JP2503437B2 - Dither processor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a dither processing device, and in particular, even if there is a variation in the printing portion of each thermal transfer device, the effect thereof affects the printed image quality. The present invention relates to a dither processing device that does not come out.

(Prior Art) The configuration and operation of a printing unit (thermal head) of a conventional thermal transfer device will be described with reference to FIGS. 6 and 7. FIG. 6 shows the structure of the main part of the printing section, and FIG. 7 shows the time chart of the signals applied thereto.

In FIG. 6, 1 is a heating element arranged on one line, C1 and C2 are common electrodes for selecting elements to be printed in the heating elements, 2 is a driver, and 3 is for printing. It is a register that latches pixel signals.

Now, as shown in FIG. 7, the latch signal L1 is input to the register 3 at an appropriate timing to generate the pixel signal D _N-1.
When ~ D _{N + 5} is latched in the register 3, the driver 2 is controlled to be turned on and off according to the pixel signal. Next, when the H-level signal C1 ′ is applied to the common electrode C1, the driver 2 corresponding to the pixel signal “0” (black) is turned on, while
The driver 2 corresponding to the pixel signal "1" (white) is turned off, a current flows through the heating element 1 located between the common electrode C1 and the driver 2 turned on, and the heating element 1 generates heat. To do. On the contrary, no current flows in the heating element 1 located between the common electrode C1 and the off driver 2. As a result, black is printed on the recording paper (not shown) at the position corresponding to the heated heating element 1, while the position corresponding to the unheated heating element 1 is not printed and the background color is retained. It

When the H voltage application time to the common electrode C1 elapses, the next latch signal L2 is input to the register 3 and new data is latched in the register 3. Next, H voltage is applied to the common electrode C2.
When C2 'is applied, the pixel signal is "0" (black) as above.
The driver 2 corresponding to is turned on, while the driver 2 corresponding to the pixel signal “1” (white) is turned off. Therefore, a current flows through the heating element 1 located between the common electrode C2 and the driver 2 which is turned on, and the heating element 1 generates heat, and conversely, the common electrode C2 and the driver 2 which is off. Current does not flow in the heat generating element 1 located between and, and heat is not generated.

As described above, when the H voltage is applied to the common electrodes C1 and C2 once, the printing of one line is completed.

By the way, a dither threshold value as shown in FIG. 8A is used for the thermal transfer device, and a uniform image having a density of 5 as shown in FIG. Consider a case where the thermal head prints on the recording paper 4 moving in the direction of arrow A in FIGS.
Now, the dither threshold "1""3","7""5","16"
The image data processed by “14”, “10” and “12” is printed when the H voltage is applied to the common electrode C1, while the image data processed by the dither threshold other than the above is applied to the common electrode C2.
If printing is performed when a voltage is applied, a print image as shown in FIG.

On the other hand, dither thresholds “3” “15” “5” “9” “1”
The image data processed by 4 ", 2", 12 "and 8" is printed when the H voltage is applied to the common electrode C2, and the image data processed by the dither threshold other than the above is the H voltage on the common electrode C1. If it is printed when the voltage is applied, a print image as shown in FIG.

That is, when the phase of the H voltage applied to the common electrodes C1 and C2 of the thermal head and the phase of the dither threshold used to obtain the image data printed by the common electrode change, the image of the same content is obtained. (A uniform image with a density of 5) results in different print images as shown in FIGS. In other words, the density of a uniform image having a density of 5 is recorded in different darkness.

Next, when trying to perform color printing by using the above-mentioned thermal heads alternately printed every two dots, normally four thermal heads are prepared, and four color heads, that is, C, It is common to supply M, Y, K (black) image information and print C, M, Y, K obtained by each thermal head to print a color image.

In this case, for example, the phase of the dither threshold used to obtain the image information applied to the thermal head for printing C and the phase of the H voltage applied to the common electrode of the thermal head are, for example, as shown in FIG. c), on the other hand, for example, the phase of the dither threshold used to obtain the image information applied to the thermal head for printing M and the phase of the H voltage applied to the common electrode of the thermal head. If, for example, the relationship shown in FIG. 8 (d) is present, and the Y, K colors also have the phase relationship shown in FIG. 8 (c) or (d), this phase relationship changes. And 4 colors will be superimposed in different combinations. Therefore, the color of the printed image, that is, the reproduced color changes according to the phase relationship.

Further, in the color thermal transfer device, for example, when the thermal heads of four colors are displaced in the main scanning direction, the reproduction dots of four colors corresponding to the same image signal are not superposed at one point.

(Problems to be Solved by the Invention) As described above, in the conventional thermal transfer apparatus, when the phase of reading the dither threshold value and the phase of the H voltage applied to the common electrode of the thermal head are deviated, When obtaining a print image of one color, the density changes. On the other hand, when obtaining a print image of color, the reproduced color changes, and the intended color expression cannot be achieved.

Further, if the thermal heads of the respective colors of the color thermal transfer device are displaced in the main scanning direction, the color of the reproduced image cannot be faithfully expressed.

It is an object of the present invention to provide a dither processing device that solves the above-mentioned problems of the prior art all at once.

(Means and Action for Solving Problems) In order to solve the above problems, the present invention provides a dither threshold generator, a sub-count and a main power counter for determining a read address of the dither threshold generator, Comparing means for comparing the threshold output from the dither threshold generator with the input image signal data to generate a binary image signal, a buffer to which the binary image signal is input, and an address generator for generating an address of the buffer. By inputting a capture signal formed on the basis of the input timing of the image signal data to the main counter and the address generator and resetting these, the grayscale or reproduction of the reproduced image is reproduced. It is characterized in that the color variation is eliminated and the reproduced color matches or approximates to the primary color.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

 FIG. 1 is a block diagram of an embodiment of the present invention.

In the figure, reference numeral 11 denotes a threshold value generator, which generates a dither threshold value as shown in FIG. 8 (a), for example. 12
Is a sub-counter, which counts up by 1 each time the sub-scanning reference signal is input. Further, 13 is a main counter, which counts the video clock. The outputs of the sub-counter 12 and the main counter 13 are the addresses of the threshold value generator 11, and the dither threshold value stored in the threshold value generator 11 is a 4 × 4 matrix as shown in FIG. 8 (a). In addition, both the main counter 13 and the sub-counter 12 are composed of counters that are reset and return to their original values each time four input pulses are counted. The main counter 13 is also reset by the capture signal.

An address generator 14 generates, for example, an address 1 when a capture signal is input, and thereafter advances the address in synchronization with the video clock. This address becomes the address of buffer 15. Reference numeral 16 denotes a comparator, which compares the dither threshold value read from the threshold value generator 11 with the input multivalued image signal data and buffers the binary image signal.
Output to 15. The buffer 15 stores the binary image signal at the address designated by the address generator 14.

Reference numerals 2 and 3 are the same drivers and registers as those in FIG. 6, and the heating elements are not shown.

FIG. 2 shows a time chart of the sub-scanning reference signal, image signal data, and capture signal.

The operation of FIG. 1 will be described with reference to FIG. As shown in FIG. 2, first, when the first sub-scanning reference signal is input, the sub-counter 12 is counted up by this, and addresses the uppermost row of the rows of the dither threshold. Next, the capture signal is generated in synchronization with the image signal data,
When it enters the main counter 13, the main counter 13 is reset and addresses the leftmost column of the dither threshold column. That is, the threshold value of the coordinate (1,1) of the 4 × 4 matrix dither threshold value is output from the threshold value generator 11. On the other hand, at this time, the address generator 14 designates the first address of the address of the buffer 15.

Therefore, the first pixel data of the input image signal data is compared with the threshold value of the coordinate (1,1) by the comparator 16, and the binary image signal obtained thereby is stored in the buffer 15
It is stored in the first address.

Next, when the second video clock comes in, the count value of the main counter 13 becomes 2, so the threshold value of the coordinate (2,1) of the threshold value generator 11 is selected and output to the comparator 16. It On the other hand, the address generator 14 designates the second address of the buffer 15. Therefore, the second pixel data is the comparator 16
Is compared with the threshold value of the coordinate (2,1) and the binary image signal obtained as a result is stored in the second address of the buffer 15.

Thereafter, the same operation is performed, and when the fifth video clock is input, the main counter 13 returns to 1 and outputs the threshold value of the coordinate (1,1) to the comparator 16 again. Also, the comparator 16
The binary image signal of the fifth pixel data, which is the output of, is stored in the fifth address of the buffer 15.

In this way, the binary image signal for one line is buffered.
Once stored in 15, then common electrode C of the thermal head
Switching means synchronized with the H voltage applied to 1, C2
Every other two 17's are turned on. As a result, the binary image signal stored in the buffer 15 is transferred to the register 3 through the turned-on switching means. When the binary image signal is transferred to the register 3, the heating element of the thermal head is excited by the same operation as the conventional device,
The image information is reproduced on the recording paper.

As described above, according to this embodiment, the main counter 13 is reset by the fetch signal, and the address generator
Since 14 accesses the first address of the buffer 15, the dither threshold selected by the threshold generator 11 and the address of the buffer 15 always correspond. Further, the address of the buffer 15 and the storage position of the register 3 correspond to each other, and the transfer timing from the buffer 15 to the register 3 corresponds to the H voltage applied to the common electrodes C1 and C2 of the thermal head. The binary image signal binarized with a specific dither threshold is always printed when the H voltage is applied to one of the common electrodes C1 and C2.

Therefore, when the dither processing apparatus of this embodiment is used for a thermal transfer apparatus, there is no problem that the same input image is reproduced with different densities by individual thermal transfer apparatuses as in the conventional apparatus.

Next, a second embodiment of the present invention will be described with reference to FIG. This embodiment shows an example in which the present invention is applied to a color thermal transfer device. In the figure, the numbers forming the reference numerals are the same as or equivalent to those in FIG. 1, and Y, M, C and K attached to these numbers respectively represent four colors of yellow, magenta, cyan and black. Show.

In this embodiment, each of the Y, M, C and K dither processing devices has the same configuration and operates as in the first embodiment. Therefore, Y, M, C, and K image signal data Yo, Mo, Co, and Ko at the timings shown in FIG.
Are input to the comparators 16Y, 16M, 16C and 16K, respectively, the binary image signals processed by the thresholds of the dither threshold generators 11Y to 11K are stored in the same addresses of the buffers 15Y to 15K. To be done.

Therefore, when the H voltage is applied to the common electrodes C1 and C2 of the thermal head of each color, the dither threshold generator of each color is generated.
The binary image signal processed with the dither threshold of 11Y to 11K is printed, and the variation in color overlap is eliminated. Therefore, when the dither processing device of this embodiment is used for a color thermal transfer device, there is no problem that the same input image is reproduced in different colors by each thermal transfer device as in the conventional device.

Next, a third embodiment of the present invention will be described with reference to FIG.

If the Y, M, C, and K thermal heads are misaligned in the main scanning direction, the color image signals sequentially sent from the end of the thermal element of the thermal head, for example, the left end, may be printed. The same image information of Y, M, C, and K does not overlap on the same dot, and the quality of the reproduced image is greatly reduced.

For example, as shown in FIG. 4, when the Y, M, C, and K thermal heads, that is, the buffers 15Y to 15K are shifted by one dot in the main scanning direction, the color image signal sent The data is stored at the left end of each buffer 15, i.e.
Sequentially stored from address 1 to address N, for example, the fourth dot of Y image signal data, the third dot of M image signal data, the second dot of C image signal data, and the first dot of K image signal data. The eyes will be superimposed. Hereinafter, the image signal data of each color are superimposed in the same phase relationship. Therefore, a clear reproduced image cannot be obtained.

This embodiment solves this problem. Now M
If the physical position of the head of is in the nominal position and the physical position of the Y, C, and K heads deviates from the nominal position,
When this relationship is expressed by the Y, M, C, K buffers 15Y to 15K, it can be expressed as shown in FIG.

That is, the 1st bit of the image signal data corresponds to the 1st address of the M buffer, the Y buffer is shifted by 1 bit to the left, while the C and K buffers are shifted by 1 bit and 2 to the right, respectively. It is assumed that the bits are misaligned.

At this time, in this embodiment, the Y capture signal is sent out one clock earlier than the M capture signal which is the nominal timing. The C capture signal is transmitted 1 clock later than the nominal timing, and the K capture signal is transmitted 2 clocks later. Applying these color capture signals to the circuit shown in FIG. 3, for example, and resetting the Y to K address generators 14Y to 14K and the main counters 13Y to 13K, the Y to K buffers are assigned to the respective addresses. , Image signal data 1Y, 2Y, 3Y, ...; 1M, 2 which has been subjected to dither processing as shown in FIG.
M, 3M, ...; 2C, 3C, ...; 3K, ... are stored, and left and right resist adjustments are combined. In addition, -in the figure represents non-printing data (invalid data).

FIG. 5 shows an image on the recording paper obtained by this embodiment. As is clear from the figure, each dot can be formed on the recording paper by superimposing the signals obtained by processing the same image signal data with the dither threshold for each color, and it is possible to obtain a clear reproduced image that is faithful to the original image. You can

As described above, according to the above-described embodiments, the main counter and the address generator of the dither processing device are reset by the capture signal and the address of the buffer is designated by the address generator. When the devices are different, there is no problem that the densities are different or the reproduced colors are different, regardless of the same input image signal data.

(Effects of the Invention) As is clear from the above description, according to the present invention, the following effects are achieved.

(1) Since the phase in which the dither threshold is read out and the phase in which the H voltage is applied to the common electrode of the thermal head always match, there is no change in the density of the print image or change in the reproduced color of the color print image. There is an effect.

(2) Even if the thermal head for each color of the color thermal transfer device is displaced in the main scanning direction, the left and right resist adjustments are achieved, and the reproduced color faithful to the original image can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a waveform diagram of a signal of a main part thereof, FIG. 3 is a block diagram of a second embodiment of the present invention, and FIG. 4 is a block diagram of the present invention. 3 is an explanatory view of an embodiment, FIG. 5 is an explanatory view of an image on a recording paper, FIG. 6 is a schematic explanatory view of an example of a conventional thermal head, FIG. 7 is a time chart of signals of its main part, and FIG. Shows a diagram explaining that a grayscale or color change appears in a reproduced image when there is a phase shift between the conventional dither threshold and the H voltage applied to the common electrode of the thermal head. 11 ... Threshold generator, 12 ... Sub counter, 13 ... Main counter, 14 ... Address generator, 15 ... Buffer, 16 ... Comparator

Claims (2)

(57) [Claims] 1. A dither threshold generator, a sub-counter and a main counter that determine a read address of the dither threshold generator, and a threshold value output from the dither threshold generator and input image signal data are compared to each other. A comparison means for making a value image signal,
A capture signal which is provided with a buffer to which the binary image signal is input and an address generator which creates an address of the buffer, and which is formed on the basis of the input timing of the image signal data to the main counter and the address generator. Is input and these are reset. 2. The dither processing apparatus according to claim 1, wherein the timing of the fetch signal for each color is shifted in correspondence with the amount of deviation of the thermal head for each color in the main scanning direction.