JP2001069350A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an output image of high quality while a high toner saving rate is realized. SOLUTION: An image forming device has an edge detection means 102 outputting an objective pixel in multivalue image data and edge information detected in the objective pixel, an input image gradation modulation means 103 converting the gradation of an image with the objective pixel and edge information from the edge detection means 102, an error quantity calculation means 104 calculating error data on the output image, an error weighting means 106 operating error diffusion by referring to error data and pixel data after a gradation conversion processing and weighting error data to objective pixel data, a dot size decision means 107 deciding a dot size corresponding to the image from toner saving mode setting information, edge information and image data after the error weighting processing and a dot coordinate deciding means 108 referring to the dot size and image data after the error weighting processing, deciding the coordinate of the dot and executing a binarization processing.

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 for forming an image on a recording medium based on image data.

[0002]

2. Description of the Related Art An error diffusion method is known as one of the methods for converting a multi-valued image into a binary image.

Hereinafter, a conventional image forming apparatus using the error diffusion method will be described.

FIG. 5 is a block diagram showing a conventional image forming apparatus using an error diffusion method, and FIG. 6 is an explanatory diagram showing an example of an error matrix.

As shown in FIG. 5, the image forming apparatus refers to an image memory 1 in which multi-value data of a pixel of interest is read, and refers to stored correction data in accordance with printing characteristics of an output device such as a printer. Γ correction RO for correcting multi-value data
M2 and an error diffusion device 9 that performs a binarization process on an image by an error diffusion method and outputs a binary signal.

The error diffusion device 9 includes an adder 3 for adding the error data stored in the error amount storage means 4 to the multi-value data from the γ correction ROM 2, and a binarization of the multi-value data to which the error data has been added. A comparator 5 for comparing the threshold value with a threshold value and outputting a predetermined binary signal; a multiplier 8 for calculating a binary signal corresponding to the number of gradations of the input data from the binary signal; A subtractor 7 for calculating a binarization error in the binarization processing from the added multi-valued data; and a weighting error calculator for weighting the binarization error and outputting the weighted error to the error amount storage means 4. 6 is comprised.

According to such an image forming apparatus, multivalued data D for performing binarization processing is read from the image memory 1, and the gamma correction ROM 2 refers to the correction data and refers to the printing characteristics of an output device such as a printer. Data D 'according to
Is corrected by .gamma. The error data E is added by the adder 3 of the error diffusion device 9 to the γ-corrected multi-value data D ′, and multi-value data F is output.

Next, in the comparator 5, the multi-value data F of the pixel of interest to which the error data E has been added is compared with a binarization threshold Th, and when F> = Th, the binary signal B = “1”. Is output, and when F <Th, the binary signal B = "0" is output. Then, from this output result, a binarization error E ′ at the time of the binarization processing is calculated by the subtractor 7 as E ′ = FB ′.

Here, when the input data has 256 gradations (0 to 255), the multiplier 8 calculates B ′ = B ×
255. Therefore, for example, when the input multi-value data D is 230 and the binarization threshold Th is 128, the output data after binarization is B = 1, and the binarization error E is

[0010]

(Equation 1)

More required. That is, E = D−B ×
255 = 230-1 × 255 = −25.

The binarization error E is stored in the error amount storage means 4 by a weighting calculator 6 using a predetermined error matrix Mxy in order to distribute the data to the pixels to be processed thereafter. 3 is added to the multi-value data of the next pixel, and the error data is propagated.

That is, in this case, since the input multi-value data D is 230, as a result of comparison with the binarization threshold value Th = 128, the output data after binarization is 1 and 255 at 256 gradations. Therefore, 23 of the input multi-value data D
There are 25 errors for 0. Therefore, the error 25 with respect to the multi-valued data D = 230 is defined as a binarization error E, and the binarization error E is distributed to the error amount storage means 4 of the unprocessed pixel using the error matrix in the weighting error calculator 6. Then, it is reflected in the binarization processing in the subsequent pixels.

FIG. 6 shows an example of the error matrix Mxy.

In FIG. 6, a pixel indicated by * is a current pixel to be processed, and a binarization process is performed on this pixel.

The error generated when the target pixel is binarized is
With the weighting coefficients (7, 1, 5, 3) shown in FIG. Then, when performing the binarization processing of the target pixel indicated by *, the error distribution value stored in the error amount storage means 4 is read, and the next error read from the image memory 1 using this error distribution value. Is corrected for the input value of.

As described above, the error diffusion method distributes a binarization error generated in the binarization processing of a certain pixel to pixel data to be binarized thereafter, and outputs the binarized image data. This is a technique for minimizing an error between the image data and the original multi-valued image data.

Conventionally, when a toner save process is performed in the error diffusion method, the print density is uniformly changed over the entire image area by switching the number of gradations represented by the multi-value data D 'by the gamma correction ROM 2 in the color image data. The amount of toner consumed.

[0019]

However, in the prior art as described above, since the print density is reduced uniformly over the entire area of the image, when the toner save ratio is increased, the entire output image becomes extremely thin and the color appearance changes. As a result, with respect to image data in which the edge is important such as text and graphics, the content of the output image is lost such that the edge of the image cannot be recognized.

Conversely, in order to obtain an output image in which the color appearance does not change and which can be recognized even in text or graphics, the toner saving rate must be suppressed over the entire image, so that the toner saving effect is sufficiently obtained. Can not do.

Accordingly, an object of the present invention is to provide an image forming apparatus capable of obtaining a high quality output image while realizing a high toner saving rate.

[0022]

In order to solve this problem, an image forming apparatus according to the present invention is an image forming apparatus for generating binary image data from multi-valued image data, and includes toner save setting information. Means for outputting a target pixel and edge detection processing from a target pixel and adjacent pixels in the multi-valued image data stored in the image input means, and outputting the target pixel and edge information detected in the target pixel. An input image gradation converting means for converting a gradation of an image based on a target pixel and edge information from the edge detecting means, an error amount calculating means for calculating error data of an output image, Error weighting for performing error diffusion calculation with reference to the pixel data after the gradation conversion processing from the input image gradation conversion means and weighting the error data to the target pixel data Means for determining a dot size corresponding to an image from the toner save mode setting information from the toner save mode setting means, the edge information from the edge detecting means, and the image data after error weighting processing from the error weighting means. And a dot coordinate determination unit that determines the coordinates of the dot with reference to the dot size determined by the dot size determination unit and the image data after the error weighting process from the error weighting unit and performs the binarization process. It is what it was.

As a result, a high quality output image can be obtained while realizing a high toner saving rate.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is an image forming apparatus for generating binary image data from multi-valued image data, wherein a toner save mode for outputting toner save setting information is provided. Setting means, edge detection means for performing edge detection processing from the target pixel and adjacent pixels in the multi-valued image data stored in the image input means, and output the target pixel and edge information detected in the target pixel, Input image gradation conversion means for converting the gradation of an image based on the target pixel and edge information from the edge detection means, error amount calculation means for calculating error data of the output image, error data and input image gradation conversion means Error weighting means for performing error diffusion calculation with reference to the pixel data after the gradation conversion processing from the pixel data, and weighting the error data to the target pixel data; and a toner save mode. Dot size determining means for determining a dot size corresponding to an image from toner save mode setting information from the setting means, edge information from the edge detecting means, and image data after error weighting processing from the error weighting means; A dot coordinate determining unit that determines the coordinates of the dot with reference to the dot size determined by the above and the image data after the error weighting process from the error weighting unit and performs the binarization process. This has the effect that a high quality output image can be obtained while realizing the toner save rate.

According to a second aspect of the present invention, in the first aspect, the edge detecting means fetches the multi-valued image data obtained from the image input means as a target image and an adjacent image, and executes edge window processing. And an edge determining unit that receives image data from the edge window forming unit, calculates a multi-valued edge amount, and outputs edge information. It has the effect that it is possible to obtain a high-quality output image while realizing it.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. In these drawings, the same members are denoted by the same reference numerals, and duplicate description is omitted.

FIG. 1 is a block diagram showing an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram showing an edge detecting means in the image forming apparatus of FIG. 1, and FIG.
FIG. 4 is an explanatory view showing an edge window formed by an edge window forming means in the edge detecting means, and FIG. 4 is an explanatory view showing dots formed by the image forming apparatus of FIG.

As shown in FIG. 1, the image forming apparatus according to the present embodiment has a toner save mode setting means 100 for outputting toner save setting information, and an image storing data of an input image to be subjected to gradation modulation processing. An input unit 101 and an edge detection unit 102 that performs edge detection processing on a target pixel and an adjacent pixel obtained by the image input unit 101 and outputs a target pixel and edge information detected on the target pixel.
And an input image gradation conversion unit 10 for converting the gradation of an image based on the target pixel and the edge information from the edge detection unit 102
3, error amount calculating means 104 for calculating error data of the output image, error amount storing means 105 storing the error data calculated by the error amount calculating means 104, and error amount storing means 105 Error weighting means 106 for performing error diffusion calculation with reference to the error data and the pixel data after the gradation conversion processing from the input image gradation conversion means 103 and weighting the error data to the target pixel data; A dot size determining unit 107 for determining a dot size corresponding to an image from the toner save mode setting information from the setting unit 100, the edge information from the edge detecting unit 102, and the image data after error weighting processing from the error weighting unit 106; Dot size determination means 107
The dot coordinate determination unit 108 and the dot size determination unit 107 determine the coordinates of the dots and perform the binarization process by referring to the dot size determined in the above and the image data after the error weighting process from the error weighting unit 106. The image output unit 109 stores binary image data in which the output dots of the dot size are output at the coordinates determined by the dot coordinate determination unit 108.

Here, the toner save mode is set by inserting a command to execute the toner save mode by the toner save mode setting means 100 into a print code transferred from an external device such as a host computer to the image forming apparatus. The setting can be made by input from a key of the image forming apparatus. Note that the toner save mode setting unit 100 outputs a toner save mode signal to the input image gradation conversion unit 103, the dot size determination unit 107, and the error amount calculation unit 104.

The multi-valued image to be subjected to the gradation modulation processing is first stored in the image input means 101, and the stored image is
The following processing is performed for each raster and each pixel.

Next, FIG.
This will be described with reference to FIG.

As shown, the edge detecting means 102
Is a multi-valued image data acquired from the image input means 101 as a target image and an adjacent image, and a 3 × 3 edge window using a matrix (see FIG. 3)
And an edge determining unit 111 that receives image data from the edge window forming unit 110, calculates a multi-valued edge amount, and outputs edge information.

Here, the edge window forming means 110
In the case of a color image, four independent CMYK (cyan, magenta, yellow, black) color components
Of edge windows. In addition, the edge determination unit 111 is configured by a second differential operation of Laplacian, and in the case shown in FIG. 3, the edge window forming unit 110 outputs 3 × 3 image data (d1 to d9).
Received, and the image data and a preset 2
Next derivative operation coefficients (a, b, c, d, e, f, g, h,
The edge amount is calculated using i). The edge amount ED
GE is

[0034]

(Equation 2)

Is calculated. Then, the calculated edge amount EDGE is compared with a preset threshold value EdgeTh, and if EDGE> EdgeTh, it is determined as an edge.
If EDGE <EdgeTh, edge information is output as a non-edge.

The input image gradation conversion means 103 shifts the target pixel data from the edge detection means 102 in the lower bit direction n times (n = 0, 1, 2), and outputs the shifted upper bits to the upper bits. Substitute “0”. As a result, the number of gradations is reduced to 1/1, 1/2 or 1/4. Note that the input image gradation conversion means 103 is based on the toner save information from the toner save mode setting means 100, and based on the edge information from the edge detection means 102 at the time of toner save setting, when the image is an edge or non-edge. The value of n is switched between and. At this time, the value of n in the non-edge portion is set to be equal to or larger than that in the edge portion. In the present embodiment, at the time of the toner save setting, n = 2 (the number of gradations: 1/4) for a non-edge, and n for an edge.
= 1 (the number of gradations: 1/2). When the toner save is not set, the gradation conversion is not performed.

The error data stored in the error amount storage means 105 is referred to when the error weighting means 106 weights the error data at the target pixel. At this time,
An error matrix (see FIG. 6) used at the time of error diffusion is applied to the data on the error amount storage unit 105, and error data of a pixel adjacent to the target pixel value td is weighted.

The error weighting means 106 outputs the target pixel data value td 'subjected to the weighting process.

The dot size determination means 107 determines the dot size from the toner save information from the toner save mode setting means 100, the edge information from the edge detection means 102, and the value td 'of the target pixel data output from the error weighting means 106. Make a decision.

FIG. 4 shows dot formation when the dot size is changed in four stages. FIG.
In C, the dot size changes to 1 dot, D to 2 dots, E to 3 dots, and F to 4 dots. Specifically, if the edge detection result from the edge detecting means 102 is a non-edge area, any of C, D, E or F according to the weighted pixel data value output from the error weighting means 106, that is, the density level Determine the dot size
If the result of the edge detection from the edge detecting means 102 is an edge area, the fixed dot size is one dot size C regardless of the level of the weighted pixel data output by the error weighting means 106.

The dot coordinate deciding unit 108 weights the dot size information outputted from the dot size deciding unit 107 and the target pixel data outputted from the error weighing unit 106 with the error data of the processed pixel. 'Is entered. Then, the input image data td 'is compared with a threshold value Th set in advance for determination of coordinates, and dots are output using the pixel satisfying td'> Th as dot coordinates. The dot size data shown in FIG. 4 corresponding to the dot size is output at the determined coordinates.

The error amount calculating means 104 includes pixel data sd output from the input image gradation converting means 103, dot size information Dsize output from the dot size determining means 107, and dots output from the dot coordinate determining means 108. The coordinate data (dx, dy) is input. Then, after the dot coordinates are determined by the dot coordinate determination means 108, error data at the target pixel is calculated.

Here, the dot size information is Dsize =
0, 1, 2, 3, 4 (four-step dot size). Further, at the time of setting the toner save, the input dot size information Dsize is multiplied by m (m is an integer), and the error amount is calculated.

The dot coordinates (x,
The error data E (x, y) in y) is

[0045]

(Equation 3)

Is calculated. Here, since 255 is the density data at the time of outputting one dot, by adding it to the error data according to the number of output dots, error data corresponding to the dot size can be stored.

The error data calculated by the error amount calculation means 104 is transferred to the error amount storage means 105 and stored in a memory corresponding to the dot coordinates determined by the dot coordinate determination means 108.

[0048]

As described above, according to the present invention, an effective effect that a high quality output image can be obtained while realizing a high toner saving rate can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a block diagram illustrating an edge detecting unit in the image forming apparatus of FIG. 1;

FIG. 3 is an explanatory diagram showing an edge window formed by an edge window forming means in the edge detecting means of FIG. 2;

FIG. 4 is an explanatory diagram showing dots formed by the image forming apparatus of FIG. 1;

FIG. 5 is a block diagram showing a conventional image forming apparatus using an error diffusion method.

FIG. 6 is an explanatory diagram showing an example of an error matrix.

[Explanation of symbols]

 Reference Signs List 100 toner save mode setting means 101 image input means 102 edge detection means 103 input image gradation conversion means 104 error amount calculation means 106 error weighting means 107 dot size determination means 108 dot coordinate determination means

Continued on the front page F-term (reference) 2C262 AA24 AA26 AB13 BB08 BB10 CA08 CA16 DA03 5B057 AA11 BA30 CA01 CA08 CA12 CB01 CB07 CB12 CC03 CE12 CE13 CH07 CH11 DC16 5C077 LL17 LL19 MP07 MP08 NN05 NN11 PP41 PP43 RR11

Claims (2)

[Claims] 1. An image forming apparatus for generating binary image data from multi-valued image data, comprising: toner save mode setting means for outputting toner save setting information; and multi-valued image data stored in an image input means. Edge detection means for performing edge detection processing from the target pixel and adjacent pixels in the image data, and outputting the target pixel and edge information detected at the target pixel; and An input image gradation conversion unit for converting gradation, an error amount calculation unit for calculating error data of an output image, and the pixel data after the gradation conversion processing from the input image gradation conversion unit. An error weighting means for performing error diffusion calculation with reference to the error data and weighting the error pixel data to the target pixel data; A dot size determination unit that determines a dot size corresponding to an image from the save mode setting information, the edge information from the edge detection unit, and the image data after the error weighting process from the error weighting unit; and a dot size determination unit that determines the dot size. An image forming apparatus comprising: dot coordinate determination means for determining dot coordinates with reference to a dot size and image data after error weighting processing from the error weighting means and performing binarization processing. 2. An edge window forming means for fetching multi-valued image data obtained from said image input means as a target image and an adjacent image to form an edge window, and 2. The image forming apparatus according to claim 1, further comprising an edge determination unit that receives data, calculates a multi-value edge amount, and outputs edge information.