JPH03252269A - Picture recorder - Google Patents

Abstract

PURPOSE:To always obtain a recorded picture of high quality which has good gradient and color balance even at the time of replacement of a recording head or the occurrence of secular change by variably setting a gradation correction curve in accordance with the gradation characteristic of the recording head. CONSTITUTION:Three-color input signals 11a to 11c of cyan, magenta, and yellow are inputted to gradation correcting parts 14a to 14c, where plural gradation correction curves are stored, after being subjected to color correction processing like masking by a color correcting part 12. Values corresponding to optimum correction curves according with gradation characteristics of respective heads, namely, curve selecting numbers or the like are preliminarily set to optimum gradation correction curve information indicating parts 19a to 19c of recording heads 18a to 18c, and control signals 21a to 21c corresponding to values read from these parts are sent as addresses of correcting parts 14a to 14c to select optimum correction curves. Thus, the proper gradation correction is always performed in accordance with gradation characteristics of recording heads to obtain a color picture having a good color balance.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image recording device such as a printer or a facsimile machine that records characters, images, etc. on a recording material such as paper in accordance with a human-powered image signal. In particular, the present invention relates to an image recording apparatus that records an image using a recording head.

[Prior Art] Conventionally, as this type of image recording apparatus, a dot-type type that records an image using a recording head such as an inkjet printer or a thermal transfer printer is known. Since these devices perform recording using digital signals, they are becoming more widespread with the spread of digital office equipment such as word processors and personal computers.

By the way, in a recording device using a recording head, the major factors that control the image quality level (also referred to as print quality) are recording density and gradation.

The recording density can be improved by integrating the recording elements of the recording head at a high density, but it is not easy to create a recording head with ideal gradation. An image recording device having a correction function is provided.

FIG. 8 shows a schematic circuit configuration of a conventional image recording apparatus having such a gradation correction function. As shown in the figure, each of the input signals 1a, lb, and lc of cyan (C), magenta (M), and yellow (Y) is a zero color that is subjected to color correction processing such as masking by the color processing section 2. Three color signals 3a that have been corrected.

3b and 3c are 3-color multivalued signals 5a, 5b, and 5c, which are subjected to 6-gradation correction, and are binarized. The processing unit 6 binarizes the signal using a dither method, an error diffusion method, or the like. The three-color signals 7a, 7b, and 7c after binarization are supplied to recording heads 8a, 8b, and 8c for the corresponding colors, that is, cyan, magenta, and yellow, respectively. Cyan, magenta, and yellow recording heads 8a, 8b
, 8c record a color image on recording paper in response to input signals 7a, 7b, and 7c.

If the gradation characteristics of the recording heads ga, 8b, and 8c are, for example, as shown by the curves in FIG. 9, the gradation will be distorted in high-density areas, and the image quality will deteriorate. Therefore,
In the tone correction section 4, by correcting the input signal using a tone correction curve as shown in FIG.
Each recording head 8a, 8b for lb, lc,
The gradation characteristics of 8c now have ideal linearity as shown in FIG. 11, and a good image with good gradation can be obtained.

[Problems to be Solved by the Invention] However, in the conventional example described above, the gradation correction curve is fixed, so if there are variations in the gradation characteristics of the recording heads, the optimum gradation cannot be achieved for all recording heads. There was a problem that key correction could not be performed. In particular, when color images are recorded using a plurality of recording heads of different colors as shown in FIG. 8, the color balance varies depending on the gradation, which becomes a more serious problem.

In view of the above-mentioned points, an object of the present invention is to perform appropriate gradation correction according to the individual gradation characteristics (i.e., variations in gradation characteristics) of a recording head, thereby eliminating variations in gradation characteristics and changes over time. It is an object of the present invention to provide an image recording device that can always obtain good gradation characteristics regardless of the situation, and can also provide stable image quality and improved quality.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a tone correction means for correcting the tone of an image signal according to a tone correction curve, and a tone correction means corrected by the tone correction means. In an image recording device that records an image by driving a recording head according to an image signal,
characteristic signal generation means for generating a signal according to the tone characteristics of the recording head; and a tone correction curve for setting the tone correction curve of the tone correction means in accordance with the signal generated from the characteristic signal generation means. and setting means.

Further, as an aspect of the present invention, the characteristic signal generating means includes an optimum tone correction curve information indicating means for presenting information according to an optimum tone correction curve peculiar to the recording head; and control signal generation means for generating a control signal in accordance with the information instructed by the information instruction means.

Furthermore, as another aspect of the present invention, the characteristic signal generation means includes a pattern output means for outputting a test pattern for measuring tone characteristics of the recording head, and a pattern output means for outputting a test pattern for measuring tone characteristics of the recording head, and a pattern output means for outputting a test pattern for measuring tone characteristics of the recording head, an image reading means for reading a test pattern for measuring characteristics; a calculating means for calculating an ideal gradation correction curve based on the data of the reading result of the image reading means; and a signal output means for outputting data of the key correction curve.

[Function] In the present invention, in an image recording apparatus that records an image by driving a recording head according to an image signal whose gradation has been corrected by a gradation correction means, a signal is generated according to each gradation characteristic of the recording head. Since the recording head is provided with a means for setting a gradation correction curve in accordance with this signal, good gradation characteristics can always be obtained no matter what kind of gradation characteristics a recording head is mounted.

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

Figure 1 shows a schematic circuit configuration of an image recording apparatus according to an embodiment (referred to as the first embodiment) of the present invention.

In the same figure, lla, llb, llc are cyan,
Magenta and yellow input image signals, 12 is input signal 1
1a.

11b and llc are color correction units that perform color correction processing such as masking; 13a, 13b, and 13c are image signals after color correction; and 14a, 14b, and 14c are image signals 13a,
This is a gradation correction section that corrects the gradation characteristics of the recording head with respect to 13b and 13c. 15a, 15b, 15c
are image signals after gradation correction, 16a, 16b, 16c
are image signals 15a and 15b after gradation correction.

A binarization processing unit that binarizes 15c by a dither method, error diffusion method, etc. 17a, 17b, and 17c are 2 after binarization.
Value image signals 18a, 18b, 18c are binary image signals 17a, 17b.

These are cyan, magenta, and yellow recording heads that record color images in accordance with 17c.

19a, 19b, 19c are each recording head 18a,
18b and 18c are the optimum gradation correction curve information indicating sections attached to the sections 18b and 18c.

These instruction units 19a, 19b, and 19c are ROMs.
In addition to the data and the resistance value of the variable resistor, marks, barcodes, notches, etc. can also be used* 20a, 2
0b.

20c is optimum tone correction curve information reading means for reading the optimum tone correction curve information of these instruction sections 19a, 19b, and 19c. These reading means 20a, 20b, 20
In addition to the memory reading circuit, c is an optical type (for example,
A sensor such as a photocoupler), a mechanical type (for example, a micro switch), or a magnetic type (for example, a magnetic sensor) can be used. signals, and the tone correction sections 14a and 14b described above.
, 14c.

Next, the operation will be explained.

The three color input signals 11a, llb, and llc of cyan, magenta, and yellow input to this device are sent to the color correction section 12.
After undergoing color correction processing such as masking, the signals are input to tone correction units 14B, 14b, and 14c. As shown in FIG. 2, the gradation correction units 14a, 14b, and 14c are ROMs (read-only memories) in which a plurality of gradation correction curves, for example, 20 types, having different curve shapes, which are read out using input signals as read addresses, are stored in advance. It consists of

On the other hand, the optimum gradation correction curve information indicating section 19a, 19b, 19c of each recording head 18a, 18b, 18c stores a value corresponding to the optimum correction curve according to the gradation characteristics of each recording head (that is, a curve selection number) is
For example, it is preset as ROM data or the resistance value of a variable resistor at the time of shipment from the factory. Optimal gradation correction curve information reading means 20a, 20b, 20c
reads this set value and sends a control signal (correction curve selection signal) 21a according to the read value.

21b, 21c are replaced by tone correction units 14a, 14b, 1
4c, and select the most suitable correction curve. In the ROM of the gradation correction units 14a, 14b, 14c, the signals 21a, 21b, 21c and the input signals 13a, 13b, 13c are assigned to ten-digit addresses,
An appropriate gradation-corrected signal is output using the readout signal combined as the lower address.

As a result, the image signals 13a, 13b, and 13c are always subjected to appropriate tone correction in the tone correction sections 14a, 14b, and 14c according to the tone characteristics of the recording head.

The gradation-corrected signals 15a, 15b, 15c are binarized by the dither method, error diffusion method, etc. in the binarization processing units 16a, 16b, 16c, and then sent to the recording head 18a,
The signals are input to 18b and 18c, and color image recording is performed.

In this way, according to this embodiment, tone correction can be performed using the optimum correction curve according to the tone characteristics of the recording head.
As a result, a color image with good gradation and well-balanced color can be obtained.

Especially, like cassette type inkjet printers,
When the present invention is applied to an image recording apparatus with a replaceable recording head, there is an advantage that gradation is always good even if the type of recording head changes.

(2) M-ball - Example FIG. 3 shows the circuit configuration of a second embodiment of the present invention. 1st
The same numbers as in the figures indicate the same components.

In FIG. 3, 30 indicates recording heads 18a, 1llb.
, red and green recorded on recording paper at 18c,
eco reads the gradation (density) of three colors of blue
Image reading units 31a, 31b, and 31e each include a fixed image sensor such as a charge-coupled device (charge-coupled device).
Red, green, and blue read signals output from 0, 32 are these read signals 31a, 31b,
31c is a RAM (random access memory) for storing, 33 is a CPU (central processing unit) that performs predetermined calculations based on the output signal of the RAM 32, 34a, 34b, 3
4c is a correction curve selection signal output from the CPU 33. These correction curve selection signals 34a, 34b, 34c are supplied to tone correction sections 14a, 14b, 14c.

Next, the control operation of the CPU 33 according to the embodiment of the present invention will be explained with reference to the flowchart shown in FIG.

First, the correction curve selection signals 14a, 14b,
14e, the gradation correction curve is set to a straight line with a slope of 1.0 (step SL).

Next, a predetermined tone characteristic measurement pattern is outputted and recorded on the recording paper from the recording heads 18a, 18b, and 18e according to a signal from a tone characteristic measurement pattern generating section (not shown) (step S2).

This gradation characteristic measurement pattern is, for example, a plurality of patterns with different gradations as shown in Fig. 5, and the printing duty (print rate) for each color is 10% from 10% to 100% (solid image). This is a pattern that changes in 10 steps in % increments.

Next, this output pattern is read by the image reading section 30, and the read signals of each gradation are stored in the RAM 32 (step S3).

Next, after converting the read signal read out from the RAM 32 into density, averaging processing is performed to obtain the average density C for each gradation.
m (m=1 to 10) is determined (step S4).

Next, the above average density Cm is stored in the built-in ROM of the CPU 33.
Table conversion is performed using the gradation correction table stored in (step S5).

Furthermore, the square error between the gradation characteristics obtained by this table conversion and the ideal straight line is calculated (step S6).

In other words, the average density of each gradation after table conversion is C'
m (m = 1 to 10), the value on the ideal straight line is Cow (
m=1 to 10), then calculate. Here, E indicates the squared error.

Furthermore, this calculation of the squared error E is performed for all 20 types of gradation correction curves, and the gradation correction curve with the smallest squared error is determined (step S8).

Based on this judgment, the selection signals 34a, 34b, 34c corresponding to the optimal tone correction curve are output to the corresponding tone correction sections 14a, 14b, 14e (step S
9).

By doing so, the recording head 18a.

Even if the gradation characteristics of 18b and 18c change over time, it is possible to always select the optimum gradation correction curve and maintain good image quality.

In the present embodiment, the correction pattern printed on the recording paper can be read by a user or a service person by placing an output sample of the pattern on the reading section. Alternatively, a dedicated reading sensor may be provided on the recording paper conveyance path so that the dedicated reading sensor automatically reads the sample after being output and recorded.

111 yu lost 11 Next, a third embodiment of the present invention will be described.

In this embodiment, after the gradation characteristics of the recording head are actually measured within the apparatus, an optimal correction curve is created and used by the CPU based on the measurement results. FIG. 6 shows the circuit configuration of this embodiment. In this embodiment, gradation correction section], 4a
, 14b, 14. c is composed of RAM rather than ROM. Also, 40a and 40b in the same figure.

The difference from the second embodiment shown in FIG. 3 is that 40c is not a correction curve selection signal (but is data of the correction curve itself).

Next, the control procedure of this embodiment will be explained with reference to the flowchart of FIG. Steps 5ll-314 in the figure are the same as steps 31 to S4 in the second embodiment. In the next step S15, an ideal gradation correction curve is calculated from the average density Cm for each gradation obtained by measurement.

In the next step S16, ideal correction curve data 40a obtained by calculation, 4. Ob, 40c is the gradation correction section 14a.

The data is stored in the RAM of 14b and 14c.

By doing this, optimum gradation correction can always be performed for any storage head with any gradation characteristics.

Also, in the embodiment described above, the optimum gradation correction curve information indicating sections 19a, 19b, 1.9c in FIG.
Although the description has been made using M or a variable resistor, a switch with several stages may also be used.Furthermore, the uneven shape of some of the recording heads 18a, 11Sb, and 18c may be changed according to the optimum curve, and the connection with the recording apparatus may be made. A configuration may also be adopted in which a control signal is generated by a microswitch or a photocoupler when the parts are combined, depending on the shape. Further, optimum gradation correction curve information instruction sections 19a and 19b.

19c does not necessarily have an integral structure with the recording head (for example, R 19c stores tone correction curve information).
The OM may be prepared separately from the recording head, and when the recording head is installed, the ROM may also be installed at the same time.

Furthermore, in each of the above embodiments, the present invention was applied to a color image recording device that obtains a color image using three colors, cyan, magenta, and yellow. Of course, similar effects can be obtained by applying.

[Effects of the Invention] As explained above, according to the present invention, the gradation correction curve is variably set according to the gradation characteristics of the recording head. Also, it is possible to always obtain high-quality recorded images with good gradation and color balance.

[Brief explanation of drawings]

1 is a block diagram showing a circuit configuration of an image recording apparatus according to a first embodiment of the present invention; FIG. 2 is a graph showing a specific example of a gradation correction curve used in the embodiment of the present invention; FIG. 4 is a block diagram showing the circuit configuration of an image recording apparatus according to the second embodiment of the present invention. FIG. 4 is a flowchart showing the control procedure of the second embodiment of the present invention. FIG. FIG. 6 is an explanatory diagram schematically showing an example of a tone characteristic measurement pattern (test pattern) used in the second embodiment of the present invention. 7 is a flowchart showing the control procedure of the third embodiment of the present invention. FIG. 8 is a block diagram showing the circuit configuration of a conventional image recording apparatus. FIG. 9 is a flowchart showing the control procedure of the third embodiment of the invention. Figure 10 is a graph showing an example of a gradation correction curve used in a conventional image recording device; Figure 11 is a graph showing an ideal gradation characteristic after gradation correction. This is a graph showing. 2 14a, 14b, 14c 15a, 16b, 16c 18a, 18b, 18c 19a, 19b, 19c 20a, 20b, 20c 0 2 3 ... Color correction section, ... Gradation correction section, ... Binarization Processing section, ... Recording head, ... Optimum gradation correction curve information instruction section, ... Optimum correction curve information reading section, ... Reading section, ... RAM, ... CPU. Figure 4 Figure Figure Figure Figure Gr3'Fr' Neity 10% 20% 30% 40% Figure 9 Figure 10

Claims (1)

[Scope of Claims] 1) A tone correction means for correcting the tone of an image signal according to a tone correction curve, and a recording head is driven in accordance with the image signal corrected by the tone correction means to produce an image. In an image recording apparatus that performs recording, characteristic signal generating means generates a signal according to tone characteristics of the recording head, and tone correction of the tone correction means according to the signal generated from the characteristic signal generating means. An image recording apparatus comprising: tone correction curve setting means for setting a curve. 2) The characteristic signal generating means includes: an optimum tone correction curve information indicating means for presenting information according to an optimum tone correction curve specific to the recording head; 2. The image recording apparatus according to claim 1, further comprising a control signal generating means for generating a control signal in accordance with information. 3) The characteristic signal generating means includes: a pattern outputting means for outputting a test pattern for measuring tone characteristics of the recording head; and an image reading means for reading the test pattern for measuring tone characteristics output and recorded via the recording head. means, a calculation means for calculating an ideal gradation correction curve based on the data of the reading result of the image reading means, and a signal for outputting data of the ideal gradation correction curve calculated by the calculation means. The image recording apparatus according to claim 1, further comprising an output means.