JPH03253174A - Color original reader - Google Patents

Abstract

PURPOSE:To read even a small uneven change by making a contrast range of contrast information outputted from a monochroic sensor means the same independently of kinds of color/monochroic originals by means of a revision means. CONSTITUTION:The reader is provided with a clamp circuit 102 clamping contrast information outputted from a white/black image sensor 101 to a prescribed voltage, an amplifier 103 amplifying an output of the clamp circuit with a prescribed amplification factor, and a contrast range revision means comprising an arithmetic unit 105 setting a reference signal of clamp to the clamp circuit 102 and setting the amplification factor to the amplifier 103. Even when the contrast range of the contrast information outputted from the white/black image sensor 101 differs from kinds of a color/monochroic original, a revision means revises the range to be the same contrast range. Thus, the contrast information is obtained in the same contrast range independently of the kinds of the color/ monochroic originals and uneven print is read with uniform gradation and low cost independently of the color/monochroic originals.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color document reading device, and more particularly to a color document reading device that reads uneven printing and the like and is used for head correction of an inkjet printing device.

[Conventional technology]

Conventionally, in an inkjet printing device for monochrome printing using black ink, uneven printing occurs due to variations in print heads, so head shading correction has been performed to correct the uneven printing. In this method, the print head to be corrected prints a test pattern, and the print result is read by a correction black and white sensor to detect the correction amount of each part of the head to be corrected. C), magenta (M),
Since there are four types, yellow (Y) and black (K), it is necessary to correct the printing unevenness of each head. Possible methods for correcting this unevenness include using a color sensor as a sensor for reading uneven print samples, and adding a color filter to a monochrome sensor.

However, both methods require a color sensor and a color filter, resulting in a problem of extremely high costs.

In addition, only the black and white sensor can display cyan (C) and magenta (M).
When trying to read four types of single-color originals: , yellow (Y), and black (K), changes in unevenness make it difficult to read them properly. The reason is explained below.

Figure 10 shows cyan (C), magenta (M), yellow (
It is a graph showing the output pattern of each black and white sensor when a monotonous print sample printed with a printing spatula in four colors of Y) and black (K) is read by a black and white sensor. The horizontal axis shows the read pixel density, and the vertical axis shows the output from the black and white sensor. As can be seen from the figure, the output of the black and white sensor differs depending on the type of ink: cyan (C), magenta (M), yellow (Y), and black (K). For example, the dynamic range of yellow (Y) is extremely narrow compared to the dynamic range of black (K).

For example, the analog signal of the output of the monochrome sensor is converted to black (K), which has the widest dynamic range of the output of the monochrome sensor.
All four colors are clamped, amplified, and A/D converted in the same way. In this case, colors with a narrow dynamic range of the black and white sensor output, especially yellow (Y), end up being assigned digital values even to analog signal regions that are not output.

The output of the black and white sensor is read as black (K).
This is a graph showing changes in digital data read pixel density when clamped according to the dynamic range of , amplified at the same amplification degree, and A/D converted. In the example in Figure 11, the digital data obtained for black (K) is 8
If the range is from "00" to "FF" (256 gradations) in hexadecimal bits, the digital data that can be obtained for yellow (Y) is only from "AO" to "FF" (96 gradations).

In this way, when trying to read unevenness changes, the number of gradations of digital data obtained will be small for colors with a narrow dynamic range of monochrome sensor output.
There is a problem in that small variations in unevenness cannot be detected simply by using a black and white sensor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a color document reading device that can read printing unevenness with uniform gradation regardless of the type of color document at low cost. With the goal.

[Means to solve the problem]

This invention was made to solve the above problems,
Monochrome sensor means for reading a color monochrome original and outputting shading information; and changing means for changing the shading range of the shading information output from the monochrome sensor means according to the type of the color monochrome original and outputting it as digital data. It is characterized by having the following.

[Effect]

According to the above configuration, even if the shading range of the shading information output from the monochrome sensor means differs depending on the type of the color monochrome original, the changing means changes the shading information so that it is the same shading range, so that the color monochrome original It is possible to obtain shading information in the same shading range regardless of the type of shading.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments in which a color document reading device of the present invention is applied to an inkjet type copying machine having an ink head will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the same figure, numeral 101 is a black and white image sensor that reads a color document to detect uneven printing, and outputs grayscale information as an analog signal.

102 is a clamp circuit that clamps the grayscale information output from the monochrome image sensor 101 to a predetermined voltage, and 103 is an amplifier that amplifies the output of the clamp circuit at a predetermined amplification factor. 104 is an A/D converter that converts the output of the amplifier 103 into a digital signal; 105 is an A/D converter that sets a reference voltage signal for clamping in the clamp circuit 102;
This is a calculation device that sets the amplification factor to 3. Further, 106 is an operation unit for giving various instructions to the arithmetic device 105.

In this example, by reading print samples of four colors of heads: black (K), cyan (C), magenta (M), and yellow (Y), the amount of change in print unevenness of the heads is obtained as digital data. There is.

FIG. 3 is a top view showing the print head. In this embodiment, the print head 301 has an inkjet nozzle 302 that forms air bubbles using heat and uses the resulting pressure to eject ink droplets from an ejection port.

As for typical configurations and principles thereof, it is preferable to use the basic principles disclosed in, for example, US Pat. No. 4,723,129 and US Pat. No. 4,740,796. This method is applicable to both so-called on-demand type and continuous type. In particular, in the case of the on-demand type, the electrothermal transducer placed in correspondence with the sheet holding the liquid (ink) and the liquid path corresponds to the printed information and rapidly exceeds nucleate boiling. Applying at least one drive signal that provides a temperature increase causes the electrothermal transducer to generate thermal energy and cause film boiling on the thermally active surface of the printhead. As a result, bubbles in the liquid (ink) can be formed in a one-to-one correspondence with this drive signal, which is effective. The growth and contraction of the bubble causes liquid (ink) to be ejected through the ejection opening to form at least one drop. When this drive signal is in the form of a pulse, the growth and contraction of the bubbles is carried out immediately and appropriately, which makes it possible to eject liquid (ink) with particularly excellent responsiveness, which is more preferable.

As this pulse-shaped drive signal, US Pat. No. 446
Those described in Japanese Patent No. 3359 and Japanese Patent No. 4345262 are suitable. In addition, US Patent No. 431312 of the invention regarding the temperature increase rate of the heat acting surface
If the conditions described in Specification No. 4 are adopted, even more excellent printing can be achieved.

Next, the operation of this embodiment will be explained with reference to the flowchart in FIG.

First, in step S1, a command is given to the operation unit 106 to read a printed document sample having unevenness printed by a black (K) print head. When the operation unit 106 sends this command to the arithmetic unit 105, the clamp amount and amplification factor are selected in step S2 based on the dynamic range of the output of the black and white sensor for the black (K) print sample shown in FIG. be done. These selection information are stored in advance in the arithmetic unit 105, and, for example, a voltage between V0 and VK shown in FIG. 10 is selected as the reference voltage for the clamp.

In step s9, the arithmetic unit transfers the selected reference voltage and amplification factor to the clamp circuit 102 and the amplifier 103 in SIO.
Set to .

Next, in step Sll, the start key (
(not shown) is pressed, the sample printed by the black (K) print head is read by the monochrome sensor 101 in step S12, and a sensor output of an analog signal is obtained. This signal is sent to the clamp circuit 102, and the arithmetic unit 1
It is clamped according to the reference voltage data of the dynamic range to be clamped set by 05. Furthermore, the output signal of the clamp circuit 102 is amplified in the amplifier 103 according to the amplification factor set by the arithmetic unit 105 . In the A/D converter 104, this amplifier 10
Convert the output of 3 into a digital signal.

This digital signal becomes data on the amount of variation in unevenness of each nozzle of the black (K) head. This reading operation is repeated until all lines are completed (step 513).
. Then, the calculation device 105 calculates the correction amount for each nozzle of the black (K) head based on the average of the unevenness change amount data for all lines.

Also, cyan (C), magenta (M), yellow (Y)
The case where a command is given to read a printed document sample with unevenness printed by the print head is similar to the above-mentioned case of black (K). That is, steps S3 and S
4. In S5 and S6, and S7 and S8, the clamp amount and amplification factor are selected based on the dynamic range of the monochrome sensor output for cyan (C), magenta (M), and yellow (Y) print samples, respectively. And from step 89,
A printing sample reading operation similar to that for black (K) is performed to obtain the amount of variation in unevenness of each nozzle of each color head.

Note that original samples printed by each color head are
Each time, I set it manually and have it read.

In this embodiment, original samples printed by cyan (C), magenta (M), yellow (Y), and black (K) heads are read by a monochrome sensor 101, and the analog signal output is converted into a signal for each color. The amplifier 103 amplifies the dynamic ranges of the two signals so that they have the same dynamic range. Therefore,
When the amount of unevenness change is obtained as digital data by the A/D converter 104, it is possible to obtain the same level for all four colors, so even small changes in unevenness can be read, and unevenness correction (shading correction) can be performed in the same way for all colors. It becomes possible to do so.

Further, since this embodiment does not use a color sensor or a color filter, it can be realized at low cost.

Next, another embodiment of the present invention will be described with reference to the block diagram shown in FIG. In addition, in Figure 4, the first
Parts corresponding to those in the figures are given corresponding symbols. In this embodiment, by using a density correction plate and reading the correction plate in advance, the reference voltages of the cyan (C), magenta (M), yellow (Y), and black (K) clamps and the amplifier voltage are determined. This is to preset the amplification factor.

FIG. 5 shows the density correction plate. As shown in this figure, the density correction plates are cyan (C), magenta (M), yellow (Y),
There are four colors, black (K), and each color has the brightest part and the darkest part.

In FIG. 4, first, the cyan (C) of the density correction plate 407 is
The black and white sensor 401 sequentially reads from the dark part to the light part, and the clamp circuit 402, amplifier 403, and A/D
The data is temporarily stored as gray scale information in the arithmetic unit 405 via the converter 404. The arithmetic unit 405 determines the dynamic range of the output of the monochrome sensor 401 for cyan (C) from the stored gradation information, and uses the data to determine the dynamic range of the output of the monochrome sensor 401 for cyan (C).
Find and store the clamp reference voltage and amplification factor.

Then, perform the same operation for magenta (M) and yellow (Y).
, and black (K). In addition, the density correction plate 4
It is possible to identify which color information was read from the reading position of 07. Furthermore, when reading the density correction plate 401, the reference voltage and amplification factor of the clamp are fixed.

Next, as in the previous example, set the clamp voltage and amplification factor according to the color, read the printed document sample with unevenness printed by the four color print heads, and calculate the amount of unevenness change of each nozzle of the head. read.

According to this embodiment, even if the characteristics of the monochrome sensor 401 or its light source change, since the clamp reference voltage and amplification factor are preset in advance, the amount of unevenness change of each head corresponding to the characteristic change can be read. be able to.

Next, still another embodiment will be described with reference to the block diagram of FIG. 6. In this embodiment, the reference voltage and amplification factor of the clamp are not changed depending on the color, but are always kept constant according to black (K). Instead, two A/D converters with different precisions are used. 604 in Figure 6
is an 8-bit A/D converter, and 608 is a 12-bit A/D converter.
A D converter 609 is a switching circuit that selectively outputs the signal from the amplifier %03 to A/D converters 604 and 608.

In this embodiment, the reference voltage of the clamp circuit 602 and the amplification factor of the amplifier 603 are always constant, and are matched to the dynamic range of the output signal of the monochrome sensor 601 when reading black (K). All four color sensor outputs pass through the clamp circuit 602 and the clamp circuit 603 and are sent to the switching circuit 609. Here, the arithmetic unit 605 performs switching control so that the black (K) signal is sent to an 8-bit A/D converter 604, and the other color signals are sent to a 12-bit A/D converter 608.

As can be seen from FIG. 10, only black (K) has a wide dynamic range of output from the monochrome sensor 601. Therefore, by converting the black (K) signal into 8-bit digital data and converting other colors into 12-bit digital data, the number of gradations of the digital data in the range of unevenness can be reduced to black (K). ) will not be reduced.

Therefore, the present embodiment can achieve the same effect as in the previous embodiment in which the dynamic ranges of the four colors are expanded to the same extent.

Next, still another embodiment will be described with reference to the block diagram of FIG. 7. This is done by keeping the reference voltage of the clamp circuit 702 and the amplification factor of the amplifier 703 constant, and the A/D
The reference voltage Vref of the converter 704 is changed depending on the color.

First, when reading an uneven print sample printed by a black (K) head, the arithmetic unit 705
The reference voltage Vref of the /D converter 704 is set to, for example, 5V. It is assumed that the reference voltage of the clamp circuit 702 and the amplification factor of the amplifier 903 are set so that the output of the amplifier 703 when reading the print sample of Plaque (K) is O~5. The black (K) analog signal is converted into 8-bit 16-bit signals by the A/D converter 904.
It is converted into digital data of "OO" to "FF" in base numbers.

Next, when reading a sample of uneven print printed by a yellow (Y) head, referring to FIG. 10, the output of the amplifier 703 will be in the range of approximately 0 to 2V.

Therefore, at this time, the reference voltage Vre of the A/D converter 704
If you set f to 2v, it will be "00" like black.
Digital data of "FF" is obtained. Similarly, for other colors, the reference voltage Vref of the A/D converter 704 is set to a value corresponding to the dynamic range of the black and white sensor 701.
Do a read.

Still another embodiment will be described with reference to the block diagram of FIG. This is a 12-bit A/D converter 808
This uses a lookup table 810 for gradation conversion. The ROM 810 used as the look-up table in the figure is configured so that different data is output depending on the color, as shown in FIG.

As can be seen from FIG. 10, the output of the amplifier 803 is output in different ranges for each color at a ratio as shown on the right side of the graph in FIG. Therefore, in accordance with black (K), the reference voltage Vre of the A/D converter 808
f and set the contents of the lookup table in advance so that the output is shown in Figure 9 according to the output range of each color, it is possible to obtain digital data with 256 gradations for all four colors. can.

When reading print samples of each color, the calculation device 80
The information on the color read by 5 is given to the lookup table 810, and the table corresponding to that color is selected.

〔Effect of the invention〕

As described above, according to the present invention, the shading range of the shading information output from the monochromatic sensor means can be made the same by the changing means regardless of the type of monochromatic color original, so even small variations in unevenness can be read. becomes.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the color document reading device of the present invention, FIG. 2 is a top view showing a print head, and FIG. 3 is a flowchart explaining the operation of the embodiment shown in FIG. 1. FIG. 4 is a block diagram showing another embodiment of the present invention, FIG. 5 is a diagram showing the density correction plate of FIG. 4, and FIGS.
The figures are block diagrams showing still other embodiments of the present invention, FIG. 9 is a diagram explaining the lookup table of FIG. 8, and FIGS. , are graphs showing sensor output and digital conversion output, respectively. 101.401.601.701.801...Black and white image sensor 102.402.602.702.802...Clamp circuit 103.403.603.703.8'01...Amplifier 104.404.604. 608.704.808...
- A/D converter 105.405.605.705.805... Arithmetic unit 106.406.606.706.806-9. Operation unit 407...Density correction plate 609...Switching circuit 810...Lookup table or other function v'7 457-

Claims (4)

[Claims] (1) Monochrome sensor means for reading a color monochrome original and outputting shading information, and changing the shading range of the shading information output from the monochrome sensor means according to the type of the color monochrome original and outputting it as digital data. 1. A color document reading device comprising: changing means. (2) The changing means includes a variable amplification means that amplifies the shading information output from the monochromatic sensor means according to the type of the monochromatic color document, and converts the shading information amplified by the variable amplifying means into digital data. and output A/
2. The color document reading device according to claim 1, further comprising a D conversion means. (3) The color document reading device according to claim 1 or 2, wherein the monochromatic color document is printed by cyan, magenta, yellow, and black heads of an inkjet printing device. (4) The print head of the inkjet printing device is provided with a plurality of ejection ports for ejecting ink, and is provided for each corresponding ejection port, causing a state change in the ink due to heat, and ejecting the ink based on the state change. 4. The color original reading device according to claim 3, further comprising thermal energy generating means for ejecting the liquid from the outlet to form flying droplets.