JPH08281994A - Color recorder and recording method - Google Patents

Abstract

PURPOSE: To gradation express with stable reproducibility in the case of printing a low gradation part in a melt type color thermal transfer recorder. CONSTITUTION: A resolution conversion controller 9 is provided between a frame memory 10 and a heat pulse generator 7 to print image data in a zigzag matter as prior art except a low gradation part, but to print at odd or even rows which has not heretofore been printed at each half dot on the low gradation part to print only any one of four print points in two rows. The gradation is increased in dot diameter by adding the gradations of two rows of colors to stabilize the transfer, and the deterioration of the image quality due to the superposition of the low gradation part is avoided by eliminating only one color print at the one point. Accordingly, since the dot transfer at the low gradation part can be stabilized, accurate gradation expression is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color recording apparatus and a recording method for printing at least three colors on a recording medium such as recording paper.

[0002]

2. Description of the Related Art Generally, in a color thermal transfer recording apparatus using a thermal head in which a plurality of heating resistors are arranged in a line, a main material of a coloring material is a pigment which is a heat-meltable ink and a main material is a dye. It is roughly classified into two types using a certain thermal sublimation ink, and the former is generally called a fusion type thermal transfer recording device and the latter is called a sublimation type thermal transfer recording device. In a sublimation type thermal transfer recording device, an ink sheet in which yellow, magenta, cyan, and black are applied in this order in the case of color printing with a color material mainly composed of a sublimable dye on a base layer composed of a polyethylene terephthalate (PET) film or the like. On top of this, a thermal transfer recording paper having an image receiving layer made of a substance such as a polyester resin to which the dye is easily dyed is overlaid, and the ink is sublimated by applying heat from the thermal head to the ink sheet in the order of yellow, magenta, cyan, and black. Transfer to thermal transfer recording paper. Further, in the case of the sublimation type, the transfer amount to the thermal transfer recording paper continuously changes according to the amount of heat to which the gradation of the density is added, so that it is suitable for recording a halftone image such as a photograph,
So-called full-color printing is possible. However, the transfer temperature of the general melting type is 100 ° C. or less, whereas the transfer temperature of the sublimation type is as high as 100 to 200 ° C., and a large amount of energy is required. Therefore, the device cost becomes high and the thermal head is cooled. The time required for printing is longer than that of the fusion type, and printing time is longer.Because dyes are the main raw material, sublimable inks are less expensive and more expensive than pigments. Since plain paper cannot be used, running costs are high.

On the other hand, in the fusion type thermal transfer recording apparatus,
As shown in FIG. 2, a base layer 10 such as a PET film
In the case of color printing, a color material 102 containing a meltable pigment as a main raw material is applied to the ink sheet 19 in the order of yellow, magenta, cyan, and black, and a thermal transfer recording paper having high smoothness is superposed on the ink sheet 19 to print the ink from the thermal head. By applying heat to the sheet 19, the solid ink 102 is melted and adhered to the recording paper in the order of yellow, magenta, cyan, and black to transfer. Since the pigment is the same type as used in general printed matter such as offset printing, it can be transferred to plain paper and can be transferred with a small amount of energy, so the device cost is lower than that of a sublimation recording device. Although it has the advantage of low running cost, it is difficult to express multiple gradations with one dot because the transfer is performed due to the difference in the adhesive force between the ink paper and the base layer. It was common. When a halftone image is printed by a fusion type thermal transfer recording device, dither processing or error diffusion is used, but the resolution of the printed halftone image is low and there is a drawback that it becomes a rough image.

However, in recent years, due to improvements in thermal control technology for thermal heads, stabilization of ink sheet quality, and improvements in coating materials for recording paper, it has become possible to achieve multi-gradation expression in one dot even in a fusion type thermal transfer recording apparatus. In this case, if one line is printed simultaneously under the same control as the sublimation type, the result of
As shown in FIG. 4, the ink is hard to fill, so in order to efficiently express the gradation, a method of shifting the odd-numbered row and the even-numbered row in the sub-scanning direction by half dots is also commonly used. Hereinafter, this method is referred to as zigzag printing, and a set of dots to be printed first in one line is referred to as a first half 110 of the line, and a set of dots to be shifted by half a dot is referred to as a second half of the line 111 (see FIG. 5). . Further, in the conventional example, odd-numbered rows of heating resistors on the thermal head are printed in the first half of the line, and even rows are printed in the second half of the line.

[0005]

Generally, when the resolution of the thermal head is 300 dots per inch (dpi), if the gradation can be controlled in 256 steps for each color of yellow, magenta, cyan and black, it can be identified by human eyes. It is said that all colors can be expressed. However, for that purpose, when the resolution of the thermal head is, for example, 300 dpi, the dot diameter must be continuously controlled within the range of about 2 to 100 μm, but the ink layer has a thickness of about 2 to 4 μm. The larger the ratio of the layer thickness divided by the dot diameter required to express a certain gradation, the more unstable the actual transfer amount, sometimes not transferred at all or partially transferred. Or, in some cases, the transfer of low gradation part is extremely unstable because it is transferred several gradations higher than the predetermined gradation, and it is poor in reproducibility and printing halftone images such as natural images For example, the density of the transfer of a bright part such as cloud or skin changes every time printing is performed, and the transfer becomes unstable without reproducibility, which causes deterioration of the quality of the printed image.

As shown in FIG. 6, in the ink sheet 19 and the recording paper 27 sandwiched between the heating resistor 2 of the thermal head and the platen 12, the temperature of the heating resistor 2 on the thermal head when energized. The distribution has mountainous contour lines. For example, in the case of high-gradation printing, as shown in FIG. 7, the area a has a stronger adhesive force between the recording paper 27 and the ink 102 than the adhesive force between the ink 102 and the base layer 101. Even after being peeled, it remains on the recording paper 27. This range a is defined by an isothermal curve 112 indicating a boundary temperature between a portion where the ink 102 is transferred and a portion where the ink 102 is not transferred onto the thermal transfer recording paper 27.

Further, as shown in FIG. 8, in the case of low gradation printing, the area b is the area where the adhesive force between the recording paper 27 and the ink 102 is stronger than the adhesive force between the ink 102 and the base layer 101. Even after the strong portion is peeled off, it remains on the recording paper 27. However, in reality, variations in the heat generation of the heating resistor 2 due to the fact that the temperature and humidity corrections in the thermal transfer recording device cannot completely correct the thermal transfer recording paper 27.
The values of a and b vary due to variations in the smoothness of the.
As can be seen from FIGS. 7 and 8, the recording paper 27 and the ink 10
The inclination of the isothermal curve 112 of the temperature at which the adhesive strength of No. 2 and the adhesive strength of the ink 102 and the base layer 101 are equal at the contact surface between the ink layer 102 and the recording paper 27 is low gradation printing as compared with high gradation printing. Since the case is gradual, the variation of the value a is small enough to be ignored, but the variation of b is larger than that of a. When the low gradation part overlaps, for example, in order to express a light gray, the magenta low gradation dot overlaps the yellow low gradation dot, and the cyan low gradation dot overlaps it. In the case of transferring by transferring the color, the higher the color is, the larger the dispersion of the transfer is, and the tendency is remarkable. (Low gradation and high gradation in the text mean gradation 0 to gradation 25 for each color of yellow, magenta, cyan and black.
In the case of 256 gradation control up to 5, gradations from 0 to 64 are called low gradations, and gradations near 192 or higher are high gradations. Therefore, the conventional thermal transfer method has a problem that it is difficult to accurately express gradation in the case of fusion type color thermal transfer recording.

[0008] Therefore, an object of the present invention is to improve the quality of a print image by solving the above-mentioned conventional problems by making the printing of a low gradation portion a stable and reproducible gradation expression. A color fusion type thermal transfer recording apparatus and method capable of

[0009]

In order to solve the above problems, a color recording apparatus according to the present invention has a structure in which a printing means and color image data to be printed are provided in a color recording apparatus for printing and recording with at least three colors. A frame memory for storing the color image data, a resolution conversion control unit for reading the color image data from the frame memory, and changing the printing resolution depending on whether the color image data is within a specific gradation range or not, and the resolution conversion. A line memory for storing the output of the control means in correspondence with the print line and a print signal generating means for generating a signal for driving the print means based on the output of the line memory are provided.

Further, as a more detailed first configuration of the present invention, the resolution conversion means, for color image data in the specific gradation range, either the main scanning direction or the sub scanning direction of printing. The print resolution of each color in the main scanning direction or the sub-scanning direction is decreased while the number of print dots in the dot is increased, and the print resolution is converted to print at the dot position determined by each color in the increased dot. It was configured to do.

Further, as a more detailed second configuration of the present invention, the resolution conversion means, for color image data in the specific gradation range, either the main scanning direction or the sub scanning direction of printing. In addition to increasing the number of dots to be printed, the printing resolution is converted so that the dots are printed at the dot position determined by each color in the increased dots.

As a first method of color recording of the present invention, in a color recording apparatus for performing color printing based on color image data of at least three colors, either the main scanning direction or the sub-scanning direction of printing is performed. By increasing the number of print dot positions in and also performing printing based on the data of two pixels in the other of the main scanning direction or the sub-scanning direction of printing, a dot printing position corresponding to the number of colors is provided, When the average value of the odd number and the even number of the color image data is out of the specific gradation range, based on each color image data, each color is overlapped and printed at each predetermined dot position, and the average value is calculated. When the value is within a specific gradation range, the image data based on the odd-numbered and even-numbered color image data is used for each color, It was constructed to have a procedure for printing a predetermined dot position determined for each color.

Further, as a second method of color recording of the present invention, in a color recording apparatus for performing color printing based on color image data of at least three colors, the print dot positions in the sub-scanning direction of printing are increased, When the color image data is out of the specific gradation range, when the color image data is in the specific gradation range, printing is performed by superimposing each color at a predetermined dot position based on the color image data. Is configured so as to have a procedure for printing at a predetermined dot position determined for each color based on the color image data.

Furthermore, in order to solve the above problems,
In the third configuration of the color recording apparatus of the present invention, at least three or more colors are recorded on the recording medium by heating the heat-meltable ink using a thermal head in which a plurality of heating resistors are arranged in the main scanning direction of a color image. The color thermal transfer recording apparatus for transferring is configured to have a resolution conversion control means for changing the printing resolution according to the image signal.

Further, as a fourth structure of the color recording apparatus of the present invention, in the color recording apparatus of the third structure, the resolution conversion means has print dots in the same print area in a specific gradation area of print image data. The number of prints is increased and the print resolution of each color is lowered to transfer only one color to one dot.

Further, as a fifth configuration of the color recording apparatus of the present invention, in the color recording apparatus of the third configuration, the resolution conversion means has print dots in the same print area in a specific gradation area of print image data. With the increase in the number of dots, it was configured to transfer at most two or less colors to one dot.

[0017]

In the more detailed first structure of the present invention, the image data other than the low gradation portion is printed in a zigzag manner as usual, but the dot diameter required for expressing the low gradation in the low gradation portion. Therefore, the even numbered columns 122 in the first half of the line and the odd numbered columns 123 in the latter half of the line, which are not printed in the conventional configuration, are also printed. That is, as shown in FIG. 9, two pixels, that is, two columns (indicated by the one-dot chain line in FIG. 9) are considered as one set for one line of image data, and two columns in one set include the first half of the line and the second half of the line. With respect to a frame (indicated by a dotted line in FIG. 9) composed of four printing points of 1), one color is printed only at any one point in the frame. The gradation to be printed for that color is a value obtained by adding or multiplying the gradations of two columns, and instead of lowering the printing resolution for each color, the gradation is added or multiplied to create a larger dot diameter than before the addition. The printing and recording performance is stable by using this, and since only one color can be put on one point, there is no low gradation dot of another color under that color in the printing of any color. It is possible to avoid the deterioration of the image quality due to the overlapping of.

Further, in the more detailed second structure of the present invention, as in the case of the first structure, the zigzag printing of the data other than the low gradation portion is performed as usual, but in the low gradation portion the first half of the line is printed. Printing is performed even on the even-numbered columns and the odd-numbered columns on the latter half of the line. However, in the third configuration of the present invention, as shown in FIG. 10, the line first half portion 130 in one column of image data is used.
And two points of the latter half of the line 131 are considered as one set (indicated by a dotted line in FIG. 10), and only two colors are printed at one point for two print points in the set. are doing. That is, any one of yellow, magenta, cyan, and black within the one frame is 2
By dividing the printing of the color and the other two colors into the first half of the line and the latter half of the line, the printing resolution is improved compared to the first configuration, and the number of overprinted layers in the low gradation part is reduced to achieve low gradation. The image quality of the part can be stabilized.

Therefore, in the color recording apparatus having the structure of the present invention, it is possible to stabilize the printing and recording of dots in the low gradation portion, so that accurate gradation expression can be achieved.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. 11 and 12 show the outline of the configuration of the color thermal transfer recording apparatus used in the present invention.

A heat generating resistor 2 is arranged in the thermal head 20 so as to face the platen roller 12, and the platen roller 12 and the pair of paper feed rollers 13 and 14 are controlled by a stepping motor A controlled by a controller (not shown).
By 25, the forward and reverse rotations can be performed in the sub-scanning direction line by line, and the thermal transfer recording paper 27 is conveyed. Platen roller 12
A pair of paper feed rollers 28 and 29 for feeding paper to the platen roller 12 and a paper feed guide (not shown) are arranged in front of the above. Further, a pair of paper discharge rollers 15 and 16 and a paper discharge guide (not shown) are arranged at the ends of the paper feed rollers 13 and 14. Paper feed rollers 28, 29, paper discharge roller 1
Both 5 and 16 can be rotated in the sub-scanning direction by a DC motor 26 controlled by a controller (not shown), and convey the color thermal transfer recording paper 27. Further, the ink sheet supply roller 17 and the ink sheet take-up roller 18
Is arranged, and the ink sheet take-up roller 18 can be rotated by a stepping motor B24 controlled by a controller (not shown). Immediately after the thermal head 20, a peel plate 21 for stably peeling off the ink sheet 19 after thermal transfer and the thermal transfer recording paper 27 is arranged. Further, an ink sheet guide roller 23 is interposed between the peel plate 21 and the ink sheet take-up roller 18 in order to prevent the peel angle from changing due to the change in the diameter of the take-up side due to the ink sheet 19 being taken up. The peel angle is fixed by. 11 shows a state in which the thermal head 20 contacts the thermal transfer recording paper 27 and the ink sheet 19 and presses them, and FIG. 12 shows the thermal head 20 pressing the thermal transfer recording paper 27 and the ink sheet 19. It shows that there is no.

The thermal head 20, as shown in FIG.
3520 heat-generating resistors 2 arranged at 300 dpi intervals in the main scanning direction, switching elements 3 such as transistors for controlling energization of the respective heat-generating resistors 2 and logic elements such as a latch 5, shift register 6 and the like. The thermal head drive power supply 1 for supplying a current to the heating resistor 2 is connected to the thermal head 20. The output of the AND gate 4 is connected to each terminal (base) that controls the energization of the switching element 3. The thermal head 20 itself can be moved up and down. When the thermal head 20 is down, the heating resistor 2 applies pressure to the platen roller 12 as shown in FIG. 11, and when the thermal head 20 is up, no pressure is applied as shown in FIG. 2 and the platen roller 12 are separated.

The AND gate 4 has two inputs, one of which is connected to the output of the latch 5, and the other of which is input with the strobe signal generated from the heat pulse generator 7. The output of the shift register 6 is connected to the input of the latch 5, and the output of the heat pulse generator 7 is connected to the input of the shift register 6. The heat pulse generator 7 can read data from the line memory 8. Resolution conversion control unit 9
Can read data from the frame memory 10 and can write to the line memory 8. The frame memory 10 includes an image signal interface unit 11
The image signal sent via the is stored for one screen or more. Frame memory 10 and line memory 8 are S-RA
Although it is composed of semiconductor elements such as M and D-RAM, it may be another storage device such as a magnetic disk. The image signal interface unit 11 is connected to a host computer that supplies image data to the thermal transfer recording device,
Also, enlargement of the image sent from the host computer,
It also has reduction, rotation, and RGB → CMYK conversion functions.

Further, various setting instructions such as starting and stopping the operation of the thermal transfer recording apparatus and changing the print mode can be given from the host computer to the color thermal transfer recording apparatus. As shown in FIG. 2, the ink sheet 19 comprises a base layer 101 made of a film such as PET, and a yellow, magenta, cyan, and black heat-melting ink 102 on each screen in the order of yellow, magenta, cyan, and black. It has been applied. The ink sheet 19 has a configuration in which colors are sequentially switched by rotation of the ink sheet take-up roller 18. Further, the color detection sensor 22 allows a controller (not shown) to determine the current ink color of the ink sheet 19.

Next, the operation of this device will be described. A host computer (not shown) sends a signal for giving an instruction to start the printing operation to the thermal transfer recording device, and the thermal transfer recording device starts the printing operation, and the image data signal sent from the host computer (not shown) is transferred to the frame via the image signal interface unit 11. It is stored in the memory 10. The image data sent from the host computer to the image signal interface unit 11 here is a digital signal, and generally has a width of 8 bits per color, but it is not limited to this. The colors are cyan, magenta, and yellow.
It may be composed of data for four colors including colors and / or black (hereinafter referred to as CMYK data), or may be composed of data for three colors of red, green, and blue (hereinafter referred to as RGB data).

For example, image data consisting of CMYK data of 100 pixels has 100 × 4 × 8 = 3200 bits (40
It has a data capacity of 0 bytes). The image signal sent from the host computer to the thermal transfer recording device may be an RGB image, a CMYK image, or a resolution of 3
Since the image may be other than 00 dpi, the image signal interface unit 11 converts the received image to a CMYK image if the image is an RGB image, and if the resolution is other than 300 dpi, converts the image to a 300 dpi image using the scaling function. To the frame memory 10. That is, the image data signal written from the image signal interface unit 11 to the frame memory 10 is CMYK data and is naturally a digital signal. In addition, one pixel in the image data signal (total of 4 for cyan, magenta, yellow, and black)
The unit composed of the bite corresponds to the pixel printed by any one resistor of the thermal head 20 in a one-to-one correspondence. These enlargement, reduction, and RGB → CMYK conversion are configured by a digital logic integrated circuit, but since the specific circuit is known and is not the essence of the present invention, description thereof will be omitted. In parallel with the transfer of image data, the paper feed roller 2
By rotating 8, 29, one thermal transfer recording paper 27 placed in a paper feed guide (not shown) is drawn into the apparatus.
When the thermal transfer recording paper 27 is conveyed to the positions of the paper feed rollers 13 and 14, the subsequent conveyance is performed by the paper feed rollers 13 and 1.
4 is the main activity. When the print start line portion of the thermal transfer recording paper 27 is conveyed to below the heat generating resistor 2 of the thermal head 20, the conveyance is temporarily stopped. Next, the ink sheet take-up roller 18 rotates to take up the ink sheet 19. When the color detection sensor 22 detects yellow, the ink sheet winding is temporarily stopped, the thermal head 20 goes down, and the thermal transfer recording paper 2
The print start line portion 7 and the ink sheet 19 are sandwiched between the heating resistor 2 and the platen roller 12, and wait for a print start instruction from the controller.

Frame memory 10 for image data to be printed
When the data is stored in the memory, the resolution conversion control unit 9 reads the data of the first line of yellow from the frame memory 10 and performs digital processing, and writes the result in the line memory 8 in which the gradation is written in advance to 0. . The processing performed by the resolution conversion control unit 9 is a combination of two columns such that the first pixel, the second pixel, the third pixel and the fourth pixel in one line are combined in the same manner, and the subsequent 3519th pixel and 3520th pixel are combined. (1760 sets) is processed.

Hereinafter, as shown in FIG. 9, the first column in each combination is called an odd column, and the next column is called an even column. The line memory 8 has a capacity of 3520 × 16 bytes and has a structure as shown in FIG. When the average of the gradations of the pixels in the odd-numbered columns and the even-numbered columns is 65 or more, it is the same as the normal zigzag printing, and the gradations of the pixels in the odd-numbered columns are in the first half of the line shown in FIG. In order to print, the gradation is written as it is at the address corresponding to the same row of the line A in the line memory 8. Further, since the gradations of the pixels in the even-numbered columns are printed at the locations corresponding to the even-numbered columns in the first half of the line shown in FIG. 9, they are written as they are at the addresses corresponding to the same columns of the line B of the line memory 8. Addresses corresponding to the odd columns in line B and the even columns in line C of the line memory 8 for printing in other places than the odd columns in the latter half of the line and the even columns in the latter half of the line shown in FIG. 0 is written in each. If the average gray level of the pixels in the odd and even rows is 64 or less, the value obtained by adding the yellow gray levels of the odd and even rows in each set is printed on the odd rows in the first half of the line shown in FIG. Therefore, writing is performed in the odd-numbered column of the line A of the line memory 8. For printing on the pixels in the even-numbered columns in the first half of the line and the second half of the line other than that shown in FIG.
Odd and even columns of line B and line C of line memory 8
0 is written in the memory address corresponding to the even column of.
These conversions are performed in units of two columns up to the final column, and when the processing in the resolution conversion control unit 9 for one line is completed, the resolution conversion control unit 9 then reads the data of the second line of yellow from the frame memory 10. The same process as the first line is performed, and the result is written in the line memory 8. That is, in the resolution conversion control unit 9, the 1st pixel, the 2nd pixel, the 3rd pixel and the 4th pixel in the two lines, and the like in the same manner, continue 351
2 such as combining at 9th pixel and 3520th pixel
The processing is performed in a combination (1760 sets) in units of columns.

In each set, when the average of the gradations of the pixels in the odd-numbered columns and the even-numbered columns is 65 or more, it is the same as the normal zigzag printing, and the gradations of the pixels in the odd-numbered columns are the first half odd number shown in FIG. Since printing is performed at a position corresponding to a column, the same value is written in the address of the line C of the line memory 8 corresponding to the same column, and the gradation of the pixel in the even column corresponds to the even column in the first half of the line shown in FIG. Since the data is printed at the location, the value is written as it is at the address corresponding to the same row of the line D of the line memory 8. Corresponding to the odd-numbered columns in line D and the even-numbered lines in line memory 8 for printing in other locations than the odd-numbered columns in the latter half of the line and the even-numbered columns in the latter half of the line shown in FIG. Write 0 to each address. When the average gray level of the pixels in the odd and even columns is 64 or less, the value obtained by adding the yellow gray levels of the odd and even columns in each set is shown in FIG.
In order to print on the odd-numbered columns in the first half of the line shown in (1), writing is performed on the odd-numbered columns of the line C of the line memory 8. In the memory addresses corresponding to the odd and even columns of the line D and the even column of the line E of the line memory 8 for printing on the pixels in the even columns and the latter half of the lines in the other half of the line shown in FIG. Is written with 0. These conversions are 2
When the process for the second line of yellow in the frame memory 8 is completed, the same process is performed for the third line of yellow in the frame memory 8, and so on until the last line of yellow. Processing is performed.

When the processing in the resolution conversion control unit 9 of the first line of yellow in the frame memory 10 is completed, the heat pulse generation unit 7 first reads the gradation data of line A in the line memory 8 and reads out the line A. Shift register 6 by binarizing every pixel in every pixel
Transfer to When the reading of the line A is completed, the resolution conversion control unit 9 can rewrite the line A after the line P, and the rewriting of the line memory is sequentially repeated.

As a specific process of the heat pulse generator 7, for the grayscale data read from the line A of the line memory 8, first, the pixel portion having a grayscale of 1 or more is set to 1, and the rest is set to 0 in the shift register. 6 (hereinafter, the transferred data is referred to as heat data). Shift register 6
Is 3520 dots and is latched by the latch 5 when the transfer to the shift register 6 is completed. At the time of being latched, the heat pulse generating unit 7 next sets 1 to the pixel portion having gradation 2 or more, and similarly starts the transfer to the shift register 6. At this point, the print preparation is completed, so the paper feed roller 1
3, 14 and the platen roller 12 are heat transfer recording sheets 27.
The ink sheet take-up roller 18 starts to take up the ink sheet 19 at the same time that the feeding of the ink sheet is started. The heat pulse generator 7 generates a strobe pulse for a gradation 1 for a preset time, and the base of the switching element 3 of the heating resistor 2 whose latch output (heat data at the gradation 1) is 1 during that time. It becomes high, and the heat generating resistor 2 is energized to generate heat to transfer the ink to the thermal transfer recording paper 2
Transfer to 7. By the end of the strobe signal for gradation 1, the heat pulse generation unit 7 transfers the gradation data of line A to the shift register 6 by setting the pixel portion of gradation 2 or more to 1 and outputs the strobe signal of gradation 1. Latch at the end of. When the latch is completed, the heat pulse generator 7 generates a strobe pulse for the gradation 2 for a preset time, and during that time, switching of the heating resistor 2 whose latch output (heat data in gradation 2) is 1 If the base of the element 3 is gradation 1, then h
When it becomes high, the heat generating resistor 2 continues to be energized to generate heat, thereby further transferring the ink to the thermal transfer recording paper 27.

Thereafter, these operations are repeatedly executed up to the gradation 255 for the data read from the memory address corresponding to the line A of the line memory 8. The pulse width of the strobe signal at each gradation from gradation 1 to gradation 255 is the same for all the resistors on the thermal head 20, but the pulse width at each gradation is different for each color and for each gradation, and the thermal storage of the thermal head 20 is different. , Is set in consideration of the gradation continuity of the print result.

When the printing of the line A is completed in this way, the heat pulse generator 7 reads out the gradation data of the line B of the line memory 8 and binarizes all the pixels of the line B for each gradation to the shift register 6. Forward. Thereafter, the same operation as that of line A is performed, the heat data corresponding to gradation 1 on line B is latched, and the line B is printed at the point when the thermal transfer recording paper 27 is conveyed by half a dot from the time when the line A is printed. Start, and then gradation 2
The same operation is performed up to 55. When printing of line B is completed, lines C, D, E, F, G, H, I, J, K, are sequentially printed.
L, M, N, O, P, A, B, C, D ... Are read and the process is performed up to the final yellow line.

When the printing of the final line is completed and the final line portion of the thermal transfer recording paper 27 is peeled off, the thermal head 20 goes up and the ink sheet take-up roller 18 stops rotating. Next, the paper feed roller 13,
The thermal transfer recording paper 27 is returned to the print line start portion by the reverse rotation of 14 and the platen roller 12. At the same time, the ink sheet take-up roller 18 rotates to feed the ink sheet 19 until the color detection sensor 22 detects magenta. Further, the line memory 8 is all rewritten to 0.

When magenta is detected, the ink sheet winding is once stopped, the thermal head 20 goes down, and waits for a magenta printing start command from a controller (not shown). The resolution conversion control unit 9 reads the data of the first line of magenta from the frame memory 10 and performs the same processing as that for yellow, and writes it in the line memory 8. In the following two-column unit combination similar to yellow printing, when the average gray level of the pixels in the odd-numbered and even-numbered columns is 64 or less, the added value of the gray-scaled numbers in the magenta odd-numbered and even-numbered columns is shown in FIG. The operation similar to that for yellow printing is the same as that for yellow printing except that writing is performed at the position of the even-numbered column in the first half of the indicated line (for example, the first line of magenta in the frame memory is written in the even-numbered column of line B of the line memory 8). The printing of lines is performed.

When the printing of the final line of magenta is completed and the final line portion of the thermal transfer recording paper 27 is peeled, the thermal head 20 is in the up state and the ink sheet take-up roller 18 stops rotating. Next, the paper feed rollers 13 and 14 and the platen roller 12 rotate in the reverse direction, so that the thermal transfer recording paper 27 is returned to the print line start portion. At the same time, the ink sheet take-up roller 18 rotates to feed the ink sheet 19 until the color detection sensor 22 detects cyan. The contents of the line memory 8 are rewritten to 0.

At the time when cyan is detected, the ink sheet winding is once stopped, the thermal head 20 goes down, and waits for a cyan print start command from a controller (not shown). The resolution conversion control unit 9 reads the data for the first line of cyan from the frame memory 10 and performs the same processing as for yellow and writes it to the line memory 8. In the following two-column unit combination similar to yellow printing, when the average gray level of the pixels in the odd-numbered and even-numbered columns is 64 or less, the added value of the gray-levels in the odd-numbered and even-numbered cyan columns is shown in FIG. The same operation as that for yellow printing is performed except for writing to the odd-numbered columns of the latter half of the lines (for example, the first cyan line of the frame memory is written to the odd-numbered columns of line B of the line memory 8). The printing of lines is performed.

When the printing of the cyan final line is completed and the final line portion is peeled off, the thermal head 20 goes up and the ink sheet take-up roller 18 stops rotating. Next, the paper transfer rollers 13 and 14 and the platen roller 12 are rotated in the reverse direction, so that the thermal transfer recording paper 27
Is returned to the beginning of the print line. At the same time, the ink sheet take-up roller 18 rotates to feed the ink sheet 19 until the color detection sensor 22 detects black. The contents of the line memory 8 are rewritten to 0.

At the time when black is detected, the ink sheet winding is once stopped, the thermal head 20 goes down, and waits for a black print start command from a controller (not shown). The resolution conversion control unit 9 reads the data of the first black line from the frame memory 10 and performs the same processing as that of the yellow data, and writes it to the line memory 8. Same as 2 for yellow printing
In the combination in units of columns, when the average gradation of the pixels of the odd and even columns is 64 or less, the added value of the gradations of the black odd column and the even column is shown in FIG. The same operation as the yellow printing is performed up to the printing of the last black line except that the data is written in the position (for example, the first black line of the frame memory is written in the even column of the line C of the line memory 8).

When the printing of the final black line is completed and the final line portion is peeled off, the thermal head 20 goes up and the ink sheet take-up roller 18 stops rotating. Next, as the paper discharge rollers 15 and 16 rotate, the thermal transfer recording paper 27 is discharged to the outside of the apparatus, and printing is completed.

FIG. 13 shows a simple example of the actual print result. FIG. 13A is an example of 8 × 4 (32 pixels) CMYK data stored in the frame memory 10.
FIG. 13B shows a special state of printing based on the CMYK data shown in FIG. In the image data of this example, the central portion is a low-density gray, and the peripheral portion is a high-density gray.
This shows the result of printing on the thermal transfer recording paper 27 by the above processing through the resolution conversion control unit 9 when x4 = 32 pixels.

As can be seen from FIG. 13 (B), the resolution for each color is reduced to about half in the low gradation portion, but the diameter of one dot is correspondingly increased and the transfer amount is stabilized, and in addition, for each color. In printing, the image quality is stable because there are no low-gradation other-color dots below. Further, even if the resolution of each color in the low gradation part is lowered, it is almost indistinguishable to the human eye.

Further, in the above-described embodiment, the added value of yellow in each color in the resolution conversion control section 9 is an odd number column in the first half of the line shown in FIG. 9, and the added value of magenta is the first half of the line shown in FIG. The even-numbered columns of the parts, the added value of cyan is the odd-numbered columns of the latter half of the line as shown in FIG. 9, and the added value of black is the even-numbered columns of the latter half of the line as shown in FIG. Other arrays may be used as long as they do not overlap. Further, in the above-mentioned embodiment, the conversion process of the low gradation part is addition, but other processes such as multiplication may be combined.

In the above embodiment, the resolution conversion control section 9 processes two columns as one set, but it is also included in the present invention to process each column as shown in FIG. . That is, for the image whose gradation is 64 or less with respect to the image read out from the frame memory 10 by the resolution conversion control unit 9, yellow is the first half 130 of the line in the same row as shown in FIG. , Cyan is written in the line first half 130 of the same line, and black is written in the line memory at the address corresponding to the line second half 131 of the same line so that only two colors can be transferred at maximum for one point. This method may have one color below depending on the color, but has the advantage that the resolution for each color is the same as the conventional one.

Whether the printing method shown in FIG. 9 or the printing method shown in FIG. 10 is used depends on the required printing quality. That is, if priority is given to resolution, the printing method shown in FIG. 10 is advantageous, and if priority is given to image quality stability, the printing method shown in FIG.
The printing method shown in is advantageous.

It should be noted that in the above embodiment, the gradation values are from 0 to 2
In the case of 256 gradations up to 55, the low gradation is set to the gradation value 64 or less, but the present invention is not limited to the gradation value of the low gradation being 64 or less, and various gradation values However, it goes without saying that it is applicable. The present invention can be applied even if the number of gradations is not 256. The gradation value that defines the low gradation is determined by various conditions such as the characteristics of the ink of the ink sheet and the characteristics of the thermal head.

Further, although the present invention has been described by taking the melting type thermal transfer recording apparatus as an example in the above-mentioned embodiments, it is needless to say that the present invention can be applied to other types of color print recording apparatus.

[0048]

As described above, according to the present invention, in the printing of the low gradation part, the number of times of printing is increased and the gradation is controlled by the print recording of only one color or two colors at one place. Since the structure is adopted, there is an effect that an accurate gradation expression can be stably obtained even in a low gradation part.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a thermal head driving section in an embodiment of a color recording apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a configuration of an ink sheet.

FIG. 3 is an explanatory diagram showing a state of dots in a high density area on a thermal transfer recording sheet in conventional printing.

FIG. 4 is an explanatory diagram showing a state of dots in a high density area on a thermal transfer recording sheet in zigzag printing.

FIG. 5 is an explanatory diagram showing the definitions of the first half of the line and the second half of the line according to the present invention.

FIG. 6 is a diagram showing an outline of temperature distribution in heat generation of a resistor of a thermal head during energization.

FIG. 7 is an explanatory diagram of transfer of high gradation dots.

FIG. 8 is an explanatory diagram of low-gradation dot transfer.

FIG. 9 is an explanatory diagram showing a printing state in the color recording apparatus of the present invention.

FIG. 10 is an explanatory diagram showing another printing state in the color recording apparatus of the present invention.

FIG. 11 is a diagram showing an outline of a color thermal transfer recording apparatus embodying the present invention when a thermal head is down.

FIG. 12 is a diagram showing an outline of a color thermal transfer recording apparatus for carrying out the present invention when a thermal head is raised.

13A is a diagram showing an example of CMYK data stored in a frame memory of the color recording apparatus according to the present invention, and FIG. 13B is an explanatory diagram showing a printing result based on the CMYK data of FIG. 13A. Is.

FIG. 14 is a diagram showing a configuration of a line memory of a color thermal transfer recording apparatus embodying the present invention.

[Explanation of symbols]

 1 Thermal Head Driving Power Supply 2 Heating Resistor 3 Switching Element 4 AND Gate 5 Latch 6 Shift Register 7 Heat Pulse Generator 8 Line Memory 9 Resolution Conversion Controller 10 Frame Memory 11 Image Signal Interface 12 Platen Roller 13 Paper Feed Roller B 14 Paper feed roller A 15 Paper discharge roller B 16 Paper discharge roller A 17 Ink sheet supply roller 18 Ink sheet take-up roller 19 Ink sheet 20 Thermal head 21 Peel plate 22 Color detection sensor 23 Ink sheet guide roller 24 Stepping motor B 25 Stepping motor A 26 DC motor 27 Thermal transfer recording paper 28 Paper feed roller B 29 Paper feed roller A

Claims (5)

[Claims] 1. A color recording apparatus for printing and recording with at least three colors, a printing means, a frame memory for storing color image data to be printed, and color image data read from the frame memory,
A resolution conversion control means for changing the printing resolution depending on whether the color image data is within a specific gradation range or not, and a line memory for storing the output of the resolution conversion control means in correspondence with the printing line. A print signal generating means for generating a signal for driving the print means based on the output of the line memory. 2. The resolution conversion unit increases the number of print dots in one of the main scanning direction and the sub-scanning direction of printing for color image data in the specific gradation range, and at the same time, performs the main scanning of printing. The printing resolution of each color in the other direction or the sub-scanning direction is lowered, and the printing resolution is converted so that printing is performed at a dot position determined by each color in the increased dots. Color recording device. 3. The resolution conversion unit increases the number of print dots in one of the main scanning direction and the sub scanning direction of printing for the color image data in the specific gradation range, and increases the number of dots. 2. The color recording apparatus according to claim 1, wherein the print resolution is converted so that the dot is printed at a dot position determined by each color. 4. A color recording device for performing color printing based on color image data of at least three colors, wherein the number of print dot positions in either the main scanning direction or the sub scanning direction of printing is increased and the main scanning of printing is performed. In the other of the direction and the sub-scanning direction, it is possible to perform printing based on the data of two pixels, thereby providing dot printing positions corresponding to the number of colors, and averaging the odd and even number of the color image data. When the value is out of the specific gradation range, printing is performed by superimposing each color at a predetermined dot position based on each color image data, and when the average value is within the specific gradation range. Uses the image data based on the odd-numbered and even-numbered color image data for each color, and prints at a predetermined dot position determined for each color. Color recording method according to claim Rukoto. 5. A color recording device for performing color printing based on color image data of at least three colors, wherein the number of print dot positions in the sub-scanning direction of printing is increased, and the color image data is out of a specific gradation range. In this case, printing is performed by superimposing each color at a predetermined dot position based on the color image data, and when the color image data is within a specific gradation range, each color is printed based on the color image data. A color recording method characterized by printing at a predetermined dot position defined in 1.