JPH08290596A - Full-color recorder - Google Patents

Abstract

PURPOSE: To provide a full-color recorder which does not suffer from a marked decline in resolution and does not produce moire streaks. CONSTITUTION: Print dots are printed at a pitch of DT×2 in the main scanning direction and at a pitch of DT×1/2 in the subsidiary scanning direction. Adjacent dots form triangles, an array of hound's tooth checks as a whole on a image area. Four kinds of pixels 14a, 14b, 15a and 15b which are composed of four print dots respectively are set in the array. These pixels are selected when appropriate, and arranged on the extended lines of one sides of parallelograms to set three kinds of image areas which form apparent screen angles of 0, -27 or 27 degrees. For instance, C (cyan) is printed at a screen angle of -27 degrees, M (magenta) at a screen angle of 27 degrees, and Y (yellow) at a screen angle of 0. Thus since these three colors which are to be painted one over another have different screen angles, an occurrence of moire streaks are prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a full-color recording apparatus which does not cause uneven printing, especially moire.

[0002]

2. Description of the Related Art Conventionally, when expressing the gradation of a printing dot in a thermal recording device, the density gradation method using a sublimation type ink ribbon and the size of one dot like a halftone dot in offset printing etc. There is an area gradation method that obtains gradation by changing In either case, an ink ribbon in which ink is applied on a long base film having almost the same width as the recording paper is used. Above all, in the case of an ink ribbon used for multicolor printing (full color recording), the subtractive color Y is usually used.
(Yellow: yellow), M (magenta: red dye), and C (cyan: greenish blue), or Bk (black: black) dedicated to printing characters, etc. on these three colors An ink ribbon having a shape in which the added four color inks are repeatedly applied face-sequentially in the longitudinal direction on the base film and repeatedly applied is used. Then, these colors are mixed in various proportions on the recording paper by overcoating to express various hues and gradations.

Particularly, the latter area gradation method utilizes the fact that the heat generation distribution of the heating element of the recording head is radial, and gradation control is realized by controlling the energy applied to the heating element. it can.

FIGS. 12A and 12B show the arrangement of print dots in such a conventional thermal recording apparatus. The arrow A in the figure indicates the main scanning direction of the print dots, and the arrow B in the figure indicates the sub-scanning direction of the print dots. The arrangement interval (printing pitch) of these print dots is the distance DOP in both the main scanning direction and the sub scanning direction. This printing pitch is also the arrangement interval of the heating elements of the recording head described above. The heating elements are respectively connected to the electrodes, and are selectively supplied with applied energy (usually an applied voltage pulse) by these electrodes to generate heat, and the heat energy based on this heat generation is transferred to the ink ribbon, and the ink of the ink ribbon is transferred. Is transferred to the paper.

In this case, paying attention to one print dot, when the applied energy to the heating element is small, the print dot is very small, for example, as shown in FIG. 2B, while when the applied energy is large, the print dot is large. Is getting bigger,
When the applied energy is 100%, this density (gradation) is the density at which the ink is solidly applied. Therefore, as shown in Figure (a), there should be no gaps between the dots printed in a circle. Dots are formed so that adjacent dots overlap.

As described above, the size of the print dots increases concentrically as the density changes from low density to high density, but the ink density of the print dots themselves is always the maximum value regardless of the size of the print dots. However, there is no further darkening, and the lightness (gradation) of the image is expressed by the size change of the print dots described above.

Further, when the gradation is expressed by the change of the area as described above, the size of the print dot is not changed for each pixel as described above, but the size of the print dot for each pixel is fixed, A plurality of pixels are grouped, and this one group is a new pixel (for avoiding confusion, the pixel is hereinafter referred to as one print dot or simply a print dot, and a group of these print dots is referred to as one pixel or There is a type in which effective (coloring) print dots are distributed in pixels to perform gradation control with one pixel as a gradation expression unit.

FIG. 1C shows an example in which one pixel consists of four print dots. The pixel PX shown at the left end of FIG. 7C shows the gradation 1 (white). From the right, the print pixels are distributed to each one pixel by one, two, three, and four, which shows a density change of five stages, that is, a change of five gradations. That is, 5 gradations are obtained for each color of Y (yellow), M (magenta), and C (cyan). If this is overlaid on a pixel-by-pixel basis for each color, 5 × 5 × 5
This means that colors of 125 gradations can be reproduced. As described above, the generation of a full-color image is performed by superimposing the ink amounts of the densities corresponding to the image information of each of the yellow Y (Yellow), magenta M (Magenta), and cyan C (Cyan) inks (or toners). Can be obtained at.

[0009]

By the way, the above-mentioned full-color recording apparatus is a dot-sequential system such as an ink jet printer in which a print head jets ink from a fine opening for printing, or a sheet is wound around a drum one by one. hand,
With a recording apparatus such as a drum winding method that performs printing while rotating this, accurate dot positioning can be performed, and there is no problem in color reproducibility.

However, when full-color printing is performed by a frame sequential printing method such as a thermal transfer printer using the above-mentioned ink ribbon or an electrophotographic printer, the recording paper (paper) is reciprocated in the color overlapping process. Due to the operation and the feeding operation of the ink ribbon, a positional deviation is likely to occur between each ink and the recording paper. Then, depending on how the respective colors are overlapped due to the positional deviation, there arises a problem that the gray scale is colored or the hue is different for each print.

In particular, when each color has the same pattern, a low-frequency density unevenness (color moire fringes) occurs due to a slight positional deviation of the superposition of the respective colors in the image reproduction of the intermediate gradation, and the image quality is remarkably increased. Will lower it.

FIGS. 13 (a) to 13 (d) are schematic diagrams showing the generation of moire fringes caused by positional deviation when such colors are superposed. The array of print dots is the array of square lattices shown in FIGS. 12A and 12B, and the size of each print dot is represented by the dot area corresponding to the density level near 30%.

FIG. 13 (a) shows a case where two printing surfaces on a sheet are overlapped with each other without any positional deviation. On the other hand, FIG. 2B shows a case where the two print surfaces are overlapped with each other with a relative angle offset (rotated) about the first dot in the upper left corner.

Further, FIG. 3C shows a case where the two print surfaces are overlapped with each other with a relative angle difference of 3 degrees from the first dot in the upper left corner. Then, FIG. 3D shows a case where the two print surfaces are similarly offset by 5 degrees and overlap each other.

The shift amount of 1 degree in the above example corresponds to a shift of 1/2 dot at the right side of the figure, that is, at the maximum displacement position. It can be confirmed that large interference fringes are two-dimensionally generated on the entire overlapping surface at that time. When two color printing surfaces, for example, yellow Y and cyan C overlap, color moiré fringes will appear, and a large image defect will occur in an image area with halftone and uniform gradation. Deviation amount 3
It can be seen that even more intense moire fringes occur when the angle is 5 degrees.

Such moire fringes are superposed on the same pattern regardless of whether the gradation is expressed in gradations of print dots (gradation control) or the gradation is expressed in pixels shown in FIG. 12 (c). In the case of printing, it occurs in the image area of intermediate gradation.

There is known an example in which the occurrence of such color moire fringes is attempted to be eliminated by increasing the mechanical accuracy of a sheet or an ink ribbon which is conveyed. this is,
If the resolution is 200 dpi (dots / inch),
Experience has shown that extreme color moire fringes occur with a displacement of 64 μm, so the mechanical position accuracy is adjusted within 64 μm. However, mechanically position control of the overlapping state of print dots (or pixels) with such fine precision requires severe technical conditions and is generally extremely difficult to realize.

Therefore, in the field of halftone dot printing (offset printing), different screen angles (consecutive angles of pixels) are provided for each color so that print dots are randomly overlapped and the color overlap is uniform. The properties are averaged to prevent moire fringes from occurring.

However, in an ink jet system, a thermal transfer system and the like, various difficulties occur when the above-mentioned screen angle technique is used in a recording device using print dots having only binary density changes. For example, when trying to secure 256 gradations, a pixel having a 12 × 12 dot structure is formed, and this causes a problem that the pixel structure is too large and the resolution is drastically reduced, which is not practical. Then, if an attempt is made to increase the resolution, the pixel becomes small, and the number of gradations greatly decreases, which is a problem.

In view of the above-mentioned conventional circumstances, the present invention is to provide a full-color recording apparatus in which the resolution does not significantly decrease and moire fringes do not occur.

[0021]

The structure of a full-color recording apparatus according to the present invention will be described below. The present invention is premised on a full-color recording apparatus that separates image information into colors and superimposes colors on a pixel-by-pixel basis to record a full-color image.

The full-color recording apparatus of the present invention includes image information conversion means for converting the original image information for each color depending on the original pixel arrangement into image information based on the pixel arrangement formed by the printing mechanism, and the image information conversion means. And gradation information conversion means for expressing the image information converted by the above by dividing it into basic pixels composed of a plurality of specific pixels in the pixel arrangement formed by the above-mentioned printing mechanism. The printing process is sequentially performed on the printing surfaces having different arrangements, and the respective colors are superimposed to record a full-color image.

The basic pixel is formed, for example, so that the shape of a line connecting and closing each pixel forming the basic pixel is a parallelogram. Further, for example, as described in claim 3, it is composed of at least four pixels.

[0024]

In the full-color recording apparatus of the present invention, the image information conversion means converts the original image information for each color, which depends on the original pixel arrangement, into the image information which depends on the pixel arrangement formed by the printing mechanism. The gradation information converting means distributes and represents the image information converted by the image information converting means to basic pixels composed of a plurality of specific pixels arranged in a pixel formed by the printing mechanism. Then, the printing process is sequentially performed on the printing surface in which the arrangement of the basic pixels is different for each color, and the respective colors are superimposed to record a full-color image.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a partial cross-sectional view of a printing section of a full-color recording apparatus and an ink ribbon cassette mounted in the printing section, as viewed from the side. The full-color recording apparatus includes a printing unit (thermal transfer unit) including the thermal head 1 and the platen 2 shown in FIG. 1, and a drive unit for driving the thermal head 1 and the platen 2 and heat generation of the thermal head 1 although not particularly shown. Is provided with a print data processing device for controlling the print data according to the image information. Then, as shown in the figure, the cassette case 4 accommodating the ink ribbon 3 is detachably mounted.

As shown in the figure, the ink ribbon cassette 4 is composed of a ribbon supply side provided with a supply reel 5a and a ribbon winding side provided with a take-up reel 5b. By rotating the used portion of the ink ribbon 3 by rotating in the clockwise direction shown by arrow C in the figure, the unused ink ribbon 3 wound and held on the supply reel 5a on the ribbon supply side is illustrated. Is drawn out to the left as indicated by the arrow D, and the new ink ribbon 3 drawn out is supplied to the printing unit formed of the facing portion of the platen 2 and the thermal head 1.

The above-mentioned printing portion is located in the opening 6 of the mounted ink ribbon cassette 4. The platen 2 is rotationally driven in the counterclockwise direction by a drive device of the apparatus main body (full color recording apparatus). On the other hand, thermal head 1
Is disposed above the platen 2, moves upward during non-printing, and moves downward during printing to press the ink ribbon 3 and the paper P against the platen 2 for printing.

The paper P is carried in from the lower right to the upper left in the figure by a paper carrying roller (not shown) of the apparatus main body, abuts on the upper surface of the platen 2 to perform a printing process, and is carried out to the lower left. It

As described above, the ink ribbon 3 is drawn from the supply reel 5a by the take-up reel 5b, the thermal energy corresponding to the print data is transmitted by the thermal head 1, and the ink of the ink ribbon 3 is transferred onto the paper P ( In the figure, it is wound on the take-up reel 5b while being transferred (to the upper surface of the paper). The ink ribbon cassette 4 is replaced with a new ink ribbon cassette when the ink ribbon on the supply side runs out.

The thermal head 1 is a print head having substantially the same width as the width of the paper P, and has the maximum number of print dots in the main scanning direction (paper width direction) (in this example, odd-numbered main scanning in the sub-scanning direction). The same number of print elements (heating elements) as the print dots and the maximum number of print dots of even-numbered main-scan print dots in the sub-scanning direction are combined. Then, the ink of the ink ribbon 3 is transferred to the paper P by the heat generation of these printing elements. On the other hand, the ink ribbon 3 also
Corresponding to the thermal head 1, a wide ink ribbon having a width substantially the same as the width of the paper P is formed and held in the ink ribbon cassette 4 in a long length. When the ink ribbon cassette 5 is mounted on the main body of the apparatus, the ink ribbon cassette 5 is provided between the supply side and the take-up side in order to accommodate the printing portion including the platen 2 and the thermal head 1 between the supply side and the take-up side as described above. Has a large opening 6.

FIGS. 2 (a) and 2 (b) show the arrangement of print dots in the printing method of this embodiment executed in the above configuration. In the example of the conventional arrangement shown in FIG. 12 (a), the adjacent print dots form a square and form a lattice-like arrangement as a whole, but the book shown in FIG. 2 (a)-(c) In the example arrangement, adjacent print dots form a triangle, forming an overall staggered arrangement.

In FIG. 3A, if the basic fixed resolution of the thermal head 1 described above, that is, the arrangement interval of the printing elements (heat generating elements) is the pitch DT, in this embodiment, the main scanning indicated by the arrow E in the figure. The print pitch is "2DT" (= DT x 2) in the direction, and the print pitch is "1 / 2DT" (= DT x 1/2) in the sub-scanning direction indicated by arrow F in the figure. This means that the sheet conveyance in the sub-scanning direction (the sheet conveyance in the direction indicated by the arrow G in the drawing) is 1/2 DT for each main scanning line.
And the first and third in the sub-scanning direction.
In the printing in the main scanning direction, which is an odd number of the 5th, 5th, ..., The heating elements of the 1st, 3rd, 5th, ... Are controlled, and the 2nd, 4th, ... .., 2nd, 4th in printing in the main scanning direction, which is an even number of ...
・ It is realized by controlling the heat generation of the heating element. The print dots 11a, 11b, 11c, etc. shown in FIG. 9A indicate the array of print dots in the main scanning direction that is the first (odd number) in the sub scanning direction (hereinafter referred to as odd dots). Further, the print dots 12a, 12b, 12c, etc. indicate the array of print dots in the main scanning direction that is the second (even number) in the sub scanning direction (hereinafter referred to as even dots). For convenience of explanation, FIG. 7A shows a print dot in the case of the maximum density (area maximum) when the applied energy of the heating element to be controlled is 100%. In this embodiment, as described above, the arrangement of the heating elements is controlled so as to alternately print the odd dots and the even dots for each main scanning line.

In the printing method in which the printing dots are arranged in a zigzag pattern as described above, the heating elements of the summer head 1 are alternately heated by one dot (one heating element) at the printing timing described above. Since the control is performed, it has been confirmed that it is effective in controlling the influence of thermal interference of adjacent dots when performing the energy control of the print dots of the intermediate density level.

Further, in general, data conversion such as magnification and coordinates in a printer is processed by an integer ratio as in data processing based on a square dot array. In the present embodiment, as shown in FIGS. 2 (a) and 2 (b), the main / sub scanning line ratio is set to "2": "1/2" (DT: 1 / 2DT), so that an integer can be easily calculated. It can deal with ratio processing. This has the advantage that interpolation is easy in the process of data conversion and information deterioration of data does not occur. However, if printing is performed with the density control for each print dot in this staggered array, moire fringes are generated as in the conventional case.

FIGS. 3 (a) and 3 (b) are simulations of the print screen when the two print surfaces are misaligned. The figure (a) shows the printing of the density level of the highlight part, and the figure (b) shows the printing of the medium density level. Figure (a),
(b) shows the case where the two print surfaces are overlapped by rotating (rotating) by 0 °, 1 °, 3 °, and 5 ° relative to the first dot in the upper left corner from the top. There is. Also in this case, as in the case of FIG. 13, a large amount of interference fringes is generated on the entire printing surface with a deviation of 1 degree, and a strong moire fringe is generated with a deviation of 3 degrees and 5 degrees.

In this embodiment, the minimum pixel is constructed in order to prevent the occurrence of moire fringes as described above and to maintain a sufficient resolution. FIG. 4 shows a basic configuration of 2 × 2 dots used as a basic pixel in the arrangement of the print dots in the houndstooth check pattern of this embodiment. In the figure, basic pixels 14a, 14b, 15a and 15b are shown.
Are each composed of four print dots, and each four print dots form a parallelogram. The basic pixels 14a and 14b are vertical and horizontal pixels,
One corresponds to the mirror image of the other. Further, the basic pixels 15a and 15b are flat pixels in the main scanning direction, and in this case, one also forms a mirror image of the other. A straight line connecting the odd dots and the even dots of the print dots forming one side of the parallelogram of these pixels (in the figure, the broken line 1
6a, 16b, 16c and 16d) forms an angle with the main scanning direction in either case based on the equation "θ = based on the main and sub scanning print dot intervals DT and 1 / 2DT shown in FIG. 2 (a). tan ⁻¹ (1/2) ”and the angle θ = 26.
57 (≈27) degrees or angle θ = −26.57 (≈−2
7) degrees. The angle θ is the basic angle in this embodiment. The flat pixel 15a or 15b in the main scanning direction is configured to minimize the deterioration in resolution in the sub-scanning direction that occurs when gradation control is performed based on pixelization of pixels.

In the present embodiment, pixels having such a configuration are used to selectively arrange these pixels to generate an apparent screen angle in a printed image.

FIG. 5A shows an example of the first pixel array screen, and the pixel 14b shown in FIG. 2C is adopted as each pixel. When selecting an array of these pixels, first, the position of each dot within the pixel is set in advance corresponding to the density level to be expressed by the pixel.

FIG. 5 (b) shows the positions of the dots in the pixel, which correspond to the density levels, in numerical order.
The upper left of the four print dots is the first dot, and the second dot, the third dot, and the fourth dot are set in the clockwise direction. Each of the four print dots forming these pixels is responsible for 25% of the total density level at any one of the density levels of 0% to 100%, and the first dot is 0 to The density level is 25%, the second dot is 26 to 50%, the third dot is 51 to 75%, and the fourth dot is 71 to 100%.

In FIG. 5 (c), the first dot in the pixel is indicated by a black circle. This shows the case where this pixel expresses the density of 10%, and shows the spread area of the ink of the first dot which shares the density expression in this case.
This density corresponds to the example of the density of the highlight part shown in FIG. The double circle outside the black circle of the first dot shown in FIG. 6 (c) shows the spread of the ink surface when the inner circle frame has a density of 20%, and the ink surface when the outer circle frame has a density of 25%. Shows the spread of. As described above, the ink surface at 25% is the maximum density of the first dot (the same applies to the other three print dots). Following this, the concentration 2
From 6%, the second dot changes by 1% to 25%, and the density of 25% of the first dot and 26% of the whole pixel
Express a concentration of 50%. Similarly, the third dot is 5
Expressing a density of 1 to 75%, the fourth dot is 71 to 100
Express the concentration of%. When 256 gradations are to be expressed by the pixel of this 2 × 2 dot configuration, if 64 gradations (25% of the whole pixel) are expressed for each print dot, 64 × 4 gradations, that is, 256 gradations. Can be generated.

The array of pixels shown in FIG. 5 (a) above is
In arranging the pixels in the main scanning direction indicated by the arrow H in the drawing, the first arrangement is such that the pixels 22 arranged next to the first pixel 21 in the main scanning direction 2 are arranged in the sub scanning direction indicated by the arrow J in the drawing. The line is shifted (see the position of the first dot of each pixel), and this arrangement is sequentially repeated.
This means that pixels are sequentially selected from left to right on the extension line of one side of the parallelogram forming the basic angle of the pixel. As a result, the apparent screen angle shown in the pixel array 23a in the figure is formed. The screen angle of the pixel array 23a is "-27 degrees" which is the basic angle.

Next, the second array is the above-mentioned pixel array 2
3a are arrayed by shifting by one basic fixed resolution in the main scanning direction (see the first dots of the pixel 21 and the pixel 24 in FIG. 9A). Then, the first pixel array 23a and the second pixel array 23b are arranged alternately. This pixel array 23b is also "-2" like the pixel array 23a.
Form an apparent screen angle of 7 degrees. And
By forming the second pixel array 23b with respect to the first pixel array 23a, a third pixel array 25 composed of even-numbered pixels of the first pixel array 23a and odd-numbered pixels of the second pixel array 23b is formed. Can be formed. This third pixel array 25 forms the sub-screen angle. This sub-screen angle is "+63 degrees" according to the equation "θ '= tan ^-1 (2)".

In this way, a 2 × 2 dot is used as a basic pixel, and a repeating array of 8 dots each in the main and sub-scanning directions (8 columns in the main scanning direction shown in the block 26 shown by a dot-dash line in the figure, sub-scanning By arranging (arrangement of 8 lines in the direction) according to the above-mentioned arrangement rule, the same print screen can be formed by printing the square screen at a screen angle as if tilted by -27 degrees. In this embodiment, C (cyan) is printed using this print screen.

Next, FIG. 6A shows an example of the second pixel array screen. In this second pixel array screen, the pixel 14a shown in FIG. 2 (c) is adopted for each pixel. Also in this case, the acceptance of the density of each print dot in the pixel is preset.

In FIG. 6B, in this pixel array screen, the pixels are set to the second dot, the third dot, and the fourth dot in the counterclockwise direction with the upper right of four print dots as the first dot. It has been shown that. Then, FIG. 6C shows the state of change in the density level of the first dot, which is the same as in the case of FIG. 5C described above, in this pixel configuration. Also in this case, the sharing of the density expression of the first to fourth dots corresponding to the density of the pixel is the same as in the case of FIG. It should be noted that the fact that only the second dot shown in FIG. 6 (a) is shown by a black circle does not indicate the density (coloring of the dot), and the pixel array in this example is shown in FIG. The pixel array shown in a) and FIG. 7 described later.
The second dot located at the upper left is shown by a black circle so that the difference can be easily distinguished by listing for comparison with the pixel array shown in (a).

In this pixel array screen, pixels are sequentially selected from left to right on an extension line of one side of a parallelogram forming a basic angle of pixels. That is, in arranging the pixels in the main scanning direction indicated by the arrow K in the drawing, first, in the first arrangement, the pixels 32 arranged next to the first pixel 31 are arranged in the direction opposite to the sub-scanning direction indicated by the arrow L in the drawing. Then, the main scanning is shifted by two lines (see the position of the second dot of each pixel), and this arrangement is sequentially repeated. As a result, the apparent screen angle shown in the pixel array 34a in the figure is formed in this case as well. The screen angle of the pixel array 34a is "+27 degrees" which is the basic angle.

Next, the second array is the above-mentioned pixel array 3
4a are arranged by shifting by one basic fixed resolution in the main scanning direction (see the second dot of pixel 31 and pixel 33 in FIG. 9A). Then, the first pixel array 34a and the second pixel array 34b are arranged alternately. This pixel array 34b is also "+2" like the pixel array 34a.
Form an apparent screen angle of 7 degrees. And
By forming the second pixel array 34b with respect to the first pixel array 34a, a third pixel array 35 including even-numbered pixels of the first pixel array 34a and odd-numbered pixels of the second pixel array 34b is formed. Can be formed. This third pixel array 35 forms the sub-screen angle. This sub-screen angle is "-63 degrees" according to the expression "θ '= tan ^-1 (-2)".

As described above, in this case as well, 2 × 2 dots are used as basic pixels, and a repeating array of 8 dots each in the main and sub-scanning directions (8 columns in the main scanning direction shown in the block 36 shown by the chain line in the figure). , 8 rows in the sub-scanning direction) are arranged according to the above-mentioned arrangement rule, so that the same printing screen can be formed by printing dots at a screen angle as if the square screen is tilted +27 degrees. In this embodiment, M (magenta) is used by using this print screen.
Is printed.

FIG. 7A shows an arrangement of basic pixels forming a Y (yellow) print screen for the third color. The pixels of the Y (yellow) print screen have the same shape as those used for the C (cyan) or M (magenta) print screen described above. In this embodiment, C
The same pixel 14b shown in FIG. 2 (c) as used for the (cyan) print screen is adopted. In this pixel, the same figure (b) shows the arrangement of the first to fourth dots.
(c) shows the ink surface of 10%, 20%, and 25% density of the first dot.

As shown in FIG. 9A, in this pixel array screen, the pixels are sequentially arrayed in the main scanning direction indicated by an arrow M in the figure to form a first pixel array 41a. Similarly to the pixel array 41a, the second pixel array is also sequentially arranged in the main scanning direction from the beginning. Then, this is repeated in the sub-scanning direction. The screen angle formed by the array in the main scanning direction is 0 degree, and there is no difference in basic fixed resolution between the first pixel array 41a and the second pixel array 41b, so the sub screen angle is 90 degrees. Also in this case, the above-mentioned C
(Cyan) and M (magenta) blocks 26 and 36
It can be seen that the pixel array in the block 42 indicated by the alternate long and short dash line in FIG. 7A corresponding to is repeated in the main scanning direction and the sub scanning direction.

In the present embodiment, the three screen colors C (cyan), M (magenta), and Y (yellow) are used for the printing screens having different screen angles of -27 degrees, +27 degrees, and 0 degrees. It is possible to prevent the occurrence of moire by repeatedly applying. Then, it is possible to construct pixels with a configuration of 2 × 2 print dots whose resolution corresponds to ½ of the basic resolution.

FIGS. 8A, 8B, and 8C are examples of print surfaces obtained by simulation with the print method of this embodiment. The figure (a) is the printing surface of the gradation of the highlight part,
This is a pattern in which only one dot of the 2 × 2 dot pixel structure is colored. The first surface of the overlay is the cyan print surface with a screen angle of "-27 degrees", and the second surface
The surface is a magenta printing surface with a screen angle of "+27" degrees. FIG. 9A is a diagram in the case where the overlapping angles of cyan and magenta are 0, 1, 3, and 5 degrees in order from the top. FIG.
As described in 3, the deviation of 1 degree corresponds to a deviation of 1/2 dot, and the deviation of 3 degrees or 5 degrees corresponds to a positional deviation of 1.5 dots or 2.5 dots, respectively. . FIG.
As shown in (a), it can be seen that a large moire pattern does not occur up to a 5 degree level positional deviation (corresponding to a deviation of 2.5 dots).

FIG. 8B shows the print surface in the case where the gradation of the pixel corresponds to the intermediate density in the overlapping of cyan and magenta as in the above, and 2 of 2 × 2 dot pixel structures are shown. This represents the state in which the dots are colored. This figure also shows the results of the simulation from the top when the overlapping angles of cyan and magenta are 0, 1, 3, and 5 degrees. As shown in FIG. 7B, it can be seen that in this case as well, a moire pattern having a large positional deviation up to a level of 5 degrees does not occur.

Further, in FIG. 8C, the screen angle is "-
FIG. 10 is a diagram showing a case where a cyan print surface having a 27 ”degree and a yellow print surface having a screen angle of“ 0 ”are overlapped. Also from the top of this figure, the overlapping angles of cyan and yellow are 0, 1, 3, 5
I have a degree. As shown in FIG. 3B, even in this case, there is almost no problem as compared with the appearance of the strong moire fringes in FIGS. 3A and 3B in the case where the positional deviation is up to the 5 degree level and the screen angle processing is not performed. It is a level.

In the above simulation, the pixels 14a, 14b, 1 having the 2 × 2 dot structure shown in FIG.
Of the shape groups 5a and 15b, pixels 14a and 1
Although the combination of 4b is used, the combination of pixels is not limited to this, and any combination of four pixels may be used, and 3 of C (cyan), M (magenta), and Y (yellow) may be used. On the surface, if the combination achieves the combination of the screen angles of 0 ° and ± 27 °, it is possible to suppress the occurrence of color moire.

Further, in the above-described embodiment, the zigzag lattice is arranged so that the interval between the print dots in the sub-scanning direction is “DT × 1/2” with respect to the print dot interval in the main scanning direction “DT × 2”. Although the shape is set, if the interval of the print dots in the sub-scanning direction is set to “DT × 1 / √3”, the shape of the houndstooth check is that the six dots surrounding the dot of interest are regular hexagons. It is configured to form vertices. This has the disadvantage that a non-integer value of √3 is used for the conversion coefficient of the image information, which causes an interpolation error, but since the interval between the print dot of interest and each print dot surrounding it is the same, the screen The spread of the printed dots as a whole is uniform. Therefore, in the arrangement shown in FIG. 12 (a) described above, there are eight surrounding print dots surrounding one print dot of interest, and the space between print dots adjacent vertically and horizontally to the print dot of interest (1 / square of one side of regular square). 2) and the interval between the print dots diagonally adjacent to each other (1/2 of the diagonal line of the regular quadrangle) are clearly different from each other, but the spread of the print dots in the entire screen is unequal. The staggered arrangement in which six print dots surrounding one print dot form a regular hexagonal apex is a uniform halftone image print because the print dots spread uniformly over the entire screen. Will be possible. Even in the case of the houndstooth check pattern forming the regular hexagon, four types of pixels shown in FIG. 4 can be configured.

FIG. 9 shows a pixel array on the printing surface of C (cyan) when the houndstooth array forming the regular hexagon is used. The method of arranging the pixels is similar to the case of FIG. 5, except that the screen angle is “−30” degrees.

FIG. 10 shows a pixel array on the M (magenta) printing surface in the above-mentioned staggered array. The method of arranging the pixels is the same as that in the case of FIG. 6, except that the screen angle is “30” degrees.

FIG. 11 shows a pixel array on the Y (yellow) printing surface in the above-mentioned staggered array. This pixel arrangement method is the same as in the case of FIG. 7, and the screen angle is also “0” degrees.

These C (cyan), M (magenta) and Y
Even if the (yellow) printing surface is used, good results of moire fringe control can be obtained.

[0061]

As described above, according to the present invention,
Since an apparent screen angle is generated by forming an array of pixels with a predetermined regular period, three types of printing surfaces having different screen angles are selected to select C (cyan), M (magenta), and Y ( (Yellow) printing can be performed, and therefore, it is possible to eliminate the generation of color moire fringes due to the positional deviation of color superposition that occurs in the halftone dot printing system. Further, since the pixel is composed of four print dots, it is possible to minimize the decrease in resolution that occurs when gradation control is performed based on pixelization of the pixel.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a printing unit and an ink ribbon cassette mounted in the printing unit of a full-color recording apparatus according to an embodiment of the present invention as viewed from the side.

2A and 2B are diagrams showing an arrangement of print dots in the print method of the embodiment.

3 (a) and 3 (b) are diagrams simulating a print screen when the two print surfaces overlap with each other when the density control by pixels is not performed in the configuration of the embodiment.

FIG. 4 is a diagram showing a basic configuration of 2 × 2 dots used as a basic pixel in an array of print dots in a houndstooth check pattern of the embodiment.

FIG. 5A is a diagram showing an example of a first pixel array screen for printing C (cyan), and FIG. 5B is a diagram showing the positions of dots in pixels corresponding to density levels in numerical order. ,
(c) is a figure explaining the 1st dot density representation state in a pixel.

FIG. 6A is a diagram showing an example of a second pixel array screen for printing M (magenta), and FIG. 6B is a diagram showing positions of dots in a pixel, which are assigned in order of number, corresponding to density levels. , (C) are diagrams illustrating a first dot density representation state in a pixel.

FIG. 7A is a diagram showing an example of a third pixel array screen for printing Y (yellow), and FIG. 7B is a diagram showing positions in which each dot in a pixel is assigned in order of number corresponding to a density level. , (C) are diagrams illustrating a first dot density representation state in a pixel.

FIGS. 8A, 8B, and 8C are diagrams illustrating that the generation of color moire fringes is prevented in the embodiment.

FIG. 9 is a diagram showing an example of a pixel array on a C (cyan) print surface when a houndstooth array forming a regular hexagon is used.

FIG. 10 is a diagram showing an example of a pixel array on a printing surface of M (magenta) when a houndstooth array forming a regular hexagon is used.

FIG. 11 is a diagram showing an example of a pixel array on a Y (yellow) print surface when a houndstooth array forming a regular hexagon is used.

12A and 12B are diagrams showing an arrangement state of print dots in a conventional thermal recording device, and FIG.
It is a figure which shows the example in case it consists of individual print dots.

13 (a), (b), (c), and (d) are diagrams schematically showing moire fringes caused by positional deviation of conventional color superposition.

[Explanation of symbols]

1 Thermal Head 2 Platen 3 Ink Ribbon 4 Ink Ribbon Cassette 5a Supply Reel 5b Take-up Reel 6 Opening P Paper DT Heater Element Arrangement Intervals 11a, 11b, 11c Odd-numbered Print Dots 12a, 12b, 12c Even-numbered Print Dots 14a , 14b, 15a, 15b Basic pixels H, K, M Main scanning direction J, L, N Sub-scanning direction 21, 22, 24, 31, 32, 33 pixels 23a, 23b, 25, 34a, 34b, 41a, 41
b Pixel array 26, 36, 42 Block with repeating period

Claims (3)

[Claims] 1. A recording device for color-separating image information and recording a full-color image by superimposing colors on a pixel-by-pixel basis, and a pixel arrangement in which a printing mechanism forms original image information for each color depending on the original pixel arrangement. Image information conversion means for converting into image information based on the image information, and the image information converted by the image information conversion means is distributed to a basic pixel composed of a plurality of specific pixels arranged by the printing mechanism and expressed. A full-color recording apparatus comprising: gradation information converting means; and performing full-color printing by sequentially performing printing processing on printing surfaces having different basic pixel arrangements for each color. 2. The full-color recording apparatus according to claim 1, wherein the basic pixel is formed such that a line connecting and closing each pixel forming the basic pixel has a parallelogram shape. 3. The full-color recording apparatus according to claim 1, wherein the basic pixel is composed of at least four pixels.