JPH05103194A - Picture input device - Google Patents

Abstract

PURPOSE:To enable the picture input with the uniform half tone by providing an A/D converter with the intermediate reference voltage and setting the intermediate reference voltage to the output voltage of each light receiving element for grey document in a memory. CONSTITUTION:The output voltage of each light receiving element of an image sensor 1 for white original and grey original is stored in a white memory 3 and an grey memory 4. The memory 3 is read out by an address generator 2, and supplied to the upper-limit reference voltage Vrh through a white D/A converter 5. Similarly, the intermediate reference voltage Vrm from the memory 4 is supplied through an grey D/A converter 6. The converter 7 inputs a picture input signal Vin of the image sensor 1, which is A/D converted among the upper-limit reference voltage, the intermediate reference voltage, and the ground voltage for each light receiving element. Thus, the correction output for the grey original is uniformed even when the linearity of each light receiving element differs, enabling the uniform half tone picture input.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image input device used in facsimiles, copying machines and the like.

[0002]

2. Description of the Related Art In recent years, an image input device is required to have a uniform output from each light receiving element of an image sensor at each reflectance due to the demand for sharpening and multi-gradation of facsimiles and copying machines. There is. The output voltage of each light receiving element of the image sensor is

[0003]

[Equation 1]

It is represented by Where Vo (n) is the output voltage of the n-th light receiving element, A is a constant, E is the exposure dose, γ (n)
Indicates the linearity of the n-th light receiving element.

On the other hand, the output voltage of each light receiving element does not become a uniform output voltage even for a white original document having a uniform reflectance due to variations in the light receiving elements, variations in the light source, variations in the lens, and the like. Shading correction is performed to correct such variations. Shading correction is

[0006]

[Equation 2]

It is represented by Here, Vo ′ (n) is the output of the n-th light receiving element after shading correction, Vl
(N) is the output voltage of each light receiving element for a white original, and K is a constant, which is 255 in the case of 8-bit processing. If the nth pixel is a white document, Vo (n) = Vl (n), and the output after shading correction is 255, which is an output for a white document. By doing so, the output voltage of each light receiving element with respect to the white original can be made uniform.

An example of a conventional image input device will be described below with reference to the drawings. FIG. 5 shows the configuration of a conventional image input device. In FIG. 5, 1 is an image sensor, 2 is an address generator, 3 is a white memory, 5 is a white DA converter, 7 is an AD converter, and 8 is an output terminal.

The operation of the image input device configured as described above will be described below.

First, the image sensor 1 having a plurality of light receiving elements is sequentially driven by a synchronizing signal from the outside, and analog image signals of the respective light receiving elements of the image sensor 1 are sequentially output. On the other hand, before the image input is started, the output voltage of each light receiving element for the white original is stored in the white memory 3 in advance. The digital signal stored in the white memory 3 is read by the address generator 2 corresponding to each light receiving element,
The white DA converter 5 restores the analog signal for the white original of each light receiving element, and the upper limit reference voltage Vrh of the AD converter 7 is returned.
Is entered as. The analog image signal from the image sensor 1 is converted from analog to digital on the basis of the upper limit reference voltage Vrh and output from the output terminal 8. In this case, if the image input result is the same as the data stored in the white memory, that is, if the input image is white, the result of the shading correction is K, indicating that the document is a white document. In this way, shading correction for a white original can be performed.

(Japanese Patent Laid-Open No. 60-81977) In the following description, the reflectance of a white original document is set to 100%. FIG. 6 shows the corrected output of each light receiving element having various γ of the image sensor. In FIG. 6, a white original, that is, a reflectance of 1
The output for 00% is the same for each light receiving element, but the output of each light receiving element is not the same when the gray original, that is, the reflectance is between 0% and 100%. FIG. 7 shows the corrected output difference between the case where γ is 1 and the case where γ is not 1 at each reflectance. FIG. 8 shows outputs before and after correction of all light receiving elements of the image sensor. When the γ value of each light receiving element of the image sensor is different, the output for the white original is uniform, but the output for the gray original is not uniform. In particular, the output difference becomes large when the reflectance is between 20% and 50%. The cause is described below. The output of the light receiving element is convex with respect to the reflectance when γ is smaller than 1, and is concave with respect to the reflectance when γ is larger than 1. Therefore, as shown in (Equation 2), if the proportional calculation is simply performed on the output for the white original, the output difference for the gray original when γ is 1 and when γ is not 1 is γ.
When γ is smaller than 1, an error in the positive direction appears, and when γ is larger than 1, an error in the negative direction appears.

[0012]

However, in the above-mentioned structure, when the linearity with respect to the document reflectance of each light receiving element is different, the corrected output for the white original becomes uniform, but the corrected output for the gray original does not. There is a problem in that it is not uniform and uniform halftone images cannot be input.

In view of the above-mentioned problems, the present invention provides an image input device capable of uniforming a corrected output for a gray original even when the linearity of each light receiving element is different and inputting a uniform halftone image. is there.

[0014]

In order to solve the above problems, an image input device of the present invention is an image sensor having a plurality of light receiving elements, and each light receiving element of the image sensor for a white original and a gray original. A memory for storing the output voltage of the memory, a DA converter for converting each data in the memory into an analog signal, an address generator for reading out the data in the memory corresponding to each light receiving element of the image sensor, and an upper reference voltage. And an AD converter having an intermediate reference voltage between the ground voltage and the ground voltage, the upper limit reference voltage of the AD converter being the output voltage of each light receiving element for the white document in the memory, and the intermediate reference voltage being the gray in the memory. The output voltage of each light receiving element with respect to the original is set.

[0015]

According to the present invention, both the output voltage of each light receiving element with respect to a gray original and the output voltage of each light receiving element with respect to a white original are corrected by the above-described structure, thereby making a uniform original uniform. Output is obtained, and uniform halftone image input is possible.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image input apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an image input apparatus according to an embodiment of the present invention. In FIG. 1, 1 is an image sensor, 2 is an address generator, 3 is white memory, 4 is gray memory, 5 is a white DA converter, 6 is a gray DA converter, and 7 is A.
D converter, 8 is an output terminal.

The operation of the image input device configured as described above will be described below with reference to FIGS. 1, 2, 3, and 4.

First, the white memory 3 stores the output voltage of each light receiving element of the image sensor 1 for a white original, and the gray memory 4 stores the signal output of each light receiving element of the image sensor 1 for a gray original. In this embodiment, the reflectance of the gray original is 30% of the reflectance of the white original. The upper limit reference voltage Vrh of the AD converter 7 is read from the white memory 3 by the address generator 2 and converted from digital to analog by the white DA converter 5 with respect to the white original of each light receiving element of the image sensor 1. The output voltage, on the other hand, is read as the intermediate reference voltage Vrm of the AD converter 7 from the gray memory 4 by the address generator 2 and converted from digital to analog by the gray DA converter 6 in each light receiving element of the image sensor 1. The output voltage for the gray original is input. The image input signal of the image sensor 1 is input to the AD converter 7, and is converted from analog to digital between the upper limit reference voltage, the intermediate reference voltage and the ground voltage for each light receiving element. When corrected by the above method, when Vo (n) <Vm (n),

[0020]

[Equation 3]

[0021]

[Equation 4]

[0022]

[Equation 5]

It is represented by Here, Vm (n) is the output voltage of each light receiving element for the gray original, Vh (n) is the output voltage of each light receiving element for the white original, and Em is the reflectance of the gray original in the present embodiment, 30%, Eh. Is the reflectance of a white original, which is 1 in this embodiment, and K is a constant, which is 255 in the case of 8-bit processing.

FIG. 2 shows the corrected output of each light receiving element having various γ of the image sensor. In the image input device according to the present embodiment, as shown in (Equation 3), (Equation 4), (Equation 5), when the output of each light receiving element of the image sensor is smaller than the output for the gray original, the gray Shading correction is performed based on the output for the original, and when the output of each light receiving element of the image sensor is larger than the output for the gray original, the output for the gray original and the output for the white original are set as the reference, and the shading correction is performed between them. FIG. 3 shows the output difference between when γ is 1 and when γ is not 1 at each reflectance. In FIG. 3, the corrected output has a reflectance of 0.
%, 30%, and 100%, a constant value is obtained regardless of γ of each light receiving element of the image sensor, and variations in the corrected output are small even in the areas other than the above reflectances. FIG. 4 shows the output characteristics of all the light receiving elements of the image sensor. Even if the γ values of the respective light receiving elements of the image sensor are different, the output for the white original document and the output for the gray original document are uniform, and the outputs are almost uniform for the original documents having other reflectances.

As described above, according to this embodiment, an image sensor having a plurality of light receiving elements, a memory for storing the output voltage of each light receiving element of the image sensor with respect to a white document and a gray document, and the memory. A DA converter for converting each data in the inside into an analog signal, an address generator for reading out data in the memory corresponding to each light receiving element of the image sensor, and an intermediate reference voltage between the upper limit reference voltage and the ground voltage. An AD converter is provided, and the upper limit reference voltage of the AD converter is set to the output voltage of each light receiving element for the white original in the memory, and the intermediate reference voltage is set to the output voltage of each light receiving element for the gray original in the memory. As a result, both the output voltage of each light-receiving element for gray originals and the output voltage of each light-receiving element for white originals are corrected to ensure uniform output. Uniform output can be obtained with respect to paper,
It is possible to input a uniform halftone image.

In the present embodiment, the reflectance of the gray original is set to 30% of the reflectance of the white original, but the gray original may be corrected at a place where the output difference with respect to the gray original is large. The ratio is 20% to 50% of the reflectance of the white manuscript.
It may be between%.

[0027]

As described above, according to the present invention, an image sensor having a plurality of light receiving elements, a memory for storing the output voltage of each light receiving element of the image sensor with respect to a white document and a gray document, and the memory in the memory are provided. A DA converter for converting each data of the above into an analog signal, an address generator for reading out data in the memory corresponding to each light receiving element of the image sensor, and an AD having an intermediate reference voltage between the upper limit reference voltage and the ground voltage. And an upper limit reference voltage of the AD converter is set to the output voltage of each light receiving element for the white original in the memory, and an intermediate reference voltage is set to the output voltage of each light receiving element for the gray original in the memory. By correcting both the output voltage of each light receiving element for gray originals and the output voltage of each light receiving element for white originals, Uniform output is obtained, it is possible to image input uniform halftone.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an image input device according to an embodiment of the present invention.

FIG. 2 is a diagram showing corrected output of a light receiving element of an image sensor using the image input device of the present invention.

FIG. 3 is a diagram showing a corrected output of a light receiving element having a γ of 1 and a corrected output of a light receiving element having a non-γ of an image sensor using the image input device of the present invention.

FIG. 4 is a diagram showing outputs of all light receiving elements of an image sensor after correction using the image input device of the present invention.

FIG. 5 is a configuration diagram of a conventional image input device.

FIG. 6 is a diagram showing corrected output of a light receiving element of an image sensor using a conventional image input device.

FIG. 7 is a diagram showing a difference between a corrected output of a light receiving element having a γ of 1 and a corrected output of a light receiving element having a non-γ of an image sensor using a conventional image input device.

FIG. 8 is a diagram showing outputs of all light receiving elements of an image sensor after correction using a conventional image input device.

[Explanation of symbols]

 1 Image Sensor 2 Address Generator 3 White Memory 4 Gray Memory 5 White DA Converter 6 Gray DA Converter 7 AD Converter 8 Output Terminal

Claims (2)

[Claims] 1. An image sensor having a plurality of light receiving elements, a memory for storing respective output voltages for a white original and a gray original of each light receiving element of the image sensor, and each data in the memory as an analog signal. A D / A converter for converting, an address generator for reading out in-memory data corresponding to each light receiving element of the image sensor, and an A / D converter having an intermediate reference voltage between an upper limit reference voltage and a ground voltage are provided. An image input device, wherein an upper limit reference voltage of the container is set to an output voltage of each light receiving element for a white original in the memory, and an intermediate reference voltage is set to an output voltage of each light receiving element for a gray original in the memory. 2. The reflectance of the gray original is 20% of the reflectance of the white original.
The image input device according to claim 1, wherein the image input device is set in a range from 1 to 50%.