JP2000350024A - Dot image recorder, dot image recording method and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a dot image with satisfactory image quality over the entire density region. SOLUTION: Density region of a received image signal is divided into three: a highlight region, an intermediate tone region and a shadow region, and a dot where number of medium tone gradation pixel/number of highest gradation pixel in a single multi-value dot in each density region is respectively ∞ to a ratio A, a ratio A to a ratio B and a ratio B to '0' is outputted. Since the ratio of a pixel number of a medium tone gradation to that of a highest gradation in the dot is suitable for each density region, roughness of an image and the instability of a dot density (dot area rate) over the entire density region are suppressed to obtain a dot image with satisfactory image quality.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dot image recording apparatus, a dot image recording method, and a recording medium for recording a dot image based on an input image signal.

[0002]

2. Description of the Related Art When a printing plate image is formed from a continuous tone original image by using a film and a printing plate, a binary network which can take any one of a density (gradation) of "0" and a maximum density per pixel has conventionally been used. Points are used.

[0003] On the other hand, in recent years, directly without using a film or printing plate,
Electrophotographic direct printing machines, ink jet printers, and the like for printing on paper have been used, and these devices can express a plurality of densities for one pixel.

FIG. 10A shows an example of a binary halftone dot.
(B) is a figure which shows the example of a multi-valued halftone dot, respectively, and each rectangle represents the pixel P. FIG. As shown in FIG.
In a multi-valued halftone dot, not only the maximum density (m) but also a plurality of levels of intermediate density (n: 0 <n <m) can be output. , A pixel with a higher density is set. By using such multi-valued halftone dots, problems such as "a large quantization error" and "a flat halftone or the like is likely to be rough" in the binary halftone dots are improved.

[0005]

By the way, even in a multi-valued halftone dot, since an intermediate density pixel and a highest density pixel coexist, in an image belonging to a density range from a half tone to a shadow, the intermediate density pixel still remains. There is a problem that the halftone dot density (halftone dot area ratio) tends to be unstable due to the fact that the density tends to be unstable.

On the other hand, JP-A-61-189774 discloses a technique for limiting the number of intermediate-density pixels, and JP-A-7-57104 discloses a technique for limiting the number of intermediate-density pixels. A technique for limiting the ratio to the number of output pixels is shown. Thus, the instability of the halftone dot density (halftone dot area ratio) from the halftone to the shadow is improved, but on the contrary, there is a problem that the roughness is slightly noticeable in the highlight density range. As described above, even in the related art using the multi-valued halftone dots, some problems occur depending on the density range of the image.

The present invention intends to overcome the above-mentioned problems in the prior art, and provides a dot image recording apparatus, a dot image recording method, and a recording medium capable of obtaining a dot image of good image quality over the entire density range. The purpose is to provide.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, an image is recorded by a multi-valued halftone dot as a set of pixels having a plurality of gradations based on an input image signal. A dot image recording apparatus, comprising: a signal acquisition unit for acquiring an input image signal; and a halftone dot generation unit for generating a halftone dot having a different ratio of the number of pixels among a plurality of gradations for each density region to which the input image signal belongs. And

According to a second aspect of the present invention, there is provided the halftone dot image recording apparatus according to the first aspect, wherein the halftone generating means stores a threshold matrix corresponding to each pixel position;
A threshold value at the pixel position of the input image signal is read out from the threshold value matrix, and a comparing unit that compares the threshold value with the input image signal, and a maximum threshold value not exceeding the density value of the input image signal is read out based on the obtained comparison result. Output means for outputting a halftone signal corresponding to the threshold matrix.

According to a third aspect of the present invention, in the halftone image recording apparatus according to the second aspect, the ratio of the number of pixels of each of the plurality of gradations in the halftone dot is different for each density range to which the input image signal belongs. A plurality of thresholds are arranged in the threshold matrix so as to fall within different predetermined ratio ranges.

According to a fourth aspect of the present invention, there is provided a dot image recording method for recording an image by a multi-valued halftone dot as a group of pixels having a plurality of gradations based on an input image signal,
A signal obtaining step of obtaining an input image signal; and a halftone generating step of generating a halftone dot having a different ratio of the number of pixels among a plurality of gradations for each density region to which the input image signal belongs.

According to a fifth aspect of the present invention, in the halftone image recording method according to the fourth aspect, the halftone generating step obtains a threshold value of the pixel position of the input image signal from a threshold matrix prepared in advance. A threshold value obtaining step, a comparing step of comparing the obtained threshold value with the input image signal, and a threshold value matrix in which a maximum threshold value not exceeding the density value of the input image signal is read based on the obtained comparison result. And an output step of outputting a halftone signal.

According to a sixth aspect of the present invention, there is provided the halftone dot image recording method according to the fifth aspect, wherein the ratio of the number of pixels of each of the plurality of gradations in the halftone dot is different for each density range to which the input image signal belongs. A plurality of thresholds are arranged in the threshold matrix so as to fall within different predetermined ratio ranges.

According to a seventh aspect of the present invention, in recording an image based on a multi-valued halftone dot as a set of pixels having a plurality of gradations based on an input image signal, the computer generates a halftone dot. An arrangement of a plurality of thresholds which generates a halftone dot having a different ratio of the number of pixels of each of a plurality of gradations for each density region to which an input image signal belongs, which is a recording medium on which a threshold matrix in which a plurality of thresholds are collected is recorded. Is recorded.

In the present invention, the gradation of the input image signal is called "density", and the gradation of each pixel within the multi-valued halftone dot (the gradation of the output image signal) is called "tone". I will. In addition, it is assumed that drawing is not performed in the “plurality of gradations” in the present invention, that is, the “0” gradation is not included.

[0016]

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

<1. First Embodiment> FIG. 1 is a block diagram showing a device configuration of a dot image recording device 1 according to one embodiment of the present invention. The halftone dot image recording device 1 is a device that outputs multi-valued halftone dots, specifically, ternary halftone dots. Hereinafter, a schematic device configuration and a schematic operation of the dot image recording device 1 will be described with reference to FIG. In the following description of the embodiment, Y (yellow) and M (magenta)
The tone of the input image signal in each color component of C (cyan) and K (black) is called “density”, and the tone (tone of the output image signal) of each pixel in the multi-valued halftone dot is called Tone ".

In the halftone image recording apparatus 1, an input image signal is first input to a color operation circuit 10, where Y, M,
The digital signals are converted into digital signals of the C and K color components, sent to the image signal memory 20, and stored. The matrix memory 30 has a threshold matrix (1/2 gradation,
2/2 gradations) are recorded, and a threshold value at a position corresponding to the input image signal in each of the threshold value matrices;
And the input image signal after the color calculation from the image signal memory 20 described above is read into the comparator 40, and
Then, the read threshold value is compared with the input image signal, and the comparison result is sent to the gradation selection circuit 50.

The tone selection circuit 50 determines the tone corresponding to the maximum threshold value not exceeding the density of the input image signal as the tone of the output image from the comparison result, and converts the halftone image signal into a direct printing machine. To an output unit 60 such as an ink jet printer, which has an output unit capable of outputting multiple gradations, and the output unit 60 generates an output image.

The halftone dot image recording apparatus 1 includes a reading unit 70, which reads a threshold matrix from a recording medium RM such as a magnetic disk or an optical disk in which the threshold matrix is recorded, if necessary, and stores it in the matrix memory 30. You can also do it.

In the halftone dot image recording apparatus 1, the ratio of the number of pixels among a plurality of gradations in the halftone dot in the output image falls within a predetermined ratio range corresponding to the density range to which the input image signal belongs. In particular, the higher the input image signal belongs to the higher density range, the higher the ratio of the highest gradation pixel is.

FIG. 2 is a flowchart of the halftone image recording process. Hereinafter, the halftone image recording process according to the first embodiment will be described with reference to FIG. Prior to the start of the processing, an externally input image signal is subjected to color operation in a color operation circuit 10 and then recorded in an image signal memory 20.

First, the input image signal of the target pixel is read from the image signal memory 20 into the comparator 40 (step S).
1).

Next, the threshold value at the position corresponding to the target pixel is read out from each threshold value matrix recorded in the matrix memory 30 to the comparator 40 (step S2).

FIG. 3 is a diagram showing an example of a threshold value matrix according to the first embodiment. In the first embodiment, it is possible to output a ternary halftone dot having a maximum grayscale, an intermediate grayscale, and “0” (no drawing) as grayscales in a halftone dot. In contrast, a threshold matrix of 1/2 gradation shown in FIG. 3A and a threshold matrix of 2/2 gradation shown in FIG. When the pixels to be processed in the image recording process are shifted by one pixel at a time, and the pixels to be processed are set as target pixels, both threshold matrices are applied to the input image, and the target matrices are set in the threshold matrices. The threshold at the position corresponding to the pixel (threshold of 1/2 gradation, threshold of 2/2 gradation) is read.

Next, in the comparator 40, the obtained threshold value is compared with the input image signal, and the gradation selection circuit 50 obtains the gradation of the target pixel based on the result (step S).
3). That is, the two threshold values read by the comparator 40 are compared with the density of the input image signal of the read target pixel. By comparing with the two thresholds, the corresponding gray scale of the threshold matrix that includes the maximum threshold that does not exceed the density of the input image signal (in the first embodiment, the threshold is １ ／ gray scale) If the threshold matrix exceeds the density of the input image signal, the maximum grayscale is included in the threshold matrix of the input image signal, and the halftone is included in the threshold matrix of 2/2 grayscale. Is “0”) as the gradation of the target pixel.

For example, if the density of the input image signal of the target pixel is "10", the area AR in FIG.
3 does not exceed the density of the input image signal in FIG. 3B. Then, when the target pixel is included in the area AR2 in FIG. 3B, the output image signal of the target pixel is set to the maximum gradation, and FIG.
The region AR in FIG. 3A is not included in the region AR2 in FIG.
1, the output image signal of the target pixel is set to an intermediate gradation, and if the output image signal of the target pixel is included in an area other than the area AR1 in FIG. Is set to "0".

In this manner, the gradation of the output image signal of each target pixel is determined. In the present invention, the ratio of the number of pixels of the plurality of gradations included in the same multi-valued halftone dot is determined. (Hereinafter simply referred to as “pixel ratio”) is determined to be within a predetermined ratio range set for each density region to which the input image signal belongs. In particular, in the first embodiment, the ratio of the number of pixels of the intermediate gradation to the number of pixels of the maximum gradation is different depending on the density range of the input image signal as the pixel ratio in each halftone dot in the output image, particularly , The pixel ratio becomes lower as the density becomes higher.

FIG. 4 is a diagram showing a pixel ratio range in each density range of the input image signal in the first embodiment. FIG.
As shown in (a), in the first embodiment, the density range of the input image signal is divided into three areas of highlight, halftone, and shadow, and the ratio of the number of halftone pixels to the maximum number of grayscale pixels is respectively determined. A halftone dot whose (number of intermediate gradation pixels / maximum gradation pixel number) is Δ to ratio A, ratio A to ratio B, and ratio B to “0” is output. The ratios A and B represent arbitrary ratios (however, ratio A> ratio B). In the following, N / 0 = ∞ for a positive number N.

As a method of forming a halftone dot having such a ratio of the number of pixels, specifically, a threshold matrix to be used is arranged such that the threshold matrix has such a ratio of the number of pixels. The halftone dots as described above are realized by creating them in advance and using them.

FIG. 5 is a conceptual diagram for explaining a method of obtaining the arrangement of thresholds in the threshold matrix according to the present invention. In FIG. 5A, the vertical axis represents the density of the input image signal, that is, the threshold value to be set in the threshold matrix. The horizontal axis represents a pixel position. In each of the density areas of the shadow area, the halftone area, and the highlight area, the ideal arrangement of the thresholds in the halftone and 2/2 grayscale threshold matrices is represented by threshold distribution surfaces T1i and T2i in FIG. (I = 1 (shadow), 2 (halftone), 3 (highlight)). That is, the threshold distribution surfaces T1i and T1i at arbitrary pixel positions
The density value of 2i indicates a threshold value at which the ratio of the number of pixels of the highest gradation pixel to the number of intermediate gradation pixels becomes a predetermined value at the pixel position.

However, since the pixel positions in the threshold matrix actually have a two-dimensional spread as shown in FIG. 3, one cross section is shown in FIG. 5 (a). Assuming a circular halftone dot as a virtual halftone dot, FIG.
The ideal threshold value arrangement is on a rotating body (distribution curved surface) obtained by rotating a curve in the cross section of the threshold distribution curved surfaces T1i and T2i in (a) about the axis of symmetry in the vertical axis direction. FIG. 5 (b),
(C) and (d) respectively show a shadow area, a halftone area,
It is a figure showing a section in a plane (horizontal plane) perpendicular to a vertical axis and parallel to a horizontal axis of a threshold distribution curved surface in a highlight area.

Therefore, considering a halftone dot for an input image signal having an arbitrary density using the threshold matrix created by the threshold distribution surfaces T1i and T2i, the cross section (horizontal) of the threshold distribution surfaces T1i and T2i at an arbitrary density can be considered. (Cross section), a halftone dot in which the pixel inside the threshold distribution curved surface T1i has the highest gradation and the pixel between T2i and T1i is the pixel having the intermediate gradation is considered. The ratio of the area (the number of pixels) inside the threshold distribution curved surface T1i to the area (the number of pixels) between the threshold distribution curved surfaces T1i and T2i represents the pixel ratio. As can be seen from FIG. In each density range, the density is substantially constant regardless of the density. This corresponds to the fact that the pixel ratio varies depending on the density range of the input image signal in the present invention. Specifically, as can be seen from FIGS. 5B, 5C, and 5D, the ratio of the number of intermediate gradation pixels to the number of highest gradation pixels gradually decreases as the density range increases (becomes darker). I understand. That is, the area (the number of pixels) within the threshold distribution surface T1i
, The ratio of the area (the number of pixels) between the threshold distribution curved surfaces T1i and T2i decreases in the order of the highlight area, the halftone area, and the shadow area.

However, since the threshold values in the threshold value matrix do not overlap and the pixel ratio has a predetermined range (expansion) as shown in FIG. The thresholds of all the pixels cannot be exactly the values on the threshold distribution surfaces T1i and T2i, and the thresholds within a predetermined width near the threshold distribution surfaces T1i and T2i are set so as to be within the above pixel ratio range. select.
Further, in FIG. 5, the cross-sectional shapes of the threshold distribution curved surfaces T1i and T2i are circular, but actually, it is necessary to have a cross section of a desired halftone dot shape. In the present invention, the threshold matrix thus obtained is used.

Next, the output pixel 60 draws the target pixel at the obtained gradation (step S4). FIG. 6 is a diagram showing an example of a halftone dot in each density region. In FIG. 6, FIG.
A case where the ratio A = 3 and the ratio B = 0.5 in the pixel ratio range shown in FIG. Figure 6 in the highlight area
In the example of (a) in which the density value of the input image is “2” (pixels having a threshold value of “1” or less are output), the threshold matrix is applied as can be understood by referring to the threshold matrix of FIG. Only two pixels are output in a section of × 4 pixels, and the pixel ratio, that is, the number of intermediate gradation pixels / the maximum number of gradation pixels is 2
/ 0 = ∞. Similarly, in the example of FIG. 6B where the density value of the input image is “10” (pixels having a threshold value of “9” or less are output),
/ 2 = 3, which satisfies the pixel ratio range ∞ to the ratio A (= 3) in the highlight area shown in FIG.

In the halftone range, the density value of the input image shown in FIG. 6C is "13" (pixels having a threshold value equal to or less than "12" are output).
In the example of FIG. 6, the pixel ratio is 7/3, and similarly, in the example of FIG. 6D where the density value of the input image is “20” (pixels having a threshold value of “19” or less are output), 6/2 = 3. 4 (a), the pixel ratio range of the halftone region, ratio A (= 3) to ratio B (=
0.5).

Further, in the example of FIG. 6 (e) where the density value of the input image is "23" (pixels below the threshold value "22" are output) in the shadow area, the pixel ratio is 1/11, and FIG. )
Is 1/13 in the example where the density value of the input image is “27” (pixels below the threshold “26” are output), the pixel ratio range of the shadow area and the ratio B (= 0) shown in FIG. .5)-
"0" is satisfied.

By outputting at such a pixel ratio, a good image quality can be obtained over the entire density range from highlight to shadow.

If it is determined in step S5 that the processing for all the pixels has not been completed, the process returns to step S1 with the next pixel as the target pixel, and returns to steps S1 to S5.
4 is performed, and each target pixel is output while sequentially moving the target pixel. Then, when the output for all the pixels is completed, it is determined that the processing for all the pixels is completed in step S5, and the output of the halftone image is completed.

Although the above is an example in which the pixel ratio range shown in FIG. 4A is set, other pixel ratio ranges can be set. FIG. 4B shows an example in which another pixel ratio range is set. In this example, when the ratio A = ∞, that is,
An example is shown in which halftone dots are formed in all intermediate gradations.

By using such a threshold matrix, the highest gradation pixel is not output in the highlight area, and therefore, in the highlight portion of the output image,
In particular, it is possible to obtain good image quality with less image roughness.

FIG. 4C shows an example in which another pixel ratio range is set. In this example, when the ratio B = 0, that is, in the shadow area, no halftone pixel is included. An example in which halftone dots are formed by the highest gradation pixels is shown. Then, in this case, a pixel position having a threshold included in the shadow area of the threshold matrix for the halftone,
A threshold having the same value as the threshold of the threshold matrix for higher gradations (for 2/2 gradation in the first embodiment) is arranged.

FIG. 7 is a diagram showing an example of halftone dots in each density range when the pixel ratio range of FIG. 4C is set. In FIG. 7, the ratio A in the pixel ratio range shown in FIG.
= 3 and the ratio B = 0. In the highlight, the pixel ratio (the number of intermediate gradation pixels / the maximum number of gradation pixels) is 2/0 = ∞ in the example of FIG. 7A, and 6/2 = 3 in FIG. The pixel ratio range ∞ to the ratio A (= 3) in the highlight area shown in c) is satisfied.

In the halftone region, the pixel ratio is 7/3 in the example of FIG. 7C, and 1/11 in FIG. 7D.
The pixel ratio range of the highlight shown in FIG.
3) The ratio B (= 0) is satisfied.

Further, in the shadow area, the pixel ratio is 0/13 = 0 in the example of FIG. 7E, and 0/15 = 0 in the example of FIG. 7F.
0, which satisfies the highlight pixel ratio range and ratio B (= 0) to “0” shown in FIG.

Since such a threshold matrix is used, no halftone pixel is output in the shadow area, and therefore, in the shadow portion of the output image, good image quality with stable dot density (dot area ratio) is obtained. Can be obtained.

As described above, according to the first embodiment, when recording an image using multi-valued halftone dots, halftone dots having different pixel ratios for each density range to which the input image signal belongs are generated. Thus, it is possible to obtain a dot image of good image quality over the entire density range.

In order to use a threshold matrix in which a plurality of thresholds are arranged so that a pixel ratio falls within a predetermined ratio range that differs for each density region to which an input image signal belongs, such a threshold matrix is prepared. Alone, it is possible to easily generate a halftone dot having a different pixel ratio for each density area to which the input image signal belongs, and to record such a multi-valued halftone image without having a special mechanism for it. In addition, the manufacturing cost of the apparatus can be reduced.

<2. Second Embodiment> FIG. 8 is a diagram showing a pixel ratio range in each density range of an input image signal according to a second embodiment. In the second embodiment, the halftone area of the density area is divided (divided into three) to provide areas of halftone 1, halftone 2, and halftone 3. That is, the density range of the input image signal is divided into five areas of highlight, halftone 1, halftone 2, halftone 3, and shadow, and the ratio of the number of halftone pixels to the maximum number of halftone pixels (intermediate level) Number of toned pixels /
A halftone dot whose maximum gradation pixel number is Δ to ratio A, ratio A to ratio B, ratio B to ratio C, ratio C to ratio D, and ratio D to “0” is output. The ratios A, B, and C each represent an arbitrary ratio (however, ratio A> ratio B> ratio C> ratio D).

The device configuration of the halftone dot image recording apparatus 1 of the second embodiment is almost the same as that of the first embodiment.
Further, the halftone dot image recording processing in the second embodiment is almost the same as the first embodiment except that the threshold matrix is different as described above.

FIG. 9 is a diagram showing an example of halftone dots in each density range when the pixel ratio range of FIG. 8 is set. In FIG. 9, the ratio A = ∞ and the ratio B in the pixel ratio range shown in FIG.
= 2, ratio C = 0.5, ratio D = 0. In the highlight region, in the example of FIG. 9A, the pixel ratio (the number of intermediate gradation pixels / the number of highest gradation pixels) is 1/0 = ∞.
In (b), 3/0 = ∞, which satisfies the pixel ratio range ∞ to the ratio A (= ∞) in the highlight area shown in FIG.

In the example of FIG. 9 (c), the pixel ratio is 3/1 = 3 in the halftone 1 and 4/2 in FIG. 9 (d), and the pixel ratio range of the halftone 1 shown in FIG. , Ratio A (= ∞) ~
The ratio B (= 2) is satisfied.

In the case of the halftone 2, the pixel ratio is 5/3 in the example of FIG. 9E, and 4/8 = 0.5 in the case of FIG. 9F, and the pixel of the halftone 2 shown in FIG. Ratio range, ratio B (=
2) -Ratio C (= 0.5) is satisfied.

In the case of halftone 3, the pixel ratio is 2/10 = 0.2 in the example of FIG. 9 (g) and 1/11 in FIG. 9 (h), and the pixel of halftone 3 shown in FIG. Ratio range, ratio C
(= 0.5) to the ratio D (= 0).

Further, in the shadow area, the pixel ratio is 0/12 = 0 in the example of FIG. 9 (i), and 0/14 = 0 in the example of FIG. 9 (j).
0, which satisfies the pixel ratio range of the shadow area shown in FIG. 8, that is, the ratio D (= 0) to “0”.

As described above, according to the second embodiment, the same effects as those of the first embodiment can be obtained, and the halftone range is divided into halftones 1 and 2, and the halftone range is divided into two. By making the pixel ratios different, the halftone expression in the halftone region is more finely adjusted, and the instability of halftone dot density (halftone dot area ratio) in halftone and the roughness of the image are further suppressed. Even better image quality can be obtained. In the highlight region, the highest gradation pixel is not included, and in the shadow region, no intermediate gradation pixel is included. Thus, a good image can be obtained even in these density regions.

<3. Modifications> In the first and second embodiments, examples of the dot image recording apparatus 1 and the dot image recording processing by the dot image recording apparatus 1 have been described, but the present invention is not limited to this.

For example, in the above-described first and second embodiments, ternary halftone dots have been described as halftone dots that can be output. However, the present invention can be applied to an apparatus that targets halftone dots of four or more values. it can. In that case, the number of threshold matrices recorded in the matrix memory 30 is three (the number of gradations of the multi-valued halftone dot-
1) As described above, the comparator can also compare three or more threshold values with the input image signal.

In this case, the pixel ratio is (number of pixels other than the highest gradation / number of highest gradation pixels) or (number of pixels of any gradation other than the highest gradation / number of highest gradation pixels). )And it is sufficient. Specifically, in the case of a quaternary halftone dot, if the output gradation has １ ／ gradation, ／ gradation, and ／ gradation, the former is (２ gradation pixel number +＋ １). Number of gradation pixels) / (3 /
(The number of 3 gradation pixels), and the latter is, for example, (2/3 gradation pixel number) / (3/3 gradation pixel number). Then, a threshold matrix is used such that the pixel ratio falls within a predetermined ratio range corresponding to the density range of the input image signal. Correspondingly, the dot image recording process differs in that the output of the target pixel in step S4 in FIG. 2 is drawn at any gradation in the quaternary dot.

[0060]

As described above, according to the first to seventh aspects of the present invention, in recording an image using a multi-valued halftone dot, a plurality of multi-valued halftone dots for each density range to which an input image signal belongs are recorded. Since a halftone dot having a different ratio of the number of pixels between the gradations is generated, good image quality can be obtained over the entire density range.

According to the third and sixth aspects of the present invention, the ratio of the number of pixels of each of the plurality of gradations in the halftone dot image is within a predetermined ratio range that differs for each density range to which the input image signal belongs. Since a plurality of thresholds are arranged in the threshold matrix, the ratio of the number of pixels among the plurality of gradations can be easily changed for each density region to which the input image signal belongs simply by preparing such a threshold matrix. In addition to the above, it is possible to generate a different multi-valued halftone dot and record such a multi-valued halftone image without providing a special mechanism for it, so that the manufacturing cost of the apparatus can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a device configuration of a dot image recording device according to an embodiment of the present invention.

FIG. 2 is a flowchart of a halftone image recording process.

FIG. 3 is a diagram illustrating an example of a threshold matrix according to the first embodiment.

FIG. 4 is a diagram illustrating a pixel ratio range in each density range of an input image signal according to the first embodiment.

FIG. 5 is a conceptual diagram for explaining a method of determining the arrangement of thresholds in a threshold matrix according to the present invention.

FIG. 6 is a diagram illustrating an example of a halftone dot in each density region.

FIG. 7 is a diagram illustrating an example of halftone dots in each density range when the pixel ratio range of FIG. 4C is set.

FIG. 8 is a diagram illustrating a pixel ratio range in each density range of an input image signal according to the second embodiment.

9 is a diagram illustrating an example of a halftone dot in each density region when the pixel ratio range in FIG. 8 is set.

FIG. 10 is a diagram illustrating examples of a binary halftone dot and a multilevel halftone dot.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 halftone image recording device 10 color operation circuit (signal acquisition means) 30 matrix memory (storage means) 40 comparator (comparison means) 50 gradation selection circuit (halftone generation means in combination with output means, 30, 40) RM recoding media

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2C262 AA24 AB07 BB03 BB06 BB14 BB19 BB23 BB27 BC01 BC07 5B057 BA28 CA01 CA08 CA12 CA16 CB01 CB07 CB12 CB16 CC01 CE11 CE13 CH07 CH18 5C077 LL19 MP08 NN03 NN04Q08 PP08 TT02 TT06 TT08

Claims (7)

[Claims] 1. A halftone dot image recording apparatus for recording an image based on a multi-valued halftone dot as a group of pixels having a plurality of gradations based on an input image signal, comprising: signal acquisition means for acquiring an input image signal; A halftone image recording apparatus comprising: halftone dot generating means for generating a halftone dot having a different ratio of the number of pixels among the plurality of gradations for each density area to which the input image signal belongs. 2. A halftone dot image recording apparatus according to claim 1, wherein said halftone dot generating means stores a threshold matrix corresponding to each pixel position, and a threshold value of a pixel position of an input image signal. A comparison means for reading out from the threshold value matrix and comparing the input image signal with the input image signal. Based on the obtained comparison result, the maximum value threshold value not exceeding the density value of the input image signal corresponds to the threshold value matrix read out. And an output means for outputting a halftone signal. 3. The halftone dot image recording apparatus according to claim 2, wherein a ratio of the number of pixels of each of the plurality of gradations in the halftone dot falls within a predetermined ratio range that differs for each density region to which the input image signal belongs. A halftone image recording apparatus, wherein a plurality of thresholds are arranged in the threshold matrix. 4. A halftone dot image recording method for recording an image by multi-valued halftone dots as a group of pixels having a plurality of gradations based on an input image signal, comprising: a signal acquiring step of acquiring an input image signal; A halftone dot recording step of generating a halftone dot having a different ratio of the number of pixels among the plurality of gradations for each density region to which the input image signal belongs. 5. The halftone image recording method according to claim 4, wherein the halftone generation step obtains a threshold value of a pixel position of an input image signal from a threshold matrix prepared in advance. Comparing the input image signal with the threshold value obtained, based on the obtained comparison result, the halftone dot corresponding to the threshold value matrix from which the maximum threshold value not exceeding the density value of the input image signal is read out An output step of outputting a signal. 6. The halftone dot image recording method according to claim 5, wherein a ratio of the number of pixels of each of the plurality of gradations in the halftone dot is within a predetermined ratio range that differs for each density range to which the input image signal belongs. A halftone image recording method, wherein a plurality of threshold values are arranged in the threshold value matrix. 7. A computer which records a plurality of thresholds for generating halftone dots when recording an image based on multi-level halftone dots as a group of pixels having a plurality of gradations based on an input image signal. On a recording medium on which the matrix is recorded, a threshold matrix having a plurality of threshold arrangements such that halftone dots having different ratios of the numbers of pixels of the plurality of gradations are generated for each density region to which the input image signal belongs is recorded. A computer-readable recording medium characterized by the following: