Patent Grant
8387880
The present invention relates to an imaging apparatus for reading information from an object.
An imaging apparatus is used to read information printed on a medium such as a paper sheet, or information on a live body.
As illustrated in
The optical path of the light reflected by an object 15 to be shot is limited by the iris 12, and the light is received by the image sensor 14 through the lens 13.
When the information printed on a medium is read by the imaging apparatus 11, the distance between the lens 13 and the image sensor 14 is adjusted, so that the image forming surface is matched to the surface of the image sensor 14, thereby acquiring a clear image.
However, while a clear image has a large information volume, a change of a signal by the coarseness of the surface of a medium is superposed as noise on an original image signal.
When the vein inside the palm of a hand as illustrated in
As described above, the clearer an image obtained by the imaging apparatus 11 is, the higher frequency noise gets on an image signal by the coarseness of the surface of a medium.
To solve the problem, conventional techniques perform an operation of low pass filter processing on an image signal output from the image sensor 14 to remove the high frequency noise.
The 3×3 operation matrix illustrated in
An image signal treated by the Gaussian filter processing can be obtained by performing the above-mentioned operation on each pixel.
Similarly, the operation matrix illustrated in
However, it is necessary to perform the operation for the number of elements of the operation matrix (for example, nine times for the 3×3 matrix) on all pixels read by the imaging apparatus in the low pass filter processing using the above-mentioned operation matrix. When there are a large number of pixels, the processing time of image processing becomes long.
The patent document 1 describes preventing an occurrence of moiré of an image by defocusing the reflected light of an original formed on an image sensor.
The patent document 2 describes a drive mechanism of a camera in which an AF coil is fixed to a moving object for supporting an image pickup element, and the AF coil is a plane coil positioned on the plane on which parallel to an optical axis.
The patent document 3 describes an imaging unit including a moving device for moving an imaging device in an arbitrary direction on a plane perpendicular to a subject light, and a position detection device for detecting the position of the imaging device.
The patent document 4 describes an imaging apparatus having a camera shake correction function including a shooting optical axis as a Z axis direction with an intersection between an X-Y plane perpendicular to the Z axis direction and the Z axis defined as an origin, and an origin position forcibly holding mechanism for mechanically holding an image pickup element at an origin position where an optical center of the image pickup element matches the origin.
The above-mentioned patent documents do not describe performing a desired filtering process on an image without increasing the processing time of image processing.
The present invention aims at performing a desired filtering process on an image in a shorter time in an imaging apparatus for reading information.
The imaging apparatus for reading information according to the present invention includes a lens for forming an image of the light from an object to be shot, an image sensor for receiving the light from which an image is formed by the lens, a drive unit for changing the position of the image sensor so that the resultant exposure energy distribution of received light on each pixel of the image sensor can be the low pass filter characteristic, and a control unit for controlling the drive unit.
Since the imaging apparatus for reading information requires no low pass filter operation, the processing time for the image processing can be shortened.
The preferred embodiments of the present invention are described below.
The imaging apparatus 21 for reading information can be used in a bar code reader for reading a 1- or 2-dimensional bar code, a living body authentication device for reading a fingerprint, a vein, etc. Since a clear image can be obtained by setting the position of an image sensor 27 as an image forming position, it can be used also in a normal image shooting device.
The first embodiment of the present invention relates to an image-side telecentric optical system in which the light from a lens to an image sensor is parallel to the optical axis, and is an example of the case where the image sensor 27 moves from the image forming surface to lense 25.
The imaging apparatus 21 for reading information includes a lens module 26 having a plurality of lenses 22 through 25, a 2-dimensional image sensor 27, a printed circuit board 28 on which the image sensor 27 is implemented, an actuator 29 for moving the printed circuit board 28 in the optical axis direction (Z axis direction) of the lens module 26, and a control unit 30 for controlling the actuator 29. The actuator 29 is, for example, the piezoactuator 29 with a piezo-element. Hereinafter, the actuator 29 is referred to as a piezo actuator 29.
The printed circuit board 28 on which the image sensor 27 is implemented can be moved in the optical axis direction (in the perpendicular direction illustrated in
The position of the image sensor 27 indicated by the dotted lines in
By moving the image sensor 27 upward in the optical axis, the spread size (the size of light power distribution) of an image at the point A′ of the light-receptive surface of the image sensor 27 can be changed.
The imaging apparatus 41 for reading information is configured by the lens module 26 having a plurality of lenses 22 through 25 and the image sensor 27. Although not illustrated in
In the first and second embodiments, the relationship between the position of the image sensor 27 and the image forming surface when the image sensor 27 is moved in the optical axis direction of the lens module 26 and the power density of the vicinity of the target point of the image sensor 27 are described below with reference to
The power density distribution (W/m2) of the received light of the vicinity of a target point on the image sensor 27 when the image sensor 27 is at each position of A, B, and C illustrated in
The central axis in
The output of each pixel of the image sensor 27 is proportional to the value obtained by multiplying the power (W) of incident light by the exposure time (second), that is, the exposure energy. Assuming that the exposure time at each of the positions A, B, and C in
F(x,y)=a(x,y)×ta+b(x,y)×tb+c(x,y)×tc
The equation above clearly indicates that arbitrary output distribution can be obtained by appropriately selecting the position in the optical axis direction (Z axis direction) of the image sensor 27 and the exposure time.
The a (x, y), b (x, y), or c (x, y) above is the power density distribution of the point image (the image of one point on the object to be shot) on the image sensor 27, and can be obtained by a strict optical system simulation. Otherwise, it can be empirically obtained using the measurement system illustrated in
In the measurement system in
The above-mentioned power density distribution is measured in advance to determine the exposure time ta, tb, and tc for the respective distributions for obtaining the target filter function F (x, y).
In the example above, the energy density distribution centering one point on the image sensor 27 corresponding to one point of the object 31 to be shot is described for simple explanation. However, the output distribution F (x, y) can be obtained for every pixel on the image sensor 27 centering on itself by changing the position of the pinhole 52 on the light shield plate 51 in
Since the output of the image sensor 27 can be expressed by F (x, y)=a (x, y)×ta+b (x, y)×tb+c (x, y)×tc, the output characteristic of the Gaussian distribution illustrated in
The image sensor 27 is moved to the initial position Z=A (position A in
The timer is reset (S12), and the exposure of the image sensor 27 is started at the position A (S13).
Next, it is determined whether or not the counting time t of the timer is equal to or exceeds ta (S14). In step S14, when it is determined that the counting time of the timer falls short of ta (NO in S14), the exposure is continued, and the determination in step S14 as to whether or not the counting time of the timer in step S14 is equal to or exceeds ta is repeated.
If it is determined in step S14 that the counting time t of the timer is equal to or exceeds ta (YES in S14), control is passed to step S15, the piezoactuator 29 is driven to move the image sensor 27 to the position Z=B (position B in
Until the counting time t of the timer is equal to ta by the process in step S11 through S14, that is, for the time ta at the position A, the exposure of the image sensor 27 can be performed. Thus, the power density distribution of any target pixel of the image sensor 27 and the peripheral pixels can be the power density distribution a (x, Y) in
Next, it is determined whether or not the counting time t of the timer is equal to or exceeds ta+tb (S16). If it is determined n step S16 that the counting time t falls short of ta+tb (NO in S16), the determination in step S16 is repeated.
On the other hand, if it is determined in step S16 that the counting time t of the timer is equal to or exceeds ta+tb (YES in S16), control is passed to step S17 to drive the piezoactuator 29 and move the image sensor 27 to the position Z=C (position C in
By the process in steps S15 and S16, the exposure of the image sensor 27 is performed for the time tb at the position B. Thus, the power density distribution of the target point of the image sensor 27 and the peripheral pixels can be the power density distribution b (x, y) in
Next, it is determined whether or not the counting time t of the timer is equal to or exceeds ta+tb+tc (total exposing time) (S18).
If it is determined in step S18 that the counting time of the timer falls short of ta+tb+tc (NO in S18), the exposure is continued at the position, and the determination in step S18 is repeated.
On the other hand, if it is determined in step S18 that the counting time t of the timer is equal to or exceeds ta+tb+tc (YES in S18), that is, if the exposure for the time determined for each of the positions A, B, and C, then control is passed to step S19, and the exposure terminates.
By the process in steps S17 through S18, the exposure of the image sensor 27 is performed at the position C for the time tc. Thus, the power density distribution of the target pixel of the image sensor 27 and its peripheral pixels can be expressed by the power density distribution c (x, y) in
When the time required to move the image sensor 27 cannot be ignored with respect to the exposing time, the exposure is suspended at the time P1 at which the counting time t of the timer reaches ta in step S14. Then, after moving the image sensor 27 from the position A to the position B, the exposure and the count of the timer are resumed at the time P2. Similarly, in step S16, the exposure is suspended at the time P2 at which the counting time of the timer reaches ta+tb, and the count of the timer is suspended. Then, after moving the image sensor 27 from the position B to the position C, the exposure and the count of the timer are resumed at the time P4. Thus, although the moving time cannot be ignored, the exposure time at each position can be correctly controlled.
In the above-mentioned process, the position of the image sensor 27 is moved by the piezoactuator 29 in the Z axis direction (optical axis direction), and the exposure is performed at each position for a predetermined time (for example, ta, tb, and tc), thereby assigning arbitrary low pass filter characteristic (for example, the characteristic of the Gaussian distribution) as the output distribution of each pixel and the peripheral pixels of the image sensor 27. That is, the low pass filter process can be optically realized instead of the arithmetic process of the low pass filter illustrated in
According to the above-mentioned first and second embodiments, the position in the optical axis direction of the image sensor 27 or the printed circuit board 28 with the image sensor 27 is changed, and the exposure time at each position is controlled, thereby arbitrarily changing the range of the light from each point of the object 31 to be shot on the image sensor 27. Thus, the low pass filter process can be optically realized on the output signal of the image sensor 27. As a result, the conventional low pass filter operation is not required, thereby shortening the processing time of the image processing. In addition, since the process load of the image processing can be reduced, a less expensive CPU of a relatively low processing speed can be used, thereby reducing the cost of the imaging apparatus for reading information.
In the examples above, the exposure time of the image sensor 27 is controlled at three positions, but the exposure time can be controlled at three or more positions. If the number of positions is increased, a low pass filter having more smooth characteristic can be realized.
In addition, in the examples above, the exposure is performed with the image sensor 27 stopped at the three positions (positions A, B, and C), but the substantial exposure time can be controlled at each position by continuously changing the position of the image sensor 27 and controlling the moving speed. In this case, if the power density distribution is expressed by the functions of not only x and y, but also z, the power density distribution changing with the movement in the Z axis direction is expressed by a function into f (x, y, z) (w/m2), the moving speed is expressed by a function of z as V(z), the movement range is set as Z=0 (image forming surface) through Z=Z0, then the output distribution F (x, y) of the image sensor 27 can be expressed by the following equation.
F(x,y)=∫(f(x,y,z)×1/V(z))dz (the integral range is 0˜Z0)
The moving speed V(z) in the Z axis direction is obtained so that F (x, y) can be a desired distribution, for example, the Gaussian distribution, and the piezoactuator 29 can be controlled for the moving speed V(z).
In this case, as with the above-mentioned first and second embodiments, f (x, y, z) can be obtained by a strict optical simulation. Otherwise, the power density distribution for the position in the Z direction can be measured using the measuring system in
The imaging apparatus 61 for reading information includes an iris 63, a lens 64, the image sensor 27 implemented on the printed circuit board 28, an X-Y stage 62 for moving the printed circuit board 28 on the XY plane, and the control unit 30 for controlling the X-Y stage 62. The X-Y stage 62 has a piezoactuator etc. not illustrated in
In the third embodiment, the light-receptive surface of the image sensor 27 and the image forming surface 32 match each other, and the light at the point A of the object 31 to be shot forms an image at one point (A′) of the light-receptive surface of the image sensor 27. The light of any other points of the object 31 to be shot similarly forms an image. In the third embodiment, the image sensor 27 moves on the XY plane. Therefore, the size of an image in the image sensor 27 is constant. Accordingly, an image-side telecentric optical system is not necessary.
In the third embodiment, the X-Y stage 62 is moved on the XY plane, and the exposure time t (x, y) of the target pixel (x, y) and its peripheral pixels is controlled. Thus, a low pass filter of a desired characteristic can be realized.
Assume that the X-Y coordinates of the central pixel (target pixel) a0 in
When the exposure is performed with the X-Y stage 62 moved clockwise pixel by pixel by setting as the starting point the position in which the pixel (1, 1) at the upper right of the central pixel a0 is the center, the filter characteristic illustrated in
Since the exposure is not performed at the central pixel a0, the exposure energy of the central pixel a0 is 0. By performing the exposure of the eight pixels at the upper right, right adjacent, lower right, . . . of the central pixel a0, the singular point removal filter for removing an image at a specific point of the object 31 to be shot can be realized.
The contents of the process performed when the singular point removal filter are described below with reference to the flowchart illustrated in
The initial position (x, y) of the X-Y stage 62 is moved to the position where the pixel (1, 1) is centered (S21 in
If the X-Y stage 62 is moved to the initial position, the count of the timer is started (set) (S22), and the exposure is started at the position (S23).
Next, it is determined whether or not the counting time t of the timer is equal to or exceeds T/8 (S24). The time T is the total exposure time of the eight peripheral pixels around the central pixel a0 in
If it is determined in step S24 that the counting time t of the timer is T/8 (NO in step S24), the determination in step S24 is repeated.
On the other hand, if it is determined in step S24 that the counting time t of the timer has reached T/8 (YES in S24), control is passed to step S25, and the position (x, y) of the X-Y stage 62 is moved to the position where the pixel (1, 0) is centered. The pixel (1, 0) is a pixel at the position (1, 0) to the right of the central pixel a0 in
If the time required to move the X-Y stage 62 cannot be ignored with respect to the exposure time at each position, the exposure and the count of the timer are suspended at the time P1 at which the exposure time reaches T/8, the X-Y stage 62 is moved to the position where the pixel (1, 0) is centered, and then the exposure and the count of the timer are resumed at the time P2. Thus, although it takes a long time in moving the X-Y stage 62, the exposure time of each pixel can be correctly controlled, and a desired filter characteristic can be realized.
In the same manner, if the moving time of the X-Y stage 62 cannot be ignored with respect to the exposure time in the following steps, then the exposure and the count of the time are suspended before (at the time P1) the exposure at one position is terminated and the X-Y stage 62 is moved to the next position, and exposure and the count of the timer are resumed after the completion of the movement (at the time P2), thereby removing the influence of the time required to move the X-Y stage 62.
Next, it is determined whether or not the counting time t of the timer is equal to or exceeds 2T/8 (S26). Assuming that the time required to move the X-Y stage 62 can be ignored with respect to the exposure time, the exposure at this position can be terminated when the counting time t of the timer reaches the total time 2T/8, that is, the sum of the exposure time of the first pixel (1, 1) and the exposure time of the second pixel (1, 0). In the process in step S26, it is determined whether or not the counting time t of the timer has reached the total exposure time 2T/8 of two pixels.
If it is determined in step S26 that the counting time t of the timer falls short of 2T/8 (NO in step S26), then the process in step S26 is repeated.
On the other hand, if it is determined in step S26 that the counting time t of the timer has reached 2T/8 (YES in step S26), control is passed to step S27, and the X-Y stage 62 is moved to the position where the pixel (1, −1) is centered. The pixel (1, −1) is a pixel at the position (1, −1) at the lower right of the central pixel a0 (0, 0).
Next, it is determined whether or not the counting time t of the timer is equal to or exceeds 3T/8 (S28). The process in step S28 is the process of determining whether or not the exposure time of the pixel (−1, −1) has reached T/8.
In step S28, if it is determined that the counting time t of the timer falls short of 3T/8 (NO in S28), the process in step S28 is repeated.
On the other hand, if it is determined in step S28 that the counting time t of the timer has reached 3T/8 (YES in S28), then control is passed to step S29, and the X-Y stage 62 is moved to the position where the pixel (0, −1) is centered. The pixel (0, −1) is a pixel at the position (0, −1) one pixel below the central pixel a0 in
Next, it is determined whether or not the counting time t of the timer is equal to or exceeds 4T/8 (S30). The process is performed to determine whether or not the exposure time of the pixel (0, −1) has reached T/8.
If it is determined in step S30 that the counting time t of the timer falls short of 4T/8 (NO in S30), the process in step S30 is repeated.
On the other hand, if it is determined in step S30 that the counting time t of the timer has reached 4T/8 (YES in S30), control is passed to step S31, and the X-Y stage 62 is moved to the position where the pixel (−1, −1) is centered. The pixel (−1, −1) is the pixel at the position (−1, −1) at the lower left of the central pixel a0 in
Next, it is determined whether or not the counting time t of the timer is equal to or exceeds 5T/8 (S32). The process is performed to determine whether or not the exposure time of the pixel (−1, −1) has reached T/8.
If it is determined in step S32 that the counting time t of the timer falls short of 5T/8 (NO in S32), the process in step S32 is repeated.
On the other hand, if it is determined in step S32 that the counting time t of the timer is equal to or exceeds 5T/8 (YES in S32), control is passed to step S33, and the X-Y stage 62 is moved to the position where the pixel (−1, 0) is centered. The pixel (−1, 0) is a pixel at the position (−1, 0) left adjacent to the central pixel a0 in
Next, it is determined whether or not the counting time t of the timer is equal to or exceeds 6T/8 (S34). The process is performed to determine whether or not the exposure time of the pixel (−1, 0) has reached T/8.
If it is determined in step S34 that the counting time t of the timer falls short of 6T/8 (NO in S34), the process in step S34 is repeated.
If it is determined in step S34 that the counting time t of the timer is equal to or exceeds 6T/8 (YES in S34), control is passed to step S35, and the X-Y stage 62 is moved to the position where the pixel (−1, 1) is centered. The pixel (−1, 1) is the pixel at the position (−1, 1) at the upper left of the central pixel a0 in
Next, it is determined whether or not the counting time t of the timer is equal to or exceeds 7T/8 (S36). The process is performed to determine whether or not the exposure time of the pixel (−1, 1) has reached T/8.
If it is determined in step S36 that the counting time t of the timer falls short of 7T/8 (NO in S36), then the process in step S36 is repeated.
On the other hand, if it is determined in step S36 that the counting time t of the timer is equal to or exceeds 7T/8 (YES in S36), control is passed to step S37, and the X-Y stage 62 is moved to the position where the pixel (0, 1) is centered. The pixel (0, 1) is a pixel at the position (0, 1) one pixel above the central pixel a0 in
Next, it is determined whether or not the counting time t of the timer is equal to or exceeds T (S38). The process is performed to determine whether or not the exposure time of the pixel (0, 1) has reached T/8.
If it is determined in step S38 that the counting time t of the timer falls short of T (NO in S38), the process in step S38 is repeated.
On the other hand, if it is determined in step S38 that the counting time t of the timer is equal to or exceeds T (YES in S38), control is passed to step S39, and the exposure is terminated.
In the above-mentioned process, a singular point removal filter for removing an image at an arbitrary point of the object 31 to be shot can be realized by performing the exposure of the peripheral pixels and controlling the X-Y stage 62 not to expose the central pixel.
The above-mentioned process is realized by controlling the position on the XY plane of the image sensor 27, and it is not necessary to perform the image processing for removing a singular point from an output image of the image sensor 27 by arithmetic operations. Therefore, the processing time of the image processing can be shortened. Thus, since the arithmetic process of a singular point removal filter etc. is not required, a less expensive CPU having a relatively low processing speed can be used. Thus, the cost of the imaging apparatus for reading information to be treated in real-time processing, for example, a bar code reader, a living body authentication device, etc. can be reduced.
The above-mentioned process relates to eight peripheral pixels around the central pixel a0, but the number of pixels is not limited to eight, that is, seven or less, or nine or more pixels can be processed.
In the process in
For example, the X-Y stage 62 is moved to the position where the central pixel a0 is centered so that the exposure time of the central pixel a0 can be the longest (>T). Then, the X-Y stage 62 is moved to the position where the peripheral pixels on the concentric circles are centered, the exposure time of the pixels on the same concentric circle is made shorter than that of the central pixel a0, and the exposure time of the pixels on the outside concentric circle (second concentric circle) is made further shorter. Thus, a desired low pass filter characteristic (for example, the Gaussian filter illustrated in
According to the above-mentioned embodiment, the imaging apparatus for reading information requires no low pass filter operation on an image, thereby shortening the processing time in image processing. Thus, for example, a less expensive CPU having a relatively low processing speed can be used. Accordingly, the cost of the apparatus can be reduced.
In all embodiments described above, the move of the image sensor is controlled to make a specific exposure energy distribution. Since all pixels move simultaneously, the resultant output of the image sensor is the convolution of a specific exposure energy distribution and an image signal, and thereby a low pass filter can be optically performed. This concept is common in all embodiments.
The present invention is not limited to the above-mentioned embodiments. For example, the following configuration can be realized.
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| 20100079825 A1 | Apr 2010 | US |
