JPH04207462A - Image recorder - Google Patents

Abstract

PURPOSE:To decrease unequal densities and to uniformize images by randomly changing one of the number of the picture elements to be recorded with an image recording element by adding random numbers and image input signals, the size of the picture elements and the density of the picture elements and outputting the same. CONSTITUTION:A random number generating means 11 which generates the random numbers and an adding means 13 which outputs the image signals obtd. by randomly changing at least one of the number of the picture elements to be recorded with the image recording element by adding the random numbers and the image input signals inputted to an image recorder, the size of the picture elements and the density of the picture elements are provided. One of the number of the picture elements, the size of the picture elements and the density of the picture elements is substantially randomly changed with the value corresponding to the image input signal as a central value. Then, the obtd. images have no regularity in the appearance of the dark parts and pale parts and the unequal densities are visually extremely inconspicuous. The uniform images are obtd. in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image recording device, and particularly to a recording head provided with a plurality of image recording elements (hereinafter also referred to as a multi-head).
The present invention relates to an image recording apparatus that performs recording using.

[Prior Art] In recent years, with the spread of computers and communication equipment, as image recording devices used with these equipment, recording methods that use recording heads to record digital images, such as inkjet recording methods or thermal transfer recording methods, have become popular. Image recording devices of this type are rapidly becoming popular.

In the above-mentioned image recording apparatus, a multihead in which a plurality of image recording elements are integrated is generally used as a recording head in order to improve the recording speed.

For example, in an inkjet recording head, a multi-head that integrates multiple liquid paths or ink ejection energy generating elements is generally used, and a thermal head used for thermal transfer recording has a recording head that integrates multiple heaters. is commonly used.

[Problems to be Solved by the Invention] However, it is difficult to manufacture the image recording elements constituting a multi-head so that all of them have uniform characteristics, and as a result, a certain degree of variation occurs in the characteristics of the image recording elements. For example, in a multi-head used for inkjet recording, an ejection port is one image recording element.

There are variations in the dimensions of the liquid path and the shape of ejection energy generating elements such as electrothermal transducers and electromechanical transducers (piezo elements), and in multi-heads used for thermal transfer recording, there are variations in the shape and electrical resistance of the heater. Variations occur.

Such non-uniformity in characteristics between image recording elements causes non-uniformity in the size and density of dots recorded by each image recording element, resulting in uneven density in the recorded image. There was a problem.

To solve this problem, various methods have been proposed for correcting the level of the signal input to each image recording element to obtain a uniform image.

For example, in a multi-head 1 in which image recording elements 2 are arranged at regular intervals as shown in FIG. 8(A), the level of the input signal input to each image recording element is set to be the same as shown in FIG. 8(B). If density unevenness occurs between each recording element as shown in FIG. 10(C), the input signal level is corrected as shown in FIG. 2(D).

That is, an input signal with a high level is applied to an image recording element exhibiting a low dot density, and an input signal with a low level is applied to an image recording element exhibiting a high dot density. By adjusting the level of the signal input to each image recording element in this way, the dot density between each image recording element can be made uniform as shown in FIG. 8(E).

In the case of a recording method in which the dot diameter or dot density can be changed, the dot diameter recorded by each image recording element may be changed in accordance with the level of the input signal.

For example, in an inkjet recording head that uses piezo elements as ejection energy generating elements, the drive voltage or pulse width applied to each piezo element, which is the recording element, is changed depending on an input signal input to the recording head. On the other hand, in inkjet recording heads and thermal transfer recording heads that use electrothermal transducers (heaters) as ejection energy generating elements, drive is applied to each heater, which is a recording element, in accordance with an input signal input to the recording head. Vary the voltage or pulse width.

In this way, the dot diameter or dot density of the dots recorded by each recording element is made uniform, and the density distribution in each recording element is made uniform as shown in FIG. 8fE).

If it is impossible or difficult to change the dot diameter or dot density, you can change the image by changing the number of dots used for recording (the number of times ink is ejected from one dot) according to the input signal. Adjust concentration. That is, by using a large number of dots in the image recording element corresponding to the low density area and a small number of dots in the image recording element corresponding to the high density area, the density distribution in each recording element is determined as shown in FIG. 8(E). Equalize it like this.

By using such a method, it is possible to correct density unevenness in an image. However, with this method, −
Even if the density unevenness can be corrected, if the density unevenness changes due to some factor after the correction, the amount of correction for the input signal level must be changed.

In the case of an inkjet recording head, as the recording head is used, the density distribution of dots changes due to deposits from the ink adhering to the vicinity of the ink ejection ports or foreign matter from the outside. I can see it.

Furthermore, even in inkjet recording heads and thermal transfer recording heads that use heaters, the density distribution of dots may change due to deterioration or alteration of each heater. In such a case, the initially set input correction amount is no longer sufficient to correct density unevenness, so there is a problem that density unevenness gradually becomes noticeable as the recording head is used. .

In particular, as shown in FIG. 9, the multi-head 1 is scanned in the direction indicated by arrow A to record an image of width d, then sub-scanned in direction B by width d, and then further scanned in direction A by width d. (In the serial scan type image recording method, the density unevenness caused by the multi-head is repeated at a pitch d, so the density unevenness is very noticeable visually.

This is because human vision has an excellent ability to detect periodically repeated patterns; for example, d =
In the case of lfo+m, if there is an optical density unevenness of about 0.05 in the density distribution of the multi-head, it becomes a problem in terms of image quality. However, it is extremely difficult to further suppress changes in the density distribution of dots in a multihead, and image density unevenness has been a major problem in multiheads, especially in serial scan multiheads.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide an image recording apparatus that can obtain uniform images with less density unevenness.

[Means for Solving the Problem] In order to achieve such an object, the present invention provides a random number generating means for generating random numbers in an image recording apparatus that performs recording using a recording head having a plurality of image recording elements. and the number of pixels recorded by the image recording element by adding the random number and the image input signal input to the image recording device,
The image forming apparatus is characterized by comprising an adding means for outputting an image signal in which at least one of pixel size and pixel density is randomly changed.

The present invention also provides an image recording apparatus that performs recording using a recording head having a plurality of image recording elements, including a random number generating means for generating random numbers, and a correction method for correcting density unevenness that the recording head has as a characteristic. a storage means for storing a value; an addition means for adding the random number and the correction value and outputting a correction selection signal; and the correction selection signal is input and corrects an image signal input to the image recording device. The present invention is characterized by comprising a correction means.

[Function] In the present invention, the number of pixels recorded by a plurality of image recording elements constituting a recording head.

By substantially randomly changing at least one of the pixel size and the pixel density with the value corresponding to the image input signal as the center value, the regularity and periodicity of density unevenness is reduced, and visual perception is improved. First, a uniform image with less noticeable density unevenness can be obtained.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a first embodiment of the invention. Here, the input image signal 100 is input to the image recording device from a reading device or an external storage device (not shown), for example, “0” to “2”.
The random number generator 11 randomly generates an integer in the range of, for example, "-25" to "+25". The input image signal 100 and the random number signal 120 are added in the adder 13, A post-addition image signal 140 is output.

The added image signal 140 is input to a binarization circuit 15 where the signal is binarized by using a dither method or an error diffusion method, and is converted into a binary image signal 16 (l) and sent to a multi-herad 17. is output to.

The multi-herad 17 is driven by a binary image signal 160.

FIG. 2 shows the signals in the device shown in FIG. Second
When a uniform input image signal 100 as shown in FIG. 2(A) is input, addition with a random number signal 120 as shown in FIG. 2(B) is performed, and addition as shown in FIG. 2(C) is performed. A post-image signal 140 is obtained.

The image signal 140 after addition is input to the binarization circuit 15 and converted into 2
It is converted into a digitized image signal 160 and input to the multihead 17. Image signal 1 after addition by multi-herad 17
A dot is recorded on the recording medium with a probability proportional to 40.

In this way, by obtaining a signal for driving the multi-herad 17, even if a uniform input image signal 100 is input to the image recording device, at a certain point in time, 256
A pixel row recorded by driving the image recording elements 2A,
In other words, the relationship between each recording element and the recording probability is shown in FIG. 3 (A
), the relationship is random.

As shown in FIG. 3(B), the next 256 pixel rows following this have a random relationship different from that in FIG. 3(A). Furthermore, the relationship between each recording element and the recording probability changes for each pixel column, such that the next 256 pixel columns have a random relationship as shown in FIG. 3(C). As a result, an effect similar to that in which the density distribution in a multi-nozzle head changes for each pixel column can be obtained.

Therefore, in images obtained by such processing, there is no regularity in the appearance of the binding part and the manufacturing part, and the manufacturing part and the manufacturing part appear in a band-like manner as when the above-mentioned processing is not performed. Never. Therefore, density unevenness in the recorded image becomes visually less noticeable.

Therefore, even in the case of a serial printer that records by serially scanning multiple heads, there is no constant density unevenness that appears with each scan, so the density unevenness has no periodicity and is less visually noticeable. ,For this reason,
This has the effect that a uniform image can be obtained.

Next, a second embodiment of the present invention will be described. In the first embodiment, since no correction is applied to the input signal according to the density unevenness of the multi-head l, the density unevenness is not noticeable (even if it is, the characteristics inherent to each multi-head If the density unevenness caused by this is large, there is a risk that the density unevenness will appear on the image.

The second embodiment is an improvement on this point in the first embodiment, and after first correcting the density unevenness that multi-heads originally have, the amount of correction is further changed randomly, so that the head In addition to dealing with cases where the density unevenness is large due to the characteristics of

FIG. 4 shows a block diagram of a second embodiment of the invention. An input signal 210 inputted to the image recording apparatus from a reading device or an external storage device (not shown) is converted by the density unevenness correction table 28 so as to correct density unevenness occurring in the multi-head 32.

The density unevenness correction table 28 has Y=
0.70X Kara Y=1.30X Gusset, slope is 0. O
It has 61 correction straight lines that are different by l, and the correction straight lines are switched according to the correction selection signal 270. When a pixel signal that causes recording to be performed by a recording element with a large dot diameter is input, a correction straight line with a small slope is selected. When a pixel signal printed by a nozzle with a small dot diameter is generated manually, the human input signal 210 is corrected by selecting a correction straight line with a large slope.

The density unevenness correction ROM 22 stores correction values created according to density unevenness characteristics for each head used. That is, the selection signal necessary for correcting the density unevenness inherent in the multi-head 32 using the density unevenness correction table 28 is stored. More specifically, the density unevenness correction ROM 22 stores correction signals having 61 types of values from integer "O" to "60" for 256 image recording slips, and synchronizes with the input image signal 210. A density unevenness correction signal 230 is output.

The random number generator randomly generates integers in the range of "-10" to "+10" and outputs a random number signal 250 to the adder 26. The adder 26 outputs the density unevenness correction signal 230 and the random number signal 2.
50 and output to the density unevenness correction table 28 as a correction selection signal 270. In response to the correction selection signal 270, an appropriate correction straight line is selected from among the 61 correction straight lines included in the density unevenness correction table 28.

The corrected signal 290 corrected by the selected correction straight line and output from the density unevenness correction table 28 is binarized by the binarization circuit 15. The multi-head 32 is driven by the binary image signal 310 output from the binarization circuit 15.

In this way, even if the multi-head inherently has significant density unevenness, by applying correction suitable for that head, the density unevenness can be reduced to a level that poses no problem in practice.

In addition, since the correction amount is changed randomly for each pixel, even if density unevenness occurs due to the use of the print head, the pattern of the unevenness will no longer have regularity or periodicity. It becomes more noticeable and a uniform image can be obtained.

Next, a third embodiment of the present invention will be described.

This example is a modification of the first example. In the first embodiment, the probability of printing dots by each recording element was varied at random, but in the third embodiment, the width of the drive pulse applied to each recording element was varied.

A third embodiment is shown in FIG. 6, where the same numbers as in FIG. 1 indicate the same components.

The added image signal 140 to which the random number signal 120 has been added is input to the drive circuit 31 . The drive circuit 31 outputs a drive pulse 320 with a pulse width corresponding to the added image signal 140,
Drive the multi-herad 17.

When the multi-head is in the form of an inkjet recording head, it is possible to change the amount of ink ejected depending on the drive pulse width, for example. Since the multi-head is configured in this way and the dot diameter or dot density by each recording element is changed randomly, the density unevenness loses regularity and periodicity, and it is possible to suppress the density unevenness to a range that does not pose a practical problem. can.

Next, a fourth embodiment of the present invention will be described.

This example is a modification of the third example. In the third embodiment, the drive pulse width was changed, but in this embodiment, the drive voltage is changed. Although the block diagram is the same as that in FIG. 6, the function of the drive circuit 31 is as follows:
It outputs a driving pulse of a voltage corresponding to 0. By doing so, effects completely equivalent to those of the third embodiment can be obtained.

Next, a fifth embodiment of the present invention will be described.

This example is a modification of the third example. This example is also the second
In this embodiment, the method of changing the correction value in the embodiment is replaced with a method of changing the drive pulse width. FIG. 7 is a block diagram thereof, and the same numbers as in FIG. 6 indicate the same components.

In this embodiment, the corrected signal 290 is input to the drive circuit 30. The drive circuit 30 outputs a drive signal 310 with a pulse width corresponding to the corrected signal 290, and drives a multi-head 32 using an inkjet recording method that can change the amount of ink ejection, for example.

As a result, in the case of the inkjet recording method, the amount of ink ejected from each company's outlet is corrected according to the density unevenness inherent in the head, and this correction value is further randomly changed. Therefore, it is possible to record images with little density unevenness even when using a head with significant density unevenness, and even if the density unevenness increases with the use of the recording head, there is no regularity or periodicity in the density unevenness. Therefore, it is possible to obtain a uniform image in which density unevenness is less noticeable.

Next, a sixth embodiment of the present invention will be described.

This example is a modification of the fifth example. In the fifth embodiment, the drive pulse width was varied, but in this embodiment, the drive voltage is varied. That is, although the structure of this example is generally the same as that in FIG. 6, the drive circuit 31
The function is to output a drive signal 310 with a voltage corresponding to the corrected image signal 290. By doing so,
This example also provides the same effects as the fifth example.

In each of the embodiments described above, in addition to depending on the form of an inkjet recording head as the multi-head, the same implementation can be performed even when a thermal head for thermal transfer is used.Furthermore, as an inkjet recording head, Needless to say, in addition to the piezo method, it is also possible to use a method in which bubbles are generated using a heater provided in the liquid path, and ink is ejected using the output of the bubbles.

Furthermore, the multi-head may be a so-called full multi-head in which recording elements are arranged over the same range as the entire width of the recording medium, or a so-called semi-multi-head in which a plurality of recording elements are arranged in the sub-scanning direction. It does not matter if it is a serial scan.

Further, the range of the random number value is not limited to the range described in each embodiment, and may be determined by taking into consideration the value of the image signal or the degree of density unevenness.

Furthermore, the random numbers generated by the random number generator need not be strictly random numbers, but may be numbers that are substantially random and have the effect of visually reducing the regularity and periodicity of density unevenness.

In addition, when using a binarization circuit as in the first and second embodiments, in addition to adding random numbers to the input image signal or density unevenness correction signal, it is also possible to add random numbers to the threshold value during binarization. The present invention can also be implemented in the same manner.

[Effects of the Invention] As explained above, in the present invention, the regularity and periodicity of density unevenness is lost by randomly changing the density distribution inherent in the multi-head. This has the effect of making it less visually noticeable and providing a uniform image.

In addition, by adding density unevenness correction according to the density unevenness characteristics of multi-heads and changing the density distribution randomly, it becomes possible to use heads with significant density unevenness, and after correction, the unevenness of the head does not change. This is because even if the correction becomes insufficient, the regularity of the density unevenness will be lost.

This has the effect of providing a uniform image with less noticeable unevenness.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the first embodiment of the present invention, FIGS. 2 and 3 are explanatory diagrams of signal processing in the first embodiment of the present invention, and FIG. 4 is a diagram showing the second embodiment of the present invention. FIG. 5 is a diagram showing the density unevenness correction table in the second embodiment of the present invention. FIG. 6 is a diagram showing the configuration of the third and fourth embodiments of the present invention. FIG. FIG. 8 is an explanatory diagram of a conventional density unevenness correction method, and FIG. 9 is an explanatory diagram of an image forming method by serial scanning. 1, 17.32...Multi-head, 2 people...Image recording element, 11.24...Random number generator, 13.26...Adder, 15.30...Binarization circuit, 22... Density unevenness correction ROM, 28... Density unevenness correction table, 31... Drive circuit. Figure 1 Figure 2 Figure 3 Figure 6 Figure 7

Claims (1)

[Claims] 1) In an image recording apparatus that performs recording using a recording head having a plurality of image recording elements, a random number generating means for generating a random number; and the random number and an image input input to the image recording apparatus. at least one of the number of pixels, the size of the pixels, and the density of the pixels recorded by the image recording element.
1. An image recording device comprising: an adding means for outputting an image signal in which one of the two images is randomly changed. 2) In an image recording apparatus that performs recording using a recording head having a plurality of image recording elements, a random number generating means for generating random numbers and a correction value for correcting density unevenness that the recording head has as a characteristic are stored. a storage means; an addition means for adding the random number and the correction value and outputting a correction selection signal; and a correction means for correcting an image signal inputted to the image recording device to which the correction selection signal is input. An image recording device comprising: