JP3043397B2 - Image recording apparatus and image recording method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus, and in particular, to an image recording apparatus that performs recording using a recording head provided with a plurality of image recording elements (hereinafter, also referred to as a multi-head). And an image recording method.

[Related Art] In recent years, with the spread of computers and communication devices, as an image recording device used together with these devices, recording that performs digital image recording using a recording head such as an ink jet recording method or a thermal transfer recording method. -Type image recording apparatuses are rapidly spreading.

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

For example, a multi-head in which a plurality of liquid paths or ink ejection energy generating elements are integrated is generally used in an inkjet recording head, and a recording head in which a plurality of heaters are integrated in a thermal head used for thermal transfer recording. Is generally used.

[Problems to be Solved by the Invention] However, it is difficult to manufacture such that all the characteristics of the image recording elements constituting the multi-head are uniform, so that the characteristics of the image recording elements vary to some extent. For example, in a multi-head used for ink-jet recording, variations occur in the dimensions of the ejection ports, liquid paths, and the shapes of ejection energy generating elements such as electrothermal transducers and electromechanical transducers (piezo elements), which are image recording elements. In a multi-head used for thermal transfer recording, variations occur in the shape and electric resistance of the heater.

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 a recorded image. was there.

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

For example, in the multi-head 1 in which the image recording elements 2 are arranged at equal intervals as shown in FIG. 8 (A), the levels of the input signals input to the respective image recording elements are the same as shown in FIG. 8 (B). When density unevenness occurs between the recording elements as shown in FIG. 7C, the input signal level is corrected as shown in FIG.

That is, a high level input signal is supplied to an image recording element exhibiting a low dot density, and a low level input signal is supplied to an image recording element exhibiting a high dot density. As described above, by adjusting the level of the signal input to each image recording element, FIG.
As shown in (1), the dot density between the image recording elements becomes uniform.

In the case of a recording method capable of changing the dot diameter or the dot density, the dot diameter to be recorded by each image recording element may be changed according to the level of the input signal.

For example, in an ink jet print head using a piezo element as an ejection energy generating element, a driving voltage or a pulse width applied to each piezo element as a print element is changed according to an input signal input to the print head.
On the other hand, in an ink jet recording head or a thermal transfer type recording head using an electrothermal transducer (heater) as an ejection energy generating element, a drive applied to each heater as a recording element in accordance with an input signal input to the recording head. Change 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. 8 (E).

When it is impossible or difficult to change the dot diameter or the dot density, the number of dots used for recording (the number of times ink is ejected from one dot) is changed in accordance with an input signal, so that the Adjust the concentration.
That is, by using a large number of dots in an image recording element corresponding to a low-density portion and a small number of dots in an image recording element in a high-density portion, the density distribution in each recording element is changed as shown in FIG. And make it uniform.

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

In the case of an ink jet recording head, with the use of the recording head, a deposit from the ink adheres to the vicinity of the ink discharge port or a foreign substance adheres from the outside, so that the dot density distribution changes. Is common.

Also, in an ink jet recording head or a thermal transfer recording head using a heater, the density distribution of dots may change due to deterioration or deterioration of each heater. In such a case, since the correction of the density unevenness is not sufficiently performed with the initially set input correction amount, there is a problem that the density unevenness gradually becomes conspicuous with the use of the recording head. .

In particular, as shown in FIG.
After scanning in the direction shown by the arrow and performing image recording for the width d, B
In the serial scan type image recording method in which an image is formed sequentially by sub-scanning in the width d in the direction and further performing image recording in the width A in the direction A, the density unevenness by the multi-head is repeated at the pitch d. Therefore, the density unevenness is very conspicuous visually.

This is due to the excellent ability of human vision to detect patterns that repeat periodically, for example, d = 16
In the case of mm, if the density distribution of the multi-head has an optical density of about 0.05, it may cause a problem in image quality. However, it is very difficult to suppress the change in the density distribution of the dots in the multi-head more than this, and the density unevenness of the image has been a serious problem in the multi-head, especially in the multi-head of the serial scan.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image recording apparatus and an image recording method capable of solving the above-mentioned problems and making the density unevenness less noticeable even when the density unevenness changes with time.

[Means for Solving the Problems] The image recording apparatus of the present invention is provided with a multi-valued image signal,
In an image recording apparatus that performs recording using a recording head having a plurality of image recording elements, a random number generating unit that generates a random number in a predetermined range, and according to density unevenness characteristics of the plurality of image recording elements of the recording head, Correction means for correcting the corresponding multi-valued image signal, and driving means for driving the recording head based on the multi-valued image signal corrected by the correction means, wherein the correction means It is characterized in that the density unevenness correction amount of the multi-level image signal is randomly changed based on the generated random number in a predetermined range.

An image recording method according to the present invention is an image recording method in which recording is performed using a recording head having a plurality of image recording elements, wherein a generating step of generating random numbers within a predetermined range, and a supplying step in which a multi-valued image signal is supplied. A correcting step of correcting the multi-level image signal supplied in the supplying step in accordance with the density unevenness characteristics of the plurality of image recording elements of the recording head; and a multi-level image signal corrected in the correcting step. And a driving step of driving the recording head, wherein the correcting step randomly changes the density unevenness correction amount of the multi-level image signal based on a random number in a predetermined range generated by the generating step. I do.

[Operation] In the present invention, when correcting a corresponding multi-valued image signal according to the density unevenness characteristics of a plurality of image recording elements in a print head, the density unevenness of the multi-valued image signal is corrected based on a random number within a predetermined range. The correction amount is changed at random.

[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 present invention. Here, the input image signal 100 is input to the image recording apparatus from a reading device or an external storage device (not shown), for example, “0” to “255”.
, Ie, a multi-level image signal. The random number generator 11 randomly generates, for example, an integer in a range from “−25” to “+25”. The adder 13 adds the input image signal 100 and the random number signal 120, and outputs an added image signal 140.

The added image signal 140 is input to a binarization circuit 15 that performs signal binarization by using a dither method, an error diffusion method, or the like, is converted into a binary image signal 160, and is output to the multi-head 17. You. The multi-head 17 is driven by a binary image signal 160.

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

The added image signal 140 is input to the binarization circuit 15, converted into a binarized image signal 160, and input to the multi-head 17. The dots are recorded on the recording medium by the multi-head 17 at a probability proportional to the added image signal 140.

In this way, by obtaining signals for driving the multi-head 17, even when a uniform input image signal 100 is input to the image recording apparatus, 256 image recording elements 2A are driven and recorded at a certain point in time. The relationship between the pixel row, that is, each recording element and the recording probability is a random relationship as shown in FIG. 3 (A).

In the subsequent 256 pixel columns following this, as shown in FIG. 3B, a random relationship different from that in FIG. 3A is obtained. Further, in the next 256 pixel rows, the relationship between each recording element and the recording probability changes for each pixel row such that a random relationship as shown in FIG. 3C is obtained. As a result, the same effect as that in which the density distribution in the multi-nozzle head changes for each pixel row can be obtained.

Therefore, in an image obtained by such a process, the appearance of the dark portion and the light portion is not regular, and the dark portion and the light portion appear as a band as in the case where the above process is not performed. Never. Therefore, the density unevenness in the recorded image becomes very inconspicuous visually.

Therefore, even in the case of a serial printer that performs recording by performing serial scanning with a multi-head, since there is no occurrence of constant density unevenness for each scan, the density unevenness has no periodicity and is visually inconspicuous. Therefore, there is an effect that a uniform image can be obtained.

Next, a second embodiment of the present invention will be described. First
In the embodiment, since the correction according to the density unevenness of the multi-head 1 is not performed on the input signal, even if the density unevenness becomes less conspicuous, the density caused by the characteristics of each multi-head body is reduced. If the unevenness is large, the unevenness in density may appear on the image.

The second embodiment improves this point in the first embodiment, and reduces the density unevenness inherent in the multi-head by one.
After correcting the density, the correction amount is also changed randomly to cope with the case where the density unevenness is large due to the characteristics of the head. By eliminating regularity,
This is to make density unevenness less noticeable.

FIG. 4 shows a block diagram of a second embodiment of the present invention.
An input signal 210 input 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 the density unevenness generated in the multi-head 32.

As shown in FIG. 5, the density unevenness correction table 28
There are 61 correction straight lines having inclinations different from each other by 0.01 from 0.70X to Y = 1.30X. The correction straight lines are switched according to the correction selection signal 270. When a pixel signal is input which causes a recording element having a large dot diameter to perform recording, a correction straight line having a small inclination is selected. When a pixel signal to be printed by a nozzle having a small dot diameter is input, the input signal 210 is corrected by selecting a correction straight line having a large inclination.

The density unevenness correction ROM 22 stores a correction value created according to the density unevenness characteristic for each head to be used. That is, a selection signal required to correct the density unevenness inherent in the multi-head 32 with the density unevenness correction table 28 is stored. For more details, RO
M22 stores correction signals having 61 kinds of values of integers “0” to “60” for 256 image recording elements.
In synchronism with 10, an uneven density correction signal 230 is output.

The random number generator randomly generates an integer in the range of “−10” to “+10” and outputs a random number signal 250 to the adder 26. The adder 26 adds the density unevenness correction signal 230 and the random number signal 250,
It is output to the density unevenness correction table 28 as a correction selection signal 270. The correction selection signal 270 selects an appropriate one of 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.

As described above, even when the density unevenness inherently possessed by the multi-head is remarkable, the density unevenness can be reduced to a level having no practical problem by performing a correction suitable for the head.

In addition, since the correction amount is randomly changed for each pixel, even when density unevenness occurs due to the use of the recording head, the unevenness pattern is lost in regularity and periodicity. It becomes less 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,
Although the printing probability of dots by each recording element is changed at random, in the third embodiment, the width of the drive pulse applied to each recording element is changed.

FIG. 6 shows a third embodiment, in which the same reference numerals as in FIG. 1 denote the same components. Random number signal 120
After the addition, the image signal 140 is input to the drive circuit 31. The drive circuit 31 outputs a drive pulse 320 having a pulse width according to the added image signal 140, and drives the multi-head 17.

When the multi-head is in the form of an ink jet recording head, it is possible to change the amount of ink ejected according to, for example, the drive pulse width. Since the multi-head is configured as described above, and the dot diameter or dot density of each recording element is changed at random, regularity and periodicity are lost in the density unevenness, and the density unevenness can be suppressed to a range where there is no practical problem. it 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,
Although the drive pulse width is changed, in the present embodiment, the drive voltage is changed. The block diagram is the same as FIG. 6, but the function of the drive circuit 31 is to output a drive pulse of a voltage corresponding to the added image signal 140. By doing so, the same effect as in 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 embodiment also replaces the method of changing the correction value in the second embodiment with the method of changing the drive pulse width. FIG. 7 is a block diagram showing the same components as those in FIG. 6 showing the same components.

In the present embodiment, the corrected signal 290 is input to the drive circuit 30. The drive circuit 30 outputs a drive signal 310 having a pulse width corresponding to the corrected signal 290, and drives the multi-head 32 by an ink-jet recording method capable of changing an ink ejection amount, for example.

As a result, in the case of the ink jet recording system, the amount of ink ejected from each ejection port is corrected in accordance with the density unevenness inherent in the head, and this correction value is further randomly changed. Therefore, it is possible to print an image with less density unevenness even when using a head having remarkable density unevenness, and even if the density unevenness increases with the use of the recording head, the density unevenness has no regularity and periodicity. Therefore, it is possible to obtain a uniform image in which unevenness in density 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 is changed, but in the present embodiment, the drive voltage is changed. That is, although the configuration is almost the same as that of FIG. 6, the function of the drive circuit 31 is to output a drive signal 310 of a voltage corresponding to the corrected image signal 290. By doing so, the same effect as that of the fifth embodiment can be obtained by this embodiment.

In each of the embodiments described above, the multi-head can be implemented in the same manner even when a thermal head for thermal transfer is used, in addition to the form of the ink jet recording head. Further, it goes without saying that the ink jet recording head is not limited to the piezo type, but may be a type in which bubbles are generated by a heater provided in the liquid path and ink is ejected at that pressure.

The multi-head may use a so-called full multi-head in which recording elements are aligned 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 can be scanned.

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

Furthermore, the random number generated from the random number generator is not limited to an exact random number, but may be any number that is substantially random and has an effect of visually reducing the regularity and periodicity of density unevenness.

In the case of using a binarizing circuit as in the first and second embodiments, in addition to a method of adding a random number to an input image signal or a density unevenness correction signal, it is also possible to add a random number to a threshold for binarization. However, the present invention can be similarly implemented.

[Effects of the Invention] As described above, in the present invention, when correcting a corresponding multi-valued image signal according to the density unevenness characteristics of a plurality of image recording elements in a recording head, the correction is performed based on random numbers in a predetermined range. In order to randomly change the density unevenness correction amount of the multi-valued image signal, even if the density unevenness between a plurality of image recording elements changes over time, the density unevenness is reduced by eliminating the regularity and periodicity of the density unevenness. A good image can be obtained by making the image less noticeable, and a recording head having remarkable density unevenness between a plurality of image recording elements can be used.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a 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 second embodiment of the present invention. FIG. 5 is a view showing a density unevenness correction table according to a second embodiment of the present invention, FIG. 6 is a view showing a configuration of the third and fourth embodiments of the present invention, FIG. Is a configuration diagram of the fifth and sixth embodiments of the present invention, 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 scan. 1,17,32… Multi head, 2A… 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.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masami Izumizaki 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-63-100873 (JP, A) (58) Survey Fields (Int.Cl. ⁷ , DB name) H04N 1/23-1/31 H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (8)

(57) [Claims] An image recording apparatus to which a multi-valued image signal is supplied and performs recording using a recording head having a plurality of image recording elements, a random number generating means for generating a random number in a predetermined range, Correcting means for correcting a corresponding multi-valued image signal in accordance with the density unevenness characteristics of the plurality of image recording elements; and driving means for driving the recording head based on the multi-valued image signal corrected by the correcting means. An image recording apparatus, wherein the correction unit randomly changes the density unevenness correction amount of the multi-level image signal based on random numbers in a predetermined range generated by the random number generation unit. 2. The image recording apparatus according to claim 1, wherein said driving means has a binarizing circuit for binarizing the corrected multi-level image signal. 3. An image recording apparatus according to claim 1, wherein said driving means has a driving circuit for changing a driving signal for driving said recording head in accordance with said corrected multi-level image signal. . 4. The image recording apparatus according to claim 3, wherein the drive circuit changes a pulse width of a drive signal for driving the recording head according to the corrected multi-level image signal. 5. The correction means according to claim 1, wherein said correction means comprises a correction table having a plurality of correction straight lines for converting multi-valued image signals supplied to said plurality of image recording elements, and a density unevenness characteristic of said plurality of image recording elements. 2. The image recording apparatus according to claim 1, further comprising: a correction ROM for storing a correction signal for selecting a correction straight line of the correction table in correspondence with the plurality of image recording elements. 6. The correction means according to claim 6, wherein said correction means stores said random number and said correction ROM.
The image recording apparatus according to claim 5, further comprising an adder that adds the correction signal stored in the correction table and outputs the result to the correction table. 7. The image recording apparatus according to claim 1, wherein said image recording element ejects ink by heat. 8. An image recording method for performing recording using a recording head having a plurality of image recording elements, comprising: a generating step for generating a random number within a predetermined range; a supplying step for supplying a multi-valued image signal; A correction step of correcting the multi-level image signal supplied in the step according to the density unevenness characteristics of the plurality of image recording elements of the recording head; and the recording head based on the multi-level image signal corrected in the correction step. A driving step of driving the image recording apparatus, wherein the correcting step randomly changes a density unevenness correction amount of the multi-level image signal based on random numbers in a predetermined range generated by the generating step. Method.