JP2003348350A - Image input device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image input device in which an image is stably read with a high picture quality by reading the image while using a power range of a CCD as great as possible for high picture quality image reading, and correcting nonlinearity of an output voltage of the CCD included in the area by means of a gradation correction in the image input device for reading an original image as image data through the CCD. <P>SOLUTION: An exposure time of the CCD is controlled, an output voltage value relative to a plurality of input light quantity values with a quantity of input light changed step by step is measured and as illustrated in figure 3, a CCD characteristics curve 6 is prepared. Based upon the CCD characteristics curve 6, a corrected curve 8 is determined such that a relationship of an input light quantity and a CCD output voltage becomes a corrected CCD output straight line 7. In a real image reading operation, the gradation correction is applied to a voltage value outputted from the CCD by the corrected curve 8, nonlinear characteristics are corrected linearly and the image is read. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
An image input device that irradiates light with a fluorescent lamp or a fluorescent light and receives the reflected light or transmitted light by a CCD that is a photoelectric conversion device, reads an original image, converts the image into an electric signal, and reads the image as image data. The present invention relates to an image input device that corrects a color signal error due to nonlinear characteristics of an input light amount and an output voltage of a CCD and realizes stable image reading with high image quality.

[0002]

2. Description of the Related Art An original image is illuminated with light such as an LED or a fluorescent lamp, and the reflected light or transmitted light is received by a photoelectric conversion device such as a CCD to convert the image into an electric signal and read the image as image data. In an image input device, in order to obtain high image quality, it is desirable that the maximum value of the CCD accumulated charge amount (output voltage) used for image reading is large.
As shown in FIG. 8, when the intensity of light incident on the CCD and the output voltage exceed a certain amount of light, the output voltage exhibits nonlinear characteristics.

When an image is read using such a non-linear area, an error occurs in the read color information, and image data of a color different from the color of the actual original image is read.

Therefore, it has been usual to use only a low voltage portion in which the light amount and the output voltage have a linear characteristic. However, in this case, the resolution of the image reading color is lowered,
High-quality image reading cannot be performed.

It is desirable to use the largest region showing linearity as much as possible. However, the characteristics of the output voltage with respect to the input light amount of the CCD differ depending on the individual difference of the CCD even if the CCD of the same product is used. Inevitably, image reading including nonlinear characteristics is performed.

Further, the characteristics of the output voltage with respect to the input light quantity of the CCD change due to aging or the like.
Even when the same original image is read by an image input device using the same CCD, the color information may be read differently.

[0007]

As described above, the prior art has the following problems.

An original image is irradiated with light from an LED, a fluorescent lamp, or the like, and the reflected light or transmitted light is a photoelectric conversion device.
In order to perform high-quality image reading in an image input device that reads an image as image data by converting it into an electric signal by receiving light with a CCD, the amount of accumulated charge (output voltage) of the CCD used for image reading must be reduced. It is desirable that the maximum value is large, but the relationship between the intensity of light incident on the CCD and the output voltage becomes non-linear when a certain amount of light is exceeded, and a region with an excessively large output voltage cannot be used for image reading. Since only the voltage region is used, there is a problem that high-quality image reading cannot be performed.

Further, the relationship between the amount of light incident on the CCD and the output voltage has individual differences for each CCD, and the same CCD changes with time, so that even if the same image is read, it differs for each image input device. Read in different colors,
There has been a problem that the same image input device may not always read an image in the same color.

An object of the present invention is to irradiate light on an original image with an LED or the like, and receive the reflected light or transmitted light by a CCD, which is a photoelectric conversion device, to convert the image into electric signals and convert the image as image data. In the image input device to read, in order to perform high-quality image reading, image reading is performed with the voltage range of the CCD used for image reading as large as possible, and the nonlinearity of the output voltage of the CCD included in this region It is an object of the present invention to provide an image input device capable of performing stable image reading with high image quality by correcting gray scale by gradation correction.

[0011]

In order to solve the above problems, the present invention employs the following means.

The CCD exposure time is controlled, the output voltage value is measured for a plurality of input light values with the input light amount changed stepwise, and a CCD characteristic curve 6 as shown in FIG. 2 is created. As shown in FIG. 3, the correction curve 8 is determined from the CCD characteristic curve 6 such that the relationship between the corrected input light amount and the CCD output voltage is the corrected CCD output straight line 7.

During an actual image reading operation, the voltage value output from the CCD is gradation-corrected by the correction curve 8, and the image is read by linearly correcting the non-linear characteristic.

A process of preparing the CCD characteristic curve 6 from the above-described measurement of the output voltage with respect to the input light quantity and determining the correction curve 8 based on the curve may be performed every time an image is read, or when the power is turned on. Alternatively, it may be performed every certain time.

As a method of determining the correction curve 8, as shown in FIG. 4, an effective range is determined from a predetermined effective minimum output value 9 and an effective maximum output value 10, and the CCD characteristic is determined for this effective range in the same manner as described above. As shown in FIG. 4 from the curve 6, the correction curve 8 may be determined such that the relationship between the corrected input light quantity and the CCD output voltage is the corrected CCD output straight line 7.

As shown in FIG. 5, an effective range is determined from the black stored value 11 and the white stored value 12, and the effective range is determined as follows.
Similarly to the above, as shown in FIG. 5 from the CCD characteristic curve 6, the correction curve 8 may be determined so that the relationship between the corrected input light amount and the CCD output voltage is the corrected CCD output straight line 7. good. As the values of the black storage value 11 and the white storage value 12 at this time, the average value of the white storage value and the black storage value in the reading range (main scanning direction) is used as the value of the white storage and the black storage.

In the case of a color image input device having signals of two or more colors, a CCD characteristic curve 6 is prepared for each color by measurement, and a correction curve 8 for each color is determined from the CCD characteristic curve 6 for each color. Tone correction may be performed for each color using the correction curve 8 for that color. (The effective range may be determined in the same manner as described above, and a correction curve may be determined for the effective range.)

In the case of a color image input device having signals of two or more colors, as shown in FIG.
A CCD characteristic curve 6 is created by measurement, a difference between the CCD characteristic curve 6 for each color and the corrected CCD output straight line 7 is obtained, and one CCD characteristic curve 6 is created from an average value of the differences, and a correction curve for this is created. 8 may be determined, and gradation correction may be performed for each color using the correction curve 8. (The effective range may be determined in the same manner as described above, and a correction curve may be determined for the effective range.)

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has the following embodiments.

As shown in FIG. 1, an original image is irradiated with light by an LED or the like, the reflected light is received by a CCD, converted into an electric signal, and an image reading section 3 for reading the original image as image data is provided. CCD built in image reading unit 3
And a CCD exposure time control unit 1 for controlling the exposure time of the CCD.

Thus, by controlling the exposure time of the CCD and measuring the output voltage value for a plurality of input light values in which the input light amount is changed stepwise, a change in the light amount is obtained.
D output value data can be obtained.

A CCD characteristic curve and a correction curve generator 2 for generating a CCD characteristic curve and a correction curve for the CCD characteristic curve based on the above measured data are provided.

Thus, the non-linear characteristics of the CCD can be created from the measured data, and a correction curve for converting the non-linear characteristics into a linear one can be calculated from the non-linear characteristic curve.

The above-mentioned CCD characteristic curve and correction curve creating section 2
An image correction execution unit 4 that applies correction to image data using the correction curve created in step 1 and an image data storage unit 5 that stores the corrected image data.

Thus, by applying the correction curve obtained by actual measurement to actual image data and performing gradation correction, accurate and stable image data can be obtained each time.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A representative embodiment according to the present invention will be described.

This apparatus, as shown in FIG.
An image reading unit 3 is provided, which irradiates light with an LED or the like and receives reflected light with a CCD, which is a photoelectric conversion device, to convert image information into an electric signal and read the image information.
The CCD of the present apparatus can freely change the exposure time by the CCD exposure time control unit 1, and has a function of increasing or decreasing the amount of light input to the CCD by changing the exposure time. .

In image reading by CCD, in order to perform high-quality reading, it is desirable that the range of the output voltage of the CCD used for reading is as wide as possible. As shown in (1), nonlinearity occurs in a region where the output voltage is large.

In order to perform high-quality image reading in this apparatus, the output voltage of the CCD is used up to the maximum region of the linear characteristic portion. However, the output characteristics of the CCD depend on individual differences of the CCD. Because they are different, linear characteristics are not always obtained.

Even if the same original image is read due to the difference in characteristics, the image may be read in a different color for each image input device, and the output characteristics of the CCD may change due to the aging of the CCD. The image input device may read a different color.

In order to correct the nonlinear characteristics of the input light quantity and output voltage of the CCD, first, the CCD exposure time control unit 1
The exposure time of the CD is controlled, and the output voltage value is measured for a plurality of input light intensity values in which the input light intensity is changed stepwise, and the CCD characteristic curve and the correction curve creating unit 2 generate the CCD characteristic as shown in FIG. A curve 6 is created.

As shown in the figure, the CCD characteristic curve 6 shows a non-linear characteristic when the output voltage increases, and correct image reading cannot be performed as it is, and as shown in FIG. A correction curve 8 for converting to a linear characteristic as shown by an output straight line 7 is calculated by the CCD characteristic curve and correction curve creation unit 2.

By applying the correction based on the correction curve 8 to the image data read by the image reading unit 3 by the image correction execution unit 4, the image data read as erroneous color information due to the nonlinear characteristics of the CCD. Can be corrected by gradation correction and stored in the image data storage unit 5.

Since the more accurate gradation correction can be performed by measuring the CCD characteristic curve 6 more accurately, the CCD exposure time control unit 1 controls the CCD exposure time and changes the input light quantity stepwise. A process of measuring output voltage values for a plurality of input light intensity values and creating a CCD characteristic curve 6 in the CCD characteristic curve and correction curve creating section 2 may be performed each time an image is read.

Each time the image is read, the CCD characteristic curve 6
Is too redundant, the CCD characteristic curve 6 may be created by measuring the output voltage with respect to the input light quantity of the CCD when the power is turned on or after a certain time has elapsed.

In actual image reading, even when reading a pure white image (when the maximum light quantity is incident on the CCD) or a pure black image (when the minimum light quantity is incident on the CCD), the output of the CCD is not affected. Not all regions from 0 to maximum voltage are used.

Therefore, when calculating the correction curve 8 in the CCD characteristic curve and the correction curve creating section 2 from the CCD characteristic curve 6, it is considered that the correction curve 8 is used in advance for actual image reading as shown in FIG. An effective minimum output value 9 and an effective maximum output value 10 may be determined, an effective range is determined from these predetermined values, and the correction curve 8 may be calculated for the effective range.

The effective range for calculating the correction curve was actually measured from white and black images which are generally used as references, instead of the effective minimum output value 9 and the effective maximum output value 10.
The black storage value 11 and the white storage value 12 may be used.

The black stored value 11 and the white stored value 12 show a drop in the level at both ends of the line scan because the light quantity from the illumination light source such as a fluorescent lamp is smaller than that at the center, as shown in FIG. As shown in the figure, the level fluctuates in the main scanning direction.

Therefore, when calculating the correction curve, the average value of the white stored value and the black stored value in the main scanning direction is obtained, and this is used as the black stored value 11 and the white stored value 12, as shown in FIG. May be determined, and the correction curve 8 may be calculated for this effective range.

When the image input device is a color image input device having two or more color signals, the CCD exposure time control unit 1 controls the CCD exposure time for each color, and changes the input light amount stepwise. The output voltage values for the plurality of input light quantity values thus measured are measured, and a CCD characteristic curve and a correction curve creation unit 2
, A CCD characteristic curve 6 is created.

The correction curve 8 for each color is calculated from the obtained CCD characteristic curve 6 for each color, and is applied to the image data read for each color to perform correction.

Alternatively, as shown in FIG. 6, for each color
The CCD exposure time control unit 1 controls the exposure time of the CCD, measures the output voltage value for a plurality of input light intensity values in which the input light intensity is changed stepwise, and the CCD characteristic curve and correction curve creation unit 2 A curve 6 is created, and the difference ΔR between the CCD characteristic curve 6 for each color and the corrected CCD output straight line 7,
ΔG and ΔB are obtained, and one CC is calculated from the average value ΔAV of the differences.
The D characteristic curve 6 may be created, the correction curve 8 corresponding thereto may be determined, and tone correction may be performed for each color using the correction curve 8 calculated in this manner.

[0044]

According to the present invention, the following effects can be expected.

An original image is irradiated with light from an LED, a fluorescent lamp, or the like, and the reflected light or transmitted light is used as a photoelectric conversion device.
In an image input device that reads an image as image data by converting it into an electric signal by receiving light by a CCD, in order to perform high-quality image reading, it is desirable that the output voltage range of the CCD used for image reading be large. However, in a region where the output voltage is large, the relationship between the intensity of light incident on the CCD and the output voltage shows a non-linear characteristic, and there is a problem that it cannot be used for image reading.

Also, since the non-linear characteristics of the CCD have individual differences for each CCD, and even the same CCD changes with time, even if the same image is read, the same image is read in different colors for each image input device. There has been a problem that the same image input device may not always read an image in the same color.

According to the present invention, it is used for image reading.
Provided is an image input device that can use a region where the output voltage range of the CCD is as large as possible and correct the nonlinear characteristics of the CCD included in this region by gradation correction so that high-quality and stable image reading can be performed. Will be able to do it.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of the present invention.

FIG. 2 is an output voltage characteristic diagram of a CCD when the light amount is changed.

FIG. 3 is an explanatory diagram of a correction curve for a CCD characteristic curve.

FIG. 4 is an explanatory diagram of a method for determining a correction curve for a predetermined effective range.

FIG. 5 is an explanatory diagram of a method of obtaining an effective range from white memory and black memory and determining a correction curve.

FIG. 6 is an explanatory diagram of a method of determining a correction curve from an average value of differences between colors.

FIG. 7 is an explanatory diagram of a change state of a white stored value and a black stored value in a main scanning direction.

FIG. 8 is an output voltage characteristic diagram of a CCD.

[Explanation of symbols]

1: CCD exposure time control unit 2: CCD characteristic curve and correction curve generator 3: Image reading unit 4: Image correction execution unit 5: Image data storage 6: CCD characteristic curve 7: CCD output straight line after correction 8: Correction curve 9: Effective minimum output value 10: Effective maximum output value 11: Black memory value 12: White memory value

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H04N 1/19 H04N 1/04 103E (72) Inventor Yusuke Nakajima 98 Address No. 2 PFU Co., Ltd. (72) Inventor Masahiko Kobox 98 Uno-Ku, Unoki-cho, Kawakita-gun, Ishikawa Pref. F-term in PFU Co., Ltd. CA12 CA16 CB08 CB12 CB16 CC01 CE11 CH07 CH08 5C051 AA01 BA03 DA03 DB01 DB07 DE11 EA01 5C072 AA01 BA20 EA05 FB19 RA15 UA17 5C077 LL04 MM03 MP01 PP15 PP43 PQ08 PQ12 PQ23 SS01 TT06

Claims (5)

[Claims] An image input device that reads image data by irradiating light on a document image and receiving reflected light or transmitted light with a photoelectric conversion device such as a CCD, thereby controlling the exposure time of the CCD. A means for creating a CCD characteristic curve by measuring the output value of the CCD with respect to the exposure time changed twice or more at every reading, at power-on, or every elapse of a certain time, and using the CCD characteristic curve to generate a CCD characteristic curve. Means for correcting the output value of the image input device. 2. An image input device for reading image data by irradiating an original image with light and receiving reflected light or transmitted light by a photoelectric conversion device such as a CCD. As means for correcting the output from the predetermined effective minimum output value, determine the effective range from the effective maximum output value, create a correction curve for the effective range portion of the CCD characteristic curve, and correct the output, 2. The image input device according to claim 1, wherein: 3. An image input device for reading image data by irradiating a document image with light and receiving reflected light or transmitted light thereof by a photoelectric conversion device such as a CCD. As means for correcting the output from, the average values of the white storage value and the black storage value in the reading range (main scanning direction) are set to white storage value and black storage value, respectively, and the white storage value and the black storage value are used. 2. The image input device according to claim 1, wherein a range is determined, a correction curve for an effective range portion of the CCD characteristic curve is created, and an output is corrected. 4. A color image having two or more color signals in an image input device for reading image data by irradiating an original image with light and receiving the reflected light or transmitted light with a photoelectric conversion device such as a CCD. In the case of an input device, as a means for correcting the output from the CCD using the CCD characteristic curve, a correction curve is created for each color from the CCD characteristic curve for each color, and the correction curve for each color is used for each color. The image input device according to any one of claims 1 to 3, wherein an output is corrected by using the image input device. 5. A color image having two or more color signals in an image input device for reading image data by irradiating an original image with light and receiving reflected light or transmitted light by a photoelectric conversion device such as a CCD. In the case of the input device, as a means for correcting the output from the CCD using the CCD characteristic curve, a corrected CCD output line is created from the CCD characteristic curve of each color, and a difference from the corrected value is calculated. Generating a CCD characteristic curve based on the average value of the differences between the colors, calculating a correction curve for the CCD characteristic curve, and correcting the output for each color using the correction curve. Item 4. The image input device according to any one of Items 1 to 3.