JPH0365874A - Photoelectric converter - Google Patents

Abstract

PURPOSE:To obtain a proper output without deteriorating gradation resolution at a dark density by storing output information at a dark output of each picture element of an image sensor to a memory in advance, reading output information at a dark output from the memory in a relevant picture element to correct the signal obtained from the image sensor at actual original read. CONSTITUTION:Information resulting from digitizing a dark output corresponding to each picture element of a line image sensor 11 is stored in a RAM 15. At the read of an original 21, in the timing when an output signal of i-th picture element obtained by the line image sensor 11 is held in an S/H circuit 12, the information corresponding to the i-th picture element is read and supplied to a D/A converter 16, where the signal is converted into an analog signal. Thus, the dark output signal of the same picture element as that of the signal obtained at present in the i-th picture element is supplied to a differential amplifier 17 and a signal subject to differentiation is obtained at an output terminal 22. Thus, the actual output of each picture element is corrected by the dark output of its own picture element and the gradation resolution at a dark density is increased.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention relates to a photoelectric conversion unit that can be used as a photoelectric conversion unit in various devices equipped with an image sensor, such as facsimile machines and electronic copying machines. It is related to the device.

(Prior art) Conventional devices of this kind have converted the output of the image sensor into binary values, but in recent years, devices that read documents with gradations like photographs and output multi-valued information have become available. It's starting to appear. Here, in the conventional photoelectric conversion device, the CCD
When reading using a line image sensor, the black level is adjusted using the output of a light shield side cable provided in the CCD line image sensor.

However, since each pixel of a CCD line image sensor has variations in dark output characteristics, if correction is performed using the dark output of a specific pixel as described above, the gradation resolution will deteriorate in areas with high density, There was a problem in that when reading a manuscript containing photographs, etc., the spread would be collapsed.

(Problems to be Solved by the Invention) As described above, in the conventional photoelectric conversion device, the output of all pixels is corrected using the output of the light shield pixel.
Since the dark output characteristics of each pixel are not considered, there is a problem in that the gradation resolution deteriorates in areas with high density, and when reading originals containing photographs, etc., the spreads are distorted.

The present invention was made to solve these problems, and its purpose is to prevent the gradation resolution from deteriorating in areas with high density, and to maintain the same spread even when reading originals with gradations such as photographs. It is an object of the present invention to provide a photoelectric conversion device that can obtain an appropriate output without collapsing.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides an image sensor that photoelectrically converts light emitted from a light source and reflected from a document, and an output of each pixel of this image sensor during no light. a memory in which information is stored; a correction circuit that corrects the input signal of 1 using the input signal of the pond; and a correction circuit that cuts off the reflected light at a predetermined time to obtain an output signal of each pixel of the image sensor and outputs the output information to the memory. and a control circuit that corrects the signal obtained from the image sensor when reading a document by the correction circuit using a signal based on output information in the memory corresponding to the pixel from which this signal is obtained, thereby obtaining a correction output. A photoelectric conversion device was constructed.

(Function) According to the above configuration, the output information at the time of dark output for each pixel of the image sensor is stored in advance in the memory, and when the actual document is read, the signal obtained from the image sensor is used as the output information at the time of dark output of the corresponding pixel. Since it is read out from the memory and corrected, accurate correction can be performed even if there is variation in dark output from pixel to pixel.

(Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The figure is a block diagram of an embodiment of the present invention.

In the figure, 18 indicates a light source, for example a fluorescent lamp. Reference numeral 11 indicates a line image sensor, and conveyance roller 19
The light source 1 reflected by the original 21 transported by
8 (reflected light from the original 21) is photoelectrically converted, and the output signal of each pixel is sent to the sampling and hold (S/H) circuit 1.
Give to 2. Although not shown, an optical system for focusing the reflected light from the original 21 onto each pixel of the line image sensor 11 is provided. The output signal of the line image sensor 11 is sampled and held by the S/H circuit 12. The signal sampled and held by the S/H circuit 12 is digitized by the A/D converter 13 and is also provided to the differential amplifier 17.

The signal digitized by the A/D converter 13 is temporarily held in the latch 14 and stored in the RAM 15 corresponding to each pixel of the line image sensor 11. Reference numeral 20 denotes a control circuit, which controls the output timing of the image signal from the line image sensor 11, controls the sampling and holding timing in the S/H cycle, controls the timing in the A/D converter 13, and controls the latch timing in the latch 14. control, data read/write control for the RAM 15, timing control for the D/A converter 16, drive control for the light source 18 and the conveyance roller 19, etc. The information corresponding to the pixels of the line image sensor 11 successively outputted by the control circuit 20 is converted back into an analog signal by the D/A converter 16 and applied to the input terminal of the differential amplifier 17 .

The differential amplifier 17 amplifies the difference between the signal held in the S/H circuit 12 and the output signal of the D/A converter 16 and outputs it to the output terminal 22.

In a photoelectric conversion device having such a configuration, the following operations are performed to remove inappropriate multilevel output signals due to variations in dark output of each pixel.

For example, at the initialization of power-on, the control circuit 20 controls the light source 18.
is off (no irradiation light), line image sensor 1
1, the output of each pixel is taken out sequentially, and the S/H circuit 1
2. The data is stored in the RAM 15 via the A/D converter 13, latch 14, and RAM 15 route. As a result, information obtained by digitizing the dark output corresponding to each pixel of the line image sensor 11 is stored in the RAM 15.

Next, when reading the original 21, the light source 18, the transport roller 1
9 is turned on, and the output signal of the i-th pixel obtained by the line image sensor 11 is sent to the S/H circuit 1.
2, the i-th data is stored from the RAM 15.
The information corresponding to the pixel located at the th pixel is successively outputted and supplied to the D/A converter 16 to be converted into analog data. As a result, the differential amplifier 17 is given the signal currently obtained at the i-th pixel and the dark output signal of the same pixel, and a signal obtained by taking the difference is obtained at the output terminal 22. "i" corresponds to each pixel of the line image sensor 11 (for example, "0" to "o-n>")
If the above operation is performed with the value changed to "n", the actual output of each pixel is corrected by the dark output of the white pixel, and the gradation resolution can be increased in areas with high density. Therefore, even when reading a multi-gradation document such as a photograph, it is possible to eliminate the drawback that the spread is blurred.

[Effects of the Invention] As explained above, according to the present invention, the output information at the time of dark output for each pixel of the image sensor is stored in advance in the memory, and the signal obtained from the image sensor is used to correspond to the signal obtained from the image sensor during actual document reading. Since the output information at the time of dark output of the pixel is read out from the memory and corrected, accurate correction can be performed even if there is variation in the dark output from pixel to pixel. Therefore, the gradation resolution does not deteriorate in areas with high density, and even when reading a document with gradation such as a photograph, the spread does not collapse, and an appropriate output can be obtained.

[Brief explanation of drawings]

The figure is a block diagram of one embodiment of the present invention.

Claims (1)

[Scope of Claims] An image sensor that photoelectrically converts light emitted from a light source and reflected from a document; a memory that stores output information of each pixel of the image sensor when there is no light; and one input signal. a correction circuit that corrects the output signal using another input signal; a control circuit for correcting a signal obtained by the correction circuit using a signal based on output information in the memory corresponding to a pixel from which the signal is obtained, thereby obtaining a correction output.