JPH0681246B2 - Halftone recording method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording method using area gradation in a heat-sensitive or thermal transfer recording device, and particularly for obtaining an image with multiple gradations and high resolution. The present invention relates to a suitable halftone recording method.

[Conventional technology]

Generally, it can be said that the dot density of a heat-sensitive or thermal transfer recording apparatus is relatively low resolution as compared with electronic plate making. In such a recording device, special measures are required to maintain the resolution and obtain multiple gradations.

By the way, in a halftone recording method using an area gradation method that expresses a halftone by the number of recording dots in a unit pixel or a pattern, if the pixel unit is increased in order to increase the number of gradations, the resolution will decrease.

In the conventional area gradation method, one picture element is expressed by an N × M matrix, and the number of heat generation dots is increased by one dot so that the recording density level monotonously increases, for example, a concentrated heat generation pattern or a distributed heat generation pattern. To produce halftones.
(For example, refer to the Journal of the Electrophotographic Society, Vol. 24, No. 1.) As one method of halftone image processing, several types of matrix pattern groups with different gradation characteristics are provided, and the groups are specified according to the required gradation characteristics. A method has been proposed in which all or part of image data is extracted from the group by specifying a matrix pattern according to the gradation data. (See, for example, JP-A-60-113582.) [Problems to be Solved by the Invention] However, in high-density recording in which the number of heat-generating dots is concentrated during high-speed recording by using a high-definition head, recording with respect to the heat-generating dot area is performed. The area becomes large due to the heat storage effect of the thermal head, and it is not possible to obtain a linear recording density with respect to the number of heating dots.

Further, in the above-mentioned halftone image processing, in order to prevent the generation of spots, patterns, pseudo contours, etc., which appear regularly or irregularly in the recorded image due to a step due to a sudden change in density in the gradation characteristics. No particular consideration was given to the pattern for connection of, that is, the organization, and there was a problem that the image quality of the recorded image deteriorates.

The object of the present invention is to maintain the texture of the pattern,
It is an object of the present invention to provide a halftone recording method in which a plurality of patterns are connected to obtain a desired gradation characteristic.

[Means for solving problems]

In order to achieve the above object, the present invention comprises (N × M) +1 matrix patterns by increasing the number of recording dots by 1 dot with respect to the matrix pattern composed of N × M dots. In the halftone recording method of creating a set of halftone dot type patterns and expressing the density of print pixels by this halftone dot type pattern, said (N × M) +1
The increasing directionality of dots in a set of halftone dot patterns each consisting of one matrix pattern has regularity between adjacent matrix patterns, and the screen angle formed by the directionality and the bottom of the matrix pattern is When a plurality of different halftone dot patterns are provided, two or more halftone dot patterns are selected from the plurality of different halftone dot pattern patterns having different screen angles, and (N × M) Extracting two or more continuous matrix patterns in which the number of recording dots in the matrix pattern differs by one dot from the halftone dot pattern consisting of one matrix pattern, and the two or more sets of dot patterns This is to create a new halftone dot pattern by connecting the matrix patterns extracted from the pattern.

[Action]

According to the above configuration, by connecting a plurality of gradation patterns having different screen angles with gradations such that the roughness is inconspicuous, it is possible to obtain an arbitrary gradation characteristic without impairing the texture between the patterns. A composite matrix pattern is obtained.

〔Example〕

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

FIG. 1 shows a gradation pattern A with different screen angles α and β.
It is the gradation characteristic III of the composite matrix pattern obtained by connecting B.

The gradation pattern A has a relatively high density when the pattern number is small, that is, the number of dots in the matrix is small,
On the other hand, in the gradation pattern B, more gradations can be obtained in the larger pattern number, that is, in the larger number of dots in the matrix, than the above-described pattern. In the figure, I and II indicate the gradation characteristics of the gradation pattern A and the gradation pattern B of the screen angle α. Here, α> β. Then, the gradation pattern A is selected in the low density region, the gradation pattern B is selected in the high density region, and both gradation patterns A and B are connected in the medium density region to form a composite matrix pattern. .

Next, a specific mode based on the screen angle will be described.

I. Figures 2 to 4 show screen angles of 45 ° and 9 respectively.
This is an example of 64 gradation patterns a, b, c of 0 °, 63.4 °, and each pattern shows the density characteristics 4, 5, 6 of FIG. 7 (a). In addition, 16 has shown the dot in a matrix pattern.

The gradation pattern a (screen angle: 45 °) has a high resolution, but the density changes greatly when the number of dots in the matrix increases, and when the number of dots further increases, the density does not become darker.

The gradation pattern b (screen angle 90 °) has a gentler density change than the gradation pattern A, and more gradations can be obtained with a larger number of dots, but roughness is more noticeable when the number of dots is smaller. .

(First Mode) FIG. 5 is a 64 gradation pattern (composite matrix pattern) obtained by connecting the gradation patterns a and b in the medium density range. This composite matrix pattern is composed of the 1st to 32nd patterns of the gradation pattern a and the 33rd to 64th patterns of the gradation pattern b, and the gradation characteristics shown in FIG. 7B are obtained.

According to this aspect, the resolution is high when the number of dots is small,
A large number of gradations can be obtained when the number of dots is large.

(Second Mode) FIG. 6 is a composite matrix pattern obtained by connecting the gradation patterns a and b with a part of the gradation pattern c (connecting matrix pattern) having an intermediate screen angle.

This composite matrix pattern is one of the gradation patterns a-1.
It is composed of No. 30, No. 31 to 34 of the gradation pattern c, and No. 35 to 64 of the gradation pattern b, and the gradation characteristic shown by the solid line 8 in FIG. 7C is obtained.

According to this aspect, since two kinds of gradation patterns having desired gradation characteristics in the low and high density regions are connected using the gradation pattern having the intermediate screen angle, the connection point of the gradation characteristics is You will be able to improve your connection and reduce steps.

II. Figures 8 and 9 show screen angles of 45 each.
This is an example of 16 gradation patterns d and e of 90 ° and 90 °, and each pattern has gradation characteristics shown by dotted lines 4A and 6A in FIG.

(Third Mode) FIG. 10 is a composite matrix pattern obtained by connecting the gradation patterns d and e in the medium density range. This composite matrix pattern is composed of gradation patterns d 1 to 8 and gradation pattern e 9 to 16, and the gradation characteristics shown by the solid line 7A in FIG. 12A are obtained.

According to this aspect, the same effect as that of the first aspect is obtained.

(Fourth Mode) FIG. 11 is a composite matrix pattern obtained by connecting the gradation patterns d and e with a part of the gradation pattern f (connecting matrix pattern) having an intermediate screen angle. This composite matrix pattern is the gradation patterns d 1 to 7,
No. 8 and 9 of gradation pattern f and 10 to 1 of gradation pattern e
No. 6 is used, and the gradation characteristic shown by the solid line 8A in FIG. 12 (b) is obtained. In addition, the patterns 8 and 9 are connection patterns formed by deciding dot positions so that the dot positions in the matrix pattern gradually approach from the dot position in the 7th pattern to the dot position in the 10th pattern. Is an example of.

According to this aspect, the same effect as that of the second aspect is obtained.

III. FIG. 13 and FIG. 14 show 32 gradation patterns g in which the screen angles of the 4 × 8 area gradation matrix of the sub-scanning recording pitch P / 2 with respect to the main scanning recording pitch P are 45 ° and 90 °, respectively. , h
, And each pattern has gradation characteristics shown by dotted lines 14 and 16 in FIG. 17 (a). Incidentally, FIG. 12, FIG. 13, FIG.
In FIG. 15, the pitch in the sub-scanning direction 14 is half the pitch in the scanning direction 13.

(Fifth Mode) FIG. 15 is a composite matrix pattern obtained by connecting the gradation patterns g and h in the medium density range. This composite matrix pattern is composed of gradation patterns g 1 to 14 and gradation pattern h 15 to 32, and the gradation characteristics shown by the solid line 17 in FIG. 18A are obtained.

According to this aspect, the same effects as those of the first and third aspects can be obtained.

(Sixth Mode) FIG. 16 is a composite matrix pattern obtained by connecting the gradation patterns g and h with a part of the connecting pattern i. This composite matrix pattern is 1 to 13 of the gradation pattern g.
No., gradation patterns i Nos. 14 to 17, and gradation pattern h
No. 18 to 32, and the solid line in Fig. 17 (b)
The gradation characteristics shown in 18 are obtained. The patterns 14 to 17 are constructed in the same manner as the patterns 8 and 9 in FIG. 11 which is the fourth mode.

According to this aspect, the same effects as those of the second and fourth aspects can be obtained.

〔The invention's effect〕

According to the present invention, since a plurality of gradation patterns having different screen angles are connected to each other with gradations such that the roughness is inconspicuous, a composite matrix pattern is formed. Since the tonal organization is maintained, recording density characteristics with good linearity can be obtained, and halftone recording without regular or irregularly appearing spots, patterns, pseudo contours, etc. becomes possible.

[Brief description of drawings]

FIG. 1 is a gradation characteristic diagram for explaining the concept of the present invention,
FIG. 2 is a diagram showing a 64-gradation pattern with a screen angle of 45 °, (a) is a diagram showing a gradation pattern represented by numbers,
(B) is a diagram showing a gradation pattern, and FIG. 3 is a screen angle
FIG. 6 is a diagram showing a 64 gradation pattern of 90 °, (a) is a diagram showing a gradation pattern represented by numbers, (b) is a diagram showing a gradation pattern, and FIG. 4 is a 64 gradation of a screen angle of 63.4 °. FIG. 5A is a diagram showing a pattern, FIG. 5A is a diagram showing a gradation pattern represented by numbers, FIG. 5B is a diagram showing a gradation pattern, and FIG. 5 is a combination of the gradation patterns of FIGS. FIG. 6 is a diagram showing a combined matrix pattern, FIG. 6 is a diagram showing a combined matrix pattern in which the gradation patterns of FIGS. 2 and 3 are connected using the gradation pattern of FIG. 4, and FIG. 2 to 4; FIG. 7 (b) is a gradation characteristic diagram of FIG. 5; FIG. 7 (c) is a gradation characteristic diagram of FIG. 6; and FIG. 8 is a screen. 16 gradation pattern of 45 ° angle, FIG. 9 shows 16 gradation pattern of 90 ° screen angle, FIG. 10 shows gradation of FIG. 8 and FIG. FIG. 11 is a diagram showing a synthetic matrix pattern in which turns are connected, FIG. 11 is a diagram showing a synthetic matrix pattern in which the gradation patterns in FIGS. 8 and 9 are connected through a connecting pattern, and FIG. 10 is a gradation characteristic diagram, FIG. 12 (b) is a gradation characteristic diagram of FIG. 11, FIG. 13 is a diagram showing 32 gradation patterns with a screen angle of 45 °, and FIG. 14 is a screen angle of 90 °. 32 gradation patterns, FIG. 15 shows a composite matrix pattern in which the gradation patterns of FIGS. 13 and 14 are connected, and FIG. 16 is FIG. 13 and FIG.
The figure which shows the synthetic matrix pattern which connected the gradation pattern of the figure through the connection pattern, FIG.17 (a) is the gradation characteristic figure of FIG. 15, FIG.17 (b) is the gradation of FIG. It is a characteristic diagram. I ... Gradation characteristics of gradation pattern of screen angle α II ... Gradation characteristics of gradation pattern of screen angle β III ... Gradation characteristics of composite matrix pattern obtained by connecting I and II.

Claims (3)

[Claims] 1. A set of halftone dot patterns consisting of (N × M) +1 matrix patterns is formed by increasing recording dots by 1 dot with respect to a matrix pattern composed of N × M dots. In the halftone recording method which is created and expresses the density of the recording pixel by this halftone dot type pattern, the (N × M) +1 matrix pattern is used.
Multiple sets of halftone dot patterns in which the increasing directionality of dots has regularity between adjacent matrix patterns, and the screen angle formed by the directionality and the bottom of the matrix pattern is different. In the case of having a dot pattern, two or more dot patterns are selected from a plurality of dot patterns having different screen angles, and (N × M) +1 matrix patterns of each selected group. In the halftone dot type pattern, the number of recorded dots in the matrix pattern is different by 1 dot, and continuous 2
A halftone recording method comprising extracting one or more matrix patterns and connecting the matrix patterns of the portions extracted from the two or more sets of halftone dot patterns to create a new halftone dot pattern. 2. A matrix pattern having a small screen angle is selected in a region where the recording density is low, and a matrix pattern having a large screen angle is selected as the recording density becomes high. Halftone recording method described. 3. When connecting matrix patterns having different screen angles, at least one connecting matrix pattern is inserted at a connecting point, the shape of one matrix pattern gradually approaching the shape of the other matrix pattern, A novel halftone dot pattern is created by forming the connecting matrix pattern by a matrix pattern in which the number of recording dots is increased by one dot from the connecting point matrix pattern of one matrix pattern. The method of recording halftones according to item 1 of the above.