JPH01215542A - Printer - Google Patents

Abstract

PURPOSE:To stably record an image increased in the number of gradations, by realizing the magnification of the number of gradations due to lower rank (m+n) bits (m and n are a positive integer) of the gradation data of one pixel unit 2<k>(k is a positive integer) gradation by aeral gradation due to a matrix of longitudinal/lateral 2<m>X2<n> pixels. CONSTITUTION:Four-bit threshold value data corresponding to the block internal position of 4X4 pixels shown by lower rank 2 hits of an address counter 6 and a line counter 10 written in an ROM 11 and the data of the lower rank bits of a line memory 5 are compared with each other by the second comparator 12 and, when the latter is larger than the former, a raising signal (b) is set to 1 and the pixel pulse width thereof is made long. As mentioned above, 2<k> gradation due to higher rank (k) bits of the gradation data stored in the line memory 5 is realized in one pixel unit on the basis of the density gradation due to the control of the current supply pulse width of both of a gradation counter 8 and the first comparator 9, and the magnification of the number of gradations due to the lower rank (m+n) bits of gradation data is realized by the areal gradation due to the matrix of the longitudinal/lateral 2<m>X2<n> pixels of the ROM 11. By this method, an image increased in the number of gradations can be stably recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to the field of computer graphics and the field of video systems such as VTRs and still video cameras. The present invention relates to a printer device that can be controlled.

Conventional technology Conventionally, image printers capable of recording multiple gradations have used an area gradation method that expresses halftones by varying the number of recorded dots, and a method that controls density and area within one pixel by controlling recording energy and timing. There are two types: the density gradation method, and the combination of both.

The area gradation method consists of one pixel consisting of a plurality of dots, and is used in printers such as the thermal melt transfer method, inkjet method, and electrophotographic method, in which it is difficult to express gradation within a pixel.

As a density gradation method, there is a thermal sublimation transfer method using dye ink, which has recently attracted attention as a method of realizing high-quality hard copies similar to photographs.

This method allows gradation recording using density gradation by modulating the energy applied to the heating element. Furthermore, in the thermal melt transfer method, a method has been proposed that allows gradation recording within one pixel by changing the shape of the recording material and the head heating element. These recording methods control the recording density by varying the applied force by changing the pulse width of the power applied to the head in stages (Japanese Patent Laid-Open No. 59-091).
Publication No. 772).

In addition, for those using both area gradation and density gradation,
There is a publication No. 2-88476.

Problems to be Solved by the Invention However, in order to increase the number of gradations in an image using the conventional area gradation method, it is necessary to reduce the dot area of the line head.
The number of dots constituting one pixel must be increased, which requires a high-density line head with a large number of dots per unit length, resulting in extremely high manufacturing and mounting costs. In addition, the number of recording lines in the sub-scanning increases, which increases the recording time, and requires the same precision in paper feeding as dots, making it difficult from a mechanical manufacturing perspective to stably reproduce extremely small dots. It is difficult to increase the number of gradations, and there is a problem in that it is not possible to increase the number of gradations as desired.

On the other hand, with the density gradation method, in order to increase the number of gradations in an image, the same dot must be printed out a number of times according to the number of gradations, and the recording time is limited due to the speed limitations of the drive circuit and memory. become longer. Since the applied energy per dot must be controlled very precisely, a thermal head with very little variation in recording characteristics from pixel to pixel is required, which also results in a very high cost. Even if the applied energy is very finely controlled using a circuit, it is difficult to obtain stable density gradations with that precision, and there is a problem in that the number of gradations cannot be increased as desired.

In addition, in a method that uses both area gradation and density gradation, the matrix size is smaller than in area gradation, so the number of dots in the line head is reduced, but the line head has less variation in recording characteristics for each pixel. It becomes necessary. Compared to density gradation, this method is advantageous in reducing variations in recording characteristics for each pixel, but the number of dots in the line head increases. In reality, a line head that is compatible with resolution and variation in recording characteristics is still expensive. In addition, due to the surface properties of the image receiving paper and the thickness of the transfer paper, if the dot area is made smaller, the area gradation and density gradation characteristics within one pixel will deteriorate, so increase the number of gradations as desired. The problem was that they were not allowed to do so.

In view of these problems, the present invention has been developed to reduce the rough variation in the recording characteristics of each pixel without increasing the number of dots in the line head, the number of recording lines in sub-scanning, or the number of steps in pulse width control. The purpose of this paper is to propose a recording method that can stably increase the number of recording gradations using a head.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a memory that stores gradation information composed of a plurality of bits per pixel;
energizing pulse generating means for generating energizing pulses of a maximum of 2 steps according to the upper bits of the gradation information stored in the memory, and a block consisting of 2 m 1 pixels in the line direction and 20 pixels in the feed direction, The output energizing pulse of the energizing pulse generator is controlled according to predetermined conditions based on the positional information of m bits in the line direction and n bits in the feed direction within the block, and the lower m+n bits of the gradation information stored in the memory. and step-increasing energization control means.

Function The present invention realizes gradation in 2 levels by upper bits of gradation information in each pixel by density gradation by controlling the current pulse width.
Expansion of the number of gradations using the lower m+n bits of gradation information is realized by area gradation using a matrix of 2" x 2n pixels vertically and horizontally.

In other words, with a resolution of one pixel, only 2 gradations can be expressed, but when viewed in units of 2'' pixels in the line direction and 2n pixels in the feed direction, t;2k+m+n gradations can be expressed.

Also, the energizing pulse width per pixel depends on the lower m+n bits of the gradation information and the position of the pixel in the matrix.
The steps are rounded up, but since one step is 1/2 of the maximum pulse width, even if the steps are rounded up,
Since the number of gradations is secured in , the resolution that can express the number of gradations in 2 is the same as when using only density gradations. Therefore, the introduction of the matrix according to the present invention does not cause deterioration in resolution like dithering in the binary case.

Furthermore, if we take advantage of the nature of human vision that small area areas with high resolution are insensitive to gradation, and large areas with low resolution are sensitive to gradation, k is 4 or more, i.e. If there are 16 or more gradations and the recording pixel resolution is p dora)/mm, and n and m are less than log2p, the image is equivalent to recording 2k+e+n gradations per pixel. can be recorded.

In other words, due to the relationship between pixel size and clear viewing distance in human vision, each pixel must have 16 or more gradations in areas where the spatial frequency of the image is high and resolution is required, that is, areas where each pixel has a different density. 64 or more gradations are necessary in areas where the spatial frequency of the image is low and pixels of the same density are concentrated. This is because humans judge the quality of gradation based on false contours where the gradation of an image changes smoothly over a large area. It is difficult to distinguish.

For example, when n and m are each 2 at 6 dots/mm, there are 16 gradations at a resolution of 6 dots/mm, 64 gradations at a resolution of 3 dots/mm, and 2 gradations at a resolution of 1.5 dots/mm.
Although 56 RW tones are obtained, the image, pixel by pixel, is essentially no different from the case where 256 tones are recorded.

Therefore, according to the present invention, the number of dots in the line head can remain unchanged, the number of recording lines in sub-scanning does not increase, so the recording time does not become long, and the number of gradations does not need to be increased by pulse width control, so line memory The speed of the head drive IC is not required, the line head variation is the same, and the area of one pixel does not become small, so the recorded pixel shape does not become unstable and the number of recording gradations can be stably increased. can.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings. Here, we will briefly discuss the case where one line has 256 pixels, k=4, that is, 16 gradations under pulse width control, n and m are each 2 to form a 4×4 matrix, and 256 gradations are recorded.

FIG. 1 is a block diagram of a printer device according to an embodiment of the present invention.

In the figure, l is a 256-dot line head, 2 is a 256 drive circuit corresponding to line head l, 3 is a 256-bit latch corresponding to line head 1, and 4 is a 256-bit shift corresponding to line head l. register, 5
6 is line memory 5, which stores data for one line and has an 8-bit address and 256 bytes.
An address counter 7 gives an 8-bit address to serially sends l lines of data, and an address counter 7 gives a common clock to the address counter 6 and shift register 4, and after transferring l lines of data, latch 3
8 is a clock generating means for sending a load pulse to
Count up after reading data for line 4
A bit gradation counter, 10 is a 2-bit line counter that counts lines, and 11 is a 4-bit data whose address is the lower 2 bits of the address counter (AO, AI) and the 2 bits of the line counter (CO, CI). 9 (
FO, Fl, F2. 12 is a second comparator that compares the output of ROMII with the lower 4 bits (Do, DI, B2.B3) of the data in line memory 5; 13 is a second comparator that compares and outputs the line memory 5; The upper 4 bits of the data in memory 5 are added to form 5 bits of data (EO.

El, F2. F3. 9 is the output of the gradation counter 8 (BO, Bl, B2. B3)
This is a first comparator that compares the output of the adder 13 with the output of the adder 13 and sends serial data to the shift register 4.

The gradation counter 8 and the first comparator 9 constitute energization pulse generation means, and the address counter 6, line counter 10, ROM II, and second comparator 12 constitute energization control means.

Data of 8 bits and 256 gradations is written in the line memory 5, and is continuously read out for 256 pixels using the 8 bit address given by the address counter 6. When the address counter 6 completes one cycle and all the contents of the line memory 5 are read out, the output of the gradation counter increases by 1, and the contents of the line memory 5 are read out again from the beginning.

The 5-bit data obtained by adding the upper 4 bits of the output of the line memory 5 and the output of the second comparator 12 by the adder 13 and the output of the gradation counter are sent to the first comparator 9.
The output C is compared in size and l is sent to the shift register 4 only when the output of the adder 13 is greater than the output of the gradation counter 8.
sent to.

In other words, recording is performed 16 times, the cycle corresponding to T in FIG. 2 being determined by the number of stages of the gradation counter 8, and at this time, the same data is read out from the line memory 5 in short cycles. However, since the value of the gradation counter 8 increases every cycle, when the output obtained by adding the round-up signal S to the output of the line memory 5 by the adder 13 becomes less than the value of the gradation counter 8, The output C of the first comparator 9 is 0
becoming. Therefore, if we always consider that b=o, the output of the latch 3 will be the top 4 of the corresponding data in the line memory 5.
The pulse width can be controlled in 16 steps with the minimum resolution T in proportion to the bit.

FIG. 2 is a time chart of this embodiment.

BO to 83 are the outputs of the gradation counter 8, and HO to H255 are data extracted from the serial data C that correspond to the pixels of each head. Therefore, if H255 is viewed vertically from the leap HO of each period T, it becomes serial data C.

When the gradation to be recorded on pixel O is 6, if b is O, IO becomes 1 from period O to period 5, 6T, and recording is performed on pixel 0 with a pulse width of 6T. When b is 1, the pulse width is 7T. Similarly, pixel 1 has a gradation of O1, and pixel 2 has a gradation of 1
5. The pixel 255 shows the case of gradation 13. In either case, the energization pulse width for each pixel is longer by T when the round-up signal is 1 than when it is 0.

Next, the operation of the energization control means will be described.

The energization control means includes the ROMII and the second comparator 12.
It consists of ROMII is the lower two bits (AO, AI) of address counter 6 and line counter 10.
4 pixels x 4 represented by the lower 2 bits (CO, C1) of
Threshold value information corresponding to the position of the pixel within the block is written.

An example of this threshold value information is shown in FIG. 3(a).

The second comparator 12 compares the 4-bit threshold value information (FO to F3) corresponding to the position within the 4-pixel x 4-pixel block with the lower 4 bits (DO to D3) of the line memory 5, and the latter is Only when the value is large, the round-up signal S is set to 1, and the pulse width of that pixel is lengthened by T. This ROM
The matrix in II functions to expand the number of gradations by 16 times to 256 gradations in an area where the spatial frequency is lower than the unit of 4 pixels horizontally and vertically. On the other hand, if we consider that the number of gradations is 128, then FO1t'! of the data in ROMII is sufficient. F#.

All you have to do is look. At this time, the threshold value information becomes as shown in Figure 3, and the matrix is considered to be 2x4 or 4x2. Similarly, if the number of gradations is 64, ignoring FO and Fl, the result will be as shown in FIG. 3C, resulting in a 2×2 matrix. When the number of gradations is 32, it becomes a 2X1 or IX2 matrix as shown in Figure 3d. Finally, if the number of gradations is set to 16, the threshold value information becomes as shown in Figure 3e, which is considered to be an IXI matrix, that is, all pixels are the same.

Therefore, by using the matrix of this embodiment, it is possible to realize a relationship in which the product of the resolution and the number of gradations is constant.

This relationship is consistent with the nature of human vision, in which a small area with high resolution is insensitive to gradation, and a large area with low resolution is sensitive to gradation.

FIG. 4 illustrates the relationship between the number of gradations and the resolution (the number of dots in 1 mm square). Although only the image in the area A in the figure could be reproduced by density gradation based on pulse width control, the present invention shows that it is possible to reproduce the image in the area A+B+C+D+E.

Also, when the recording pixel density is p dora)/mm, let n and m be I
If you set og2p or less and l( to 4 or more,
For example, if the recording pixel resolution is 6 dots/mm, = 4,
In the case of this embodiment where n=2 and m=2, when viewed from a clear viewing distance of about 25 cm or more, the area OF in the figure is extremely difficult to recognize with human vision. In particular, when k is set to 5 or more, the region of F cannot be recognized regardless of the distance.

Therefore, if the above conditions are met, the image will be equivalent to that recorded by a device capable of recording 256 gradations per pixel, which can also reproduce the area F. There is no similar problem even if the device is used as a device capable of recording 256 gradations.

Note that in this embodiment, all signals are positive logic, but
At the same time, by changing the comparison conditions of the comparator, it can also be configured with negative logic.

In order to extend the output pulse width of the energizing pulse generation means by one step, an adder 13 is used at the input of the first comparator 9, but a comparison in which a one step longer pulse is output to the first comparator 9 itself It is also possible to use one that also has a condition and switch using b.

Although the threshold value matrix is realized using ROMII, it can also be constructed using wire logic if the input/output characteristics are similar.

In this embodiment, a line head having only one serial human power is used and no split driving is performed, but even if split driving is performed, the effects of the present invention will not change in any way.

Effects of the Invention By introducing the present invention to a conventional printer device that performs gradation recording by controlling the energization time using pulse width, the number of gradations can be extremely easily increased several times or more. Moreover, there is no need to increase the number of dots in the line head, and the speed for the line memory and head drive IC can remain the same, so there is no increase in costs.
Since there is no need to increase the number of recording lines in sub-scanning, the recording time does not increase, and since the area of one pixel does not become small, the recorded pixel film does not become unstable and images with a high number of gradations can be stably recorded.

In addition, the present invention makes it possible to conversely increase the number of gradations while reducing costs by reducing the number of gradations in Fa tone recording by controlling the energization time using the pulse width.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a printer device according to an embodiment of the present invention, FIG. 2 is a timing chart of the same, FIG. 3 is an explanatory diagram of a threshold value matrix, and FIG. 4 is a relationship between resolution and number of gradations. FIG. 1... Line head, 2... Drive circuit, 3...
- Latch, 4... Shift register, 5... Line memory, 6... Address counter, 7... Clock generation means, 8... Gradation counter, 9... First comparator, lO ...Line counter, 11...ROM
, 12... second comparator, 13... adder,
20... Energization control means, 2m... Energization pulse generation means. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 3 tOJ

Claims (1)

[Claims] A head that records image information, a memory that stores tone information consisting of a plurality of bits per pixel, and a maximum of 2^k ( (k is a positive integer) step energization pulse generating means for generating energization pulses, and 2^m (m
is a positive integer) pixels and 2^n (n is a positive integer) pixels in the feed direction to form a block, and position information of m bits in the line direction and n bits in the feed direction within the block is stored in the memory. A printer device for performing gradation recording, comprising energization control means for increasing the output energization pulse of the energization pulse generation means by one step according to a predetermined condition based on the lower m+n bits of gradation information.