JPH0965052A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively suppress the generation of color slurring in a read image caused by dispersion in parallelism between both the surfaces of respective spectroscopic filters concerning a device for reading a multicolor original image by using plural kinds of spectroscopic filters while exchanging them. SOLUTION: This device is provided with light sources 13 and 14 for illuminating an original while being extended in main scanning direction and an image sensor 18 for reading its illumination light. At prescribed interposed positions in the optical path from a document D to the image sensor 18, plural kinds of spectroscopic filters are held while being exchanged by a spectroscopic filter exchanger 26 or the like and spectroscopic components corresponding to the respective spectroscopic filters are read by the image sensor 18. While considering the deviation of image reading position caused by inclination on both the surfaces of respective spectroscopic filters, the front side faces of respective spectroscopic filters held at the interposed positions are inclined toward an optical axis just at a prescribed angle in the direction to cancel this deviation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention interposes a plurality of types of spectral filters between an original and an image sensor such as a CCD while exchanging the spectral components corresponding to the spectral filters using the image sensor. The present invention relates to an image reading device configured to read.

[0002]

2. Description of the Related Art Conventionally, as a device for reading a multicolor original with a so-called 1-line type CCD image sensor, a plurality of types of spectral filters (generally red, green, blue (hereinafter, R,
Called G and B. (3 types of spectral filters corresponding to 4) are intervened while being exchanged, and scanning is performed as many times as the number of these spectral filters, and the spectral components corresponding to each spectral filter in each scanning are sequentially processed by the CCD image sensor. There is known a device configured to obtain color image data by synthesizing the data after reading the data (see, for example, JP-A-60-20678).

[0003]

In the above-mentioned device, color shift may occur in the image finally obtained. Such a color shift is caused by a variation in the insertion angle of the spectral filter that is appropriately replaced and a variation in the moving speed of the optical system in the sub-scanning direction in each scan. As a result of repeated research on the factors, it was found that variations in the parallelism between the front and back surfaces of the above-mentioned spectral filter have a significant effect on color misregistration.

The principle will be described. In FIG. 7, it is assumed that the spectral filter F and the imaging lens 22 are interposed between the document D and the image sensor 18, and the spectral filter F is separated from the document D by a distance s. Here, the front side surface (the surface on the side of the document D) F1 of the spectral filter F is oriented in the direction orthogonal to the optical axis L, and the second surface (the surface on the side of the image sensor 18) with respect to this front side surface F1. ) If F2 is inclined by a minute angle α, the optical axis L is bent by the spectral filter F by an angle corresponding to this minute angle α, and the reading position by the image sensor 18 is displaced by that amount.

Specifically, as shown in FIG. 8, the incident angle of the optical axis L on the filter front side face F1 is i ₁ , and the filter front side face F
The exit angle of the optical axis L from ₁ is i ₁ ′, the filter rear side F2
Letting i _{2 be} the incident angle of the optical axis L to the filter, i ₂ ′ be the emitting angle of the optical axis L from the rear side surface F _{2 of} the filter, and n be the refractive index of the filter F, the following equation holds (Snell's law).

[0006]

[Number 1] _{sini 1 = nsini 1 'nsini 2} = sini 2' i 2 = α-i 1 ' , where the approximate equation sinx ≒ x (here, x is assumed sufficiently small.) The number 1 When applied to Equation 1 and Equation 2, the following equation is obtained.

[0007]

On the other hand, the angle formed by the optical axis L extending from the filter F to the image sensor 18 with respect to the optical axis L extending from the original D to the filter F (hereinafter referred to as a deflection angle) is expressed as follows: i ₁ ≈ni ₁ ′ ni ₂ ≈i ₂ ′ ) Is given by the following equation.

[0008]

Δ = i ₁ + i ₂ ′ −α In the above equation, δ is approximately given by the following equation.

[0009]

[Equation 4] δ≈ (n−1) α (∵i ₁ + i ₂ ′ = n (i
₁ ′ + i ₂ ) = nα) Corresponding to this deflection angle δ, the reading position of the original image is displaced by the dimension Δy≈stan δ, so that the angle α of the spectral filter F to be replaced varies. In this case, the color shift appears by the amount of the variation.

It is conceivable to use an extremely high quality filter with high dimensional accuracy as a means for suppressing the color shift due to the parallelism of such a filter, but this means increases the cost of the entire apparatus. I cannot escape. Especially,
If the thickness of the spectral filter F is large, the optical path length is significantly increased and the focus is out of focus as compared with the case where no filter is inserted. Therefore, the thickness dimension of each spectral filter F is set to be very small. However, it is very difficult to obtain stable parallelism in such a thin filter.

In view of the above circumstances, the present invention is based on the unevenness of the parallelism on both sides of each spectral filter in an image reading apparatus for reading a multicolor original by using a plurality of spectral filters interchangeably. It is an object of the present invention to provide an image reading apparatus capable of effectively suppressing color misregistration of a read image.

[0012]

As described above, the reading position of the original image largely changes depending on the parallelism of each spectral filter, but the angle of incidence i ₁ on the front side F1 of the filter, that is, the front of the filter with respect to the optical axis L. It also changes depending on the inclination angle of the side surface F1.

The present invention has been made in view of this point, and has a light source for illuminating a multicolor original document, a scanning means for relatively moving the light source and the multicolor original document, and a level according to the amount of received light. An image sensor that outputs an electric signal, an imaging optical system that forms an illumination light flux of the document on the image sensor, and a plurality of types of spectral filters at the optical axis position between the document and the image sensor. In an image reading apparatus having a spectral filter holding means to intervene and configured to sequentially read spectral components corresponding to each spectral filter by the image sensor, the image resulting from the variation in parallelism on both sides of each spectral filter. The front surface of each spectral filter is tilted by an angle corresponding to its parallelism with the optical axis in a direction that cancels out the variation in the reading position of each spectral component by the sensor. In each spectral filter is obtained by forming the spectral filter holding means to hold to the optical axis position.

According to this structure, even when the parallelism on both sides of each spectral filter varies, the front side of each spectral filter (filter front side F in FIG. 8) is formed at an angle corresponding to the variation.
By holding 1) in a state of being inclined with respect to the optical axis, the shift (color shift) of the image reading position due to the above variation is corrected.

That is, the variation in the reading position of the image sensor due to the variation in the parallelism between the front and back surfaces of each spectral filter is greatly varied due to the subtle parallelism error of the spectral filter, but it is difficult to correct it by the parallelism. On the other hand, paying attention to the fact that the variation in the image sensor reading position caused by the inclination of the front surface of each spectral filter and the optical axis is significantly less than the influence due to the parallelism of the filter, and the variation in the image sensor reading position is This is achieved by adjusting the insertion angle of each spectral filter with respect to the optical axis, which is few and easy to adjust.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described with reference to FIGS.

The image reading apparatus 10 shown in FIG. 1 is provided with a housing 12, and a transparent document placing plate 16 is fixed to the upper surface thereof. In the housing 12, a first light source 13 and a second light source 14 that illuminate the document on the document plate 16 are provided.
An image sensor (a 1-line CCD image sensor in this embodiment) 18 and an imaging optical system are housed. The image forming optical system includes a plurality of mirrors 20A, 20B, 20C and an image forming lens 22, and the illumination light flux of the document by the light sources 13, 14 is reflected by the mirrors 20A to 20C and the image forming lens 22 causes an image sensor. It is arranged so as to form an image on 18 (that is, an optical axis L from the document D to the image sensor 18 is formed).

The first light source 13 and the second light source 14 and the mirror 20A extend in the main scanning direction (depth direction in FIG. 1) and an optical system drive motor (pulse motor) 21 as shown in FIG. The drive transmission mechanism (not shown) is configured to be driven in the sub-scanning direction (the left-right direction in FIG. 1) orthogonal to the main scanning direction, and the mirrors 20B, 2 are driven at half the speed thereof.
0C is driven in the same direction, and by such an operation, the optical path length from the document illumination position by the light sources 13 and 14 to the image sensor 18 is always kept constant. Further, at a position corresponding to the origin position of the light sources 13 and 14, an origin position switch 56 (FIG. 2) that detects whether or not the light sources 13 and 14 exist at the same position is provided.

In FIG. 1, the light sources 13 and 14 are moved to perform sub-scanning of the original.
The present invention can also be applied to a device in which the sub-scanning is performed by moving the document while fixing the documents 3 and 14.

The image sensor 18 is a linear image sensor, and has a light receiving portion 18a and a transfer portion 1 as shown in FIG.
8b. The image reading operation is performed only during the period corresponding to the drive signals (start signal and stop signal) input from the driver 17.

A heat ray cut filter 24 and a spectral filter exchange device 26 are provided between the imaging lens 22 and the mirror 20c. The heat ray cut filter 24 is
Of the light reflected by the reflection mirror 20, a predetermined value (for example,
The wavelength component of 700 nm or more is cut, and smear (the image protrudes from the edge and bleeds due to this wavelength component,
This is to prevent the occurrence of a phenomenon that the image is blurred as if it was dirty. The spectral filter exchange device 26 selectively inserts / removes the R spectral filter, the G spectral filter, and the B spectral filter with respect to the position on the optical axis L (that is, the document D).
And the image sensor 18), and has a structure as shown in FIG.

In the figure, a pair of left and right guide shafts 30 and 32 extending vertically is fixed to a housing 28, and the filter holding plate 3 is vertically movable along the guide shaft 30.
4 is supported, and the filter holding plate 36 is supported so as to be vertically movable along the guide shaft 32. Then, on the filter holding plate 34, the R spectral filter 38R and the G spectral filter 3 are provided.
The 8G and the 8G are fixed side by side, and the B spectral filter 38B is fixed to the filter holding plate 36.

A filter replacement motor 40 and a pulley 42 are vertically arranged on one side of the housing 28, and a wire 44 is provided between the pulley 41 fixed to the output shaft of the filter replacement motor 40 and the pulley 42. The filter holding plate 34 is fixed in the middle of the wire 44. Similarly, on the other side of the housing 28,
A filter replacement motor 46 and a pulley 48 are arranged vertically, and a wire 50 is stretched between the pulley 47 fixed to the output shaft of the filter replacement motor 46 and the pulley 48. The wire 50 has an intermediate portion. The filter holding plate 36 is fixed to. Therefore, the filter holding motors 34, 3 are driven by driving the filter replacement motors 40, 46.
6 are vertically driven.

An origin position sensor 52, a positioning sensor 54G, and a positioning sensor 54R are provided on one side of the housing 28 in order from the bottom, and a positioning sensor 54B on the other side of the housing 28 in order from the bottom. Also, an origin position sensor 53 is provided. Each of the above sensors is composed of an optical sensor including a light emitting element and a light receiving element. On the other hand, the detected portion 34a extends laterally from one side of the filter holding plate 34, and the filter holding plate 3
A detected portion 36a extends laterally from the other side portion of 6. Then, in the state where the detected portion 34a is detected by the origin position sensor 52, both spectral filters 38R, 3R
8G is positioned at the origin position (position deviated from the optical axis L), and the spectral filter 38G is positioned at the position on the optical axis L while the detected portion 34a is detected by the positioning sensor 54G. The spectral filter 38R is positioned at the position on the optical axis L in the state where the portion 34a is detected by the positioning sensor 54R, and the spectral filter 38B is set in the optical axis L while the detected portion 36a is detected by the positioning sensor 54B. The position of each sensor is adjusted so that the spectral filter 38B is positioned at the upper position and the detected portion 36a is detected by the origin position sensor 53, and the spectral filter 38B is positioned at the origin position (position deviated from the optical axis L). The installation position is set.

Further, as a feature of this apparatus, each of the spectral filters 38R, 38G, and 38B is, as shown in FIG.
Angles θr and θ with respect to a preset optical axis L, respectively
The filter holding plates 34 and 36 are fixed to the respective filter holding plates 34 and 36 in an inclined state so that the filter holding plates 34 and 36 are positioned at positions on the optical axis L while being inclined by g and θb (generally θr ≠ θg ≠ θb). That is, when the filter front side face F1 and the filter rear side face F2 of each of the spectral filters 38R, 38G, and 38B are not parallel to each other, the image reading position by the image sensor 18 is displaced due to this, and this is offset. The spectral filter exchanging device 26 is configured so that the front side F1 of each spectral filter is inclined with respect to the optical axis L by an angle that cancels out in each direction.

Specifically, in order to obtain the values of the tilt angles θr, θg, and θb, both surfaces F1 and F2 of each spectral filter are obtained.
The value of the incident angle i ₁ on the filter front side face F1 is set so that the deflection angle δ falls within a preset small allowable range based on the inclination angle α between them and the above (Formula 1) to (Formula 3). Is calculated by a numerical calculation (for example, scissors striking method) by
The inclination angles θr, θg, and θb of 38B may be set, or the spectral filter may be actually set in the actual machine and the appropriate angle may be found by trial and error while finely adjusting the angle. . Further, since the angle is a small angle, it is possible to obtain a value that is almost similar even if the tilt angle θ is calculated using the following approximate expression (Equation 5).

[0027]

## EQU00005 ## .theta. = (S / d) .multidot.n.alpha. Where s is the distance between the filter and the document surface, d is the thickness of the filter, and n is the refractive index of the filter.

The image reading device is provided with an operation unit 58, a line memory 19, an image processing device 70, and a control device 60 as shown in FIG.

The operation unit 58 receives signals from the operator and responds to them, for example, a scanning start signal and a scanning parameter setting signal (main scanning direction trimming range designation signal, sub-scanning direction trimming range designation signal, highlight density). Setting signals, shadow density setting signals, sharpness deletion setting signals, magnification setting signals, color / monochrome selection signals, etc.) are input to the image processing device 70 or the control device 60.

The line memory 19 plays a role of a buffer, and temporarily stores pixel data of one line transferred from the transfer section 18b of the image sensor 18 and outputs the pixel data to the image processing apparatus 70. .

The image processing device 70 includes the line memory 1
Of the pixel data for one line that is sequentially input from 9,
Only the signal corresponding to the main scanning direction trimming range (main scanning range) input by the operation of the operation unit 58 is picked up and stored in the image memory 72 to construct image data.

The control device 60 comprises a sub-scanning control means 62 and a filter exchange control means 64.

The sub-scanning control means 62 sets the light sources 13 and 14 to the origin position, that is, the origin position switch 5 before scanning.
The light sources 13 and 14 are returned to the positions detected by 6 and the current positions of the light sources 13 and 14 are grasped from the number of pulses output to the optical system drive motor 21 with this position as a reference, and the drive control thereof is executed. A control signal is output to the driver 17 to control the reading period by the image sensor 18, that is, the control of the sub-scanning range.

The filter replacement control means 64 is the origin position sensor 52, 53 and the positioning sensor 5 shown in FIG.
Based on the detection signals of 4R, 54G, and 54B, the R spectral filter 38R for the first scanning of one original document
The filter exchange motor 4 is configured so as to extend the G spectral filter 38G during the second scanning and the B spectral filter 38B during the third scanning to the positions on the optical axis L, respectively.
0 and 46 are operated appropriately.

Next, the control operation performed in this apparatus will be described with reference to the flowchart of FIG.

First, when a scanning request is made (YES in step S1 in FIG. 5), the above-mentioned scanning parameters are taken in (step S2), and each device is set to the initial state (step S3). Specifically, the gain setting of the A / D converter, the selection of the spectral filter and the positioning of the selected spectral filter (the R spectral filter 38R is selected in the first scan), the turning on of the light sources 13 and 14, the turning on of the light sources 13 and 14 are performed. Performs home position return, aperture setting, etc.

Next, shading correction is performed to compensate for variations in sensitivity of the CCD image sensor 18 in the main scanning direction and variations in brightness of the light sources 13, 14 in the main scanning direction (step S4). For this shading correction, for example, the CCD image sensor 18 obtained as a result of test scanning of a reference white original fixed on the back surface of the original placing plate 16 is tested.
Of the output in the main scanning direction of the CCD image sensor 18 and a shading correction value corresponding to the variation is output.
It can be performed by inputting it to an A / D converter (not shown) in the subsequent stage. In this case, the A / D converter uses a value corresponding to the shading correction value for CC
The output of the D image sensor 18 will be corrected.

The execution timing of the shading correction may be set appropriately, and may be performed each time when scanning one document, or may be performed only when the scanning parameters are changed. However, it may be performed periodically.

Next, the light sources 13 and 14 are moved to the preset scanning standby position (step S5). This scan standby position is a position on the front side (origin position side) of the trimming start position in the sub-scanning direction (that is, the sub-scanning start position), and the traveling speed of the light sources 13 and 14 before reaching the sub-scanning start position. Is set at a position where a sufficient run-up distance can be secured to increase the speed of the vehicle to a predetermined sub-scanning speed.

Next, after the conversion table for gradation correction is set (step S6), the variable magnification pattern is set (step S7), and the document scanning is started (step S8). Specifically, from the scan standby position, the light source 13,
The driving of 14 is started, and the reading by the image sensor 18 is started from the point where the light sources 13 and 14 have moved by the approach distance (start of sub-scanning). Then, at the point where the preset number of lines are scanned, that is, the point where the light sources 13 and 14 have moved by the preset trimming range in the sub-scanning direction (step S9), the image sensor 18
Reading by the light source is stopped (subscanning ends), and the light sources 13, 1
Necessary scanning end operation such as turning off of 4 is performed (step S10).

After the first scanning is completed in this way, the G spectral filter 38 is used as a spectral filter to be used.
G is selected and the second scanning is performed in the same manner as described above, and then the B spectral filter 38 is used as the spectral filter to be used.
By selecting B and similarly performing the third scanning, the image reading of one document is completed.

During this scanning, each spectral filter 38R, 3
8G and 38B have a predetermined shape in a state in which the filter front side face F1 is inclined with respect to the optical axis L in a direction to eliminate an image reading position error caused by the inclination according to the inclination angle α between the both surfaces F1 and F2. Since the light is supplied to the intervening position, even if there are variations in the parallelism between the two surfaces of these spectral filters 38R, 38G, and 38B, it is possible to effectively suppress the color misregistration of the read image due to this.

The embodiment of the present invention is not limited to the above, and the following forms can be taken as an example.

(1) In the present invention, the means for exchanging the spectral filter is not particularly limited, and it may be manually exchanged, or it may be automatically exchanged by using an apparatus different from that of FIG. 3, for example, the apparatus of FIG. You may do it. The apparatus shown in the figure includes a filter replacement rotary shaft 80 extending in a direction parallel to the main scanning direction, and three spectral filters 38R, 38G, 38B and one spectral filter 38R, 38G, 38B are provided on the peripheral surface of the filter replacement rotary shaft 80. 90 for the parallel plate (or filter for other purposes) 84 for maintaining balance
The output shafts of the pulse motors 82 are connected radially to the filter replacement rotary shaft 80. According to this apparatus, the spectral filter can be automatically replaced by rotationally driving the filter replacement rotary shaft 80 by the pulse motor 82. In the case of this device, as a means for inclining the filter front side face F1 of each spectral filter 38R, 38G, 38B with respect to the optical axis L, these spectral filters 38R, 38G, 38B are actually attached to the filter replacement rotary shaft 80. It may be fixed in a state of being tilted by the above angle, or the number of drive pulses of the pulse motor 82 at the time of filter replacement may be increased or decreased by a predetermined tilt angle.

(2) In the above embodiment, the filter tilt angle is set based on the difference in the reading position between the case where no filter is interposed and the case where each spectral filter is interposed. As the reference filter,
The front side surface F1 of this spectral filter is held in a state of being perpendicular to the optical axis L, and the difference in reading position between the case where this reference filter is interposed and the case where another spectral filter is interposed. Even if the inclination angle of the other spectral filter is set based on the above, it is possible to suppress the relative color shift of each color in the image.

(3) In the above embodiment, only the data belonging to the predetermined trimming range in the main scanning direction is stored in the image memory 72. However, all the data for one line is stored in the pixel memory regardless of the trimming range. It may be stored in 72, and image processing may be performed based on the main scanning direction trimming range after the scanning is completed. However, if the data outside the trimming range is removed in advance and only the data within the range is taken into the image memory 72 as described above, there is an advantage that the required memory number is significantly reduced.

[0047]

【Example】

A) Example of calculating the filter both-side tilt angle α When a spectral filter with a thickness of 1 mm and a refractive index n = 1.52 is used and an image is actually read under the condition of the distance s = 525 mm shown in FIG. 7, the spectral filter is not used. Compared with, the reading position was displaced by a dimension Δy = 0.12 mm in the sub-scanning direction. This 0.12 mm corresponds to about 3 pixels in the case of 600 dpi (dot per inch). In this case, the angle α formed by the filter front side face F1 and the rear side face F2 shown in FIG.
And the relational expression Δy≈stan δ, the following is obtained.

[0048]

## EQU6 ## α = {1 / (n-1)} tan ^-1 (Δy / s) = (1 / 0.52) tan ^-1 (0.12 / 525) ≈0.025 ° The tilt angle α calculated in this way Based on the above, it is possible to obtain the tilt angle of each spectral filter with respect to the optical axis L.

B) Example of calculation of the tilt angle θr (FIG. 4) of the filter front side surface F1 with respect to the optical axis L. For the lens 22 having the focal length f = 80 mm and the optical magnification m = 0.25, the original point is about 20 mm from the front main point. A spectral filter with a plate thickness of 2 mm at the position (eg, R spectral filter 38R)
When the filter front side surface F1 is orthogonal to the optical axis L, and the double-sided inclination angle α when the spectral filter is viewed from the side is 1 ′, the image sensor 1
The image reading position of 8 is displaced from the normal position by about 14 μm. An appropriate filter front side face F for eliminating this deviation
The tilt angle of 1 (the tilt angle when viewed from the side) θr is
According to the calculation based on the above (Formula 5), it becomes about 4.8 °.

[0050]

As described above, according to the present invention, an image in which a spectral component corresponding to each spectral filter in the document illumination light is read by the image sensor while holding a predetermined optical axis position while exchanging a plurality of types of spectral filters. In the reading device, considering the variation in parallelism on both sides of each spectral filter, in order to eliminate the error of the image reading position due to this variation, the tilt angle with respect to the optical axis of each spectral filter at the optical axis position is individually set. Therefore, there is an effect that the color shift of the read image caused by the variation in the parallelism of the spectral filters can be effectively suppressed without using a special device.

[Brief description of drawings]

FIG. 1 is a cross-sectional side view showing a hardware configuration of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a functional configuration of a CCD image sensor and its peripheral devices provided in the image reading apparatus.

FIG. 3 is a perspective view of a spectral filter exchange device provided in the image reading device.

FIG. 4 is a side view showing a tilted state of a spectral filter held by the spectral filter exchange device and an optical axis.

FIG. 5 is a flowchart showing a control operation performed in the image reading apparatus.

FIG. 6 is a perspective view showing another example of the spectral filter exchange device.

FIG. 7 is an explanatory diagram showing the relationship between the refraction of light in the spectral filter and the shift of the document image reading position.

FIG. 8 is an enlarged view showing a refraction state of light in the spectral filter.

[Explanation of symbols]

 10 Image Reading Device 13 First Light Source 14 Second Light Source 16 Document Placement Plate 18 Image Sensor 20A to 20C Reflecting Mirror 22 Imaging Lens 26 Spectral Filter Exchange Device (Spectral Filter Holding Means) 38R, 38G, 38B Spectral Filter F1 Front side of filter L Optical axis θ Inclination angle of front side of filter with respect to optical axis

Claims (1)

[Claims] 1. A light source for illuminating a multicolor original document, a scanning means for relatively moving the light source and the multicolor original document, an image sensor for outputting an electric signal of a level corresponding to the amount of received light, and an illumination luminous flux for the original document. An image forming optical system for forming an image on the image sensor, and a spectral filter holding means for interposing a plurality of types of spectral filters at the optical axis position between the original and the image sensor while exchanging them. In an image reading apparatus configured to sequentially read corresponding spectral components by the image sensor, a direction for canceling variations in reading positions of the spectral components by the image sensor due to variations in parallelism on both surfaces of each spectral filter. In addition, hold each spectral filter at the optical axis position while tilting the front surface of each spectral filter with respect to the optical axis by an angle corresponding to the parallelism thereof. An image reading apparatus comprising the spectral filter holding means described above.