JP2001257930A - Picture frame centering control method and image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform high-performance image pickup without any trouble of picture quality by accurately and easily matching an optical axis and the center of picture frame. SOLUTION: An image pickup information analyzing part 202 generates centering information for image segmentation by analyzing an image pickup signal provided by a CCD imaging device 105. On the basis of this centering information, a picture frame trimming position is determined by a picture frame moving setting part 201. Thus, since the position of the image pickup picture frame is controlled on the basis of the centering information provided by analyzing the image pickup signal, the optical axis and the center of picture frame can be accurately and easily matched and high-performance image pickup without trouble in picture quality can be easily performed even without preparing an especially large image circle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image frame centering adjustment method for adjusting the position of an image frame in an image pickup apparatus and an image pickup apparatus using the method.

[0002]

2. Description of the Related Art In recent years, various electronic cameras using a solid-state imaging device such as a CCD have been developed. In an electronic camera, a captured image signal is obtained by photoelectrically converting a subject image incident through an imaging lens by a solid-state imaging device such as a CCD. In an imaging device using such a solid-state imaging device, various position adjustments regarding the solid-state imaging device have been conventionally performed.

There are various items for position adjustment, and in addition to adjustment of movement of the imaging lens in the direction of the optical axis (commonly known as Z-axis adjustment) related to focus characteristics and tilt adjustment for preventing one-sided blurring of an image, Focusing on the present invention, there is a movement adjustment in a direction orthogonal to the optical axis (commonly known as XY adjustment). This X
As the Y adjustment, for example, a mechanical XY adjustment mechanism as described in JP-A-61-247169 is known.

Conventionally, such XY adjustment mainly focuses on precisely adjusting the positional relationship of pixels between image pickup elements in a multi-chip camera. Not much attention was paid.
This is an imaging area (a range as an image.
This is because even if the center of the image frame is slightly deviated from the optical axis of the lens, the problem can be avoided by providing a margin in the image circle of the lens. Therefore, such XY adjustment is often omitted in a single-chip camera.

[0005]

However, in order to provide a margin in the image circle, there is a problem that the size of the lens is increased. On the other hand, if an attempt is made to reduce the size of the lens even a little and use a lens with an image circle just below the image frame, the deviation between the image frame center and the optical axis due to the effects of mechanical manufacturing errors and the like cannot be ignored. For example, problems such as a difference in brightness between the upper, lower, left, and right sides of the screen and a vignetting of some images at four corners of the image frame are likely to occur.

[0006] Even when the image circle has a margin, in the case of a zoom lens, a problem may occur that the image position with respect to the image frame is shifted between the telephoto side and the wide-angle side. This is because if the center of the image frame and the optical axis are misaligned,
This is because when zooming between the telephoto side and the wide-angle side, the position of the zoom center (which is equal to the optical axis point), which is a fixed point without moving the image, deviates from the center of the image frame.
In addition, in the case of moving image shooting, or in the case of still image shooting, a technique such as zooming shooting during exposure is used, resulting in an unnatural image.

To avoid these problems, an XY adjustment mechanism is required, but if a mechanical mechanism is employed,
This leads to an increase in the size of the imaging device. At the same time, even if a mechanical adjustment mechanism is adopted, it is necessary to find out how they are displaced and adjust to eliminate this error in order to align the center of the image frame with the optical axis. There is no concrete method for easily and automatically performing this with high accuracy.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and enables an optical axis and the center of an image frame to be easily and accurately aligned with each other, thereby realizing high-performance imaging with no image quality defects. An object of the present invention is to provide a frame centering adjustment method and an imaging device.

[0009]

According to the present invention, there is provided an image pickup apparatus having an image pickup system including an image pickup lens and an image pickup element. An image frame centering adjustment method for setting a movement of an imaging frame in a direction orthogonal to an optical axis of the imaging lens so as to coincide with an optical axis, wherein the movement setting of the imaging frame is based on the imaging system. The method is performed based on centering information on a shift between a center position of an image frame and an optical axis of the imaging lens, which is obtained by analyzing information of an imaging signal of the imaging device using the image capturing apparatus.

According to this image frame centering adjustment method,
The position of the image frame is adjusted based on the centering information obtained by analyzing the information of the image pickup signal of the image pickup device, whereby the optical axis and the image frame center can be easily adjusted with high accuracy, and a particularly large image frame can be obtained. Even without preparing an image circle, it is possible to easily realize high-performance imaging without a defect in image quality. Further, even when zooming is performed between the telephoto side and the wide-angle side, it is possible to prevent the occurrence of problems such as a shift of the zoom center from the center of the image frame.

The centering information obtained by analyzing the imaging signal is information relating to a deviation between the center position of the imaging frame and the optical axis of the imaging lens. Therefore, unlike the case of “camera shake correction” in which the trimming position of the image is changed according to the subject image, the value of the centering information for position adjustment is a value fixedly determined for each imaging device. Therefore, the analysis process for obtaining the centering information does not necessarily need to be performed in the imaging device. For example, the analysis process is performed outside the imaging device before shipping the product, and the centering information obtained thereby is stored in the imaging device. May be stored in the storage device.
Even in this case, the optical axis and the center of the image frame can be automatically and accurately adjusted based on the stored centering information.

Further, by providing the image pickup signal analyzing means in the image pickup apparatus, it becomes possible to automatically adjust the position of the image frame by the image pickup apparatus alone. Even in this case, since it is not necessary to analyze the imaging signal each time, it is preferable to store the centering information obtained by the analysis of the imaging signal in a storage device in the imaging apparatus.

The position adjustment of the image pickup frame can also be realized by moving and setting the position of the image pickup device using a mechanical adjustment mechanism, but the image frame trimming set with respect to the effective image output of the image pickup device can be realized. By realizing the movement by setting the range (electronic zoom), it is possible to easily realize the position adjustment of the captured image frame without using a mechanical mechanism.

Further, it is important to adjust the position of the image frame to the position where the highest quality image can be taken in consideration of the characteristics of the image pickup lens. For the purpose of image processing, use the analysis of the shading information of the imaging signal regarding the peripheral light falloff characteristic of the imaging lens. When importance is placed on the contrast, use the contrast information analysis of the imaging signal to further reduce the distortion. For the purpose of reduction, it is preferable to obtain centering information by using distortion information analysis of an imaging signal. As a result, not only the physical deviation amount from the optical axis itself but also a substantial deviation amount in consideration of various characteristics including an asymmetric element of the imaging lens can be obtained as centering information. The adjustment can be performed with high accuracy.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of an imaging device according to an embodiment of the present invention. Here, a case where the present invention is implemented as a digital camera will be described as an example.

In FIG. 1, reference numeral 101 denotes an imaging lens system including various lenses; 102, a lens driving mechanism for driving the imaging lens system 101; 103, an exposure control mechanism for controlling the diaphragm of the imaging lens system 101; And an infrared cut optical filter; 105, a CCD color image sensor with a color filter; 106, a CCD driver for driving the image sensor 105; 107, a pre-processing circuit including an A / D converter; A digital process circuit for performing signal generation processing, matrix conversion processing, and other various digital processing, 109 denotes a card interface, 110 denotes a memory card, and 111 denotes an LCD image display system.

In the figure, reference numeral 112 denotes a system controller (CPU) for integrally controlling each unit, 113 denotes an operation switch system including various operation buttons, and 114 denotes an operation for displaying an operation state and a mode state. Display system, 1
Reference numeral 15 denotes a flash as a light emitting unit; 116, a lens driver for controlling the lens driving mechanism 102; 117, an exposure control driver for controlling the flash 115 and the exposure control mechanism 103; 118, which stores various setting information; 1 shows a nonvolatile memory (EEPROM).

In the digital camera 100 of the present embodiment, the system controller 112 performs overall control, and controls the driving of the CCD image pickup device 105 by the CCD driver 106 to expose (charge accumulation) and signal. The readout is performed, the readout is taken into the digital process circuit 108 via the preprocess circuit 107, and various signal processes are performed, and thereafter, the data is recorded on the removable memory card 110 via the card interface 109. When the strobe 115 is used for the above-mentioned exposure, the strobe 115 is caused to emit light by controlling the exposure control driver 117 to send each control signal for starting and stopping light emission to the strobe 115.

In the digital camera 100 of the present embodiment, operations and controls similar to those of a normal digital camera are performed, except for operations relating to centering adjustment control of an image frame described in detail below. Description of such known parts will be omitted.

The system controller 112 is provided with a function for performing a centering adjustment control of a captured image frame, which is a feature of the present embodiment. Here, the centering adjustment control of the imaging frame is defined as the optical axis (Z) of the imaging lens 101.
By moving and setting the center of the image frame of the imaging system including the imaging lens 101 and the imaging element 105 in a direction (X, Y) orthogonal to This means XY adjustment processing. This X
To implement the Y adjustment process, the system controller 1
12, an image frame movement setting unit 201, an imaging information analysis unit 202, and an image frame centering adjustment unit 20
3 are provided.

The image frame movement setting unit 201 includes an image sensor 105
By moving the position of the image frame trimming (electronic zoom) set with respect to the effective image output, the image frame is moved and set in the X and Y directions. The movement setting of the image frame is performed by, for example, variably setting a trimming range to be read as an image signal from the image sensor 105 by drive control of the image sensor 105, or the image sensor 1
This can be realized by temporarily storing the imaging signals for all the effective images read from the internal memory 05 in an internal memory and variably setting a trimming range to be taken out from the internal memory.

Note that the movement setting itself of the captured image frame by the image frame trimming is performed by a known "camera shake correction".
Also, in the camera using the separate (non-TTL) type optical finder, such as “adjustment of the image frame with respect to the finder”, the moving setting of the image frame in the present embodiment is set so that the image frame is aligned with the optical axis. In that regard, at that point, the normal "image stabilization" for setting the image frame movement for following the subject image or the like, or "changing the cutout position of the image frame according to the finder image" Adjustment of viewfinder image frame ''
Is different from

The imaging information analysis unit 202 includes the imaging device 105
The centering information for aligning the center of the captured image frame with the optical axis is obtained by analyzing the image signal obtained from. This centering information is information relating to the amount of deviation between the center position of the imaging frame and the optical axis of the imaging lens 101, and is specifically given by the coordinates (x, y) of the center position of the imaging frame to be moved. .

An image frame centering adjustment section 203 is for setting and controlling the center position of the image frame, and based on the centering information obtained by the image information analysis section 202, the image frame movement setting section 201 sets the image frame. Control the movement settings.

Here, the principle of the XY adjustment processing in this embodiment will be described with reference to FIG.

FIG. 2A shows a CCD effective area 301.
An example of the default position of the image frame 302 with respect to is shown. In FIG. 2A, the center position of the image frame 302 from which the image pickup signal is to be cut out from the CCD effective area 301 is set to the center position (0.0) of the CCD effective area 301. If the center of the lens circle 303 of the imaging lens 101 (the center of the optical axis (Z axis) of the imaging lens 101) is shifted to the center position (0 of the CCD effective area 301 as shown in FIG. .0), as described above, there are problems such as a difference in brightness between the upper, lower, left, and right sides of the screen, and vignetting of some images at four corners of the image frame. In particular, FIG.
This problem becomes apparent when a lens having an image circle just below the frame of the captured image is used as shown in FIG.

In this embodiment, the centering information is obtained from the captured image signal, and the centering information is used to determine the center position (x, y) of the image frame 302 from which the image signal is to be cut out from the CCD effective area 301. FIG.
As shown in (c), an XY adjustment process is performed to match the optical axis (Z) of the lens.

A specific example of the captured image signal analysis processing for obtaining centering information will be described below. (Shading Detection) Shading detection is a process for obtaining centering information by analyzing shading information of an image pickup signal. Here, the shading information means information on a peripheral light amount drop characteristic of the imaging lens 101 caused by vignetting due to a well-known COS ⁴ rule based on an optical principle or lens characteristics.

When the centering information is obtained by using the shading information, an all white chart (referred to as a uniform white chart or an all white chart) is used.
Is photographed, and a process of comparing four corners of the imaging signal obtained thereby is performed. That is, as shown in FIG. 3, the integrated average value of the image signal output of each of the four upper and lower corners of the image signal (image frame output) after the image frame clipping is obtained, and the light amount of the upper and lower four corners is calculated. A position of the captured image frame that is uniform is obtained as centering information.

That is, the integrated averages of the four upper and lower corners are s1 (upper left), s2 (upper right), s3 (lower left), and s4 (lower right), and the evaluation amount (SFX) of the shading characteristic in each of the X and Y directions. , SFY). Here, the evaluation amount (SFX, STY) is given by SFX = (s2 + s4)-(s1 + s3) SFX = (s1 + s2)-(s3 + s4)

The coordinates (x, y) of the center position of the image frame are moved and set, and the coordinates x at which SFX takes the minimum value (SFX ≒ 0)
And the coordinate y at which SFY becomes a minimum value (SFY ≒ 0). Thus, centering information (center position coordinates of the image frame) for aligning the center of the image frame with the optical axis is obtained.

Here, a specific procedure of the XY adjustment processing using the shading detection will be described with reference to the flowchart of FIG.

First, the imaging lens 101 and the imaging device 1
05, an image of the all-white chart is taken (step S11). The imaging signal of the CCD effective area obtained by this imaging is stored in an internal memory or the like of the digital camera, and the imaging information analysis unit 112 performs the following analysis processing on the imaging signal in the internal memory.

First, the above-mentioned SFX and SFY are calculated from the integrated average outputs of the four corners of the image cut out by the default image frame (steps S12 and S1).
3). Next, SFX is evaluated (step S14). When SFX> 0, that is, when the light amount is deviated to the right, the X coordinate (x) of the center position of the imaging frame from which the imaging signal should be cut out from the CCD effective area 301 is +1.
(Step S15), and the image frame is moved rightward from the current position by +1 (Step S12).

On the other hand, if SFX <0, that is, if the light amount is deviated to the left, the X coordinate (x) of the center position of the image frame from which the image signal is to be cut out from the CCD effective area 301 is decremented by 1 (step S16). ), The image frame is moved +1 from the current position to the left (step S12).

As described above, the center position of the image frame is set to X
The SFX is evaluated while being shifted in the direction, and a coordinate x at which the SFX has a minimum value (SFX ≒ 0) is calculated as centering information about the X axis. Then, the position of the imaging frame is set at the coordinate x.

Thereafter, the SFY is evaluated (step S17). If SFY> 0, that is, if the amount of light is deviated upward, the Y coordinate (y) of the center position of the imaging frame from which the imaging signal should be cut out from the CCD effective area 301
Is incremented by 1 (step S18), and the captured image frame is moved upward by +1 from the current position (step S12). on the other hand,
When SFY <0, that is, when the light amount is biased downward,
The Y coordinate (y) of the center position of the imaging frame from which the imaging signal is to be cut out from the CCD effective area 301 is decremented by 1 (step S19), and the imaging frame is moved +1 downward from the current position (step S12). In this way, the evaluation of SFY is performed while shifting the center position of the captured image frame in the Y direction, and the coordinate y at which SFY has a minimum value (SFY ≒ 0) is calculated as centering information on the Y axis. Then, the position of the image frame is set at the coordinate y.

As described above, by performing the shading information analysis using the light amounts at the four left and right corners, even if the imaging lens 101 includes an asymmetric element, the light amounts at the four left and right corners can be calculated. It is possible to adjust the position of the captured image frame to an optimal position that can be made uniform. In other words, when the asymmetric element is included in the imaging lens 101, it is not the center of the physical lens optical axis,
The center position of the captured image frame that can make the light amount at the corner uniform can be regarded as the substantial center of the optical axis.

Note that the shading information analysis does not necessarily need to be performed in the digital camera. For example, before the product is shipped, the imaging output of the digital camera is analyzed by a computer or the like, and the centering information obtained thereby is converted into EE.
It may be stored in the PROM 118 and shipped.
In this case, the procedure of the XY adjustment performed in the digital camera is as shown in FIG.

That is, the system controller 112
First, the centering information is read from the EEPROM 118 (step S21), and the coordinate position (x, y) specified by the centering information is set as an image frame center position for extracting an image frame (step S22).

As described above, by storing the centering information in the EEPROM 118 in advance, the digital camera does not need the above-described imaging processing analyzing unit 202, and
It is only necessary to provide only the function of setting the movement of the image frame based on the centering information of the EPROM 118.

Next, another example of the captured image signal analysis processing for obtaining centering information will be described. (Contrast Detection) Contrast detection is a process for obtaining centering information by analyzing contrast information of an imaging signal. That is, since the resolution of the imaging lens 101 is usually highest at the center of the lens, analysis of contrast information is performed to check characteristics of the resolution.

When the centering information is obtained by using this contrast information, a uniform dot chart as shown in FIG. 6 is taken, and the coordinate position where the contrast becomes maximum among the imaging signals obtained thereby is centered. Required as information.

(Distortion Detection) The distortion detection is a process for obtaining centering information by analyzing distortion information of an image pickup signal. That is, usually, the imaging lens 101
When imaging is performed by using, there is a case where the influence of the distortion of the lens appears in the imaging signal. Therefore, the distortion information is analyzed in order to examine the characteristic regarding the distortion.

When the centering information is obtained by using the distortion information, a lattice chart as shown in FIG. 7A is photographed, and the state of the distortion of the image signal obtained thereby is analyzed. Specifically, when a lattice chart is photographed, if the imaging lens 101 has distortion, for example, a captured image distorted in a pincushion shape as shown in FIG. Thus, a distorted captured image or the like can be obtained. In this case, the integral value (line integral value) of the imaging signal on each horizontal line and each vertical line of the captured image is calculated by utilizing the fact that only the straight line passing through the optical axis is not bent but kept straight. , The position of the horizontal line at which the line integration value is the maximum is defined as the y coordinate of the center of the image frame.
What is necessary is just to determine the position of the vertical line at which the line integration value becomes the maximum as the x coordinate of the center of the captured image frame. Further, by taking advantage of the symmetry of the image, the captured image is divided into two at a certain horizontal line or vertical line position, and the correlation between the two images is evaluated when one of the two divided images is a mirror image. The distortion center position may be obtained for both the horizontal and vertical directions, and the distortion center position in each of the horizontal and vertical directions may be determined as the center position coordinates (x, y) of the captured image frame.

As described above, in the present embodiment, the centering information is obtained by analyzing the imaging output in consideration of the characteristics of the imaging lens, and the XY adjustment for aligning the center of the image frame with the optical axis is performed using the centering information. By doing so, it is possible to set the imaging frame at an optimal position even when the lens includes an asymmetric element, and to provide a high-quality image without deterioration in image quality without providing an extra adjustment margin in the image circle. A captured image can be obtained. Further, in the present embodiment, since the position of the captured image frame is adjusted by setting the movement of the image frame trimming range, it is not necessary to use a mechanical adjustment mechanism, and the imaging system can be reduced in size.

Regarding which of the above-described shading detection, contrast detection, and distortion detection is used for image analysis, emphasis is placed on shading detection and contrast when the purpose of uniforming the brightness of an image signal is to be achieved. In this case, the selection may be made according to the purpose of the XY adjustment, such as detecting the contrast and detecting the distortion when the purpose is to reduce the distortion.

As described in connection with the shading detection, the contrast detection and the distortion detection may be performed outside the digital camera, and the centering information obtained thereby may be stored in the EEPROM 118.

Further, in the present embodiment, only the case where the position of the image frame is adjusted by moving the image frame trimming range has been described. However, in the case of a relatively large image pickup apparatus or the like, mechanical position adjustment is performed. Needless to say, a mechanism may be provided so that the position of the solid-state imaging device 105 itself may be set.

[0050]

As described above, according to the present invention,
By adjusting the position of the image frame based on the centering information obtained by analyzing the image signal, the optical axis and the center of the image frame can be easily adjusted with high accuracy, and no special large image circle is prepared. In both cases, it is possible to easily realize high-performance imaging without a defect in image quality.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a digital camera according to an embodiment of the present invention.

FIG. 2 is an exemplary view for explaining the principle of XY adjustment processing used in the embodiment.

FIG. 3 is an exemplary view for explaining information on four corners in a captured image used in shading detection according to the embodiment;

FIG. 4 is an exemplary flowchart illustrating an example of a specific procedure of XY adjustment processing when shading detection is used in the embodiment.

FIG. 5 is an exemplary flowchart illustrating another example of the XY adjustment processing according to the embodiment;

FIG. 6 is an exemplary view showing an example of a dot chart used in contrast detection processing of the embodiment.

FIG. 7 is an exemplary view showing an example of a grid chart used in the distortion detection processing of the embodiment and an image pickup signal obtained by photographing the grid chart.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 ... Imaging lens 105 ... CCD color imaging device 106 ... CCD driver 112 ... System controller 118 ... Non-volatile memory (EEPROM) 201 ... Image frame movement setting unit 202 ... Image information analysis unit 203 ... Image frame centering adjustment unit

Claims (8)

[Claims] 1. An image pickup apparatus having an image pickup system including an image pickup lens and an image pickup device, wherein an optical axis of the image pickup lens is adjusted so that a center of an image frame of the image pickup system coincides with an optical axis of the image pickup lens. An image frame centering adjustment method for setting a movement of an image frame in a direction orthogonal to the image frame, wherein the movement setting of the image frame is obtained by analyzing information of an imaging signal of the imaging apparatus using the imaging system. An image frame centering adjustment method for an image pickup apparatus, wherein the method is performed based on the obtained centering information on the deviation between the center position of the image frame and the optical axis of the imaging lens. 2. An image pickup system comprising an image pickup lens and an image pickup device, and storage means for storing the centering information obtained at the time of the image frame centering adjustment performed using the image frame centering adjustment method according to claim 1. An image frame setting unit that adjusts a position of the image frame by performing a movement setting of the image frame in a direction orthogonal to an optical axis of the imaging lens based on the centering information stored in the storage unit; An imaging device comprising: 3. An image pickup system comprising an image pickup lens and an image pickup element, and information of an image pickup signal as an output signal of the image pickup system is analyzed,
Imaging information analysis means for obtaining centering information on a shift between the center of the image frame of the imaging system and the optical axis of the imaging lens; and an imaging image frame in a direction orthogonal to the optical axis of the imaging lens based on the centering information. An image frame setting unit that adjusts the position of the image frame by setting the movement of the image frame. 4. A storage unit for storing the centering information obtained by the imaging information analysis unit, wherein the image frame setting unit sets the movement of the image frame based on the centering information of the storage unit. The imaging device according to claim 3, wherein: 5. The image frame centering adjustment method according to claim 1, wherein the centering information is obtained based on shading information analysis of the imaging signal. An imaging device according to any one of the preceding claims. 6. The image frame centering adjustment method according to claim 1, wherein the centering information is obtained based on a contrast information analysis of the image pickup signal. An imaging device according to any one of the preceding claims. 7. The image frame centering adjustment method according to claim 1, wherein the centering information is obtained based on a distortion information analysis of the imaging signal. An imaging device according to any one of the preceding claims. 8. The image frame setting means is configured to set the movement of the photographed image frame by moving an image frame trimming range set for an effective image output of the image sensor. The imaging device according to any one of claims 2 to 4, wherein the imaging device is provided.