JPS6174447A - Shading correction circuit - Google Patents

Abstract

PURPOSE:To obtain a picture with good color reproducibility by obtaining a shading data at each reference color so as to correct the difference of a spectrum characteristic of each color filter. CONSTITUTION:A color original read section 1 is connected to a CPU 4 of a color original reader via a control circuit 2, color reference signals BS, WS and an original read data DA from black and white reference boards read by the read section 1 are fed to a read data switching circuit 31 of a shading correction circuit 3 under the control of a CPU 1. Each output from the circuit 31 is stored in a parameter memory 32 and white/black reference data memories 34, 35. The memories 33-34 are connected to a CPU data switching circuit 36 of the correction circuit 3 and operation device input switching circuits 37, 38 and an input switching circuit 40 and an operation device 41 are connected to the circuits 37, 38. Then the output of the operating device 41 is fed to an operating device output switching circuit 32, the memories 33, 35 are controlled by the output of the circuit 32 to obtain a shading data at each reference color and the difference of the spectrum characteristic of each filter is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a shading correction circuit used in a color document reading device that reads color documents.

[Technical background of the invention and its problems]

For example, when a color printer is used to express a grayscale image, the image data must carry density information. In this case, if the luminance levels of the original images are the same, their density information must also be the same. However, in reality, due to various physical factors, such as spatial variations in the sensitivity of solid-state image sensors and spatial variations in the emission intensity of light sources, in real equipment, the brightness vs. concentration conversion characteristics vary spatially. It may cause unevenness. Generally, this is called shading, and image input devices are equipped with a shading correction circuit for correcting this shading.

Incidentally, there are known shading correction methods such as analog type, digital type, and analog/digital type, but recently, as image data is increasingly handled exclusively in digital form, digital shading Correction circuits have come into widespread use.

When performing shading correction in a monochrome document reading device, for example, COD (Charge
Coupled Device) A line image sensor scans a white reference density plate and a black reference density plate in advance, and A/D converts the output of the image sensor.
White reference data and black reference data (these are referred to as shading data) are obtained in advance. To apply shading correction to the image data read by the image sensor, the black reference data is subtracted from the output signal of the image sensor, and that value is divided by the value obtained by subtracting the black reference data from the white reference data. Good.

On the other hand, in a color original reading device that reads color originals, it is necessary to provide a transmission filter for each of the three primary colors of light (red, blue, green) or their complementary colors (cyan, magenta, yellow) on the image sensor side. The shading characteristics may change each time. Therefore, it is necessary to store shading data for each color in memory.

Incidentally, in a color document reading device, in addition to the above-mentioned shading correction, it is necessary to perform, for example, color balance adjustment. In this case, if you correct the shading data by multiplying the shading data for each color by the color balance adjustment coefficient in advance, you can simplify the subsequent signal processing and also speed up the signal processing. can.

However, when modifying shading data in this way, in conventional devices, the CPU, which controls the entire device,
(Centrai Processing Unit
), and the arithmetic processing takes an extremely long time. In particular, as the resolution of image sensors has improved significantly in recent years, it was expected that such problems would become even more prominent due to the accompanying increase in the amount of image data.

[Purpose of the invention]

The present invention has been devised in view of these problems, and its purpose is to enable shading data to be corrected in a short time as necessary, thereby contributing to high-speed processing in color document reading devices. The object of the present invention is to provide a shading correction circuit that obtains the desired results.

[Invention! Essential]

The present invention provides a shading correction circuit which includes a memory for storing shading data, a memory for storing coefficients used for modifying the shading data, and a memory for storing the shading data and the coefficients. It is characterized by comprising an arithmetic circuit for correction.

〔Effect of the invention〕

According to the present invention, since the shading correction circuit includes an arithmetic circuit for correcting shading data, extremely high-speed arithmetic processing is possible even when handling a large amount of image data, unlike software calculations performed by a CPU. becomes possible. Therefore, according to the present invention, it is possible to contribute to high-speed processing of a color document reading device.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A color document reading device incorporating a shading correction circuit according to an embodiment of the present invention will be described below with reference to the drawings.

That is, as shown in FIG. 1, this color document reading device includes a color document reading section 1 that scans a color document to obtain an image signal, and converts this image signal from analog to digital to generate image data; A mechanical control section 2 that controls the color document reading section 1, a shading correction circuit 3 that performs shading correction on image data output from the color document reading section 1, and a shading correction circuit 3 that controls the mechanical control circuit 2 and the shading correction circuit 3. It is composed of CPU4.

The color document reading section 1 is configured as shown in FIG. 2, for example. That is, at a position facing the original 12 placed on the original table 11, a one-dimensional solid-state image sensor 14 made of, for example, a COD is installed via a lens 13.
is located. This image sensor 14 has a yellow filter YF and a cyan filter CF as shown in FIG. 3 in its light receiving window.

Magenta filters MF are repeatedly arranged in this order. Therefore, the image sensor 14 outputs each color signal as a serial color image signal. Further, a fluorescent lamp 15 that is slightly longer than the width of the original @ 12 is installed near the image sensor 14, and the light from the fluorescent lamp 15 is directed to the image sensor 14 through the surface of the original 12 and the lens 13. I'm trying to guide you. Manuscript table 1
A black reference density plate 16 and a white reference density plate 17 having substantially the same width in the lateral direction as the original 12 and a slight length in the vertical direction are arranged in this order at one end of the document 1 . A metal fitting 18 for attaching a belt is fixed to the side end of the document table 11, and a timing belt 19 is fixed to this metal fitting 18. This timing belt 19 is supported by a pulley 20 at one end and by a pulley 21 at the other end.
Further, the pulley 20 is rotatably supported by a fixture 22,
Further, the pulley 21 is fixed to a pulse motor 23.

That is, by the rotation of the pulse motor 23, the document table 11 is configured to move in the sub-scanning direction of the document 12 as indicated by arrow A in the figure. Therefore, the original 12 on the original table 11 is scanned in the main scanning direction by the electrical self-scanning of the image sensor 14, and is scanned in the sub-scanning direction by the movement of the original table 11 by the pulse motor 23.

The shading correction circuit 3 is a main part of the apparatus of this embodiment, and its specific configuration is shown in FIG. 4.

That is, this shading correction circuit 3 has a read data switching circuit 31 and an arithmetic unit output switching circuit 32 in its input section, and the outputs of these two cutting circuits 31 and 32 are used as parameter memory 33 and white reference data, respectively. The data is input to the memory 34 and the black reference data memory 35. Each of these memories 33 to 35 is a line memory capable of storing one line of image data. The parameter memory 33 stores coefficients to be corrected for each color in order to adjust the level of image data of each color of yellow, cyan, and magenta to achieve color balance. The white reference data memory 34 and the black reference data memory 35 are memories that store the aforementioned shading data, and store the aforementioned shading data for each color. The outputs of these memories 33 to 35 are input to a CPU data switching board 36, an arithmetic unit input switching circuit 37, and an arithmetic unit input switching circuit 38, respectively.

Further, the output of the black reference data memory 35 is supplied to one input of the subtracter 39. This subtracter 39 performs shading correction of the black level. This shading correction circuit 3 is connected to the other input of the subtracter 39.
An input signal is supplied to the

The outputs of the three subtracters are supplied to one input of the input switching circuit 40. The other input of the input switching circuit 40 has
The output of the arithmetic unit input switching circuit 38 is supplied.

The output of the input switching circuit 40 is roughly supplied to one input of the arithmetic unit 41. This arithmetic unit 41 performs shading correction of the white level and correction of shading data. The output of the arithmetic unit input switching circuit 37 is supplied to the other input of the arithmetic unit 41. The output of the arithmetic unit 41 is output to the outside via an output buffer 42 and is also supplied to the input of the arithmetic output switching circuit 32. Note that the CPU data switching board 36 is
P (connected to the data bus of J4, this boat 3
6, data is exchanged between each of the memories 33 to 35 and the CPU 4.

Next, the operation of the color document reading device configured as described above will be explained.

That is, before starting document scanning, the CPU 4 first performs the following steps.
The pulse motor 23 of the color original reading section 1 is driven via the mechanical control circuit 2, and the scanning start point of the original table 11, that is, the image sensor 14 is set to the black reference density plate 16.
Move it to a position opposite to.

At this position, the image sensor 14 scans the surface of the black reference density plate 14 and outputs black reference signals for each color.

Each black reference signal is AID-converted by an A/D converter (not shown) and transferred to the shading correction circuit 3 as black reference data BS of each color.

Each black reference data BS input to the shading correction circuit 3 is transferred to the black reference data memory 35 by the read data switching circuit 31 and stored therein.

Similarly, the CPU 4 drives the pulse motor 23 via the mechanical control circuit 2 to move the document table 11 to a position where the image sensor 14 faces the white reference density plate 17. At this position, the image sensor 14 scans the white reference density plate 17 and outputs a white reference signal for each color.

These signals are A/D converted and transferred to the shading correction circuit 3 as white reference data WS. The white reference data ws is transferred to the white reference data memory 34 by the read data switching circuit 31 and stored there.

On the other hand, the CPU 4 calculates coefficients for each color for color balance based on the image data of each color obtained by scanning both of these reference density plates 16 and 17, and uses the obtained coefficients to switch the CPU data. It is transferred to the parameter memory 33 via the boat 36.

In this state, scanning of the original 12 is started. That is,
First, the CPU 4 drives the pulse motor 23 via the mechanical control circuit 2 to move the document table 11 with the arrow △ in the figure.
Move slowly in the sub-scanning direction indicated by . The image sensor 14 scans itself in the main scanning direction to read image information from the original 12 . The original reading signal outputted from the image sensor 14 is A/D converted and transferred to the shading correction circuit 3 as original reading data DA of each color having gradation information of, for example, 16 gradations. This original read data OA is input to the subtracter 39. In the subtracter 39,
Black reference data BS is subtracted from this original read data DA, and shading correction of the black level is performed. The original read data DA' subjected to black level correction is then input to the arithmetic unit 41 by selection by the input switching circuit 40. At this time, since the arithmetic unit 41 is switched to the division mode, the original read data DA' is divided by the white reference data WS selected by the arithmetic unit input switching circuit 31. As a result, shading correction of the white level is performed, and the data is output as image data DB via the output buffer 42.

Next, a case will be described in which the black reference data BS and the white reference data WS are corrected in consideration of color balance.

In this case, in the input switching circuit 40, the arithmetic unit input switching circuit 38 is selected, and roughly speaking, the arithmetic unit input switching circuit 38 is selected.
8 selects the white reference data memory 34 or the black reference data memory 35. Further, the arithmetic unit input switching circuit 37 is
Select parameter memory 33.

As a result, the shading data and coefficients for correcting the shading data are input to the arithmetic unit 41. In this mode, the arithmetic unit 41 multiplies both. This operation is C
This is performed by a command from the PU 4, and one line in the main scanning direction is calculated in parallel.

The output of the arithmetic unit 41 is input to the white reference data memory 34 via the arithmetic unit output switching circuit 32 when the white reference data WS is modified, and is input to the white reference data memory 34 when the black reference data BS is modified. The black reference data is input to the black reference data memory 35 via the device output switching circuit 32.

The shading data corrected as above is
It is used to correct the document read data DA from the color document reading section 1 according to the shading correction process described above.

As explained above, according to this embodiment, shading data can be calculated and corrected in parallel, so
Compared to calculations performed by the CPU 4, the processing speed can be significantly improved.

In this way, if shading data can be corrected at high speed, it can contribute to simplifying and speeding up signal processing such as color balance adjustment, and the resulting effects are significant.

In this embodiment, the arithmetic unit 41 corrects the shape ink data in consideration of color balance, but the arithmetic unit 41 may also perform signal processing such as gamma correction. In this case, the computing unit 41 is
In addition to the multiplication of shading data and coefficients, other calculations may be performed. In addition, CPU4 is
The data may be transferred to the parameter memory 33 if necessary.

In the above embodiment, the black reference density plate 1 is used as the reference density plate.
6 and a white reference density plate 17, for example, as shown in FIG.
In addition, a yellow density reference plate 51, a cyan density reference plate 52, and a magenta density reference plate 53, each of which has the same color as the three color filters YF, CF, and MF provided in the image sensor 14, may be provided (if the filters are (in the case of a color, it is sufficient to use the same reference density plate as that color). For each reference density plate, for example, a ceramic plate or a ceramic plate coated with ink or acrylic paint may be used. Furthermore, in this case, a shading data memory may be provided for each reference density plate of each color.

With such a configuration, shading data for each reference color can be obtained, so differences in spectral characteristics of each color filter can be corrected, and an image with good color reproducibility can be obtained.

In short, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a color document reading device according to an embodiment of the present invention, FIG. 2 is a perspective view showing the configuration of a color document reading section of the device, and FIG. 3 is an image sensor of the color document reading section. FIG. 4 is a block diagram of a shading correction circuit which is a main part of the above device, and FIG. 5 is a color filter according to another embodiment of the present invention.
FIG. 3 is a perspective view showing the configuration of a reading section. 11... Original table, 12... Original, 13...
Lens, 14... Image sensor, 15... Fluorescent lamp, 16... Black reference density plate, 17... White reference density plate,
19...Timing belt, 23...Pulse motor, 51...Yellow density reference plate, 52...Cyan density reference plate, 53...Magenta density reference plate.

Claims (3)

[Claims] (1) In a shading correction circuit that performs shading correction on input image data using shading data obtained by reading a reference density plate with an image input device, the shading correction circuit includes a memory for storing the shading data and a memory used for correcting the shading data. 1. A shading correction circuit comprising: a memory for storing coefficients; and an arithmetic circuit for correcting the shading data by inputting the shading data and the coefficients. (2) The shading correction circuit according to claim 1, wherein the reference density plate is white and black. (3) The image input device is characterized in that a plurality of types of color filters are arranged in the light receiving section, and the reference density plate is made of black, white, or the same color as the color filter. A shading correction circuit according to claim 1.