A precise adjustment method for image sensor tilt correction

Abstract

The present invention discloses a precise adjustment method for image sensor tilt correction, comprising: arranging the image sensor at the end of a visible light path, and placing a converging lens in front of the image sensor; under the action of an adjustment device, the image sensor's image plane is initially perpendicular to the principal optical axis, and the light spot falls at the center of the image plane; rotating the image sensor to obtain the light spot on the image plane at this time, using an image contour detection algorithm to identify the light spot contour, and calculating the circumference L1 of the light spot, and recording the angle value θ1 at this time; rotating the image sensor in the opposite direction to obtain the light spot on the image plane at this time, and using the same method to obtain the circumference L2 of the light spot; slightly rotating the image sensor to L2 = L1, and recording the angle value θ2 at this time; rotating the image sensor to a position θ0 between the two angle values ​​θ1 and θ2; and removing the converging lens to complete the image sensor tilt correction. The tilt correction adjustment of the present invention is simple to operate, highly accurate, time-saving, and highly reproducible.

Description

Technical Field

[0001] The present invention relates to the field of optical path adjustment, and in particular to a precise adjustment method for tilt correction of an image sensor. Background Art

[0002] Precision optical systems are increasingly being used in cutting-edge fields such as aerospace and high-end equipment manufacturing. High-precision optical path adjustment is becoming increasingly important in optical systems, especially in high-resolution imaging and precision measurement. The accuracy of optical path adjustment directly impacts the imaging quality and measurement accuracy of optical systems. Therefore, the research on optical path adjustment technology has become a key topic in optical engineering.

[0003] The image sensor is a crucial component of the optical system. Tilting the image sensor's image plane normal relative to the principal optical axis can lead to image distortion and reduced image quality. For example, image sensor tilt can cause uneven light intensity distribution, resulting in inconsistent image brightness. It can also shift the focal plane position, affecting image quality. It can also introduce additional aberrations, such as coma and astigmatism, which can further reduce image clarity and compromise imaging performance.

[0004] In existing technology, image sensor tilt correction primarily involves pre-calibrating the offset distance between the intersection of the optical system's principal optical axis and the image sensor relative to the image sensor's center position, as well as the travel distance of the optical system relative to the image sensor's central axis. The relationship between these two values ​​is then fitted to determine the tilt angle of the optical system's principal optical axis relative to the image sensor's image plane normal, which is then used for correction. This method requires pre-calibration data, increasing the complexity of image sensor tilt correction. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, in order to reduce the impact of image sensor tilt on the received optical path information, the present invention proposes a precise adjustment method for image sensor tilt correction. This method combines mechanical adjustment and precise adjustment methods of image processing to achieve precise correction of image sensor tilt, effectively solving the problems of image distortion and image quality degradation caused by the tilt of the image sensor image plane normal relative to the main optical axis, and is suitable for various high-precision imaging systems.

[0006] The specific technical solutions are as follows:

[0007] A precise adjustment method for tilt correction of an image sensor, characterized by comprising the following steps:

[0008] S1: The image sensor is arranged at the end of the visible light path, and a converging lens is placed in front of the image sensor; the image sensor is preliminarily adjusted in angle using an adjustment device so that the image plane of the image sensor is initially perpendicular to the principal optical axis and the light spot falls in the center of the image plane of the image sensor;

[0009] S2: Rotate the image sensor and obtain the light spot on the image plane of the image sensor at this time;

[0010] S3: Use the image contour detection algorithm to identify the light spot contour and calculate the perimeter L1 of the light spot, and use it as a reference to record the angle value displayed by the adjustment device at this time as θ1;

[0011] S4: Rotate the image sensor in the opposite direction and obtain the light spot on the image plane of the image sensor at this time;

[0012] S5: Use image contour detection algorithm to identify the light spot contour and calculate the perimeter L2 of the light spot;

[0013] S6: Compare L1 and L2. If they are not equal, continue to slightly rotate the image sensor until L2 and L1 are equal. Record the angle value displayed by the adjustment device at this time as θ2.

[0014] S7: Rotate the image sensor to the middle position between the two angle values ​​θ1 and θ2. The calculation expression of the angle value θ0 corresponding to the middle position is as follows:

[0015]

[0016] S8: Remove the converging lens to complete the tilt correction of the image sensor.

[0017] Furthermore, the adjustment device includes a rotation stage and a translation stage, the translation stage is arranged on the rotation stage, and the image sensor is arranged on the translation stage; the rotation stage is used to control the rotation angle of the image sensor, and the translation stage is used to control the displacement of the image sensor in the plane.

[0018] Furthermore, the image sensor is selected from CCD or CMOS.

[0019] Furthermore, the image contour detection algorithm in S3 and S5 uses the Hough transform detection algorithm, and the specific detection process is as follows:

[0020] (1) Preprocess the input image, convert the image into a grayscale image, use an edge detection algorithm to extract the edges in the image, and use a filter to remove noise in the image;

[0021] (2) defining the parameter space based on a specific shape;

[0022] (3) Initializing an accumulator array for counting the number of points in the parameter space. For each edge point in the image obtained in step (1), the corresponding value in the parameter space, i.e., the eigenvalue of the corresponding graph, is counted into the accumulator array.

[0023] (4) Look for peaks of high counts in the accumulator array, corresponding to shape features in the image.

[0024] A point diffraction interferometer, wherein the tilt angle of an image sensor is adjusted according to the precise adjustment method for image sensor tilt correction, the point diffraction interferometer comprising: a light source, a beam expander collimator lens group, a microscope objective lens, a pinhole plate, an image sensor, and a reflector to be measured, which are sequentially arranged along an optical axis;

[0025] The light source is used to generate a coherent light source; the beam expander and collimator lens group is used to expand and collimate the light generated by the light source; and the microscope objective lens is used to converge the expanded and collimated light onto the pinhole plate;

[0026] The submicron-sized pinhole on the pinhole plate is used to diffract the converged light beam into a spherical wave, which is divided into a reference wave and a detection wave; the reference wave directly reaches the image sensor; the detection wave reaches the reflector to be measured, and after reflection, reaches the pinhole plate, and then reaches the image sensor after reflection from the metal surface of the pinhole plate; the reference wave and the detection wave form an interference pattern at the image sensor.

[0027] The beneficial effects of the present invention are:

[0028] (1) The present invention first adjusts the image plane of the image sensor to a position approximately perpendicular to the main optical axis through an adjustment device, so that the adjustment range can be quickly locked, which greatly saves the adjustment time of the image sensor tilt correction; secondly, the corresponding light spot is obtained by performing positive and negative rotations on the existing position of the image sensor, and the light spot contour is marked by an image contour detection algorithm. According to the equal circumferences of the two light spot contours, two angle values ​​are accurately obtained, thereby obtaining the angle value when the image sensor is perpendicular to the main optical axis, thereby avoiding blind adjustment.

[0029] (2) The present invention places a converging lens in front of the image sensor, so that the light spot of the light beam passing through the converging lens and reaching the image sensor becomes smaller, thereby increasing the angle adjustment range of the adjustment device and improving the accuracy of tilt correction. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 4 is a flow chart of a precise adjustment method for image sensor tilt correction in an embodiment of the present invention.

[0031] Figure 2 3 is a schematic diagram of the principle of precise adjustment of image sensor tilt correction in an embodiment of the present invention.

[0032] Figure 3 Schematic diagram of the structure of the regulating device in an embodiment of the present invention.

[0033] Figure 4 1 is a diagram of the optical path structure of a point diffraction interferometer in an embodiment of the present invention.

[0034] In the figure, there are an image sensor 1, a translation stage 2, a rotation stage 3, a light source 4, a beam expander and collimator lens group 5, a microscope objective lens 6, a pinhole plate 7, and a reflector to be measured 8. DETAILED DESCRIPTION

[0035] The present invention will be described in detail below based on the accompanying drawings and preferred embodiments. The purpose and effects of the present invention will become more apparent. The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0036] like Figure 1 As shown, a precise adjustment method for tilt correction of an image sensor includes the following steps:

[0037] S1: Image sensor 1 is positioned at the end of the visible light path, and a converging lens is placed in front of image sensor 1. An adjustment device is used to perform preliminary angular adjustment on image sensor 1, so that the image plane of image sensor 1 is initially perpendicular to the principal optical axis and the light spot falls at the center of the image plane of image sensor 1. The converging lens is used to reduce the light spot size of the light beam that reaches the image sensor after passing through the converging lens, thereby increasing the angular adjustment range of the adjustment device and improving the accuracy of tilt correction.

[0038] Preferably, the image sensor 1 is CCD or CMOS.

[0039] like Figure 2 As shown, the adjustment device includes a rotation stage 3 and a translation stage 2. The translation stage 2 is arranged on the rotation stage 3, and the image sensor 1 is arranged on the translation stage 2. The rotation stage 3 is used to control the rotation angle of the image sensor 1, and the translation stage 2 is used to control the displacement of the image sensor 1 within the plane.

[0040] S2: Rotate the image sensor 1 and obtain the light spot on the image plane of the image sensor 1 at this time.

[0041] S3: Use the image contour detection algorithm to identify the light spot contour and calculate the perimeter L1 of the light spot, and use it as a reference to record the angle value θ1 displayed by the adjustment device at this time, such as Figure 3 shown.

[0042] The image contour detection algorithm uses the Hough transform detection algorithm, which is often used to detect shape features. The specific detection process is as follows:

[0043] (1) Preprocess the input image, convert the image into a grayscale image, use an edge detection algorithm to extract the edges in the image, and use a filter to remove noise in the image.

[0044] (2) Define the parameter space based on a specific shape. For example, when detecting a circle, define the parameter space (a, b, r), that is:

[0045] (xa) 2 +(yb) 2 =r 2

[0046] Where (a, b) is the coordinate of the center of the circle and r is the radius.

[0047] (3) Initialize the accumulator array to count the number of edge points in the parameter space. For each edge point in the image obtained in step (1), count its corresponding value in the parameter space, that is, the eigenvalue of the corresponding graph, into the accumulator array. For example, for circle detection, each edge point (x, y) needs to be iterated through all possible radius r and center (a, b), and then add the count of the corresponding position to the accumulator array.

[0048] (4) Find peaks with high counts in the accumulator array, which correspond to shape features in the image. For example, a peak (a, b, r) in the accumulator array corresponds to a circle in the image.

[0049] S4: Rotate the image sensor 1 in the opposite direction and obtain the light spot on the image plane of the image sensor 1 at this time.

[0050] S5: Use the image contour detection algorithm to identify the light spot contour and calculate the perimeter L2 of the light spot.

[0051] S6: Compare L1 and L2. If they are not equal, continue to slightly rotate the image sensor 1 until L2 and L1 are equal. Record the angle value displayed by the adjustment device at this time as θ2. Figure 3 shown.

[0052] S7: Rotate the image sensor 1 to the middle position between the two angle values ​​θ1 and θ2. The calculation expression of the angle value θ0 corresponding to the middle position is as follows:

[0053]

[0054] Theoretical analysis of the expression for the angle value θ0 corresponding to the middle position: Taking the position where the image plane of image sensor 1 is perpendicular to the principal optical axis as the reference, the image sensor 1 is rotated left and right by the same angle θ. The horizontal width scaling factor of the light spot is cosθ, so the perimeter of the light spot contour obtained after the two rotations is consistent. Therefore, two symmetrical angle values ​​θ1 and θ2 can be obtained based on whether the perimeters of the light spot contours obtained after the two rotations are consistent. At this time, θ satisfies the following formula:

[0055] θ=θ0-θ1

[0056] θ=θ2-θ0

[0057] From the above formula, it can be deduced that the expression for the angle value θ0 corresponding to the middle position is valid.

[0058] S8: The converging lens is removed. At this time, the image plane of the image sensor 1 is perpendicular to the main optical axis, and the tilt of the image sensor 1 is accurately corrected.

[0059] like Figure 4 The figure shows a schematic diagram of the optical path of a point diffraction interferometer using an image sensor. The point diffraction interferometer includes: a light source 4, a beam expander and collimator lens group 5, a microscope objective lens 6, a pinhole plate 7, an image sensor 1 and a reflector to be measured 8 arranged in sequence along the optical axis.

[0060] The light source 4 is used to generate a coherent light source; the beam expander and collimator lens assembly 5 is used to expand and collimate the light generated by the light source 1; and the microscope objective 6 is used to converge the expanded and collimated light onto the pinhole plate 7. The pinhole in the pinhole plate 7 is of submicron size, so that the converged light beam diffracts into an ideal spherical wave, which is then divided into a reference wave and a detection wave. The reference wave directly reaches the image sensor 1, while the detection wave is reflected back to the vicinity of the pinhole in the pinhole plate 7 by the under-test reflector 8, and then reflected by the metal surface of the pinhole plate 7 to reach the image sensor 1. As a result, the reference wave and the detection wave form an interference pattern at the image sensor 1.

[0061] In the optical path system of a point diffraction interferometer, the tilt of the image sensor 1 significantly affects the quality of the interference pattern, thereby significantly reducing the accuracy of the surface shape measurement of the reflector 8 to be measured. Therefore, it is necessary to use the precise adjustment method for image sensor tilt correction to accurately adjust the tilt of the image sensor 1.

[0062] The precise adjustment method for image sensor tilt correction provided by the present invention can complete the correction of image sensor tilt without the need for pre-calibration data, thereby reducing the optical path adjustment technical requirements for operators.

[0063] Those skilled in the art will understand that the foregoing descriptions are merely preferred embodiments of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art will still be able to modify the technical solutions described in the foregoing examples or substitute equivalents for some of the technical features therein. Any modifications, equivalent substitutions, etc. made within the spirit and principles of the invention shall be included within the scope of protection of the invention.

Claims

1. A precise adjustment method for image sensor tilt correction, characterized in that: The following steps are involved: S1: The image sensor is arranged at the end of the visible light path, and a converging lens is placed in front of the image sensor; the image sensor is preliminarily adjusted in angle using an adjustment device so that the image plane of the image sensor is initially perpendicular to the principal optical axis and the light spot falls in the center of the image plane of the image sensor; S2: Rotate the image sensor and obtain the light spot on the image plane of the image sensor at this time; S3: Use the image contour detection algorithm to identify the light spot contour and calculate the perimeter L1 of the light spot, and use it as a reference to record the angle value displayed by the adjustment device at this time as θ1; S4: Rotate the image sensor in the opposite direction and obtain the light spot on the image plane of the image sensor at this time; S5: Use image contour detection algorithm to identify the light spot contour and calculate the perimeter L2 of the light spot; S6: Compare L1 and L2. If they are not equal, continue to slightly rotate the image sensor until L2 and L1 are equal. Record the angle value displayed by the adjustment device at this time as θ2. S7: Rotate the image sensor to the middle position between the two angle values ​​θ1 and θ2. The calculation expression of the angle value θ0 corresponding to the middle position is as follows: S8: Remove the converging lens to complete the tilt correction of the image sensor.

2. The precise adjustment method for image sensor tilt correction according to claim 1, characterized in that: The adjustment device includes a rotating stage and a translation stage. The translation stage is arranged on the rotating stage, and the image sensor is arranged on the translation stage. The rotating stage is used to control the rotation angle of the image sensor, and the translation stage is used to control the displacement of the image sensor in a plane.

3. The precise adjustment method for image sensor tilt correction according to claim 1, characterized in that: The image sensor is selected from CCD or CMOS.

4. The precise adjustment method for image sensor tilt correction according to claim 1, characterized in that: The image contour detection algorithm in S3 and S5 uses the Hough transform detection algorithm, and the specific detection process is as follows: (1) Preprocess the input image, convert the image into a grayscale image, use an edge detection algorithm to extract the edges in the image, and use a filter to remove noise in the image; (2) defining the parameter space based on a specific shape; (3) Initializing an accumulator array for counting the number of points in the parameter space. For each edge point in the image obtained in step (1), the corresponding value in the parameter space, i.e., the eigenvalue of the corresponding graph, is counted into the accumulator array. (4) Look for peaks of high counts in the accumulator array, corresponding to shape features in the image.

5. A point diffraction interferometer, wherein the tilt angle of the image sensor is adjusted according to the precise adjustment method for image sensor tilt correction according to any one of claims 1 to 4, characterized in that: The point diffraction interferometer comprises: a light source, a beam expansion collimator lens group, a microscope objective lens, a pinhole plate, an image sensor and a reflector to be measured, which are sequentially arranged along the optical axis; The light source is used to generate a coherent light source; the beam expander and collimator lens group is used to expand and collimate the light generated by the light source; and the microscope objective lens is used to converge the expanded and collimated light onto the pinhole plate; The submicron-sized pinhole on the pinhole plate is used to diffract the converged light beam into a spherical wave, which is divided into a reference wave and a detection wave; the reference wave directly reaches the image sensor; the detection wave reaches the reflector to be measured, and after reflection, reaches the pinhole plate, and then reaches the image sensor after reflection from the metal surface of the pinhole plate; the reference wave and the detection wave form an interference pattern at the image sensor.

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