JPH0750755A - Picture reader - Google Patents

Abstract

PURPOSE:To appropriately perform shading correction and to improve picture quality by performing conversion by the characteristic saturating the conversion output for the input in the input area higher than the reference level performing the shading correction. CONSTITUTION:A film 2 is irradiated by a lamp light source 1 and the film picture is read by a CCD color line sensor 4 through a lens 3. An RGB signal being the output of the CCD 4 is inputted to an analog processing circuit 5 and to a gamma conversion circuit 6 and is gamma-converted in an analog signal state. The gamma conversion is performed to expand the dynamic range and the polygonal characteristic to saturate the conversion output for the input in the input area higher than the reference level performing the shading correction. The analog output after the gamma conversion is inputted to the AD converter 7 and to a digital signal processing circuit and is converted into a digital signal, then the shading correction is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device for reading an image using an image sensor such as a CCD line sensor.

[0002]

2. Description of the Related Art In this type of image reading apparatus, C
It is customary to convert an analog output from a CD sensor into a digital signal by using an analog-digital (A / D) converter and perform digital signal processing. As described above, when the A / D converter is used, the density resolution is limited, and in order to optimize the density resolution, the CCD area sensor is used, and the relationship between the input and the output is y = x in the analog signal state. ^An amplifier having a characteristic of ^γ (γ = 0.45) is passed, and then A / D conversion is performed. Further, when the CCD line sensor is used, in particular, in order to correct the variation in the sensitivity of each pixel of the CCD and the shading of the illumination, a constant coefficient is applied to each pixel in a digital signal state after A / D conversion. It has been proposed to perform a multiply operation.

[0003]

However, when the characteristic of the signal processing system of the image data reading device is not linear and has a broken line characteristic in a large input area, the A / D converted data is y = ax + b. Since the linear characteristic as shown is not satisfied, the shading correction by multiplying the constant coefficient as described above causes a correction error and deteriorates the image quality.

This situation will be described with reference to FIGS. 2, 3 and 4. When the CCD output voltage with respect to the main scanning position when a subject of uniform density is read using the CCD line sensor is as shown in FIG. 2 due to the sensitivity of each pixel of the sensor and the variation of the light source. If the CCD output voltage at the x1 position is A and the CCD output voltage at the x2 position is B, and the CCD output voltage A at the x1 position is the target value, the CCD output voltage B at the x2 position is Consider to correct. FIG. 3 shows the relationship between the CCD output voltage (horizontal axis) and the value after A / D conversion (vertical axis). Here, the relationship between the two is set as a straight line y = ax indicated by a solid line. Strictly speaking, the straight line y = ax + b indicated by the broken line is obtained, but if the black level (value b in the formula) with zero light quantity is immediately removed by A / D conversion, a solid line is obtained. 2 and 3, x
In order to correct the pixel level Xx2 of the two points and match it with the level of the point x1, the following calculation may be performed when the corrected level is Yx2.

[0005]

## EQU1 ## Yx2 = (Ad / Bd) × Xx2

On the other hand, as shown in FIG. 4, when the signal processing system of the device has a polygonal line characteristic, shading correction is performed on the upper side of the polygonal line characteristic, that is, A and B in the area of a large CCD output voltage. When this correction processing is performed in the same manner when the CCD output voltage changes to A ′ and B ′, Bd ′ becomes YB′d and A ′ is obtained.
There is a difference from d. Thus, A for input
If the data after D / D conversion does not satisfy the linear characteristics,
An error occurs in shading correction. The present invention has been made in order to solve the above-mentioned problems, and when the signal processing system of the device has a polygonal line characteristic, performs shading correction on data of a low light level below the polygonal line. Thus, it is an object of the present invention to provide an image reading apparatus that can effectively utilize the density resolution of the A / D converter, perform appropriate shading correction, and improve the image quality.

[0007]

In order to achieve the above object, the present invention provides an analog circuit for performing a predetermined conversion process on an output signal from an image sensor in an image reading apparatus for reading an image using the image sensor. And a digital signal processing circuit for converting the output of this analog circuit into a digital signal and performing shading correction processing with the digital signal. The conversion processing in the above analog circuit is performed in an input area larger than a reference level for performing shading correction. The conversion output for the input is saturated with the characteristic.

[0008]

According to the above structure, the analog circuit performs the conversion process with the characteristic that the conversion output for the input is saturated in the input region larger than the reference level for shading correction with respect to the output signal from the image sensor. The signal processing circuit converts the output of the analog circuit into a digital signal and performs shading correction processing.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image reading apparatus according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic block configuration of an image reading apparatus. The film 2 is illuminated by the lamp light source 1, and the film image is read by the CCD color line sensor (hereinafter referred to as CCD) 4 through the lens 3.
The RGB signal output from the CCD 4 is input to the analog processing circuit 5 and the γ conversion circuit 6, and in the state of the analog signal γ
To be converted. This γ conversion is performed in order to expand the dynamic range, and is performed with a polygonal line characteristic in which the converted output with respect to the input is saturated in the input area larger than the reference level for shading correction. The analog output after the γ conversion is input to the A / D converter 7 and the digital signal processing circuit 8, is converted into a digital signal, and is subjected to shading correction processing.

For the above-mentioned reason, as shown in FIG. 5, if the maximum value of the data subjected to the shading correction process does not exceed the break point, that is, the data subjected to the shading correction process is the γ conversion circuit 6. If the level becomes equal to or lower than the break point of the broken line characteristic in, the shading correction error will not occur. Also, if there is an input more than the break point, an error will occur, but by setting the break point higher than usual, the frequency of error occurrence will be reduced, and moreover,
The luminance level that causes an error also rises, and the higher the luminance level, the lower the density resolution of the human eye, and the less noticeable the error.

Further, when the data is in an area above the break point,
A shading error occurs, and the color is originally placed where there is no color, and it is not only noticeable but also unsightly. Therefore, in the region above the break point, the degree of color saturation is reduced (chroma suppress) to reduce the unpleasantness. Further, even if the shading correction is performed only in the low light amount region below the break point and the shading correction is not performed in the region above the break point, the unsightly image quality due to the error occurrence can be eliminated.

[0012]

As described above, according to the present invention, conversion processing is performed with the characteristic that the conversion output with respect to the input is saturated in the input area larger than the reference level for shading correction, and the converted analog data is converted into digital data. Since the shading correction is performed on the image data, the shading correction can be appropriately performed, and the image quality can be improved. Further, the density resolution of the A / D converter can be effectively utilized, which is advantageous in terms of cost.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a characteristic of a CCD output voltage with respect to a main scanning position when a subject having a uniform density is read by using a CCD sensor.

FIG. 3 is a diagram showing a relationship between an A / D value and a CCD output voltage.

FIG. 4 is a diagram showing a relationship between an A / D value and a CCD output voltage when a system characteristic is a broken line.

FIG. 5 is a diagram showing a relationship between an A / D value and a CCD output voltage when a system characteristic is a broken line.

[Explanation of symbols]

 4 CCD 5 analog processing circuit 6 γ conversion circuit 7 A / D converter 8 digital processing circuit

Claims (1)

[Claims] 1. An image reading apparatus for reading an image by using an image sensor, an analog circuit for performing a predetermined conversion process on an output signal from the image sensor, and an output of the analog circuit is converted into a digital signal to obtain a digital signal. A digital signal processing circuit that performs shading correction processing on a signal is provided, and the conversion processing in the analog circuit is performed with the characteristic that the conversion output for the input is saturated in the input area higher than the reference level for performing the shading correction. An image reading device characterized by the above.