JP2002086786A - Image recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To record an image of high image quality without lowering the gray scale representation performance even when a multivalued error diffusion method is employed in a line thermal printer. SOLUTION: The image recording method comprises a step for color converting input image data into pixel data of a plurality of pixels for each color, a step for sequentially processing each pixel data by error diffusion method with reference to peripheral pixel data and comparing the processed data with a specified threshold value to generate multivalued print out data of ternary or above, a step for extracting the print out data in zigzag based on a decision means comprising a matrix of a plurality of pixels, and a step for recording an image having a variable dot diameter on a recording sheet by conducting at least every other heating element depending on the extracted print out data while moving the recording sheet relatively to a print head having a plurality of heating elements arranged in a row in the widthwise direction of the recording sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording method, and more particularly, to an image recording method in which a multi-valued error diffusion method is applied to a line thermal printer to record an image on recording paper in multiple gradations having different dot diameters. About the method.

[0002]

2. Description of the Related Art In recent years, facsimile apparatuses, personal computer apparatuses, and the like have been used as image recording apparatuses in which a printer section is of a thermal transfer (thermal) type. In such an image recording apparatus, generally, a dot is formed for each pixel (ON) or not (OFF).
It could only be expressed by gradation. For this purpose, the original image data is subjected to so-called halftone processing (halftone processing) and then subjected to image processing of an image or the like as binary data. The printer unit of the thermal transfer system has a thermal head having a plurality of heating elements arranged regularly in a line, and a ribbon cassette for accommodating an ink ribbon arranged opposite to the thermal head. In the thermal transfer printer section, a thermal head having a plurality of heated heating elements arranged in a row is pressed against the ink layer of the ink ribbon, and the ink separated from the ink layer by heating is transferred to recording paper. , For image recording.

FIG. 5 schematically shows an arrangement of dots 50 on which a heating element of a thermal head is heated to record an image in a conventional thermal transfer type image recording apparatus. As shown in the figure, the dot pitch (P
M) and the dot pitch (PS) in the sub-scanning direction are the same.

In general, in the error diffusion method, an error value generated by a plurality of pixel data already processed is distributed around the pixel data of each pixel at a predetermined ratio, and is allocated to adjacent pixel data one after another. In this way, errors are totally eliminated.

According to this error diffusion method, the extracted pixel data is sequentially processed to generate operation data, and the operation data is compared with a predetermined threshold value. , And when it is smaller than the threshold value, by generating binarized print output data that determines whether or not to print a dot, it is possible to print (print) the dot without overlapping. An image can be recorded with a smooth gradation.

When one dot is formed (generated) on a recording sheet by the ink of the ink ribbon based on the binarized data by the conventional error diffusion method and the next adjacent dot is formed, the same size is obtained. The image is recorded with dots having a dot diameter of. In this way, in the case of binary, even if dots are successively printed for each adjacent pixel, an image can be recorded without overlapping the dots.

[0007]

In recent years, it has been demanded to record digitally processed high image data and the like as high image printing corresponding to the digital image data. There is known a gradation expression by a so-called multi-value error diffusion method used in a printer.

In the printer unit of the thermal transfer system as shown in FIG. 5, instead of changing the ink concentration of dark ink or thin ink as in the ink jet system, the time for energizing each heating element is controlled. The applicant tried to record an image by an error diffusion method using a so-called dot diameter gradation (multi-value gradation) in which the size of the dot diameter differs.

However, as shown in FIG. 6, as the dot diameter increases beyond 11 gradations, the ink that has been melted and peeled off by the heated heating element is transferred to the recording paper and one dot is formed. (Generation), the ink portion corresponding to the space between adjacent dots that are subsequently generated is also peeled off, and an image is recorded on the recording paper in a state where the two dots partially overlap. When one dot is hit in this way, it affects the next adjacent dot. Therefore, even if an error diffusion method having a multi-valued gradation number is used, image recording with low gradation on recording paper is performed. There was a problem that can only be expressed.

FIG. 7 shows the relationship between the dot diameter gradation and the OD (optical) density. For example, in the case of quaternary data in which the size of the dot diameter is set to four levels, if the number of gradations exceeds “9”, the density value increases sharply, and
2 ”or more, the gradation (density) does not change linearly,
It becomes saturated. Similarly, the same applies to the case of 8 values and 16 values. As described above, when the dot diameter becomes a certain size, the fact that the OD density does not linearly change in accordance with the number of gradations even with the multi-value error diffusion method is due to the above-described ink peeling phenomenon.

On the other hand, when the number of gradations is small (dot diameter is small), the amount of ink transferred to the recording paper is small, and the ink is not sufficiently applied to the recording paper (no transfer is performed). There was a problem that the reproducibility of was poor.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image recording method capable of recording a high-quality image without lowering the resolution even when a multi-level error diffusion method is used in a thermal transfer type printer. is there.

[0013]

As a first means for solving at least one of the above-described problems, input image data is converted into pixel data composed of a plurality of pixels for each color. Converting and sequentially calculating each pixel data by an error diffusion method with reference to surrounding pixel data to generate operation data, comparing the operation data with a predetermined threshold value, Generating print output data with dot diameter gradation of three or more values, extracting print output data in a staggered manner based on an arithmetic determination unit including a plurality of pixels in a matrix, While moving the recording paper with respect to the print head provided with the elements, according to the extracted print output data, at least every other heating element is energized to generate an image record on the recording paper. Is that a degree.

As a second solution, the heating elements are arranged in a line in the width direction of the recording paper, and an image is recorded so that one row fills a space between dots of the previous row.

As a third solution, when the paper feed pitch in the sub-scanning direction for conveying the recording paper is PS, and the dot pitch in the direction orthogonal to the sub-scanning direction is PM,
The paper feed control of the paper feed pitch (PS) is performed so that the relationship PM> PS ≧ PM / 2 is established between these.

As a fourth solution, each heating element is formed in a rectangular shape, and the dimension in the sub-scanning direction is made smaller than the dimension in the direction orthogonal to the sub-scanning direction. It has been turned on.

As a fifth solution, the heating elements are arranged in a line in the paper feed direction of the recording paper, and the image recording is performed such that one row in the main scanning direction fills a space between the dots in the previous row. I did it.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image recording method according to an embodiment of the present invention will be described below with reference to FIGS. FIG.
1 is a diagram schematically showing image recording of a line thermal printer to which the image recording method of the present embodiment is applied. FIG.
Is a thermal head 10 of the line thermal printer.
FIG. 4 is a diagram schematically illustrating an image recording position according to the first embodiment. FIG.
9 is a graph showing the relationship between the dot diameter gradation and the OD density according to the error diffusion method for various samples. FIG.
FIG. 2 is a schematic diagram of the line thermal head 10.

As shown in FIG. 4, the line thermal printer has a plurality of rectangular heating elements 10a (10a) regularly arranged in a line in the main scanning direction (width direction of the recording paper).
a1, 10a2, 10a3, 10a4,...), and a sheet-like ink ribbon is sandwiched between these thermal heads 10 and a platen to be in pressure contact with each other. ing. further,
A predetermined heating element 10a of the thermal head 10 is selectively heated to melt and peel ink from the ink layer of the ink ribbon according to the print output data, and transfer it to a recording paper to print and record a desired image. It has become.

Each of the heating elements 10a has a dimension in the sub-scanning direction (Y) smaller than that in the main scanning direction (X), and the aspect ratio of these heating elements 10a is 1 or less. Then, while the recording paper is relatively moved in the sub-scanning direction (paper feed direction) with respect to the thermal head 10, power supply control including predetermined continuous power supply and intermittent power supply to each heating element 10 a is performed. The size of the dot diameter to be image-recorded on the recording paper is controlled. Provided that the aspect ratio of the heating element 10a is preferably in the range of 0.4 to 0.8,
An image of a substantially circular dot can be stably recorded.

Next, an image recording method using a multi-value error diffusion method according to the present embodiment will be described with reference to FIGS. As shown in FIG. 1, an arrow X indicates a main scanning direction (a width direction of a recording sheet), and an arrow Y indicates a sub-scanning direction (a sheet feeding direction). Further, each dot 20 in the figure is sequentially converted into dots A1, A2, B1, B2, C1,.
C2, D1, D2, E1, E2, F1, F2,... In the line thermal printer, the sub-scanning direction (paper feed direction) with respect to the thermal head 10 (see FIG. 4)
In order to convey the recording paper only to the same line, the heating elements 10a of the thermal head 10 are sequentially heated to be on the same line, 1) dot A1 and dot A2, 2) dot B
1 and dot B2, 3) dot C1 and dot C2, 4) dot D1 and dot D2, 5) dot E1 and dot E2, 6) dot F1 and dot F2... , The images are recorded in a so-called checkered (staggered) pattern.

By heating the thermal head 10 in this manner, dots corresponding to any of the 1 to 16 gradation numbers are formed on the recording paper.

Next, a paper feed control of the line thermal printer and a control method for the thermal head 10 will be described with reference to FIG. As shown in FIG.
When (= head resolution) is displayed and the sub-scanning pitch is displayed as PS, the printing position of the thermal head 10 for image processing is controlled according to the following positional relationship. PM> PS ≧ PM / 2 Image recording by each of the dots controlled in this way is
When the thermal head 10 is 600 dpi, the sub-scanning is performed in a range of 900 to 1200 dpi, preferably 1200 dpi.
dpi. By controlling the paper feed in this way,
By increasing the number of dots in the sub-scanning direction compared to that in the main scanning direction, the resolution can be further improved.

The thermal head 10 (10a1, 10a2,
10a3, 10a4,...)
The intermittent energization is performed with the aspect ratio a in the range of 0.4 to 0.8 (see Japanese Patent Application No. 12-136751).
By controlling the energization time, the size of the dot diameter on the recording paper is changed, so that a gradation range of 1 to 16 gradations is obtained as described above. The gradation range is not limited to this, and may be a range of 64 steps including zero of 1 to 63 gradations. In this case, since the number of gradations is small, smooth image recording with further improved gradation expression can be achieved.

In FIG. 2, an image is recorded by transporting the recording paper in the sub-scanning direction (paper feed direction) as in the Nth line, the N + 1th line, the N + 2th line, the N + 3rd line, and the N + 4th line. The printing position of dots in the main scanning direction, that is, each heating element 10
The arrangement of a1, 10a2, 10a3, 10a4,...
Column, m + 1 column, m + 2 column, m + 3 column,...
Odd-numbered dots such as m and m + 2 rows, and even-numbered dots such as m + 1 and m + 3 rows are simultaneously image-recorded. That is, the heating elements 10 of the head 10 are alternately arranged every other dot.
Since a is heated and image-recorded, even if the dot diameter becomes 16 or more, it is possible to prevent adjacent dots from affecting each other.

Here, in order to form each dot on a recording paper and record an image, first, the input original image data is color-converted into pixel data (color data) composed of a plurality of pixels for each color. Next, by the error diffusion method, arithmetic processing is sequentially performed on each pixel data with reference to the surrounding pixel data to generate arithmetic data. Next, print data is generated by comparing the operation data with a predetermined threshold. In order to set the threshold value to, for example, three values, two threshold values are set so that the size of the generated dot diameter becomes two levels, and each of the calculation data sets the large dot diameter, the small dot diameter, and the dot generation. Decide which of the two ranges will be included.

Next, with respect to one dot, the dots arranged next to each other in the main scanning direction (X direction) and the sub-scanning direction (Y direction) of the thermal head 10 are alternate with each other, so-called. Finally, the print output data is calculated by a matrix-shaped filter (calculation determining means) for making a checkered (staggered) shape, for example, a value "1" for a dot generation part and a value "0" for the others. To process. In addition, instead of outputting dots every other filter,
It may be formed so that every third and every third are formed.

Next, FIG. 3 shows a printout (sample A) of multilevel (16-level) data by the multilevel error diffusion method according to the present embodiment, and binary data by the conventional error diffusion method. Printed (sample B), conventional 2
A graph is shown in which the number of gradations and the density thereof are measured by the error diffusion method using three types of data (sample C) printed and printed by directly applying the values to multi-valued (16-valued) data.
In this graph, the horizontal axis plots the number of dot diameter gradations of “0 to 16”, and the vertical axis plots the OD (optical) density value. According to FIG. 3, according to the binarized data of the sample B, as the number of gradations increases, that is, as the energizing time to the heating element 10a increases, the OD density gradually increases, and the density changes almost linearly. For,
The gradation expression of image recording can be smoothly displayed.

Next, according to the sample C (16 values), as described above with reference to FIG. 7, when the dot diameter gradation number exceeds the value “9”, a steep OD density change occurs, and the dot diameter gradation changes. When the tone number is equal to or more than "12", the OD density value becomes saturated, and the image recording cannot be clearly displayed even when it is displayed in accordance with the density change. On the other hand, according to the checkered multi-valued error diffusion, as in the sample A of the present embodiment, even if the multi-valued data (those having more than 16 values) is the binary data of the sample B, Similarly to the above, since the density changes almost linearly, it is possible to display an image with improved gradation expression.

As described above, the print output data is generated by applying the multi-level error diffusion method, and the dots are generated in a checkered pattern, so that the image record is displayed clearly. further,
The resolution of image recording is enhanced by setting the aspect ratio of the thermal head 10 in the range of 0.4 to 0.8 and making the sub-scanning direction pitch (PS) approximately half of the main scanning pitch (PM). Can be.

In the embodiment of the present invention, the print head is described as a line thermal head. However, the present invention is not limited to this, and a serial type image recording apparatus may be used. In this case, since the above-described position control in the sub-scanning direction is performed, the occurrence of stitching is suppressed, and the gradation expression can be more reliably improved.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.
Changes can be made without departing from the spirit of the invention.

[0033]

According to the image recording method of the present invention described above, the input image data is converted into pixel data composed of a plurality of pixels for each color, and the pixel data is converted by the error diffusion method. Generating error operation data by performing sequential operation processing, comparing the error operation data with a predetermined threshold, and generating the error operation data into print output data having three or more dot diameter gradations; A step of extracting print output data in a zigzag manner based on a calculation determining means composed of a plurality of pixels in a matrix, and a step of extracting the print data while transporting the recording paper to a print head having a plurality of heating elements. Generating an image record on recording paper by energizing at least every other heating element in accordance with the output data, thereby forming an adjacent dot even by the multi-level error diffusion method of three or more values. Without ink bets between the portions it is transferred to the recording paper can be achieved by a thermal transfer method in a state with improved gradation.

Further, the heating elements are arranged in a line in the width direction of the recording paper, and the image is recorded so that one row fills the space between the dots in the previous row. The transfer can be achieved by the line thermal transfer method in a state in which the gradation expression is improved without transferring the image to the substrate.

If the paper feed pitch in the sub-scanning direction for conveying the recording paper is PS and the dot pitch in the direction orthogonal to the sub-scanning direction is PM, PM> PS ≧ PM / 2. By performing the paper feed control of the paper feed pitch (PS) such that the relationship of (1) is established, the print position in the sub-scanning direction (paper feed direction) is precisely controlled to the optimum position, so that the floor with higher resolution can be obtained. It can be a tone expression.

Further, the shape of each heating element is made rectangular, the dimension in the sub-scanning direction is made smaller than the dimension in the direction perpendicular thereto, and intermittent current is applied to each heating element.
The dot diameter becomes substantially circular, and the dot separation of each dot can be reliably performed. Even if the dot diameter becomes large, the substantially circular shape of the dot can be maintained.

Further, the heating elements are arranged in a line in the paper feed direction of the recording paper, and the image is recorded such that one row in the main scanning direction fills the space between the dots in the previous row, thereby forming a dot-to-dot portion. Can be achieved by the serial thermal transfer method in a state where the gradation expression is improved without transferring the ink onto recording paper.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram for schematically explaining an image recording pattern by an image recording method according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram for describing control of a thermal head by the image recording method.

FIG. 3 is a graph showing a relationship between a dot diameter gradation and an image recording density in an image recording method according to an embodiment of the present invention.

FIG. 4 is a schematic plan view showing a thermal head and a heating element formed on the thermal head in the image recording method according to one embodiment of the present invention.

FIG. 5 is an explanatory diagram for schematically explaining an image recording pattern according to a conventional image recording method.

FIG. 6 is an explanatory diagram showing an image recording pattern according to a dot diameter in a conventional image recording method.

FIG. 7 is a graph for explaining a conventional image recording method.

[Explanation of symbols]

 10 Print head (thermal head) 10a Heating element PS Paper feed pitch PM Dot pitch in main scanning direction

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C066 AA03 AB03 AC01 CD01 CD04 CD09 CD12 CD14 CD19 CD23 2C262 AA03 AA24 AA27 AB13 BB03 BB08 BB10 GA30 GA47

Claims (5)

[Claims] 1. A step of performing color conversion of input image data into pixel data composed of a plurality of pixels for each color, and sequentially calculating each pixel data by an error diffusion method while referring to peripheral pixel data. Generating the operation data, comparing the operation data with a predetermined threshold value, and generating the operation data as print output data having three or more dot diameter gradations, a plurality of pixels in a matrix form Extracting the print output data in a staggered manner based on an operation determining means comprising: moving the recording paper with respect to a print head having a plurality of heating elements, while extracting the print output data from the print output data. Responsively energizing at least every other heating element to generate an image record on the recording sheet. 2. The image recording apparatus according to claim 1, wherein the heating elements are arranged in a line in a width direction of the recording paper, and an image is recorded such that one row fills a space between dots of a previous row. The image recording method described in the above. 3. When the paper feed pitch in the sub-scanning direction for conveying the recording paper is PS and the dot pitch in the direction orthogonal to the sub-scanning direction is PM, PM> PS ≧ PM / 2. 2. The image recording method according to claim 1, wherein the paper feed control of the paper feed pitch (PS) is performed so that the following relationship is established. 4. The heating element has a rectangular shape, a dimension in a sub-scanning direction is smaller than a dimension in a direction orthogonal to the sub-scanning direction, and the heating elements are intermittently energized. The image recording method according to claim 1, wherein: 5. The image forming apparatus according to claim 1, wherein the heating elements are arranged in a line in a paper feeding direction of the recording paper, and an image is recorded such that one row in the main scanning direction fills a space between dots in a previous row. 2. The image recording method according to claim 1, wherein: