JPH05308519A - Shading correction device - Google Patents

Abstract

PURPOSE:To prevent images from being coarse at the time of overflow. CONSTITUTION:Pixel data for each picture element are outputted through a CCD 1 and a black clamp circuit 4 to a second AGC 5. When it is not overflow, a second AGC 5 does not adjust the gain but outputs the pixel data to an A/D conversion circuit 6. The A/D conversion circuit 6 performs the shading correction processing of the pixel data for each picture element and converts the data for each picture element to digital signals. When the data for each picture element are larger than the white of a reference white original, the A/D conversion circuit 6 judges overflow and outputs an overflow signal to the second AGC 5. The second AGC 5 ignores the overflow signal inputted corresponding to the odd-numbered bits of an image clock and performs control in a direction to decrease the gain for a prescribed amount based on the overflow signal inputted corresponding to the even-numbered bits.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shading correction device provided in an image reading device such as a facsimile device.

[0002]

2. Description of the Related Art For example, in an image reading apparatus such as a facsimile apparatus, a document to be read is illuminated by illumination means such as a fluorescent lamp, reflected light is converted into an analog image signal by a photoelectric conversion element, and this image signal is sent to a receiving apparatus. Is being transmitted. By the way, it is difficult for a light emitting device such as a fluorescent lamp that irradiates a document with light to uniformly irradiate the entire area of one line of the document due to a period of use, environmental temperature, and the like, and each light receiving element of the photoelectric conversion element. Shading occurs in which the amount of received light is non-uniform because it is difficult to manufacture the same with the same sensitivity. If the shading occurs, the binarization process cannot be performed accurately, and there is a problem that the image data on the document cannot be read accurately. Therefore, conventionally, a shading correction device having an automatic gain control circuit is provided. This shading correction stores the image data of each pixel when a reference white original is read by the photoelectric conversion element in the storage circuit as the shading distortion data, and when the original is read next, the pixel data of each pixel from the photoelectric conversion element is stored. The automatic gain control circuit performs processing for eliminating the shading distortion on the analog image signal based on the shading distortion data stored in the storage circuit.

[0003]

As described above, in the automatic gain control circuit, at the time of shading correction, the gain of the signal output from the photoelectric conversion element is corrected by the pixel based on the shading distortion data stored in the storage circuit. However, if an overflow occurs when scanning a white original document that is larger than the reference white original document, the gain adjustment is performed for each bit of the image clock in which the overflow occurs, so there is a reaction. There was a problem that the image became rough and an effective image could not be obtained because it was too early.

The present invention has been made to solve the above problems, and it is an object of the present invention to provide a shading correction device capable of obtaining an effective image in which the image is not rough even when an overflow occurs. Has a purpose.

[0005]

According to the present invention, there is provided a voltage adjusting means capable of adjusting a voltage of a pixel forming one line of pixel data outputted from a photoelectric conversion element, and each pixel data outputted from the voltage adjusting means. Shading correction is performed on the pixel data, and arithmetic means for determining whether or not the voltage value of each pixel data overflows; and when the arithmetic means determines overflow, the gain of the voltage adjusting means for each predetermined bit of pixel data. The gist is to have a control means for controlling.

[0006]

The control means controls the gain of the voltage adjusting means for each predetermined bit of the pixel data when the arithmetic means determines that it is in the overflow state.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied in a shading correction device for a facsimile machine will be described below with reference to FIG.

A CCD (Charge Cou) as a photoelectric conversion element
pled Device) 1 is an image sensor for reading a document. The sample hold circuit 2 samples and holds the information content of each pixel from the CCD 1. The first automatic gain control circuit (hereinafter referred to as the first AGC) 3 amplifies the voltage by applying a predetermined gain to the signal from the sample hold circuit 2 and outputs a signal having a constant amplitude.
This gain is controlled by the coding circuit 11 described later. or,
In this embodiment, the analog image signal indicating white of one line amplified by the first AGC 3 is composed of 1728 pixels on the width of A4 size paper. Then, each of the 1728 pixels is processed by the first AGC 3. The black clamp circuit 4 performs clamp processing to set the black level of the signal output from the first AGC 3, adds a DC component to the analog image signal, and outputs 1728 pixels which are one line pixel by pixel according to the image clock. ..

A second automatic gain control circuit (hereinafter referred to as a second AGC) 5 as a voltage adjusting means gives a predetermined gain to the analog image signal based on the overflow signal output from the A / D conversion circuit 6. To process. A random access memory (hereinafter referred to as RAM) 7 stores a shading correction value for each pixel corresponding to the shading distortion data. At the time of shading correction, the A / D conversion circuit 6 reads out a shading correction value corresponding to the shading distortion data from the RAM 7 and corrects the shading of pixel data based on the correction value. Then, the A / D conversion circuit 6 as an arithmetic means and a control means converts the data for each pixel after the correction by the second AGC 5 into a multivalued digital signal.

Further, when the data for each pixel is input to the A / D conversion circuit 6, and when the data for that pixel is larger than the white of the reference white original, a second AGC is generated as an overflow.
An overflow signal is output to 5.
When the overflow signal is not input, the second AGC 5 processes the data of one pixel sequentially input to the second AGC 5 without changing the gain. When the overflow signal is input, the second AGC 5 ignores the overflow signal input corresponding to the odd-numbered bit of the image clock, and when the even-numbered overflow signal is continuously input, the gain is changed. Adjust to lower by a predetermined amount.

The RAM 9 stores the pixel data of the line immediately preceding the digital signal output from the A / D conversion circuit 6. An HTP (Half Tone Processor) 8 performs a Laplacian operation based on the data for each pixel output from the A / D conversion circuit 6 and the corresponding pixel data of the pixel data of the previous line stored in the RAM 9. Edge enhancement is performed and the data is output to the line buffer 10 as binarized data. The encoding circuit 11 encodes the image signal from the line buffer 10 and outputs it to a modem (not shown) of the facsimile machine.

The operation of the shading correction device of the facsimile apparatus configured as described above will be described. First, the reference white original is read by the CCD 1 and the CCD 1 outputs an analog image signal indicating white of one line. The information content of each pixel is sent to the first AG via the sample hold circuit 2.
It is input to C3, a predetermined gain is obtained, and it is output from the first AGC 3 to the black clamp circuit 4. The black clamp circuit 4 adds a DC component to the analog image signal and outputs 1728 pixels forming one line pixel by pixel.

The second AGC 5 gives a certain gain to the analog image signal and processes it when reading the reference white original document. A /
The D conversion circuit 6 converts the data for each pixel from the second AGC 5 into a multivalued digital signal. And RAM7
In addition, the correction value for each pixel corresponding to the shading distortion data for each pixel that constitutes one line when the white reference document is read is stored.

Next, when the original to be read is read by the CCD 1, an analog image signal is output from the CCD 1. The information content of each pixel is input to the first AGC 3 via the sample hold circuit 2. The information content of each pixel is the first AG whose gain is adjusted by the encoding circuit 11.
The signal is output from C3 to the black clamp circuit 4. The black clamp circuit 4 adds a DC component to the analog image signal and outputs it to the second AGC 5 pixel by pixel. The second AGC 5 outputs the pixel data for each pixel to the A / D conversion circuit 6 without adjusting its gain in the normal case where it is not overflow.

Further, the A / D conversion circuit 6 reads out the shading correction value of the RAM 7, performs shading correction processing of pixel data for each pixel based on the shading correction value, and further adds data for each pixel. Convert to digital signal of value.

Further, when the data for each pixel is input to the A / D conversion circuit 6, and when the data for that pixel is larger than the white of the reference white original, a second AGC is generated as an overflow.
Output an overflow signal to 5. And the second A
When the overflow signal is input to the GC5, the overflow signal input corresponding to the odd bit of the image clock is ignored, and the second AGC5 is input the overflow signal of the even bit of the image clock continuously. , Adjust to reduce the gain by a predetermined amount.

For example, in FIGS. 2 (a)-(d),
The overflow signal input from the A / D conversion circuit 6 in correspondence with the even bits of the image clock is indicated by "1". In FIG. 2A, when the overflow signal is input to both the 2nd and 4th bits of the image clock, FIG. 2B shows the overflow signal to the 6th and 8th bits of the image clock. If entered,
(C) is the second and fourth bits of the image clock, and 4
When the overflow signal is input to both the 6th bit and the 6th bit in succession, (d) shows the case where the overflow signal is input to both the 4th bit and the 6th bit of the image clock. The AGC 5 controls the gain so as to decrease the gain by a predetermined amount.

The HTP 8 performs a Laplacian operation based on the data for each pixel output as a digital signal from the A / D conversion circuit 6 and the corresponding pixel data of the pixel data of the previous line stored in the RAM 9. Edge enhancement is performed and the data is output to the line buffer 10 as binarized data. The encoding circuit 11 encodes the image signal from the line buffer 10 and outputs it to a modem (not shown) of the facsimile machine.

As described above, when the shading correction apparatus of this embodiment receives the overflow signal from the A / D converter 6, it ignores the overflow signal of the odd bits of the image clock and overflows the even bits of the image clock. Focusing on the signal, the gain of the second AGC 5 is adjusted based on the even-numbered overflow signal. Since the gain of the second AGC 5 is adjusted when the overflow signal for each even bit is continuously input (for example, when the second bit and the fourth bit are both input), the response of the gain adjustment is small. The image does not get rough because it is done.

The present invention is not limited to the above-described embodiment, but is embodied in a shading correction device other than a facsimile device, or paying attention to an overflow signal input for every odd number of bits, the second AGC 5 The gain can be adjusted as desired without departing from the spirit of the present invention.

[0021]

As described above in detail, according to the present invention, when the white document larger than the reference white document is read and an overflow occurs, the gain adjustment of the voltage adjusting means is not performed for each bit, and the overflow occurs. Since the gain is adjusted for each generated predetermined bit, there is an excellent effect that an effective image in which the image is not rough can be obtained.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of a shading correction device embodying the present invention.

FIG. 2 is an explanatory diagram when an overflow signal is input when an overflow occurs.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... CCD as a photoelectric conversion element, 2 ... Sample hold circuit, 3 ... 1st AGC, 5 ... 2nd AGC as a voltage adjustment means, 6 ... A / D conversion circuit as an arithmetic means and a control means, 7 ... RAM, 11 ... Encoding circuit.

Claims (1)

[Claims] 1. A voltage adjusting means capable of adjusting a voltage of a pixel forming one line of pixel data output from a photoelectric conversion element, and a correction for shading each pixel data output from the voltage adjusting means. Comprising: calculating means for judging whether or not the voltage value of each pixel data overflows; and controlling means for controlling the gain of the voltage adjusting means for each predetermined bit of pixel data when the calculating means judges overflow. Shading correction device.