JPH0787320A - Image reader - Google Patents

Abstract

PURPOSE:To eliminate the after-images and to improve the picture quality even when a reading sensor having large after-image is used by scanning an original image via the reading sensor and in each prescribed cycle, reading the original image as a digital image and correcting the after-images. CONSTITUTION:The analog picture information received from a reading sensor is scanned by an A/D converter 19 in a prescribed cycle and then quantized into the digital picture information. Then the digital picture information is fetched by an after-image correcting circuit 21 as a signal VL1. Meanwhile, the digital picture information on the precedent line of the output signal VL1 of an original image read by the converter 19 is temporarily stored in a line buffer 20. Then, a digital picture information signal VL2 of the precedent line is transmitted from the buffer 20. The circuit 21 calculates the correction data VH1 including no after-image based on both signals VL1 and VL2 and the after-image rate A of the reading sensor. The data VH1 is turned into the binarization data by a binarizing circuit 22 and output to a system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus for reading an original image data by scanning an original image at a predetermined cycle through a reading sensor, reading it as digital image information, performing image correction, and reading the image data.

[0002]

2. Description of the Related Art Generally, an image reading apparatus for reading original image data scans an original image through a reading sensor at a predetermined cycle and reads it as digital image information. Then, the image is corrected and output.

The image correction is performed by, for example,
JP-A-62-252260 and JP-A-62-252
There is one as shown in Japanese Patent No. 261. JP 62
The one disclosed in Japanese Laid-Open Patent Application No. 252260 has a bumpless filter having a frequency lower than the Nyquist frequency corresponding to the sampling interval of the original image as a center.
By correcting the image read by the line image sensor, the original can be read with high quality and high resolution.

On the other hand, the one disclosed in Japanese Unexamined Patent Publication No. 62-252261 discloses a main scanning mechanism and a sub scanning mechanism by correcting an image with an MTF filter in which the characteristics in the main scanning direction and the sub scanning direction are set independently. This enables image correction that is not affected by the difference in scanning mechanism.

[0005]

However, the circuit configuration of these devices becomes complicated. Further, it is not necessarily suitable for correcting the afterimage phenomenon of CCD as a reading sensor as shown in FIG.

FIG. 6 shows an afterimage phenomenon of a CCD which is a reading sensor. White circle A in FIG. 6 has an afterimage ratio of 0.
% Of the reading sensor, and the black circle B shows the characteristics of the reading sensor with an afterimage ratio of 10%. Although a sensor with an afterimage ratio of 0% does not actually exist, a sensor with an afterimage ratio of about 2 or 3% has been developed.

If a reading sensor having a large afterimage characteristic is used, as shown in FIG. 6, the rise from black to white,
Also, the rising characteristics from white to black deteriorate. Therefore, the MTF characteristic in the sub-scanning direction seems to deteriorate, and the image quality deteriorates.

According to the present invention, an image reading apparatus having an improved image quality is obtained by eliminating the influence of the afterimage.

[0009]

The image reading apparatus of the present invention is an A / D converter for scanning a document image at a predetermined cycle and quantizing it into digital image information, and an A / D converter for reading the image. A line buffer that temporarily stores the digital image information of the previous line of the original image, and the afterimage content based on the digital image information in the same main scanning direction of the previous line of the line buffer and the currently read current line and the afterimage rate of the reading sensor. An afterimage correction circuit for calculating correction data excluding the above and a binarization circuit for converting an output signal of the afterimage correction circuit into binary data.

Then, the afterimage correction circuit calculates the correction data by adding the correction coefficient to the afterimage ratio of the reading sensor.

Further, a reference table of correction values for correcting the afterimage of the digital image information of the current line is provided, and the afterimage correction circuit calculates the correction data using the correction value.

On the other hand, a line buffer for temporarily storing digital image information several lines before the original image read by the A / D converter, digital image information several lines before this line buffer, and the current line currently read. An MTF correction circuit and an edge detection circuit that form a matrix from the digital image information and calculate the correction data by performing an operation in which edges in the sub-scanning direction are easily emphasized are provided.

[0013]

In the image reading apparatus of the present invention, the A / D converter scans the original image at a predetermined cycle to quantize the digital image information, and the digital image of the front line of the original image read by the A / D converter is used. Image information is temporarily stored in the line buffer, and afterimages are corrected by excluding afterimages based on the digital image information in the same main scanning direction of the previous line and the currently read current line of this line buffer and the afterimage ratio of the reading sensor. It is calculated by the correction circuit, and the output signal of this afterimage correction circuit is 2
The binarization circuit converts the data into binary data.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 is a block diagram of an image reading apparatus according to an embodiment of the present invention. The image reading apparatus of the present invention is used, for example, in a document reading section of a facsimile machine. FIG. 2 is a block diagram showing a case in which the image reading apparatus of the present invention is applied to the document reading unit 11 of a facsimile apparatus. The document reading unit 11 of the facsimile apparatus includes an image input unit 12 and an image processing unit 1.
3 and 3.

In FIG. 2, the image input section 12 is composed of a photoelectric conversion element such as a CCD and a driving section for scanning the same, and the image processing section 13 has this image input section 12
The analog image information from is converted into digital information, and shading correction, MTF correction, black and white binarization, etc. are performed. The read image information is output to the recording unit 15 which is an output unit or transmitted via the communication control unit 16 by the CPU 14 which controls the entire system. In addition, it is composed of an operation unit 17 that detects a key input, a memory 18 that is a RAM that functions as a buffer for image information, and the like.

Next, the image reading apparatus of the present invention, as shown in FIG. 1, scans the analog image information from the reading sensor at a predetermined cycle and quantizes it into digital image information, and an A / D converter 19 for quantizing the image information. A line buffer 20 for temporarily storing the digital image information VL2 of the previous line of the original image read by the A / D converter 19, and a digital line in the same main scanning direction of the previous line of the line buffer 20 and the currently read current line. Image information VL2, VL1 and afterimage rate A of reading sensor
An afterimage correction circuit 21 for calculating correction data excluding the afterimage component based on the above, and an output signal VH of the afterimage correction circuit 21.
Binarization circuit 2 for converting 1 into binary data and outputting to the system
2 and.

The analog image information from the reading sensor is first quantized by the A / D converter 19 and taken into the afterimage correcting circuit 21 as a signal VL1. Further, the digital image information VL2 of the previous line is also sequentially read to the line buffer 20 and the afterimage is corrected.

As a correction method, in the image information VL1 and VL2 of the same pixel in the main scanning, the afterimage rate of the reading sensor is set to A.
%, The correction data VH1 after the afterimage correction of VL1 is calculated as follows. By doing this,
It is possible to remove the afterimage.

(1) When VL1> VL2 VH1 = VL1 + A × (VL1-VL2) / 100 (2) When VL1 = VL2 VH1 = VL1 (3) When VL1 <VL2 VH1 = VL1-A × (VL2- VL1) / 100 where VL1: current line digital image information VL2: previous line digital image information A: afterimage ratio (%) VH1: VL1 afterimage correction data

Further, when the correction coefficient β is added to the afterimage rate A of the reading sensor of the equations (1) to (3) for the afterimage correction,
Further, it becomes possible to remove afterimages with high accuracy. The calculation formula for the afterimage correction in this case is shown below.

(4) When VL1> VL2 VH1 = VL1 + A × β × (VL1-VL2) / 100 (5) When VL1 = VL2 VH1 = VL1 (6) When VL1 <VL2 VH1 = VL1-A × β × (VL2-VL1) / 100 where VL1: current line digital image information VL2: previous line digital image information A: afterimage ratio (%) β: correction coefficient VH1: data after afterimage correction of VL1

Next, FIG. 3 shows a reference table 23 in which a correction value C for correcting an afterimage is stored in advance.
When the reference table 23 is provided, the calculation formula of the afterimage correction becomes simple as shown.

(7) When VL1> VL2 VH1 =
VL1 + C (8) When VL1 <VL2 VH1 = VL1-C (9) When VL1 = VL2 VH1 = VL1 However, 63 (white side) ≧ (VL1, VL2) ≧ 0 (black side)

Here, assuming that VL1 and VL2 are quantized image information from the white side to the black side of 63 to 0, for example, when VL1 = 40 and VL2 = 10, | VL1-V
Since L2 | = 30, the correction value C = 3 is obtained from the reference table 23. On the other hand, since VL1> VL2, the equation (7) is applied, and VL1 = 40 + 3 = 43. As a result, the afterimage can be removed.

FIG. 4 is a block diagram showing another embodiment, and FIG. 5 is an explanatory diagram of the matrix circuit 24. In this embodiment, line buffers 20A and 20B for temporarily storing digital image information VA, VB, VC and VD, VE, VF which are several lines before the original image read by the A / D converter 19, respectively, and this line. Buffer 20A, 2
Matrix circuit 24 forming a matrix from digital image information VA, VB, VC and VD, VE, VF of several lines before 0B, and currently read digital image information VG, VH, VI of the current line, and sub-scanning. MT for calculating the correction data by performing a calculation in which the edge in the direction is easily emphasized
An F correction circuit 25 and an edge detection circuit 26 are provided.

FIG. 5 shows a 3 × 3 matrix composed of three quantized pixels of the previous line, the previous line, and the current line. The MTF correction using the reading sensor with a small afterimage adopts the equation (10) shown below, and the MTF correction using the reading sensor with a large afterimage emphasizes the edge in the sub-scanning direction shown below. The effect of the afterimage in the sub-scanning direction is reduced by selecting the easy expression (11).

(10) MTF correction when a sensor with a small afterimage is used VE '= 3 × VE- (VB + VD + VF + VH) × 1/2 (11) MTF correction when a sensor with a large afterimage is used VE' = 3 × VE- (1.2VB + 0.2VD + 0.2VF + 1.8VH) × 1/2 However, 63 (white side) ≧ VB, VD, VE, VF, VH
≧ 0 (black side)

Edge detection using a reading sensor with a small amount of afterimage is performed by using the following formula (12), and edge detection using a reading sensor with a large amount of afterimage is performed in the sub-scanning direction. The influence of the afterimage in the sub-scanning direction is reduced by selecting the following equation (13) that is easy to detect edges.

(12) Edge detection when a sensor with a small afterimage is used: | VE-VB |, | VE-VH | ≧ 16 | VE-VD |, | VE-VF | ≧ 16, VE is black, Other than white. (13) Edge detection when a sensor with many afterimages is used: | VE-VB |, | VE-VH | ≧ 10 | VE-VD |, | VE-VF | ≧ 16, VE is black; .

[0030]

According to the first, second and third aspects of the present invention, since the circuit for correcting the afterimage is provided, it is possible to substantially remove the afterimage even if a reading sensor having a large afterimage is used.
The rise of the output from black to white and the change of the rise from white to black in the sub-scanning direction due to the afterimage are improved, and the image quality is improved. Further, the correction value of the processing to the subsequent processing circuit is not changed at all.

According to the second aspect, since the correction coefficient is added to the correction method according to the first aspect, the afterimage can be corrected accurately, and the correction coefficient can be set according to each actual machine, so that the versatility is high. .

According to the third aspect of the present invention, the reference table is composed of a simple correction reference table for correcting an afterimage and a correction calculation formula. Therefore, the circuit configuration is simplified, and the reference table can be changed according to each actual machine. There is redundancy because it can be set.

According to claims 4 and 5, M in the binarization circuit is
In the TF correction and the edge detection, an algorithm for emphasizing the edge portion in the sub-scanning direction is used for the reading sensor having a large afterimage, so that the output rises from black to white in the subscanning direction due to the afterimage, and The change in rising from white to black is improved and the image quality is improved.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an image reading apparatus that is an embodiment of the present invention.

FIG. 2 is a block configuration diagram when the image reading apparatus of the present invention is applied to a document reading unit of a facsimile apparatus.

FIG. 3 is an explanatory diagram of a reference table of the present invention.

FIG. 4 is a block diagram showing another embodiment of the present invention.

FIG. 5 is an explanatory diagram of a matrix circuit of the present invention.

FIG. 6 is an explanatory diagram of an afterimage phenomenon of a reading sensor.

[Explanation of symbols]

 11 reading unit 12 image input unit 13 image processing unit 14 CPU 15 recording unit 16 communication control unit 17 operation unit 18 memory 19 A / D converter 20 line buffer 21 afterimage correction circuit 22 binarization circuit 23 reference table 24 matrix circuit 25 MTF correction circuit 26 Edge detection circuit

Claims (5)

[Claims] 1. An image reading apparatus which scans an original image at a predetermined cycle through a reading sensor to read digital image information as digital image information to read the original image data, and scans the original image at a predetermined cycle. An A / D converter for quantizing digital image information, a line buffer for temporarily storing the digital image information of the previous line of the original image read by the A / D converter, the previous line of this line buffer and the current line An afterimage correction circuit for calculating correction data excluding an afterimage based on the read digital image information of the same main scanning direction of the current line and the afterimage ratio of the reading sensor, and an output signal of the afterimage correction circuit is binarized. An image reading device comprising a binarizing circuit for converting data. 2. The image reading apparatus according to claim 1, wherein the afterimage correction circuit calculates correction data by adding a correction coefficient to an afterimage rate of the reading sensor. 3. A reference table of correction values for correcting an afterimage of the digital image information of the current line is provided, and the afterimage correction circuit calculates the correction data using the correction value. 1. The image reading device described in 1. 4. A line buffer for temporarily storing digital image information several lines before the original image read by the A / D converter, and digital image information several lines before this line buffer. The image reading apparatus according to claim 1, further comprising an MTF correction circuit that forms a matrix from the digital image information of the current line and performs a calculation for easily enhancing an edge in the sub-scanning direction to calculate correction data. 5. A line buffer for temporarily storing digital image information several lines before the original image read by the A / D converter, and digital image information several lines before this line buffer. 2. The image reading apparatus according to claim 1, further comprising an edge detection circuit that forms a matrix from the digital image information of the current line and performs a calculation for easily enhancing an edge in the sub-scanning direction to calculate correction data.