JPH08142411A - Image processing apparatus and method - Google Patents

Abstract

PURPOSE: To provide an image processing apparatus capable of suppressing the generation of density irregularity. CONSTITUTION: An image processing apparatus has an RAM 10 for a multivalue image, a binarizing device 11 binarizing an image by a density pattern method, a gradation pattern memory 12, a pattern selector 13, an RAM 14 for a binary image, a dot matrix type printer 15 and an image printer 16. The binarizing device 11 scans the respective pixels of the multivalue image and reads the gradation patterns corresponding to the gradations of the respective pixels to store the same at the noticeable pixels position of the RAM 14. The pattern selector 13 selects the gradation pattern used in binarization corresponding to the horizontal position of a noticeable pixel. There are four kinds of gradation patterns corresponding to gradation levels 0-16. For example, when a printing head is shifted in the left upward direction at the time of a specific horizontal printing, the repeating cycle of the patterns in an equal density region becomes large as compared with a case using a single gradation pattern and, therefore, the density irregularity caused by the error of a printing position becomes inconspicuous.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for outputting a multi-valued image with a binary dot matrix printer.

[0002]

2. Description of the Related Art Conventionally, when a multi-valued image is output by a binary dot matrix printer, the multi-valued image is binarized by a pseudo gradation expression method such as a so-called density pattern method, systematic dither method or error diffusion method. The image is converted into an image, the converted binary image is divided into bands of the print head in units of the number of dots, and the head movement is repeated in the band unit for printing and paper feeding.

At this time, in order to prevent the occurrence of a horizontal linear void or overlap due to a mechanical error in the paper feed or the head movement in the vertical direction, the head movement amount in the paper feed or the vertical direction is set to the print head. The method of making half the number of dots of was used. That is, half the pixels in the band are printed during the first horizontal printing, and then the first half of the pixels in the lower half of the even band and the upper half of the odd band are printed during the second horizontal printing.
The printing of the pixels that were not printed during the horizontal printing was repeated.

FIG. 9 is an explanatory view showing a conventional printing method. In the figure, 80 is a print head capable of printing 8 dots at a time. While moving from left to right, the print head ejects or transfers ink to pixel positions corresponding to every two pixels to form an image on the paper.

When one horizontal printing is completed, the paper is fed by half a dot of the print head, that is, by 4 pixels. Each number indicated by 81 indicates the order of pixels printed on the paper. At the time of the first horizontal printing, the pixel of 1 in the figure is printed using the lower 4 dots of the print head. Two
At the time of the second horizontal printing, the pixel 2 in the figure is printed.
Thereafter, the entire screen is printed in the same manner.

[0006]

However, in the above-mentioned conventional example, in the case of a binary image in which the gradation pattern by the density pattern method or the systematic dither method is regularly repeated, the first horizontal printing and the second horizontal printing are performed. However, there is a defect that uneven density occurs in the uniform density portion due to a mechanical error in the printing position during horizontal printing.

Therefore, an object of the present invention is to provide an image processing apparatus capable of suppressing the occurrence of density unevenness.

[0008]

In order to achieve the above object, an image processing apparatus according to claim 1 of the present invention stores a multi-valued image storage means for storing a multi-valued image and a binary image. An image processing device for converting the multi-valued image into the binary image by a pseudo gradation expression method and printing the binary image, and a gradation pattern storage means for storing a plurality of gradation patterns. Pattern switching means for switching the plurality of gradation patterns according to the pixel position of the multi-valued image, and scanning each pixel of the multi-valued image, and changing the gradation pattern of the gradation pattern according to the gradation level of each pixel. The image binarization unit stores the gradation in the binary image storage unit, and the printing unit prints the binary image in a dot matrix according to the gradation of the stored gradation pattern.

An image processing apparatus according to a second aspect comprises a multi-valued image storage means for storing a multi-valued image and a binary image storage means for storing a binary image, and the pseudo-gradation expression method is used for the image processing apparatus. In an image processing apparatus for converting a multi-valued image into the binary image and printing the same, a threshold value for storing a plurality of threshold value masks storing a plurality of threshold values to be compared with the pixel values of the multi-valued image. Mask storage means, threshold value mask switching means for switching the plurality of threshold value masks according to the position of the pixel of the multi-valued image, each pixel of the multi-valued image is scanned, and the value of each pixel is set. An image binarizing unit for binarizing the position of the corresponding pixel of the binary image storage unit according to a comparison with the threshold value corresponding to the position of the pixel; and the binarized binary value. And a printing unit that prints an image in a dot matrix.

An image processing method according to a third aspect is an image processing method for storing a multivalued image, converting the stored multivalued image into a binary image by a pseudo gradation expression method, and printing the binary image. A gradation pattern is stored, the plurality of gradation patterns are switched according to the pixel position of the multivalued image, each pixel of the multivalued image is scanned, and the gradation is calculated according to the gradation level of each pixel. The gradation of the pattern is determined, and the binary image is printed in a dot matrix according to the determined gradation of the gradation pattern.

[0011]

In the image processing apparatus according to the first aspect of the present invention, when a multi-valued image is stored by the multi-valued image storage means, the multi-valued image is converted into a binary image by the pseudo gradation expression method and printed. Further, the gradation pattern storage means stores a plurality of gradation patterns, the pattern switching means switches the plurality of gradation patterns according to the pixel position of the multivalued image, and the image binarizing means performs the multivalued image. Scanning each pixel of the pixel and changing the gradation level of the gradation pattern to 2 according to the gradation level of each pixel.
The binary image is stored in the value image storage means, and the binary image is printed by the printing means in a dot matrix according to the gradation of the stored gradation pattern.

In the image processing apparatus according to the second aspect, the multi-valued image storage means stores the multi-valued image, and when the multi-valued image is converted into the binary image by the pseudo gradation expression method and printed, A plurality of threshold masks in which a plurality of threshold values to be compared with the pixel values of the multi-valued image are stored are stored in the threshold mask storing means, and the threshold mask switching means stores the multi-valued image of the multi-valued image. The plurality of threshold value masks are switched according to the position of the pixel, each pixel of the multi-valued image is scanned, and the threshold value corresponding to the value of each pixel and the position of the pixel is obtained by the image binarizing means. The position of the corresponding pixel of the binary image storage means is binarized in accordance with the comparison with, and the binarized binary image is printed by the printing means in a dot matrix.

[0013]

Embodiments of the image processing apparatus of the present invention will be described.

[First Embodiment] FIG. 1 is a block diagram showing the arrangement of an image processing apparatus according to the first embodiment. In the figure, 1
Reference numeral 0 is a multivalued image RAM for storing a multivalued image, 11 is a binarizing device for binarizing an image by a density pattern method, and 12 is a gradation pattern memory for storing a gradation pattern.

Reference numeral 13 is a pattern selection device for deciding which gradation pattern to use among a plurality of gradation patterns,
14 is a binary image RAM for storing a binary image, and 15 is 2
Dot-matrix printer for printing value images, 16
Is an image printing device for controlling the printer 15.

The binarizing device 11 sequentially scans each pixel of a multi-valued image, reads a gradation pattern corresponding to the gradation of each pixel from the gradation pattern memory 12, and a binary image RAM.
It is stored in 14 target pixel positions.

FIG. 2 is an explanatory diagram showing a gradation pattern.
The four types of gradation patterns have gradation levels 0 to 16 respectively.
Has a pattern corresponding to. Pattern selection device 13
Selects a gradation pattern used for binarization according to the horizontal position of the pixel of interest.

FIG. 3 is a flowchart showing the binarization process and the pattern selection process. This processing is performed by the binarization device 1
1 and the pattern selection device 13. First, the vertical position counter Y of the pixel of the multi-valued image to be processed is initialized to the value 0 (step S90). Similarly, the horizontal position counter X of the pixel of the multi-valued image to be processed is initialized to the value 0 (step S91). The gradation pattern P is selected by the horizontal position counter X (step S9).
2). Here, the remainder (Xmod4) obtained by dividing X by 4 is used to sequentially switch the four types of gradation patterns P.

Positional coordinates (X,
The density D of the pixel of Y) is read (step S93). The gradation L corresponding to the density D is obtained. For example, if the density of the input image has a value in the range of 0 to 255, the gradation L is L =
It is calculated by D × 17/256 (decimal fractions are rounded down).

The gradation pattern P selected in step S92
The pattern of gradation L is read from (step S95).
Step S95 within the range of (X × 4 + 3, Y × 4 + 3) from the position coordinates (X × 4, Y × 4) of the binary image RAM 14
The pattern read in is written (step S96).
The horizontal position counter X is incremented by 1 (step S97).

Steps S92 to S9 shown above
7 is repeated for the image data for one line (step S98). The processing of the image data for one line is completed,
When the horizontal position counter X exceeds the number of horizontal pixels, the vertical position counter Y is set to 1 in order to shift to the processing of the next line.
(Step S99). It is determined whether or not the processing for all lines has been completed (step S100). If not completed, the processing from step S91 is repeated, and if completed, this routine is terminated.

FIG. 4 shows two uniform density areas with gradation levels of 5.
It is explanatory drawing which shows the binary image of the value-ized result. In this example, the gradation pattern is switched every 4 pixels. FIG. 5 is an explanatory diagram showing a comparison of print results when the gradation pattern of this embodiment and the conventional single gradation pattern are used when the print head is displaced to the upper left in the second horizontal printing. Is. The figure (A) shows the printing result of the present embodiment, and the figure (B) shows the conventional printing result. In this way, the pattern repetition cycle in the uniform density region becomes longer than that in the case where a single gradation pattern is used, so that the density unevenness due to the error in the printing position becomes inconspicuous.

Each gradation pattern of this embodiment has a form in which the pattern is vertically shifted. Instead of storing several types of gradation patterns in the memory as in the present embodiment, the pattern selection device 13 uses one gradation pattern and the pattern selection device 13 reads out the gradation pattern memory according to the horizontal position of the multi-valued image. The same effect can be obtained by a method of switching the pattern by changing the position. Figure 6
FIG. 3 is an explanatory diagram showing that several kinds of gradation patterns can be obtained by changing the read position of the gradation pattern memory. By doing so, the capacity of the memory for storing the gradation pattern can be saved.

[Second Embodiment] Next, an image processing apparatus according to a second embodiment will be described. Although the density pattern method is assumed as the pseudo gradation expression method in the first embodiment, other pseudo gradation expression methods are also effective. FIG. 7 is a block diagram showing the arrangement of the image processing apparatus according to the second embodiment using the systematic dither method. The same components as those in the first embodiment are designated by the same reference numerals. In the figure, reference numeral 18 denotes a threshold mask selecting device, and 17 is a memory in which a plurality of threshold masks are stored.

FIG. 8 is an explanatory diagram showing a plurality of threshold masks. In the image processing apparatus of this embodiment, a plurality of threshold value masks as shown in FIG. 8 are used by switching them every 4 pixels in the horizontal position of the multivalued image.

More specifically, the image binarization device 11
Scans each pixel of the multi-valued image in order in the horizontal direction, compares the value of the pixel with the value of the threshold mask corresponding to the position of the pixel, and if the value of the pixel is larger, the corresponding pixel of the binary image. Is turned on (ink is applied), and if the pixel value is smaller, the pixel of the binary image is turned off (ink is not applied). The first horizontal image of the first line is compared with the upper left value (1) of the threshold mask 1. The second pixel in the horizontal direction on the first line is compared with the second value (9) from the left on the first line from the top of the threshold mask 1. The same applies to the third and fourth horizontal lines of the first line. The fifth pixel in the horizontal direction of the first line is compared with the upper left pixel of the threshold mask 2. The horizontal sixth, seventh, and eighth lines are similarly compared with the values of the first line of the threshold mask 2. As described above, the threshold mask is switched every 4 pixels in the horizontal direction. When the processing of the first line is completed, the same processing is performed for the pixels of the second line. At this time, the threshold mask is used for the value of the second line from the top. In the processing of the fifth line, the value of the first line from the top of the threshold mask is used again.

As another pseudo gradation representation method, when the gradation number of the multi-valued image is larger than the pseudo gradation number that can be represented by the density pattern or the systematic dither method, gradation quantization in pseudo gradation conversion is performed. Although an error occurs, a method is conceivable in which the quantization error is distributed to adjacent pixels by an error diffusion method to infinitely increase the number of pseudo gradations. The present invention is also effective in this pseudo gradation expression method. .

Further, by applying the pseudo gradation expression to the multi-valued image components corresponding to yellow, magenta, cyan, yellow, magenta, cyan, black process ink, or any special color ink,
The image processing apparatus of the present invention can be applied to color multi-valued images.

[0029]

According to the image processing apparatus of the first aspect of the present invention, the multi-valued image storage means stores the multi-valued image, and the multi-valued image is converted into the binary image by the pseudo gradation expression method. At the time of printing, the gradation pattern storage means stores a plurality of gradation patterns, the pattern switching means switches the plurality of gradation patterns according to the pixel position of the multi-valued image, and the image binarization means Each pixel of the multi-valued image is scanned, the gradation of the gradation pattern is stored in the binary image storage means according to the gradation level of each pixel, and according to the gradation of the stored gradation pattern. Since the binary image is printed in the dot matrix by the printing means, it is possible to reduce the density unevenness that occurs when there is a mechanical error in the movement of the print head.

According to the image processing apparatus of the second aspect, the multi-valued image storage means stores the multi-valued image, and the multi-valued image is converted into the binary image by the pseudo gradation expression method and printed. Further, a plurality of threshold masks in which a plurality of threshold values to be compared with the pixel values of the multi-valued image are stored are stored by the threshold mask storage means, and the multi-valued image is stored by the threshold mask switching means. The plurality of threshold value masks are switched according to the position of the pixel of the image, each pixel of the multi-valued image is scanned, and the image binarizing unit performs the above-mentioned operation according to the value of each pixel and the position of the pixel. The position of the corresponding pixel in the binary image storage means is binarized according to the comparison with the threshold value, and the binarized binary image is printed by the printing means in a dot matrix. Concentration caused by mechanical error It can be reduced.

According to the image processing method of the third aspect, in the image processing method of storing a multivalued image, converting the stored multivalued image into a binary image by a pseudo gradation expression method, and printing the binary image. Storing a plurality of gradation patterns, switching the plurality of gradation patterns according to the pixel position of the multi-valued image,
Each pixel of the multi-valued image is scanned, the gradation of the gradation pattern is determined according to the gradation level of each pixel, and the binary image is determined according to the determined gradation of the gradation pattern. Is printed with a dot matrix, it is possible to reduce density unevenness that occurs when there is a mechanical error in the movement of the print head.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image processing apparatus according to a first embodiment.

FIG. 2 is an explanatory diagram showing a gradation pattern.

FIG. 3 is a flowchart showing a binarization process and a pattern selection process.

FIG. 4 is an explanatory diagram showing a binary image as a result of binarizing a uniform density area having a gradation level of 5;

FIG. 5 shows a comparison of print results when the gradation pattern of the first embodiment and a conventional single gradation pattern are used when the print head is displaced to the upper left during the second horizontal printing. FIG.

FIG. 6 is an explanatory diagram showing that several kinds of gradation patterns can be obtained by changing the read position of the gradation pattern memory.

FIG. 7 is a block diagram showing a configuration of an image processing apparatus of a second embodiment using the systematic dither method.

FIG. 8 is an explanatory diagram showing a plurality of threshold masks.

FIG. 9 is an explanatory diagram showing a conventional printing method.

[Explanation of symbols]

 10 ... Multi-valued image RAM 11 ... Binarization device 12 ... Gradation pattern memory 13 ... Pattern selection device 14 ... Binarized image RAM 15 ... Printer 16 ... Image printing device

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H04N 1/40 101 E

Claims (3)

[Claims] 1. A multi-valued image storage means for storing a multi-valued image, and a binary image storage means for storing a binary image, wherein the multi-valued image is converted into the binary image by a pseudo gradation expression method. In an image processing apparatus for converting into and printing in a plurality of gradation patterns, a gradation pattern storage means for storing a plurality of gradation patterns, a pattern switching means for switching the plurality of gradation patterns according to a pixel position of the multi-valued image, An image binarization unit that scans each pixel of a multi-valued image and stores the gradation of the gradation pattern in the binary image storage unit according to the gradation level of each pixel; and the stored gradation. 2 according to the gradation of the pattern
An image processing apparatus comprising: a printing unit that prints a value image in a dot matrix. 2. A multivalued image storage means for storing a multivalued image, and a binary image storage means for storing a binary image, wherein the multivalued image is converted into the binary image by a pseudo gradation expression method. In the image processing device for converting into and printing the value, the threshold value mask storage means for storing a plurality of threshold value masks storing a plurality of threshold values to be compared with the pixel values of the multi-valued image; Threshold mask switching means for switching the plurality of threshold masks according to the position of the pixel of the image, and scanning each pixel of the multi-valued image, the value according to the value of each pixel and the position of the pixel Image 2 for binarizing the position of the corresponding pixel in the binary image storage means according to the comparison with the threshold value.
An image processing apparatus comprising: a binarizing unit; and a printing unit that prints the binarized binary image in a dot matrix. 3. An image processing method for storing a multi-valued image, converting the stored multi-valued image into a binary image by a pseudo gradation expression method, and printing the binary image, storing a plurality of gradation patterns, Switching the plurality of gradation patterns according to the pixel position of the multivalued image, scanning each pixel of the multivalued image, determining the gradation of the gradation pattern according to the gradation level of each pixel, An image processing method, characterized in that the binary image is printed in a dot matrix in accordance with the determined gradation of the gradation pattern.