] Print data sent from the host computer is expanded into raster data by a printer controller. The number of pixels constituting the raster data that is assumed to exist per unit area is called “data resolution”.

[0005] Based on the raster data, the O
A drive signal (video signal) for controlling N / OFF is created.

[0006] A laser beam emitted based on the laser drive signal (video signal) is applied to a photosensitive drum which has been charged with a negative charge in advance. 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 occurs between the portion and the portion not irradiated with the laser beam, and a latent image having the same shape as the raster data is formed. A visible image is formed by depositing a positively charged toner on the drum having such a latent image.

There are two types of laser light scanning directions in the above-described printer, a first direction along the recording paper transport direction and a second direction orthogonal to the first direction. First, the photosensitive drum is scanned by one line in the first direction (main scanning). When the scanning of this line is completed, in order to scan the next line, the photosensitive drum is rotated to shift the start position of main scanning, and scanning is performed in the second direction (sub-scanning).

As a result, a latent image is formed on the recording paper. Here, the number of pixels that can be expressed per unit area on the photosensitive drum is called “engine resolution”. The engine resolution in the main scanning direction (first direction) is as follows.
It is determined by the N / OFF interval. The engine resolution in the sub-scanning direction (second direction) is determined by the rotation angle of the photosensitive drum.

Incidentally, the amount of information held by each pixel of the raster data differs depending on how many bits of information are given to one pixel. Generally, in the case of a color printer, a plurality of bits are processed with one pixel having image information (that is, multi-valued information). Therefore, a printer controller that controls the color printer also processes multi-valued data. Further, the printer engine has a mechanism for realizing a multi-value recording method for expressing a plurality of gradations based on such multi-value data.

As a method of expressing a plurality of gradations, a method of expressing the density by changing the intensity of the laser light (density gradation method), changing the irradiation time while keeping the intensity of the laser light constant, A method of expressing the density by changing the toner adhesion area (area gradation method) is known.

In the case of a monochrome printer, print information is converted into binary data corresponding to ON / OFF of a laser beam, and the density and area of each pixel are always constant. Therefore, if the print data received from the host computer is multi-valued information, the monochrome printer
It is necessary to convert to binary data once. In such a case, a method is generally adopted in which a threshold value is provided for each pixel, and the threshold value is divided by comparing the pixel density with the threshold value.

When rasterizing input print data, if the number of gradations of the print data is high, the processing load on the controller increases. On the other hand, for example, in the case of the above-described density gradation method, it is actually difficult to express 256 gradations due to the characteristics of the electrophotographic process. Also, for example, in the case of the area gradation method described above,
If a large amount of toner is absorbed in a small area, there is a disadvantage that dots do not grow smoothly according to the pulse width.

In view of this, a process is provided for lowering high gradation data such as 24-bit full-color data and 8-bit monochrome multi-value data to an appropriate number of density levels in accordance with engine performance by using a multi-value dither method or the like. As a result, the processed pixel data is often converted into a number of density levels considered to be practically acceptable. The density level of these pixel data is set to 0 to 255 of the printer engine.
A corresponding value is defined as a video signal in association with a level (hereinafter, referred to as an output level).

(Method of Realizing Toner Saving Function) By the way, if the user desires test printing (so-called draft printing), instead of requesting the highest quality for the print result,
It is required to emphasize printing speed and reduce costs by minimizing toner consumption. For this reason, recent image forming apparatuses are provided with a normal mode that promises high-quality printing, and a mode that emphasizes printing speed and saves consumption of recording agent such as toner. The two modes can be switched according to the instruction. Here, the latter mode is referred to as a “recording material (toner) saving mode”, focusing on the aspect of saving the recording material.

In the toner saving mode, as a method of suppressing the amount of toner consumption, for example, (1) a method of reducing the number of lit pixels, and (2) a method of reducing the amount of applied toner in one pixel can be considered.

As a method (1) for reducing the number of lighting pixels, there is a method of masking an original image using a predetermined pattern. According to this method, the amount of toner consumption can be reliably reduced, but on the other hand, missing pixels are generated as compared with the original image data, so that the image quality is significantly deteriorated.

The method (2) for reducing the amount of applied toner in one pixel can be realized only in a printer having a multi-value recording method. In this case, the number of lit pixels in the original data is maintained as it is, utilizing the fact that the size or the density of a dot formed on one pixel changes depending on the density level of each pixel. Is set to a value lower than that during normal printing, the amount of applied toner is reduced. In this method, since there is no pixel thinning for the original data, deterioration of the image shape is small. Therefore, this method is adopted in a printer apparatus that handles multi-valued data, and toner can be saved by lowering the output level by a certain ratio with respect to normal printing.

[0018]

Although it is considered that each pixel on the page plane is theoretically arranged with square dots, a gap is opened because spherical toner adheres to a designated position. There will be overlapping round dots so that they do not overlap. For this reason, the number of lit dots and the area do not always change linearly, and the area change is sharp while the number of lit pixels is small, and the area change becomes gradual as the number of prime lights increases.

Also, when the intermediate density is expressed using the area gradation method, the change in the amount of applied toner is gradual with respect to the density level while the area is small, and the amount of applied toner increases as the area increases. Although the change becomes steep, the overlapping portion increases when the area reaches a certain size, so that there is a characteristic that the change in the amount of applied toner becomes gentle again. This characteristic is called "device (printer engine) density characteristic" of the printer device.

As described above, the method of reducing the amount of applied toner in one pixel is realized by suppressing the output level for one pixel. However, even if the output level is reduced uniformly for each density level as described above, the actual density (toner attachment area) does not change uniformly.

FIG. 11A shows an example of an output level and a printing result corresponding to each density level when the density level is converted into 2 bits (ie, quaternary). FIG. 3B shows that the output level corresponding to each density is the density characteristic curve of the device (printer engine) (the output level is 0).
FIG. 9 is a diagram showing where on an effective density (when the density is changed from 0 to 255). In the present specification, the “effective density” refers to a unit expressing the density of printing on a reflection original such as paper. The effective density generally means a value obtained by taking a minus log of the reflectance (irradiation light intensity / reflected light intensity). For example, when the reflectance is 1 (100 for irradiation 100
The effective density at the time of reflection (that is, at the time of all reflections) is -log ₁₀ 1 = 0. Conversely, low reflectivity, 0.0
The effective density at 1 (1 reflection at 100) is -log ₁₀ 0.0
1 = 2. As shown in FIG. 3A, the density level 0 (output level 0) corresponds to the effective density 0, and the density level 3 (output level 255) corresponds to the maximum value of the effective density.
The output levels corresponding to the density levels 1 and 2 are respectively
It can be seen that the output level is approximately 1/3 and 2/3 of the maximum output level 255.

The device density characteristic shown in FIG. 3B shows that the effective density change ratio differs depending on the output level. Therefore, even if the output level is reduced uniformly for each density level, the actual Density (toner adhesion area)
Does not change uniformly. As a result, the following problems are extracted. That is, (1) In the vicinity of the maximum output level, even if the output level is lowered, the effective density does not easily decrease from the maximum density level. (2) On the other hand, since the density is originally low near the minimum output level, when the output level is lowered, substantially no toner is applied. (3) In a high output level region, when a lighted pixel exists close to a target pixel, the effective density tends to be higher than when the lighted pixel is isolated. Therefore, when the pixels in the high output level area are densely packed, the amount of applied toner does not decrease much. (4) In a low output level region, when a lighting pixel is present close to a target pixel, the effective density tends to be lower than when the lighting pixel is isolated. Therefore, when the pixels in the low output level range are sparse, the toner is hardly applied.

For these reasons, there is a problem that the effect of reducing the amount of the recording material (toner) varies depending on the output level range and the state of the pixels.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to achieve a desired image quality in any output level range corresponding to the pixel density level in the recording material saving mode. It is an object of the present invention to provide an image forming apparatus, an image forming method, and a storage medium that can obtain an effect of reducing the amount of a recording agent such as toner without impairing the image quality.

[0025]

To achieve the above object, for example, an image forming apparatus of the present invention has the following arrangement. That is, a first image forming means for forming an image by depositing an amount of a recording material on a recording medium in accordance with a first output level corresponding to a density level of each pixel of the image forming data; A second image forming unit that replaces the output level with a second output level lower than the first output level, thereby forming an image while saving the consumption of the recording material. And an image forming apparatus for forming an image by selecting any one of the second image forming means, wherein the second image forming means includes the first output level and the first output level of the image forming apparatus. Density level conversion means for converting each output level corresponding to the density level of each pixel of the image forming data into an effective density level based on a density characteristic function indicating a correspondence relationship with the effective density level; Obtaining means for obtaining an expected density level with a bell reduced to a predetermined ratio; and converting the expected density level obtained by the obtaining means into the second output level based on an inverse function of the density characteristic function. Output level conversion means.

[0026]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of the image forming apparatus according to the embodiment.

As shown in FIG. 1, a laser beam printer (hereinafter, simply referred to as a “printer”) 100 as an image forming apparatus capable of performing color output includes a host computer 2.
A printer controller (hereinafter, simply referred to as a “controller”) 101 which analyzes print data, which is information including color multi-value information in a printer description language (PDL) input from 00, and outputs image data; Printer engine (hereinafter simply referred to as “engine”) for forming (printing) an image represented by the obtained image data on a predetermined recording medium (recording paper)
And a panel unit 103 for interfacing with a user and instructing the printer 100 to operate.
It is composed of

The controller 101 includes components described below, including a CPU 112, and each component is connected to a system bus 114 so that the CPU 112 can access the components.

The CPU 112 controls the components of the printer 100. This control is performed in the ROM 1
This is executed based on the control program stored in the control program 07. The control program stored in the ROM 107 is
An OS (Operating System) for performing time-division control on a load module basis called a task by a system clock, and a plurality of load modules that are executed and controlled on a function basis by the OS.
The control program including the load module is stored in an EEPROM (non-volatile memory) 113 as necessary. Note that, in addition to the control program, the ROM 107 stores a program corresponding to the flowchart shown in FIG. 4 and / or FIG. 6 (details will be described later), and a device density characteristic function of the engine 102. The RAM 110 is used as a work area for the arithmetic processing by the CPU 112.

The host I / F unit 105 includes an input buffer (not shown) for inputting print data sent from the host computer 200 and a host computer 200.
And an output buffer (not shown) for temporarily holding a signal to be sent to the host computer 200, and controls communication with the host computer 200.

The drawing processing unit 106 includes a host I / F unit 10
5 is analyzed (for example,
PDL analysis processing), and the engine 102
Expands to raster data that can be processed.

The image memory 108 stores the created image data. Reading of the image data stored in the image memory 108 is controlled by the DMA control unit 111, and the DMA control unit 111
The control for reading the image data from the
This is performed based on an instruction from U112.

The image data read from the image memory 108 is transferred to the engine 102 as a video signal via the engine I / F unit 109. Engine I / F
The unit 109 includes an output buffer (not shown) for temporarily holding a video signal to be transferred to the engine 102, and an input buffer (not shown) for temporarily holding a signal sent from the engine 102. Then, communication control with the engine 102 is performed.

An instruction on mode setting, etc., issued by an operation input from the panel unit 103 is transmitted to the panel I / F unit 1.
The panel I / F unit 104 constitutes an interface between the panel unit 103 and the CPU 112.

The hardware configuration of the image forming apparatus according to the embodiment is generally as described above. Subsequently, the processing of the present apparatus will be described with reference to the flowcharts of FIGS. The program corresponding to this flowchart is stored in the ROM 107, is loaded into the RAM 110 after power-on, and is executed by the CPU 112. This program is RAM110
At the time of loading, the RAM 110 secures an area for various variables to be described later used in the program, and a table describing the correspondence between the density level and the output level in the normal mode. In this case, an output level table which is referred to when creating a video signal is also stored.

FIG. 2 is a flowchart showing an outline of processing from input of print data to transmission of a video signal to the engine 102 in the embodiment.

First, after inputting print data from the host computer 200, various pre-processes described later are executed (step S1). Next, the print mode (normal mode / toner saving mode) is determined from the input print data.
Is determined (step S2). If the mode is the normal mode, the process proceeds to step S4, where a video signal is created with reference to a previously created output level table, and the video signal is sent to the engine 102 in step S5. To perform print processing.

If it is determined in step S2 that the mode is the toner saving mode, the flow advances to step S3 to create a toner saving mode output level table. In step S4, the video signal is referred to by referring to the toner saving mode output level table. There is a characteristic in that is created.

Hereinafter, the above-described schematic flow will be described in more detail.

FIG. 3 is a flowchart showing a specific process of step S1. In this specification, unless otherwise specified, the symbol “=” means an operation of substituting the value on the right side into the value on the left side. When the value on the right side is equal to the value on the left side, the symbol “== Is used. The symbol “+ =” means an operation of adding the result of adding the value of the right-hand side to the value of the variable on the left-hand side to the variable itself on the left-hand side. The arrow symbol “→” in the flowchart also indicates the substitution operation.

First, in step S11, when print data is received from the host computer 200, the process proceeds to step S12, in which the drawing processing unit 106 analyzes the print data and develops it into raster data. Step S13
Then, this raster data is stored in the two-dimensional array variable RAS_source
[x] [y] (where x indicates a pixel number in the main scanning direction and y indicates a pixel number in the sub-scanning direction).

Next, at step S14, the width and height information of the raster data is obtained, and the variables RAS_wd and
Store it in RAS_ht. In step S15, the number of gradations (the number of density levels) of the raster data is acquired and stored in a variable S_level.
Is stored in a variable C_level.

In the next step S17, an output level table for the normal mode (RAM
110, the output level data for the number of gradation levels C_level (see step S16) to be processed by the controller 101 is extracted from the array variables.
Output_level [m] (where m indicates the density level of raster data, and in this case, 0 ≦ m <C_level).

In step S18, a device density characteristic function LevelToDensity_func indicating an effective density value corresponding to the output level of the device (engine 102) is obtained.
This device density characteristic function LevelToDensity_func is previously stored in the ROM 107 as described above. Then, in step S19, the inverse function DensityTo of the device density characteristic function LevelToDensity_func
Calculate Level_func.

Thus, the process exits the print data input and pre-processing routine in step S1.

FIG. 4 is a flowchart showing a specific process of creating the output level table for the toner saving mode in step S3.

First, in step S31, the density reduction rate is obtained and substituted into the variable discnt (the reduction rate discnt in the normal mode is assumed to be 1). Next, in step S32, a variable n for counting the number of output levels is initialized.

In step S33, the variable Output_level
[n] is the device density characteristic function L obtained in step S18.
As input of evelToDensity_func, multiply the output of this function by the reduction rate discnt. Thereby, the output level in the saving mode, that is, the expected density value Density, with respect to the output level Output_level [n] in the normal mode
Ask for.

Then, the process proceeds to the subsequent step S34, in which the expected density value Density obtained in step S33 is replaced with an inverse function DensityT of the device density characteristic function obtained in step S19.
oLevel_func as an input, the output of this function, that is, the output level for the expected concentration value, is an array variable Output_level
Substitute [n] again.

In step S35, it is determined whether or not n <C_level. If no, the process returns to step S33 and repeats the process while incrementing n in step S36. If the result of the determination in step S35 is yes, the process exits. The output level Output_level corresponding to each value of n is obtained by this repetition processing, and the value of each n and the output level are stored as an array, so that the toner saving mode describing the correspondence between each density level and the output level is described. Can be used as an output level table.

The above-described repetition processing of steps S33 to S36 is expressed as follows in a source code example.

For (n = 0; n <C_level; n + = 1) {Density = LevelToLevel_func (Output_level [n]) * discnt; Output_level [n] = DensityToLevel_func (Density);}

FIG. 5 is a flowchart showing the specific processing of steps S4 and S5.

First, in step S41, a variable v used to specify a pixel position in the sub-scanning direction is initialized. In the next step S42, it is determined whether or not v is less than the height RAS_ht of the original raster data stored in step S14 of FIG. 3, that is, whether or not the processing has been completed up to the last line of the sub-scan. If v <RAS_ht, step S
Proceed to 43.

In step S43, first, a variable h used for designating a pixel position in the main scanning direction is initialized.
Next, in step S44, h is set in step S14 in FIG.
It is determined whether or not the width is smaller than the width RAS_wd of the original raster data stored in step 2, ie, whether or not the processing has been completed up to the last pixel of the main scanning. If h <RAS_wd, the process proceeds to step S45.

In step S45, the gradation of the target pixel RAS_source [h] [v] (see steps S13 and S15 in FIG. 3) of the original raster data having the number of gradations S_level is converted into the processing gradation C_level ( Step S16 in FIG.
) And substitute the density level for the variable D_crt.

In the next step S46, the output level corresponding to D_crt is extracted from the output level table according to the print mode and stored in the two-dimensional array variable RAS_dest [h] [v]. This operation is expressed as follows.

RAS_dest [h] [v] = Output_level [D_cnt];

If h <RAS_wd in step S44, it is determined that the processing up to the last pixel in the line has been completed, and the flow advances to step S51. In step S51,
The raster data after gradation conversion stored in RAS_dest is sent to the engine 102 as a video signal, and the process proceeds to step S52.
Is incremented by v, and the process returns to step S42.

If it is not v <RAS_ht in step S42, it is determined that the processing has been completed up to the last line of the sub-scan, and this processing ends.

Conventionally, in the toner saving mode, the output level corresponding to the density level of each pixel is simply suppressed at a fixed rate. In the embodiment, first, the normal mode is set for each density level. An expected density value obtained by multiplying the effective density level obtained by the above by the reduction rate discnt is calculated (step S33), and an output level corresponding to the expected density value is calculated from an inverse function of the device density characteristic function (step S33). Step S34). Therefore, FIG.
As shown in (b), the output level is suppressed along the device density characteristic function. Accordingly, an effective effect of reducing the amount of applied toner can be obtained in any output level range.

(Embodiment 2) When the pixels in the high output level area are densely packed, the amount of applied toner does not decrease so much. When the pixels in the low output level area are sparse, little toner is applied. This is the problem as described above. In order to solve this problem, it is considered that the output level obtained in the above-described first embodiment is corrected according to the density level of the target pixel and the density levels of the preceding and succeeding pixels.

For example, when the density level of the target pixel is in the highlight area, a predetermined correction value is added to the obtained output level (corrected in the positive direction). If it is within the range, a predetermined correction value is subtracted (corrected in the negative direction) from the obtained output level. In addition,
From the example of the processing gradation C_level of the controller 101 described above, the density levels to be handled are four levels of 0 to 3, and here, the density levels 0 to 2 are the highlight area,
It is assumed that the density level 3 represents a shadow area.

Now, how to obtain the above-mentioned predetermined correction value will be described. First, a correction reference value is determined in advance (for example, 5). Then, a coefficient for the correction reference value is determined according to the density levels of the pixels before and after the pixel of interest, and further, according to the density level of the pixel of interest,
The direction (sign) of the correction is determined.

The coefficient for the correction reference value is, for example, the sum of the density levels of the pixels before and after the pixel of interest. The correction direction (sign) is set to a positive sign so that, for example, when the density level of the target pixel is 1 or 2 (that is, when the pixel is in the highlight area), the correction is made in the dark direction. When the density level of the pixel of interest is 3 (that is, when the pixel is in the shadow area), the sign is set to be negative so that the pixel is adjusted in the thin direction. When the density level is 0, no correction is required, so that the sign may be undefined.

Such correction is performed for the following reason. That is, as a feature of electrophotography, the amount of toner adhering to the logical pixel area is affected by the charge of the surrounding pixel area. Therefore, even if the density value of the pixel of interest is the same, if the density of the surrounding pixels is high, the toner is more likely to be applied to the pixel of interest, and the density increases accordingly. vice versa,
If the density of the surrounding pixels is low, the toner amount of the pixel of interest tends to decrease. Therefore, the image quality is effectively prevented from being degraded by performing correction in accordance with the density of the surrounding pixels.

FIG. 9 is a diagram showing an example in which a coefficient for a correction reference value and a sign of correction are determined. FIG. 7A shows that the density level of the pixel of interest is 1, and the density levels of the pixels before and after it are 0 and 3, respectively. In this case, the coefficient for the correction reference value is set to “previous pixel density + next pixel density = 0 + 3 = 3”. In addition, since the pixel density of interest is 1, it can be determined that the pixel is in the highlight area, so that the correction sign is positive.

FIG. 9B shows that the density level of the pixel of interest is 3, and the density levels of the pixels before and after it are 2 and 1, respectively. In this case, the coefficient for the correction reference value is set to “previous pixel density + next pixel density = 2 + 1 = 3”. In addition, since the target pixel density is 3, it can be determined that the pixel is in the shadow area, and thus the correction sign is negative.

However, as shown in FIG. 7C, when the density level of the pixel of interest is 0, no correction is required.

FIG. 10 shows a case where the correction reference value is 5,
FIG. 9 is a diagram illustrating an example of a correction operation for an output level before correction. When the density level of the pixel of interest is 0, no correction is required as described above, so the coefficient is 0, and the output level remains at 0 before the correction.

When the density level is other than 0, the correction amount is
The correction reference value is multiplied by a coefficient. As shown in the figure, when the density level is 1 or 2 (that is, in the highlight area), the sign of the correction is positive. Therefore, by adding the obtained correction amount to the output value before correction, to correct. On the other hand, when the density level is 3 (that is, when the density level is in the shadow area), the sign of the correction is negative. Therefore, the correction is performed by subtracting the obtained correction amount from the output value before correction.

A process including the above-described output level correction calculation will be described with reference to a flowchart. The engine 102 converts a video signal from print data input in the present embodiment.
The outline of the processing up to transmission to the server is the same as the processing shown in the flowchart of FIG.
Is replaced with the flowchart of FIG.
The processing shown in the flowchart of FIG. 6 is performed. Hereinafter, the processing shown in the flowchart of FIG. 6 will be described.
The other processes are the same as those described above and will not be described.

In FIG. 6, first, in step S61,
The correction reference value (for example, 5) is substituted for the variable adjst, and in step S62, the variable v used to specify the pixel position in the sub-scanning direction is initialized. In the next step S63, v
Is smaller than the height RAS_ht of the original raster data stored in step S14 of FIG. 3, that is, whether the processing has been completed up to the last line of the sub-scan. v <R
If it is AS_ht, the process proceeds to step S64.

In step S64, first, a variable h used to specify a pixel position in the main scanning direction is initialized.

In the following steps S65 to S67, the pixel of interest and the pixels before and after it are initialized. That is, in step S65, the density level D_bf of the pixel before the target pixel is set.
Initialize r to 0. In step S66, the number of gradations S_lev
The gradation of the pixel of interest RAS_source [h] [v] (see steps S13 and S15 in FIG. 3) of the original raster data of el is converted into the processing gradation C_level of the controller 101 (see step S16 in FIG. 3). And the concentration level is set in the variable D_crt
Substitute for Then, in step S67, the density level D_nxt of the pixel following the target pixel is set to 0.

Next, in step S68, it is determined whether or not h is smaller than the width RAS_wd of the original raster data stored in step S14 of FIG. 3, that is, whether or not the processing has been completed up to the last pixel of the main scan. Judge. If h <RAS_wd, the process proceeds to step S69 in FIG.

In step S69, first, it is determined whether the pixel position of interest is the last pixel position in the main scanning, that is, h and RAS
It is determined whether or not _wd-1 is equal. If no, the process proceeds to step S70, and the gradation of the target pixel RAS_source [h] [v] of the original raster data having the gradation number S_level is determined by the controller 101. , And substitutes the density level for the density level D_nxt of the next pixel.
Proceed to. On the other hand, if the determination in step S69 is yes,
D_nxt is set to 0, and the process proceeds to step S72.

In step S72, it is determined whether or not the density level D_crt of the target pixel is 0. Density level is 0
If, the output level does not need to be corrected, so in step S74 the correction value Output_adjst is set to 0, and the process proceeds to step S75. On the other hand, if D_crt is not 0 in step S72, the process proceeds to step S73, and the sum of the pixels D_bfr and D_nxt before and after the target pixel is set as a correction value Output_adjst for the output level as a coefficient for the correction reference value adjst. This can be expressed by the following equation.

Output_adjst = (D_bfr + D_nxt) * adjst;

In step S75, it is determined whether the density level D_crt of the target pixel is in a highlight area or a shadow area. In the present embodiment, the density level handled is 0 to 3 based on the processing gradation C_level of the controller 101.
Here, the density levels 0 to 2 represent a highlight area, and the density level 3 represents a shadow area. From this, it can be determined whether or not the density level D_crt of the target pixel is in the shadow area based on whether or not D_crt> C_level / 2 (= 2). If the density level D_crt of the target pixel is in the shadow area, the sign of the output level correction value Output_adjst is set to a negative value in step S76, and the process proceeds to step S77. If the density level D_crt of the pixel of interest is in the highlight area, the process directly proceeds to step S77.

In step S77, as shown in the following equation,
Output level Output_ for density level D_crt of target pixel
The value obtained by correcting level [D_cnt] with the correction value Output_adjst is stored in RAS_dest [h] [v] as the final output level.
That is,

RAS_dest [h] [v] = Output_level [D_cnt] +
Output_adjst;

Subsequently, for the processing of the next pixel, the pixel position h of the main scanning is incremented in step S78, and D_crt is substituted for D_bfr in step S79.
In step 80, D_nxt is substituted for D_crt, and step S68 in FIG.
Return to and repeat the process.

If h <RAS_wd is not satisfied in step S68 of FIG. 6, it is determined that the processing up to the last pixel in the line has been completed, and the flow advances to step S81. In step S81, the raster data after gradation conversion stored in RAS_dest is sent to the engine 102 as a video signal, and the process proceeds to step S8.
In step 2, v is incremented, and the process returns to step S63.

If v <RAS_ht is not satisfied in step S63, it is determined that the processing has been completed up to the last line of the sub-scanning, and the printing processing ends.

As described above, according to the present embodiment, in the toner saving mode, in addition to the output level being suppressed along the device density characteristic function, the density level of the target pixel and the density levels of the preceding and succeeding pixels are reduced. It was corrected according to. This solves the problem that the amount of applied toner does not drop much when the pixels in the high output level area are dense, or the toner is hardly applied when the pixels in the low output level area are sparse. In addition, the effect of reducing the amount of applied toner can be obtained more effectively in any output level range.

In the above-described embodiment, a laser beam printer having a toner saving function by using toner as a recording agent has been described as an example. However, the present invention is not limited to this. The present invention is also applicable to an inkjet printer to be used (having an ink saving function).

[0089]

[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 (for example, a copying machine) Machine, facsimile machine, etc.).

As described above, an object of the present invention is to supply a storage medium (or a recording medium) storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and to provide the system or the apparatus. This is also achieved by a computer (or CPU or MPU) reading and executing a program code stored in a 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. When the computer executes the readout program code, 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.
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 the memory provided in the function expansion card inserted into the computer or the function expansion unit connected to the computer, the program code is read based on the instruction of the program code. , The CPU provided in the function expansion card or the function expansion unit performs part or all of the actual processing,
It goes without saying that a case where the functions of the above-described embodiments are realized by the processing is also included.

When the present invention is applied to the storage medium, the storage medium includes the above-described flowcharts shown in FIGS. 2 to 4 and FIGS. 5 and / or 6, and 7.
The program code corresponding to the flowchart shown in FIG.

[0093]

As described above, according to the present invention,
In the recording material saving mode, an image forming apparatus and an image forming apparatus capable of obtaining an effect of reducing the amount of recording material such as toner in any output level range corresponding to the density level of a pixel without deteriorating expected image quality. A forming method and a storage medium can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment.

FIG. 2 is a flowchart illustrating an outline of processing from input of print data to transmission of a video signal to a printer engine in the embodiment.

FIG. 3 is a flowchart showing data input and preprocessing in the embodiment.

FIG. 4 is a flowchart illustrating a process of creating an output level table for a toner saving mode in the embodiment.

FIG. 5 is a flowchart illustrating a process of calculating an output level corresponding to each density level according to the first embodiment.

FIG. 6 is a flowchart illustrating a process of calculating an output level corresponding to each density level according to the second embodiment.

FIG. 7 is a flowchart illustrating a process of calculating an output level corresponding to each density level according to the second embodiment.

FIG. 8 is a diagram for explaining the effect of reducing the amount of applied toner according to the embodiment of the present invention.

FIG. 9 is a diagram illustrating a process of determining a coefficient for a correction reference value and a sign of correction according to the second embodiment.

FIG. 10 is a diagram illustrating an example of a correction operation for an output level before correction according to the second embodiment.

FIG. 11 is a diagram for explaining a conventional technique.

Claims (9)

[Claims] A first image forming means for forming an image by depositing an amount of a recording material on a recording medium according to a first output level corresponding to a density level of each pixel of the image forming data; A second image forming unit that replaces the first output level with a second output level lower than the first output level, thereby forming an image while saving the consumption of the recording material; An image forming apparatus that selects one of the first and second image forming units to form an image, wherein the second image forming unit includes the first image forming unit. Density level conversion means for converting each output level corresponding to the density level of each pixel of the image forming data into an effective density level based on a density characteristic function indicating a correspondence relationship between the output level and the effective density level; The effect Obtaining means for obtaining an expected density level in which the density level is reduced to a predetermined ratio; and converting the expected density level obtained by the obtaining means into the second output level based on an inverse function of the density characteristic function. And an output level conversion unit. 2. The method according to claim 1, wherein the second image forming unit outputs the second output obtained by the output level converting unit in accordance with a density level of a pixel of interest and each density level of pixels before and after the pixel of interest. The image forming apparatus according to claim 1, further comprising a correction unit configured to correct a level. 3. When the density level of the pixel of interest belongs to a highlight area, a predetermined correction value is added to the second output level, and the density level of the pixel of interest belongs to a shadow area. 3. The image forming apparatus according to claim 2, wherein the correction is performed by subtracting the predetermined correction value from the second output level. 4. The method according to claim 3, wherein the predetermined correction value is a value obtained by multiplying a predetermined correction reference value by a sum of respective density levels of pixels before and after the pixel of interest. The image forming apparatus as described in the above. 5. A first image forming step of forming an image by depositing an amount of a recording material on a recording medium according to a first output level corresponding to a density level of each pixel of image forming data; Replacing the first output level with a second output level lower than the first output level, thereby saving the consumption of the recording material and forming an image. An image forming method in an image forming apparatus for forming an image by selecting any one of the first and second image forming steps, wherein the second image forming step is provided in the image forming apparatus. A density for converting each output level corresponding to a density level of each pixel of the image forming data into an effective density level based on a density characteristic function indicating a correspondence relationship between the first output level and the effective density level; Lebe A conversion step; an obtaining step of obtaining an expected density level in which the effective density level is reduced to a predetermined ratio; and, based on an inverse function of the density characteristic function, the expected density level obtained by the obtaining step is calculated by the 2. An image forming method, comprising: an output level conversion step of converting the output level into two output levels. 6. The second image forming step, wherein the second output obtained in the output level converting step is performed according to a density level of a target pixel and each density level of pixels before and after the target pixel. The image forming method according to claim 5, further comprising a correction step of correcting a level. 7. The correcting step includes: when the density level of the target pixel belongs to a highlight area, adding a predetermined correction value to the second output level, and the density level of the target pixel belongs to a shadow area. 7. The image forming method according to claim 6, wherein the correction is performed by subtracting the predetermined correction value from the second output level. 8. The apparatus according to claim 7, wherein the predetermined correction value is a value obtained by multiplying a predetermined correction reference value by a sum of respective density levels of pixels before and after the pixel of interest. The image forming method as described in the above. 9. A storage medium storing a program for realizing the image forming method according to any one of claims 5 to 8 by a computer.