JPH08104033A - Gradation pattern expression method, gradation pattern storage device and printing device - Google Patents

Abstract

(57) [Abstract] [Purpose] To increase the number of gradations that can be expressed without increasing the number of dots that form a pixel. [Structure] The gradation data input through the input / output interface 11 is stored in the image memory 13a. The gradation data stored in the image memory 13a is converted into print dot pattern data based on the contents of the gradation pattern table 12a, and is temporarily stored in the print buffer 13b. The print dot pattern data stored in the print buffer 13b is sequentially printed on the recording paper by the printer unit 15. The gradation pattern stored in the gradation pattern table 12a utilizes the change in effective area due to the overlapping of effective dots, and has a gradation that can be expressed in comparison with the number of dots forming one pixel. Is increasing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradation pattern expression method, a gradation pattern storage device, and a printing device, and more particularly to forming one pixel with a plurality of dots and differently arranging effective dots forming one pixel. The present invention relates to a gradation pattern expression method for expressing different gradations with the same effective dot, a gradation pattern storage device, and a printing device.

[0002]

2. Description of the Related Art When printing an image having a large number of gradations such as a video image, it is necessary to effectively express a large number of gradations. When printing such multi-tone image data, the printing device does not have the tone expressing ability,
That is, when only dots of a single gradation can be printed, a method called a gradation pattern method (density pattern method) is generally used.

In the gradation pattern method, one pixel is made up of a plurality of dots, and the number of effective dots (colored dots) in each pixel is changed to obtain the area (effective area) of the colored portion in each pixel. Is expressed to express gradation. For example, 4
Taking the dot × 4 dot matrix method as an example, FIG.
4 dots x 4 dots (= 16 dots) as 1
It is regarded as a pixel, the number of effective dots is changed from 0 to 16 to change the area to be printed (colored), and 17 gradations in total are pseudo-expressed.

When 17 or more gradations are required, the number of dots forming one pixel is increased to increase the expressible gradation. For example, by setting one pixel to 5 dots × 5 dots, 26 gradations can be expressed. Further, for example, in the case of a thermal transfer printer, there is also a method of controlling the heat generation amount of the heat generation head by adjusting the strobe time (energization time of the heat generation element) to increase the number of gradations to be expressed.

[0005]

As described above, in the gradation pattern method, the number of dots forming one pixel must be increased in order to increase the number of gradations to be expressed. However, when the number of dots is increased, the number of gradations that can be expressed increases, but the number of dots that form the entire image also increases. Therefore, if you do not change the size of the dots,
The image itself becomes large. In order not to change the size of the image, it is necessary to use a printing device with fine dots, that is, a high resolution, which increases the cost. Further, if the strobe time is adjusted to control the heat generation amount of the heat generation head to increase the number of gradations that can be expressed, there is a drawback that the print result is likely to be blurred.

The present invention has been made in view of the above-mentioned circumstances, and a gradation pattern expression that makes it possible to increase the number of gradations that can be expressed without increasing the number of dots of a matrix that constitutes a pixel. An object of the present invention is to provide a method, a gradation pattern storage device, and a printing device.

[0007]

In order to achieve the above-mentioned object, a gradation pattern expression method according to a first aspect of the present invention is such that one pixel is composed of a plurality of n × m dots and In the method of expressing a gradation pattern of a gradation image in which the density of the black dots is changed to express the gradation, the arrangement of the black dots in one pixel is changed so that the pixels having the same black dot density are different. It is characterized by expressing gradation.

In the gradation pattern storage device according to the second aspect of the present invention, one pixel is composed of a plurality of n × m dots, and the density of black dots in the one pixel is changed to change the gradation. In a storage device for storing a plurality of gradation pattern data to be expressed, a plurality of gradation pattern data in which the density of black dots in one pixel is the same and the arrangement of black dots is changed is stored.

Further, according to a third aspect of the present invention, in a printing device, one pixel is composed of a plurality of n × m dots, and the number and arrangement of colored dots in one pixel are changed to obtain the same number of dots. Storage means for storing a plurality of gradation pattern data having different effective areas, and n × for each pixel of the image to be printed.
The gradation data supplying means for supplying gradation data indicating any of the gradations greater than m + 1 and the gradation pattern corresponding to the gradation data supplied from the gradation data supplying means are stored in the memory. And a printing unit that prints the read gradation pattern.

[0010]

The gradation pattern method basically expresses gradation by changing the area of the colored portion of each pixel by changing the number of dots to be printed among a plurality of dots forming one pixel. To do. However, in an actual printing device, for example, due to the spread of the ink, an overlapping portion of the ink occurs between adjacent dots. Therefore, even when printing the same number of dots, by controlling the arrangement of the dots to be printed (effective dots), the effective area (the area of the part where ink is attached) can be made different and different gradations can be expressed. . Therefore,
By controlling the arrangement of dots, the pseudo halftone can be increased as compared with the conventional one.

The gradation pattern expression method according to the first aspect of the present invention uses such a method to change the arrangement of black dots in one pixel so that pixels having the same black dot density are different. Expresses different gradations.

A gradation pattern storage device according to a second aspect of the present invention stores gradation (density) pattern data obtained by using the above-described method, and the gradation pattern data is stored in a printing device, for example. I will provide a.

Further, the printing apparatus according to the third aspect of the present invention may configure one pixel by n × m dots by using the gradation pattern data obtained by using the above method. Instead, an image with a gradation number greater than n × m + 1 is printed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a gradation pattern expressing method according to an embodiment of the present invention will be described. As shown in FIG. 5, in the thermal transfer printer using the hot-melt ink ribbon IR, the heat generated by the heating element HE of the heating head diffuses in the ink I while spreading in the base tape BT of the hot-melt ink ribbon IR.
It is transmitted to N and melts the ink IN. Then, the melted ink IN is transferred to the recording paper.

Therefore, the dots actually printed are as shown in FIG.
Instead of the quadrangle as shown in FIG. 3, a bulge occurs depending on the characteristics of the heating head including the heating element HE, the thermal transfer ink ribbon, etc., and becomes a circle or an ellipse. The bulged dot can be approximated by a circle circumscribing an ideal rectangular dot. Therefore, depending on the arrangement of the dots to be printed, the dots may or may not overlap.

For example, when two spaced dots are printed as shown in FIG. 6A and when two vertically or horizontally adjacent two dots are printed as shown in FIG. The effective area inside (the area of the part where ink is attached) is different. Therefore, the pixel shown in FIG. 6A and the pixel shown in FIG. 6B have the same black dot density, but a difference occurs in the gradation of the pixel.

In this embodiment, the change in the effective area due to the positional relationship of the effective dots is used to form a gradation (density) pattern, and the number of dots forming one pixel +
An image can be printed with a number of gradations greater than one.

Assuming that the theoretical dot shape is a unit square with one side having a unit length of "1", the area of a circle circumscribing the unit square shown in FIG. 7A is shown in FIG. 7B. The area of the unit square, the difference between the area of the unit square shown in FIG. 7C and the area of the circumscribed circle, the area of the portion protruding to the adjacent dot of the circumscribed circle shown in FIG. 7D, and the adjacency shown in FIG. The area of the overlapping part of the circumscribing circles of the two dots, the area of the two adjacent circumscribing circles shown in FIG. 7F, and the area of the two non-overlapping circumscribing circles shown in FIG. Like

[0019]

## EQU1 ## (A) πr ² = π {√ (2) / 2} ² = π / 2
≈1.57 (B) 1 × 1 = 1 (C) (π / 2) -1≈0.57 (D) {(π / 2) -1} ÷ 4≈0.14 (E) [{( π / 2) -1} ÷ 4] × 2≈0.29 (F) (π / 2)-[{(π / 2) -1} ÷ 4] × 2
≈2.86 (G) (π / 2) + (π / 2) = π≈3.14

Taking these values into consideration, an example of a gradation pattern group selected so that the effective area changes relatively uniformly is shown in FIGS. 1 (A) to 1 (O) and 2 (A) to 2 (A). Two
(O), FIGS. 3 (A) to 3 (O), and FIGS. 4 (A) to 4 (G).

Each gradation pattern shown in FIGS. 1A to 4G is composed of a matrix of 4 dots × 4 dots and expresses 52 gradations.

The numbers at the lower left of each matrix in FIGS. 1A to 4G indicate gradation numbers (1 to 52),
The numbers in the lower right show the effective areas (0 to 16) obtained by the approximate calculation of FIGS. 7 (A) to (G).

In the gradation pattern of gradation number 1 in FIG. 1A, there are 0 effective dots and the effective area (the area of the area where the ink adheres) is 0. The gradation pattern of gradation number 2 in FIG. 1B has one effective dot and an effective area of 1.5.
7 The gradation patterns in FIGS. 1C and 1D are
Although there are both two effective dots, the gradation pattern of gradation number 3 shown in FIG. 1C has two effective dots vertically adjacent to each other and an effective area of 2.86. Figure 1 (D)
In the gradation pattern of gradation number 4, the two effective dots are diagonally arranged adjacent to each other and the printing area is 3.14. The gradation patterns of FIGS. 1E to 1G have three effective dots, but the arrangement of the effective dots is different.
The effective areas are 4.14, 4.43 and 4.71 respectively. After that, the effective area gradually increases in the same manner as shown in FIG.
The effective area of the gradation pattern of gradation number 51 in (F) is 1
5.57, the effective area of the gradation pattern of gradation number 52 in FIG. 4G is 16.00. As described above, according to the gradation pattern expression method of this embodiment, the effective area of the matrix of 4 dots × 4 dots continuously changes in 52 steps, and 52 steps of gradation can be expressed.

An embodiment of the printing apparatus using the gradation pattern set in this way will be described below with reference to FIG.
As shown in the figure, this printing apparatus includes an input / output interface (I / O) 11 and a ROM (read only memory).
12, a RAM (random access memory) 13, a display unit 14, a printer unit 15 and a CPU (central processing unit) 16 are provided.

The input / output interface 11 is an interface for connecting the printing apparatus to an external device, and fetches digital gradation data indicating any one of 52 kinds of gradations supplied from the external device.

The ROM 12 includes programs, data, etc. necessary for the operation of this printing apparatus, as shown in FIGS.
The gradation pattern data indicating each gradation pattern shown in (G) is stored, and it functions as a gradation pattern generation device.

The RAM 13 includes an image memory 13a for storing gradation data supplied from the outside and a print buffer 13b for storing image data to be printed in a bitmap format, and stores various data. The display unit 14 displays an image based on the gradation data, information regarding the operation and operation of this printing apparatus, and the like.

The printer unit 15 is composed of a thermal head, a thermal transfer ink ribbon, a carriage, and a thermal dot printer having a platen and the like. The heating head includes a plurality of heating elements HE that are linearly arranged in the sub-scanning direction, and controls energization of the heating elements HE to control the amount of heat generated by the heating elements. As indicated by a broken line DE in FIG. 5, the heat generated by the heating element HE is transferred while being diffused in the base tape BT of the thermal transfer ink ribbon IR, and melts the ink IN. The melted ink IN is transferred to the recording paper PA,
The image is printed. The ink IN transferred by one heat generation of the heating element HE corresponds to one black dot of the gradation pattern shown in FIGS. 1 (A) to 4 (G).

The CPU 16 is the input / output interface 1
1, the ROM 12, the RAM 13, the display unit 14, and the printer unit 15 are controlled to control the operation of the entire printing apparatus.
Particularly, in this embodiment, the gradation data fetching operation, the printing dot pattern data converting operation, and the printing operation are controlled.

The printing operation of the gradation image of the printing apparatus of FIG.
This will be described with reference to the functional block diagram shown in FIG. As shown in FIG. 8, the gradation data externally supplied via the input / output interface 11 is under the control of the CPU 16,
It is stored in the image memory 13a in the RAM 13. CPU
Reference numeral 16 indicates the RO gradation data stored in the image memory 13a.
The gradation pattern table 12a in M12 is referred to and converted into print dot pattern data, which is stored in the print buffer 13b in the RAM 13 in the bitmap format.

For example, when the gradation data indicates gradation "0", the CPU 16 causes the gradation pattern table 12a.
1A, the grayscale pattern data of the grayscale pattern shown in FIG. 1A is read, and the read grayscale pattern data is written in the corresponding address position of the print buffer 13b as a bitmap pattern. Similarly, when the gradation data indicates the gradation "50", the CPU 16 refers to the gradation pattern table 12a to read the gradation pattern data of the gradation pattern shown in FIG. The gradation pattern data is written in the corresponding address position of the print buffer 13b in the bitmap format.

Under the control of the CPU 16, the printer section 15 sequentially reads out the print dot pattern data stored in the print buffer 13b, controls the energization of the heating element while scanning the heating head in the main scanning direction, and controls the ink. Ribbon I
The ink IN on R is melted and transferred to the recording paper PA, and a gradation image is printed. The CPU 16 alternately repeats the operation of forming print dot pattern data in the print buffer 13b and the operation of controlling the printer unit 15 to print, for example, one line or one page, and prints gradation images sequentially. .

In this way, each pixel is composed of 16 dots and an image having 52 gradations can be printed.

In the above embodiment, the case of printing a monochromatic gradation image has been described, but the present invention can be applied to the printing of a color gradation image. The configuration and operation for printing a color gradation image will be described by taking a video printer for color printing a video image as an example.

In this case, as shown in FIG. 10, the input / output interface 11 is supplied with, for example, an analog NTSC composite video signal supplied from a video deck or the like. The input / output interface 11 is an A / D
An (analog / digital) converter 11a, an RGB conversion circuit 11b, a YMC conversion circuit 11c, etc. are provided, the NTSC composite video signal is A / D converted, the converted digital signal is converted into RGB gradation data, and further RGB The gradation data is converted into Y, M, and C gradation data indicating the gradations of YMC. The CPU 16 stores the Y, M, and C gradation data in the Y image memory 13aY, the M image memory 13aM, and the C image memory 13aC in the RAM 13, respectively.

The CPU 16 converts the Y gradation data into a print dot pattern by referring to the gradation pattern table 12a and expands it on the print buffer 13b of the RAM 13. A predetermined amount of print dot pattern data is printed in the print buffer 13b.
Then, the CPU 16 sequentially reads the print dot pattern data and supplies it to the printer unit 15.

The printer unit 15 is, for example, a thermal transfer type dot printer that prints a color image by using a color ink ribbon in which three color inks of Y, M, and C are sequentially arranged and formed, and the supplied printing is performed. Based on the dot pattern data, a Y-color image of 52 gradations is printed using Y-color ink.

When the printing of the Y-color image is completed, the CPU 1
Reference numeral 6 converts the M gradation data into print dot pattern data by referring to the gradation pattern table 12a, develops it on the print buffer 13a, controls the printing unit 15 and uses the M color inks to generate the M color data. Print the image over the Y color image. Similarly for C color, print dot pattern data is formed, and C color ink is used to perform overprinting.

Thus, 5 for each of Y, M and C
By overlapping and printing images of two gradations, a video image can be printed with 52 × 52 × 52 = 540608 colors.

In the above embodiment, the case where 52 gradations are expressed by 16 dots has been described, but fluctuations in drive voltage, printing accuracy, heat storage of the heating head, manufacturing error of the heating element, and the base tape BT of the ink ribbon IR. The area of each print dot (the area of the portion of each dot to which the ink adheres) varies due to an error in the thickness, and the gradation may not be expressed correctly. To prevent such a situation, for example, gradation 0,
27 gradations may be expressed by 16 dots by selecting gradation patterns such as 2, 4, 6, ..., 50, 52 and storing them in the gradation pattern table 12a.
By doing so, it is possible to prevent the occurrence of the gradation deviation even if the print area slightly changes due to various factors.

In the calculation of the effective area of the gradation pattern shown in FIGS. 1A to 4G, the area exceeding the area of one pixel, that is, the area protruding to the adjacent pixel is ignored. . However, the gradation may be set in consideration of the area of the protruding portion.

Further, in the above embodiment, the ink adhering portion is approximated by the circumscribing circle of the square of each dot, but depending on the characteristics of the heating element and the ink ribbon, for example, FIG.
As shown in (A) to (C), ink may adhere. Therefore, it is desirable to appropriately select the arrangement of print dots according to the characteristics of the printing apparatus.

When ink adheres as shown in FIGS. 11 (B) and 11 (C), ink overlap occurs not only between vertically and horizontally adjacent dots but also between obliquely adjacent dots. Moreover, the area of the overlapping portion between the dots adjacent in the vertical or horizontal direction is different from the area of the overlapping portion between the dots adjacent in the diagonal direction. Therefore, more gradations can be expressed by selecting the number of effective dots and the arrangement of effective dots.

In the above embodiment, one pixel is composed of a matrix of 4 × 4 dots and 52 gradations are expressed, but for example, one pixel is composed of a matrix of 5 × 5 dots,
A larger number of gradations may be expressed by controlling the number of print dots and their arrangement in this matrix. 1
The dots forming the pixels are not limited to 4 × 4 dots and 5 × 5 dots, and can be arbitrarily set to m × n dots.

In the above embodiment, the present invention has been described by taking the case where the gradation data is supplied from the outside as an example. However, for example, the image data is provided as code data from the outside, and the CPU 16 outputs the image data. You may make it convert into gradation data.

In the above embodiment, the gradation pattern table 12a is stored in the ROM 12 in advance and the print dot pattern corresponding to the gradation data is generated by referring to the gradation pattern table 12a. A print pattern may be generated.

Further, for example, as shown in FIGS. 12A and 12B and 12C and 12D, when there are a plurality of gradation patterns having the same effective area and different effective dot arrangements. Alternatively, these gradation patterns may be stored in the gradation pattern table 12a, and different gradation patterns may be randomly used. If you do this,
It is possible to prevent a false image from being generated due to regular deviation of dots.

The present invention can be applied not only to the thermal transfer printer but also to various printing apparatuses which can utilize the overlap of the printing dots. For example, it is similarly applicable to a printing apparatus of a type that forms an electrostatic latent image, forms a toner image corresponding to the electrostatic latent image, and transfers the toner image onto recording paper.

[0049]

As described above in detail, according to the present invention, by generating a gradation pattern which causes a difference in the effective area of dots depending on the arrangement of effective dots, the number of dots in the matrix of one pixel can be increased. As a result, the gradation that can be expressed can be increased.

[Brief description of drawings]

1A to 1O are diagrams showing gradation patterns (density patterns) of gradation numbers 1 to 15 of a gradation pattern according to an embodiment of the present invention.

2A to 2O are diagrams showing gradation patterns of gradation numbers 16 to 30 of the gradation pattern according to the embodiment of the present invention.

3A to 3O are diagrams showing gradation patterns of gradation numbers 31 to 45 of the gradation pattern according to the embodiment of the present invention.

4A to 4G are diagrams showing gradation patterns of gradation numbers 46 to 52 of the gradation pattern according to the embodiment of the present invention.

FIG. 5 is a diagram illustrating how an image is printed using a heating head and a thermal transfer ink ribbon.

FIG. 6 is a diagram for explaining dots that are actually printed, and FIG. 6A is a diagram showing a state in which dots do not overlap each other;
FIG. 6B is a diagram showing how dots overlap.

FIG. 7 is a diagram showing a basis for calculating an effective area of the gradation patterns shown in FIGS. 1A to 4G.

FIG. 8 is a block diagram showing a configuration of a printing apparatus according to an embodiment of the present invention.

9 is a functional block diagram for explaining the operation of the printing apparatus shown in FIG.

FIG. 10 is a functional block diagram of a video printer according to an embodiment of the present invention.

11A to 11C are diagrams for explaining an example of dots actually printed.

12A and 12B are diagrams showing examples of gradation patterns having the same effective area, respectively.

FIG. 13 is a diagram for explaining a conventional gradation pattern.

[Explanation of symbols]

11 ... I / O interface, 11a ... A / D (analog / digital) converter, 11b ... RGB conversion circuit, 11c ... YMC conversion circuit, 12 ... ROM, 12a
... gradation pattern table, 13 ... RAM, 13a ... image memory, 13b ... print buffer, 14 ... display section, 15 ...
Printer unit, 16 ... CPU (central processing unit)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04N 1/405 G06F 15/68 320 A H04N 1/40 B

Claims (11)

[Claims] 1. A gradation pattern representation method for a gradation image, wherein one pixel is composed of a plurality of n × m dots and the density of black dots in the one pixel is changed to express gradation, wherein the one pixel A gradation pattern expression method characterized in that different gradations are expressed between pixels having the same black dot density by changing the arrangement of black dots inside. 2. It is possible to express different gradations between pixels having the same black dot density by arranging a plurality of black dots in one pixel side by side vertically or horizontally or diagonally side by side. The gradation pattern expression method according to claim 1, characterized in that 3. A different gradation is expressed between pixels having the same black dot density by arranging a plurality of black dots in one pixel adjacently or apart from each other. The gradation pattern expression method described in 1 or 2. 4. The n × m plural dots forming one pixel are equal in number to n and m.
Alternatively, the gradation pattern expression method described in 3 above. 5. A storage device for storing a plurality of gradation pattern data for expressing gradation by changing the density of black dots in one pixel by forming a pixel with a plurality of n × m dots. A gradation pattern storage device characterized by storing a plurality of gradation pattern data in which the density of black dots in one pixel is the same and the arrangement of black dots is changed. 6. A plurality of gradation pattern data in which the density of black dots in one pixel is the same and the arrangement of black dots is changed,
The number of black dots is the same and a plurality of black dots are arranged vertically or horizontally side by side, and a plurality of black dots are diagonally arranged side by side or spaced apart. The gradation pattern storage device according to claim 5. 7. The gradation pattern storage device according to claim 5, wherein the n × m plural dots forming one pixel have the same number of n and m. 8. A gradation pattern storage device according to any one of claims 5 to 7, and a floor for instructing any one of a number of gradations greater than n × m + 1 for each pixel of an image to be printed. Gradation data supplying means for supplying gradation data, and printing means for reading gradation pattern data corresponding to the gradation data supplied from the gradation data supplying means from the storage device and printing the read gradation pattern data. And a printer capable of expressing gradations of a number larger than n × m + 1. 9. A plurality of dots make up one pixel, and the arrangement of each pixel is controlled to change the effective area of the effective dots between the same number of effective dots, so that the number of effective dots is larger than the number of effective dots. A gradation pattern expression method characterized by expressing tones. 10. A plurality of gradation pattern data having different effective areas by configuring one pixel by a plurality of n × m dots and changing the arrangement of the colored dots in the same number of the colored dots in one pixel. Storage means for storing the gradation data, gradation data supply means for supplying gradation data indicating any of gradations greater than n × m + 1 for each pixel of the print target image, and the gradation data supply means. A printing unit which reads a gradation pattern corresponding to the gradation data supplied from the storage unit and prints the read gradation pattern. 11. The printing device according to claim 10, wherein the printing device comprises a thermal dot printer.