JPH02218267A - Shading correction circuit - Google Patents

Abstract

PURPOSE:To prevent deterioration in picture quality in advance by using a normal reference white level signal stored in advance as a reference potential in the case of A/D conversion of an original picture signal when a shape of the reference white level signal is discriminated and there is any error. CONSTITUTION:A white level data by one line is read from an original set part having a uniform white level by an image sensor 1 and a reference white level signal amplified to a prescribed level is inputted to a reference white level signal A/D conversion circuit 4 by using an amplifier 3. Then a data from a memory 5 is read by a white level signal state discrimination circuit 6, and whether or not there is any error in the shape of the reference white level signal dut to dirt or the like is discriminated and when the presence of an error is discriminated, a control section 7 applies control to a selector 9 so that a data from a reference white level signal data storage section 8 is inputted a reference white level signal D/A conversion circuit 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a shading correction circuit for image signals in an image reading device.

2. Description of the Related Art Conventionally, in an image reading device, an original to be read is illuminated by illumination means such as a fluorescent lamp, and the original to be read is scanned by a line-shaped solid-state image sensor to obtain an image signal. Shading occurs due to the non-uniformity of the lens and the characteristics of the lens. Therefore, as shown in FIG. 3, before reading the original 21, the illuminating means 18 illuminates the original setting section 17 having a uniform white color, and the illuminating means 18 projects the image onto the image sensor 21 through the lens 19. 4
An image signal (shading waveform 22) of the document separator 17 having a uniform white color as shown in the figure is obtained, and the slice level 2 is set using this shading waveform 22 as a reference potential.
3, and performs shading correction on the original image signal 24 at the same time as A/D conversion. 5, the shading waveform 25 changes as shown in FIG. The slice level 26 also changes. Therefore, for example, when the original image signal 24 is binarized using the slice level 26, due to the movement of the slice level 26 toward the black side due to the shadow of the original, the portion that should originally be extracted as black becomes white. This poses a problem in that image quality deteriorates.

Furthermore, when the original image signal is multi-valued using multiple slice levels, the same problem arises in that the density value of areas with shadows or dirt on the original is lower than other parts, leading to deterioration of image quality. .

The present invention has been made in view of the above-mentioned conventional situation,
Therefore, an object of the present invention is to provide a novel shading correction circuit that makes it possible to solve the above-mentioned problems inherent in the conventional technology. The shading correction circuit according to the present invention reads in advance a reference white signal from a document setting section that has uniform white in the read area before setting the document, and automatically corrects shading using that signal. The reading device includes a white signal state determination circuit that determines the state of the image signal obtained from the document setting section that provides a reference white signal immediately before reading the original to be read, and a circuit that determines the state of the image signal obtained from the document setting section that applies a reference white signal immediately before reading the original to be read, and a circuit that judges the data of the reference white signal for shading correction. A storage means is stored in advance, and data of a reference white signal obtained immediately before reading the document is used as a reference white signal during shading correction according to the output state of the white signal state determination circuit, or data is stored in the storage means. a selector for switching which of the reference white signal data to use, a D/A conversion circuit for converting the reference white signal data into an analog signal, and an analog signal output from the D/A conversion circuit. A converting the original image signal into a digital signal using the reference potential as
/D conversion circuit.

That is, according to the present invention, depending on the state of the reference white signal read before reading the original, it is determined that a part of the original has reached the reading position of the reference white signal, or that there is an abnormality in the shape of the reference white signal due to dirt or the like. In this case, the data of the reference white signal stored in advance in the storage means is reproduced and used as the reference potential during A/D conversion of the original image signal, and the reference white signal before reading the original is normal. When it is determined that this is the case, the document image signal is adaptively digitized using the reference white signal.

Embodiment Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, and is a block diagram of an image signal digitization circuit equipped with a shading correction circuit.

Referring to FIG. 1, the image sensor No. 1 includes a photoelectric conversion section and shift registers 1 to 1 for charge transfer.

Reference numeral 2 denotes a clock pulse generation circuit, which inputs a clock pulse signal of a predetermined frequency to the shift register of the image sensor 1. The signal charges of the shift register of the image sensor 1 are sequentially outputted by the clock pulses.

Reference numeral 3 denotes an amplifier that amplifies a signal output from the shift register of the image sensor 1, that is, a current proportional to a signal charge representing image information corresponding to each pixel of one scanning line, to a predetermined level and outputs the amplified signal.

4 is a reference white signal A/D conversion circuit, which is connected to the output terminal of the amplifier 3 and converts the output signal of the amplifier 3 into a digital signal.

5 is a memory (RA old), which stores the digitized reference white signal output from the reference white signal A/D conversion circuit 4; Based on the state, it is determined whether the reference white signal has an abnormal shape due to dirt or the like, and a signal indicating abnormality or normality is output to the control section 7.

Reference numeral 8 denotes a reference white signal data storage section, which stores data of a reference white signal having a normal shape and not affected by dirt or the like.

Reference numeral 9 denotes a selector which selects either the reference white signal data from the memory 5 or the data from the reference white signal data storage section 8 according to the signal from the control section 7 during A/D conversion of a certain signal of the original image. This allows you to switch whether to use it.

The reference white signal D/A conversion circuit 10 converts the digitized reference white signal output from the selector 9 into an analog signal.

An image signal A/D conversion circuit 11 converts the original image signal into a digital signal 12 using the analog signal output from the reference white signal D/A conversion circuit 10 as a reference potential.

The operation of the shading correction circuit having the above-mentioned configuration will be described below.
A reference white signal amplified to a predetermined level using an amplifier 3 is input to a reference white signal A/D conversion circuit 4. Here, the reference white signal is converted from an analog signal to a digital signal and stored in the memory 5.

Next, the white signal state determining circuit 6 reads the data from the memory 5, determines whether the reference white signal has an abnormal shape due to dirt, etc., and inputs the information to the control section 7.

At this time, if it is determined that there is an abnormality in the shape of the reference white signal, for example in the case of the shading waveform 14 in FIG. Control is performed to switch the input signal to the D/A conversion circuit 10.

Thereafter, the data from the reference white signal data storage section 8 is converted from a digital signal to an analog signal by the reference white signal D/A conversion circuit, thereby reproducing the reference white signal (reproducing shading waveform 15). This converts a certain signal of a manuscript image inputted to an image signal A/D conversion circuit 11 into a digital signal 1.
It is used as a reference potential when converting to 2. In FIG. 2, for example, a slice level 16 is generated from a reproduced shading waveform 15 as a dark value during binarization.

Further, when the reference white signal obtained from the document setting section having a uniform white color is determined to be normal, a selector is selected so that the data from the memory 5 or the reference white signal is input to the reference white signal D/A conversion circuit 1 ( ). 9. In the following process, as described above, the data from the memory 5 is reproduced as a reference white signal by the reference white signal D/A conversion circuit 11]I, and the original image signal is converted to the image signal A/D conversion circuit. 11 performs A/D conversion and outputs a digital signal 12.

Effects of the Invention As described in detail above, according to the present invention, the illumination means illuminates a uniform white surface that serves as a reference white for shading correction at the document reading position, and the solid-state image sensor illuminates the uniform white surface at the document reading position. Obtain a reading reference white signal, judge the shape of this reference white signal, and if there is an abnormality, use a previously memorized normal reference white signal as A of the original image signal.
By using it as a reference potential during /D conversion, deterioration of image quality can be prevented.

Furthermore, when the read reference white signal is determined to be normal, optimal shading correction can be performed by using the reference white signal as a reference potential during A/D conversion.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of an image signal digitization circuit equipped with a shading correction circuit according to the present invention.
Fig. 2 is an explanatory diagram of an example of the operation of this circuit when the shading waveform is abnormal, Fig. 3 is an explanatory diagram of the structure of the image reading mechanism, and Fig. 4 is an explanatory diagram of the generation of the shading waveform and slice level. , FIG. 5 is an explanatory diagram of slice level generation when the shading waveform is abnormal. 1. Image sensor, 2. Pulse generation circuit, 3.
...Amplifier, 4...Reference white signal A/D conversion circuit, 5.
...Memory, 6.White signal state judgment circuit, 7 Control section,
8. Reference white signal data storage section, 9. Selector, 11]
Reference white signal D/A conversion circuit, 11... Image signal A/D conversion circuit, 12... Digital signal, 13. Black level, 1
4・]0

Claims (1)

[Claims] Relating to an image reading device that obtains a reference white signal in advance by reading a uniform white surface that serves as a reference for shading correction at a document reading position of the image reading device, and automatically corrects shading using that signal. , a means for determining a white signal state for determining the shape of a reference white signal read before reading a document, a means for storing reference white signal data for shading correction in advance, and a means for determining a reference white signal data from the reference white signal data for shading correction. A means for reproducing a reference white signal and an image signal obtained from a surface having uniform white immediately before reading the original to be read as a reference white signal used for shading correction according to the output state of the white signal state determination circuit; A shading correction circuit comprising means for adaptively switching whether to use an image signal reproduced from data stored in advance in the storage means.