JPH07177321A - Picture reader - Google Patents

Abstract

PURPOSE:To faithfully generate a picture signal with resolution higher than the arrangement density of photoelectric conversion elements in a read picture while suppressing the arrangement density of the photoelectric conversion elements to a low value and preventing the increment of cost. CONSTITUTION:A resolution converting part 4 executes processing for determining respective density levels of two picture elements corresponding to a photoelectrically converted picture element of interest based upon the level of a prescribed picture element signal of interest corresponding to an output from an optional photoelectric conversion element of interest and the levels of prescribed adjacent picture element signals corresponding to respective outputs from two adjacent photoelectric conversion elements arranged on both sides of the element of interest by using each of many photoelectric conversion elements as a photoelectric conversion element of interest.

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 which is applied to a facsimile apparatus, an image scanner apparatus or the like and which generates an image signal corresponding to a document.

[0002]

2. Description of the Related Art In general, an image reading apparatus of this type forms a reflected light image from a document when the light emitted from a light source is applied to the document on a CCD linear image sensor, and the CCD linear image sensor corresponds to the image. It is for generating an electric signal.

A CCD linear image sensor has a large number of photoelectric conversion elements arranged in a line at equal intervals on a substrate, and outputs an electric signal in which outputs of the photoelectric conversion elements are serially connected. The output of the CCD linear image sensor is an analog signal, but since a binary image is generally handled in a facsimile machine or the like, the output of each photoelectric conversion element is binarized into either white or black with a predetermined threshold value to generate an image signal. To generate.

Therefore, in the conventional image reading apparatus, the resolution is determined by the arrangement density of photoelectric conversion elements. That is, when the photoelectric conversion elements are arranged at a density of 8 pieces / mm, the maximum resolution is 8 pixels / mm.

Therefore, in order to obtain a higher resolution, it is necessary to use a CCD linear image sensor having a high arrangement density of photoelectric conversion elements. However, the CCD linear image sensor in which the photoelectric conversion elements are arranged at a high density as described above becomes expensive because the number of required elements increases and the manufacturing becomes difficult.

[0006]

As described above, the conventional image reading apparatus has a problem that the apparatus cost increases if the arrangement density of photoelectric conversion elements is increased to realize reading at high resolution. It was

The present invention has been made in view of the above circumstances, and an object thereof is to suppress the increase in cost by suppressing the arrangement density of photoelectric conversion elements to a low level and to increase the cost of photoelectric conversion elements. It is an object of the present invention to provide an image reading device capable of faithfully generating an image signal having a resolution higher than the arrangement density of the read image.

[0008]

In order to achieve the above object, the present invention uses, for example, a determination unit such as a resolution conversion unit to determine the level of a predetermined pixel signal of interest corresponding to the output of an arbitrary photoelectric conversion element of interest and the level of the pixel signal of interest. Based on the level of a predetermined adjacent pixel signal corresponding to the output of each of the two adjacent photoelectric conversion elements located on both sides of the target photoelectric conversion element, the density levels of the two pixels corresponding to the target photoelectric conversion pixel are determined. The determination process is performed by using each of the large number of photoelectric conversion elements as the photoelectric conversion element of interest.

[0009]

By taking such a measure, for each output of a large number of photoelectric conversion elements, the level of a predetermined pixel signal of interest corresponding to the output and the two photoelectric conversion elements located on both sides of the photoelectric conversion element of interest are located. Two pixels are determined based on the level of a predetermined adjacent pixel signal corresponding to the output of each of the two adjacent photoelectric conversion elements. Therefore, the number of pixels is doubled and the resolution is doubled.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the main configuration of the image reading apparatus according to this embodiment. The image reading apparatus includes a photoelectric conversion unit 1, an A / D conversion unit 2, an image correction unit 3, a resolution conversion unit 4, and a binarization unit 5.

The photoelectric conversion unit 1 has a CCD linear image sensor including a large number of photoelectric conversion elements arranged at a density of 8 pieces / mm. The photoelectric conversion unit 1 irradiates a document with light and converts the reflected light into an analog electric signal. Then, the photoelectric conversion unit 1 converts the analog electric signal into the A / D conversion unit 2
Give to.

The A / D converter 2 digitizes the analog electric signal supplied from the photoelectric converter 1 to generate multi-valued image data. Then, the A / D conversion unit 2 gives the multivalued image data to the image correction unit 3.

The image correction unit 3 has a partial variation in the light amount of the light source used in the photoelectric conversion unit 1 with respect to the multi-valued image data given from the A / D conversion unit 2 and a light source used in the photoelectric conversion unit 1. Processing for correcting changes in the light amount over time, reading characteristics peculiar to the CCD linear image sensor, and the like are performed. Then, the image correction unit 3 gives the processed multivalued image data to the resolution conversion unit 4.

The resolution conversion unit 4 has a multi-valued buffer 41, a comparison circuit 42 and an arithmetic circuit 43. The multi-valued buffer 41 extracts and holds data for three consecutive pixels in the main scanning direction from the multi-valued image data supplied from the image correction unit 3. The comparison circuit 42 determines the state of the central pixel (target pixel) of the three pixels based on the density levels of the three pixels whose data is held in the multi-valued buffer 41. The arithmetic circuit 43 determines the respective density levels of the two pixels corresponding to the target pixel based on the respective density levels of the three pixels whose data are held in the multi-valued buffer 41 and the discrimination result of the comparison circuit 42. . The arithmetic circuit 43 determines the density levels of two pixels for each pixel included in the multi-valued image data, and supplies the binarization unit 5 with data representing the density level of each pixel in multi-valued order.

The binarization unit 5 binarizes the multivalued data supplied from the arithmetic circuit 43 of the resolution conversion unit 4 with a predetermined threshold value to generate a binary image signal. Next, the operation of the image reading apparatus configured as described above will be described.

First, a large number of photoelectric conversion elements constituting the CCD linear image sensor of the photoelectric conversion unit 1 output an electric signal at a level corresponding to an integrated value of the amount of light incident on a certain unit area in a unit time. The CCD linear image sensor as a whole produces and outputs an analog electric signal by serially outputting the output of each photoelectric conversion element.

By the way, the amount of reflected light from the original is the maximum amount of reflected light from the white region, and conversely is the minimum amount of reflected light from the black region. Therefore, as shown in FIG. 2, the photoelectric conversion element 1 that receives the reflected light from the white area in the entire light receiving area
The output level of 1a becomes the maximum density level (here, level 32) indicating "white", and the output level of the photoelectric conversion element 11b receiving the reflected light from the black region in the entire light receiving region is the minimum indicating "black". It is a density level (level 0 here). Note that in FIG. 2, the hatched area indicates the area where the reflected light from the black area is incident.

When both the reflected light from the white area and the reflected light from the black area are incident, as in the photoelectric conversion element 11c of FIG. 2, the output level of the photoelectric conversion element 11b is from the white area. It is proportional to the area ratio of the area where the reflected light is incident and the area where the reflected light from the black area is incident. Therefore, as shown in FIG. 2, when the area where the reflected light from the white area is incident is equal to the area where the reflected light from the black area is incident,
The output level of the photoelectric conversion element 11c becomes an intermediate value (here, level 16) between the maximum density level indicating "white" and the minimum density level indicating "black".

The analog electric signal having such a property is converted by the A / D converter 2 into multivalued image data in which the output level of each photoelectric conversion element is represented by digital data of several bits. Further, in the image correction unit 3, the multi-valued image data has a partial variation in the light amount of the light source used in the photoelectric conversion unit 1, a change in the light amount of the light source used in the photoelectric conversion unit 1 with time, or a characteristic of the CCD linear image sensor. The reading characteristics and the like are corrected and then given to the resolution converter 4.

The resolution conversion section 4 identifies the state of each pixel based on the above-mentioned property of multi-valued image data and the redundancy of the image, as will be described later. By determining the density levels of two pixels as shown in 3, the data corresponding to 8 dots / mm is
Convert to ts / mm equivalent.

The operation of the resolution converter 4 will be described in detail below. First, the comparison circuit 42 uses the data of three pixels continuous in the main scanning direction held in the multi-valued buffer 41, and determines the state of the pixel (pixel of interest) located in the center of these three pixels as follows. Determine.

That is, the comparison circuit 42 first, in step a, as shown in FIG. 4, the absolute value of the level difference between the density level B of the pixel of interest and the density level A of the pixel on the front side in the main scanning direction (left adjacent pixel) ( | BA-) is smaller than a predetermined value M, and the absolute value (| BA-) of the level difference between the density level B of the pixel of interest and the density level C of the pixel on the rear side in the main scanning direction (right adjacent pixel). It is determined whether or not C |) is smaller than a predetermined value M. Here, the predetermined value M is set to be sufficiently smaller than the level difference between the white level WH and the black level BL, and in this step a, the density change from the left adjacent pixel to the target pixel and the right adjacent pixel to the target pixel. It is determined whether or not the change in density across pixels is small. If the density levels A, B, and C satisfy the above conditions, it is understood that the density changes gently as shown in FIG. 5A, for example, and the target pixel is a part of the halftone portion. Determine.

On the other hand, the density levels A, B and C are set to the step a.
If the condition is not satisfied, the comparison circuit 42 subsequently determines in step b whether or not the density level B is higher than either of the density levels A and C. If the density level B is higher than both the density levels A and C,
For example, since it can be seen that the state is as shown in FIG. 6A, it is determined that the pixel of interest is a white isolated point.

If the density level B is smaller than either of the density levels A and C, the comparing circuit 42 subsequently determines in step c whether or not the density level B is smaller than either of the density levels A and C. To do. And the density level B
Is smaller than either of the density levels A and C, it can be understood that the state is as shown in FIG.
It is determined that the pixel of interest is a black isolated point.

Further, when the density level B is larger than either of the density levels A and C, that is, when the density level B is larger than one of the density levels A and C and smaller than the other, for example, FIG. ) Or the state shown in FIG. 9A, it is determined that the pixel of interest is located at the black and white change point. Then, the states of change points are further classified into four states as follows.

First, in step d, the level difference (A-C) between the density level A and the density level C is calculated, and it is determined whether or not the result is positive. Here, if the calculation result in step d is negative, the left adjacent pixel is at the black level B.
On the L side, since the right adjacent pixel is on the white level WH side, it can be seen that the pixel of interest is the change point from black to white. Then, in step h, the density level B is changed to the white level W.
It is judged whether or not it is larger than 1/2 of H, and the density level B
Is larger than ½ of the white level WH, it can be seen that the white area is larger than the black area in the pixel of interest, so that it is shown at the change point from black to white and shown in FIG. 7B, for example. As described above, when it is determined that the first pattern has a large white area, and the density level B is ½ or less of the white level WH, the black area and the white area are equal or black in the pixel of interest. Since it can be seen that the area is larger, it is the second pattern in which the change point from black to white and the black area and the white area are equal, or the white area is large as shown in FIG. 7C, for example. To determine.

On the other hand, if the calculation result in step d is positive, the left adjacent pixel is on the white level WH side and the right adjacent pixel is on the black level BL side, so the pixel of interest is the change point from white to black. I understand. Then, in step g, it is determined whether or not the density level B is larger than 1/2 of the white level WH, and the density level B is 1 / of the white level WH.
If it is larger than 2, it can be seen that the white region is larger than the black region in the pixel of interest, and therefore the white region is large at the change point from white to black and as shown in FIG. 8B, for example. It is determined that it is a certain third pattern, and the density level B
Is less than 1/2 of the white level WH, it can be seen that the black area and the white area are equal to each other or the black area is larger in the pixel of interest. And the white area are equal, or, for example, FIG.
As shown in (c), it is determined that the fourth pattern has a large white area.

In this way, in the comparison circuit 42, the target pixel is the halftone, the white isolated point, the black isolated point, the first pattern, the second pattern.
It is determined which of the pattern, the third pattern and the fourth pattern is applicable. Then, the determination result is notified to the arithmetic circuit 43.

The arithmetic circuit 43 determines the density levels of the two pixels corresponding to the pixel of interest according to the discrimination result notified from the comparison circuit 42 as follows. (1) When the target pixel is determined to be halftone In this case, the density level B1 of one of the two pixels (here, the front side in the main scanning direction) is set to the density level B of the target pixel. . The other (here, the rear side in the main scanning direction)
The density level B2 of the pixel of
Set to the value obtained by interpolation processing from and. Here, as an interpolation processing method for determining the density level B2, for example, there is a processing method of taking an average value of the density level B and the density level C. In this case, the density level B2 is [(B + C) /
2] is obtained. That is, the density levels B1 and B2 in the case where the pixel of interest is halftone are as follows: B1 = B B2 = (B + C) / 2. For example, for the data shown in FIG.
Data as shown in (b) is generated.

(2) When it is determined that the pixel of interest is a white isolated point In this case, both the density levels B1 and B2 are set to the white level WH.
Set to. That is, the density levels B1 and B2 in the case where the pixel of interest is a white isolated point are as follows: B1 = WH B2 = WH. For example, for the data shown in FIG.
Data as shown in (b) is generated.

(3) When it is determined that the pixel of interest is a black isolated point In this case, both the density levels B1 and B2 are set to the black level BL.
Set to. That is, the density levels B1 and B2 when the pixel of interest is a white isolated point are as follows: B1 = BL B2 = BL. For example, for the data shown in FIG.
Data as shown in (b) is generated.

(4) When the pixel of interest is determined to be the first pattern In this case, as can be seen from FIG. 7B, the area corresponding to the pixel on the rear side (right side in the figure) in the main scanning direction is Since all are white areas, the density level B2 is set to the white level WH.
In addition, since the area corresponding to the pixel on the front side in the main scanning direction (the left side in the figure) has a black area and a white area, the white area in the area corresponding to the pixel on the front side in the main scanning direction is calculated and the area is calculated. The value doubled for ratio conversion is defined as the density level B1. That is, when the target pixel is the first pattern, the density levels B1 and B2 are: B1 = 2 (B-WH / 2) = 2B-WH B2 = WH. For example, the target pixel in the state shown in FIG. On the other hand, data as shown in FIG. 7D is generated.

(5) When the target pixel is determined to be the second pattern In this case, as can be seen from FIG. 7C, the area corresponding to the pixel on the front side in the main scanning direction is a black area. , The density level B1 is set to the black level BL. Further, since the region corresponding to the pixel on the rear side in the main scanning direction includes the black region and the white region, the white region in the region corresponding to the pixel on the rear side in the main scanning direction (corresponding to the pixel on the front side in the main scanning direction). Since all the regions are black regions, the value 2B obtained by doubling in order to convert the area ratio (corresponding to B) is defined as the density level B2. That is, the density levels B1 and B when the pixel of interest is the second pattern
2 becomes B1 = BL B2 = 2B, and for example, the data shown in FIG. 7E is generated for the target pixel in the state shown in FIG. 7C.

The density level B of the pixel of interest is WH / 2.
In this case, the black region does not extend to the region corresponding to the rear side pixel in the main scanning direction, and the region corresponding to the rear side pixel in the main scanning direction is all white region. However, according to the above equation, the density level B2 becomes WH, and the density level corresponding to all white is obtained.

(6) When the pixel of interest is determined to be the third pattern In this case, as can be seen from FIG. 8B, all the areas corresponding to the pixels on the front side (left side in the figure) in the main scanning direction are Since it is a white area, the density level B1 is set to the white level WH.
Further, since the area corresponding to the pixel on the rear side in the main scanning direction (the right side in the figure) has a black area and a white area, the white area in the area corresponding to the pixel on the rear side in the main scanning direction is calculated and The density level B2 is a value that is doubled to convert the area ratio. That is, the density levels B1 and B2 in the case where the target pixel is the third pattern are B1 = WH B2 = 2 (B-WH / 2) = 2B-WH, and for example, the target pixel in the state shown in FIG. On the other hand, the data as shown in FIG. 8D is generated.

(7) When it is determined that the pixel of interest has the fourth pattern In this case, as can be seen from FIG. 8C, all the areas corresponding to the pixels on the rear side in the main scanning direction are black areas. Therefore, the density level B2 is set to the black level BL. Further, since the region corresponding to the pixel on the front side in the main scanning direction includes the black region and the white region, the white region (the region corresponding to the pixel on the rear side in the main scanning direction) in the region corresponding to the pixel on the front side in the main scanning direction. Is a black region, so the value 2B obtained by doubling is equivalent to B) is used as the density level B2. That is, the density levels B1 and B when the pixel of interest is the fourth pattern
2 becomes B1 = 2B B2 = BL, and for example, the data shown in FIG. 8E is generated for the target pixel in the state shown in FIG. 8C.

The density level B of the pixel of interest is WH / 2.
In this case, the black area does not extend to the area corresponding to the pixel on the front side in the main scanning direction, and the area corresponding to the pixel on the front side in the main scanning direction is all white area. However, according to the above equation, the density level B2 becomes WH, and the density level corresponding to all white is obtained.

Then, the comparison circuit 42 and the arithmetic circuit 43
Terminates the above-described processing until the data of the next pixel is transferred to the multi-valued buffer 41, and when the data of the next pixel is transferred to the multi-valued buffer 41, the next pixel is set as the pixel of interest. The process of is repeated. As a result, the multi-valued image data equivalent to 8 dots / mm output from the image correction unit 3 is
The number of pixels is doubled, that is, converted into multi-valued image data equivalent to 16 dots / mm. Then, this multi-valued image data is given to the binarization unit 5 and converted into a binary image signal in which each pixel is represented by "white" or "black".

Thus, according to the present embodiment, the state of the pixel of interest is determined based on the density levels of the pixel of interest and the adjacent pixels (left adjacent pixel and right adjacent pixel) on both sides of the pixel of interest. Black isolated point, black and white change point first pattern, black and white change point second pattern, black and white change point third pattern
Two pixels that are classified into either the pattern or the fourth pattern of black and white change points and faithfully reproduce their respective states are determined. In this way, since two pixels are determined for the output of one photoelectric conversion element, the photoelectric conversion element of the photoelectric conversion unit 1 has a density of 8 pieces / mm, but 16 dots / m
An image signal equivalent to m can be generated. Therefore, it is possible to inexpensively realize a device capable of reading with high resolution.

Particularly in this embodiment, since the resolution conversion is performed after the A / D conversion and the image processing, the A / D conversion is performed.
Since the D conversion unit 2 and the image correction unit 3 need only process signals and data equivalent to 8 dots / mm, the A / D conversion unit 2 and the image can be compared with the case where a photoelectric conversion unit that outputs a signal of 16 dots / mm is used. The configuration of the correction unit 3 can be simplified and the cost can be further reduced.

Further, in this embodiment, since the density level of the multi-valued image data after the resolution conversion is set to the level corresponding to the area ratio of the white area and the black area, the binarization is performed. When the binarization processing according to the pseudo halftone processing method such as the dither method is performed in the unit 5, the binary image signal can be made faithful to the original.

The present invention is not limited to the above embodiment. For example, in the above embodiment, when the pixel of interest is the black and white change point, the density level of one pixel is set to [2B-W
H] or [2B], but when the density level of the other pixel is the white level WH, it is set to the black level BL,
On the other hand, when the density level of the other is the black level BL, it is set to the white level WH, that is, "white, black".
Alternatively, one of the “black and white” pixel patterns may be selected depending on whether it is the change point from white to black or the change point from black to white.

In the above embodiment, the resolution conversion processing is performed after image correction, but it may be performed before image correction or A / D conversion. In the above embodiment, the density level B when the pixel of interest is halftone
As the interpolation process for determining 2, the process of taking the average value of the density level of the pixel of interest and the density level of the adjacent pixel is performed, but other interpolation methods such as spline interpolation may be used.

Further, in the above embodiment, the photoelectric conversion unit 1 has 8
The photoelectric conversion elements are arranged at a density of pcs / mm, but the present invention can be applied regardless of the density of the photoelectric conversion elements. In addition, various modifications can be made without departing from the scope of the present invention.

[0045]

According to the present invention, the level of a predetermined pixel signal of interest corresponding to the output of any photoelectric conversion element of interest and the output of each of two adjacent photoelectric conversion elements located on both sides of the photoelectric conversion element of interest. 2 corresponding to the photoelectric conversion pixel of interest based on the level of a predetermined adjacent pixel signal corresponding to
Since the process of determining the density level of each pixel is performed by using each of a large number of photoelectric conversion elements as the photoelectric conversion elements of interest, the arrangement density of the photoelectric conversion elements is kept low to prevent an increase in cost. Also, the image reading device can faithfully generate an image signal having a resolution higher than the arrangement density of photoelectric conversion elements in a read image.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship between an incident state of light on a photoelectric conversion element included in a photoelectric conversion unit 1 in FIG. 1 and an output signal level.

FIG. 3 is a diagram showing a situation of resolution conversion by a resolution conversion unit 4 in FIG.

FIG. 4 is a flowchart showing a processing procedure in a comparison circuit 42 in FIG.

FIG. 5 is a diagram schematically showing an example of multi-valued image data when a pixel of interest is a part of a halftone portion and multi-valued image data obtained by resolution conversion.

FIG. 6 is a diagram schematically showing an example of multi-valued image data when a pixel of interest is an isolated point and multi-valued image data obtained by resolution conversion.

FIG. 7 schematically illustrates an example of multi-valued image data when a pixel of interest is a change point from black to white, actual distribution of white and black regions, and multi-valued image data obtained by resolution conversion. FIG.

FIG. 8 schematically illustrates an example of multi-valued image data when a pixel of interest is a change point from white to black, actual distribution of white and black regions, and multi-valued image data obtained by resolution conversion. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Photoelectric conversion part 2 ... A / D conversion part 3 ... Image correction part 4 ... Resolution conversion part 41 ... Multi-value buffer 42 ... Comparison circuit 43 ... Arithmetic circuit 5 ... Binarization part

Claims (2)

[Claims] 1. A large number of photoelectric conversion elements arranged at predetermined intervals, a level of a predetermined pixel signal of interest corresponding to an output of an arbitrary photoelectric conversion element of interest, and two photoelectric conversion elements located on both sides of the photoelectric conversion element of interest. The process of determining the density level of each of the two pixels corresponding to the target photoelectric conversion pixel based on the level of a predetermined adjacent pixel signal corresponding to each output of the adjacent photoelectric conversion elements is performed by the plurality of photoelectric conversion elements. And an deciding unit that performs each of the above as a photoelectric conversion element of interest. 2. The determining means sets the level of the pixel signal of interest and 2
When the difference between the levels of the two adjacent pixel signals is less than or equal to a predetermined value, the density level of one of the two corresponding pixels is set to the level of the target pixel signal, and the density level of the other pixel is set to the target level. The level of the pixel signal and the level of one of the two adjacent pixel signals are determined to be levels obtained by a predetermined interpolation process, and the level of the pixel signal of interest and the level of each of the two adjacent pixel signals are determined. When the difference is not less than the predetermined value and both the levels of the two adjacent pixel signals are both higher or lower than the level of the target pixel signal, the density levels of the corresponding two pixels are set to the above-mentioned values. The level of the target pixel signal is determined, and the difference between the level of the target pixel signal and the levels of the two adjacent pixel signals is not less than a predetermined value, If one of the levels of the two adjacent pixel signals is higher and the other is lower than the level of the pixel signal of interest, which of the levels of the two adjacent pixel signals is closer to the predetermined white level, and It is determined whether the level of the target pixel signal is closer to the white level than the intermediate value between the white level and a predetermined black level, and the level of the target pixel signal is closer to the white level than the intermediate value. If so, the density level of the pixel located on the side of the adjacent photoelectric conversion element that outputs the adjacent pixel signal that is closer to the white level is determined to be the white level, and the density level of the other pixel is set to the intermediate value and the target value. The level is determined according to the ratio between the level difference of the pixel signal and the intermediate value, and the level of the pixel signal of interest is closer to the white level than the intermediate value. If not, the density level of the pixel located on the side of the adjacent photoelectric conversion element that outputs the adjacent pixel signal, which is a level close to the white level, is determined to a level corresponding to the ratio between the intermediate value and the level of the pixel signal of interest. At the same time, the other pixel is determined to be the black level.
The image reading apparatus described in 1.