# Patent

## Title
Image capturing device and method for calibrating image deformation thereof

## Abstract

A method for calibrating image deformation of an image capturing device having a first and second lens, a focusing actuator, and a prestored first focusing step-to-focusing distance relation includes the following steps. A plurality of image sets are captured by the first and second lens, where each of the image sets includes a first and second image, and the images sets include a reference image set. It is detected whether the reference image set is deformed. When the reference image set is detected to be deformed, the first focusing step-to-focusing distance relation is calibrated according to a focusing step and a focusing distance corresponding to each of the image sets, where the focusing step corresponding to each of the image sets is the number of steps that the focusing actuator is required to move the first and second lens to a focusing position to generate each of the image sets.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 103103261, filed on Jan. 28, 2014. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to an image capturing device, and more particularly, relates to a method for calibrating image deformation of an image capturing device.
Description of Related Art
With development in technology, various smart image capturing devices, such as tablet computers, personal digital assistants and smart phones, have become indispensable tools for people nowadays. Camera lenses equipped in high-end smart image capturing devices provide same or better specifications than those of traditional consumer cameras, and some even provide three-dimensional image capturing features or near-equivalent pixel qualities to those of digital single lens reflex cameras.
Generally, during an autofocusing procedure, an image capturing device may be focused by adjusting positions of lenses through a focusing actuator such as a stepping motor, a voice coil motor (VCM) and so on. Hence, before such image capturing device leaves the factory, a corresponding relation between a focusing distance of a target and a moving step of the focusing actuator may be archived into a conversion table and pre-stored in the image capturing device. Accordingly, when the image capturing device executes the autofocusing procedure on an arbitrary target, the focusing distance of such target may be obtained according to depth information thereof, so that the number of steps that the focusing actuator is required to move may be acquired and the lenses may be adjusted accordingly. However, in practical use, deformation or offset usually occurs on the lenses and the focusing actuator of the image capturing device due to external factors such as drop-offs, bumps, squeezes, changes in temperatures or humidity. The auto-focusing procedure may thus cause errors when the image capturing device captures images.
SUMMARY OF THE INVENTION
Accordingly, the invention is directed to an image capturing device and a method for calibrating the image deformation thereof, which are capable of detecting whether a deformation or an offset occurs on a first lens, a second lens and a focusing actuator and calibrating the image capturing device at any time, so as to ensure a stable quality of the image capturing device.
The invention proposes a method for calibrating image deformation of an image capturing device having first and second lenses, a focusing actuator and a pre-stored first focusing step-to-focusing distance relation, and the method for calibrating image deformation includes the following steps. First, a plurality of image sets are captured by utilizing the first lens and the second lens, where each of the image sets includes a first image corresponding to the first lens and a second image corresponding to the second lens. The image sets include a reference image set, and the reference image set includes a first reference image corresponding to the first lens and a second reference image corresponding to the second lens. Next, it is detected whether the reference image set is deformed. When the reference image set is detected to be deformed, the first focusing step-to-focusing distance relation is calibrated according to a focusing step and a focusing distance corresponding to a focus target in each of the image sets, where the focusing step corresponding to the focus target in each of the image sets is the number of steps that the focusing actuator is required to move the first lens and the second lens to a focusing position for generating each of the image sets.
In an embodiment of the invention, the step of detecting whether the reference image set is deformed includes: detecting image coordinates of a feature point respectively on the first reference image and the second reference image of the reference image set; determining whether an offset between the image coordinates of the feature point respectively on the first reference image and the second reference image exceeds a threshold; and if yes, determining that the reference image set is deformed.
In an embodiment of the invention, the step of detecting whether the reference image set is deformed includes: performing a three-dimensional depth estimation on the first reference image and the second reference image to generate reference depth information of a reference focus target in the reference image set; obtaining a focusing distance corresponding to the reference focus target according to the reference depth information; determining whether a focusing step and the focusing distance corresponding to the reference focus target satisfy the first focusing step-to-focusing distance relation; and if no, determining that the reference image set is deformed.
In an embodiment of the invention, when the reference image set is detected to be deformed, before the step of calibrating the first focusing step-to-focusing distance relation according to the focusing step and the focusing distance corresponding to the focus target in each of the image sets, the method for calibrating image deformation further includes the following steps. A focusing condition of the image capturing device is detected, where the focusing condition includes a far focusing condition and a near focusing condition.
In an embodiment of the invention, when the reference image set is detected to be deformed and the focusing condition is the far focusing condition, the step of calibrating the first focusing step-to-focusing distance relation according to the focusing step and the focusing distance corresponding to the focus target in each of the image sets includes: recording the focusing step corresponding to the focus target in each of the image sets; and when the focusing step corresponding to the focus target in each of the image sets reaches a convergent value, obtaining a minimum focusing step in the first focusing step-to-focusing distance relation, and calculating a difference value between the minimum focusing step and the convergent value for calibrating the first focusing step-to-focusing distance relation.
In an embodiment of the invention, when the reference image set is detected to be deformed and the focusing condition is the near focusing condition, the step of calibrating the first focusing step-to-focusing distance relation according to the focusing step and the focusing distance corresponding to the focus target in each of the image sets includes: performing a three-dimensional depth estimation on each of the image sets to generate depth information of the focus target in each of the image sets; obtaining the focusing distance corresponding to the focus target in each of the image sets according to each of the depth information; and performing a regression according to the focusing distance and the focusing step corresponding to the focus target in each of the image sets, and calibrating the first focusing step-to-focusing distance relation according to a result of the regression.
The invention also proposes an image capturing device including a first lens, a second lens, a focusing actuator, a storage unit and one or more processing units, where the focusing actuator is coupled to the first lens and the second lens, and the processing unit(s) is coupled to the first lens, the second lens, the focusing actuator, and the storage unit. The storage unit is configured to record a plurality of modules and a first focusing step-to-focusing distance relation. The processing unit is configured to access and execute the modules recorded in the storage unit. The modules include an image capturing module, a focusing module, a deformation detection module, and a calibrating module. The image capturing module captures a plurality of image sets by utilizing the first lens and the second lens, where each of the image sets includes a first image corresponding to the first lens and a second image corresponding to the second lens. The image sets include a reference image set, and the reference image set includes a first reference image corresponding to the first lens and a second reference image corresponding to the second lens. The focusing module is configured to control the focusing actuator to move the first lens and the second lens to a focusing position. The deformation detection module is configured to detect whether the reference image set is deformed. When the deformation detection module detects that the reference image set is deformed, the calibrating modules calibrates the first focusing step-to-focusing distance relation according to a focusing step and a focusing distance corresponding to a focus target in each of the image sets, where the focusing step corresponding to the focus target in each of the image sets is the number of steps that the focusing actuator is required to move the first lens and the second lens to a focusing position for generating each of the image sets.
In an embodiment of the invention, the deformation detection module detects image coordinates of a feature point respectively on the first reference image and the second reference image of the reference image set, determines whether an offset between the image coordinates of the feature point respectively on the first reference image and the second reference image exceeds a threshold, and if yes, the deformation detection module determines that the reference image set is deformed.
In an embodiment of the invention, the deformation detection module performs a three-dimensional depth estimation on the first reference image and the second reference image to generate reference depth information of a reference focus target in the reference image set, obtains a focusing distance corresponding to the reference focus target according to the reference depth information, determines whether a focusing step and the focusing distance corresponding to the reference focus target satisfy the first focusing step-to-focusing distance relation, and if no, the deformation detection module determines that the reference image set is deformed.
In an embodiment of the invention, the image capturing device further includes a condition detection module configured to detect a focusing condition of the image capturing device, where the focusing condition includes a far focusing condition and a near focusing condition.
In an embodiment of the invention, when the focusing condition is the far focusing condition, the calibrating module records the focusing step corresponding to a focus target in each of the image sets. When the focusing step corresponding to the focus target in each of the image sets reaches a convergent value, the calibrating module obtains a minimum focusing step in the first focusing step-to-focusing distance relation, and calculates a difference value between the minimum focusing step and the convergent value for calibrating the first focusing step-to-focusing distance relation.
In an embodiment of the invention, when the focusing condition is the near focusing condition, the calibrating module performs a three dimensional depth estimation on each of the image sets to generate depth information of the focus target in each of the image sets, obtains the focusing distance corresponding to the focus target in each of the image sets according to each of the depth information, performs a regression according to the focusing distance and the focusing step corresponding to the focus target in each of the image sets, and calibrates the first focusing step-to-focusing distance relation according to a result of the regression.
Based on the image capturing device and the method for calibrating the image deformation thereof as proposed by the invention, when a deformation or an offset occurs on a first lens, a second lens and the focusing actuator of the image capturing device, the image capturing module is capable of calibrating the first focusing step-to-focusing distance relation pre-stored in the image capturing device according to the focusing distance corresponding to the focus target in each of the image sets captured by the first lens and the second lens as well as the focusing step that the focusing actuator is required to move the first lens and the second lens to the focusing position. The image capturing device and the method for calibrating the image deformation thereof as proposed in the invention may allow for a simple and quick automatic calibration on the image capturing device without even being noticed by the user when a plurality of image sets are captured by the image capturing module, so as to ensure a stable quality of the image capturing device and enhance user experience.
To make the above features and advantages of the disclosure more comprehensible, several embodiments accompanied with drawings are described in detail as follows.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating an image capturing device according to an embodiment of the invention.
FIG. 2 is a flowchart illustrating a method for calibrating image deformation of the image capturing device according to an embodiment of the invention.
FIG. 3 is a flowchart illustrating a method for calibrating image deformation of the image capturing device according to an embodiment of the invention.
FIG. 4 illustrates a schematic diagram of calibrating the first focusing step-to-focusing distance relation according to an embodiment of the invention.
FIG. 5A and FIG. 5B illustrate schematic diagrams of calibrating the first focusing step-to-focusing distance relation according to an embodiment of the invention.



DESCRIPTION OF THE EMBODIMENTS
Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. In addition, the specifications and the like shown in the drawing figures are intended to be illustrative, and not restrictive. Therefore, specific structural and functional detail disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.
FIG. 1 is a block diagram illustrating an image capturing device according to an embodiment of the invention. It should, however, be noted that this is merely an illustrative example and the present invention is not limited in this regard. All components of the image capturing device and their configurations are first introduced in FIG. 1. The detailed functionalities of the components are disclosed along with FIG. 2.
Referring to FIG. 1, an image capturing device 100 includes a first lens 10a, a second lens 10b, a focusing actuator 15, a storage unit 20 and one or more processing units 30. In the present embodiment, the image capturing device 100 is, for example, a digital camera, a digital camcorder, a digital single lens reflex camera or other devices provided with an image capturing feature such as a smart phone, a tablet computer, a personal digital assistant, a head mount display, and so on. The invention is not limited herein.
Each of the first lens 10a and the second lens 10b includes optical sensing elements for sensing light intensity entering the first lens 10a and the second lens 10b respectively, so as to generate a first image and a second image. The optical sensing elements are, for example, charge-coupled-device (CCD) elements, complementary metal-oxide semiconductor (CMOS) elements, and yet the invention is not limited thereto.
The focusing actuator 15 is coupled to the first lens 10a and the second lens 10b. The focusing actuator 15 may be, for example, a stepping motor, a voice coil motor (VCM), a piezoelectric actuator, or other actuators capable of mechanically moving the first lens 10a and the second lens 10b for focusing, and yet the invention is not limited herein.
The storage unit 20 may be one or a combination of a stationary or mobile random access memory (RAM), a read-only memory (ROM), a flash memory, a hard drive or other similar devices. The storage unit 20 is configured to record a plurality of modules executable by the processing unit 30, where the modules may be loaded into the processing unit 30 for calibrating the image capturing device 100.
The processing unit 30 may be, for example, a central processing unit (CPU) or other programmable devices for general purpose or special purpose such as a microprocessor and a digital signal processor (DSP), a programmable controller, an application specific integrated circuit (ASIC), a programmable logic device (PLD) or other similar devices or a combination of above-mentioned devices. The processing unit 30 is coupled to the first lens 10a, the second lens 10b, the focusing actuator 15 and the storage unit 20, and capable of accessing and executing the modules recorded in the storage unit 20 for calibrating the image capturing device 100.
The modules include an image capturing module 122, a focusing module 124, a deformation detection module 126 and a calibrating module 128 and may be loaded into the processing unit 30 for calibrating the image capturing device 100. The detailed steps of calibrating the image capturing device 100 are illustrated in the embodiments hereinafter.
FIG. 2 is a flowchart illustrating a method for calibrating image deformation of an image capturing device according to an embodiment of the invention, and the method for calibrating image deformation of the image capturing device of FIG. 2 may be implemented by the elements in the image capturing device 100 of FIG. 1.
Referring to both FIG. 1 and FIG. 2, the image capturing module 122 captures a plurality of image sets by utilizing the first lens 10a and the second lens 10b, where the image sets include a reference image set (step S201). The first lens 10a and the second lens 10b may capture the image sets with the same parameters, where the parameters include focal lengths, apertures, shutters, and so on, which are not particularly limited in the invention. The image sets captured by the image capturing module 122 are, for example, a plurality of preview image sets, and each of the image sets includes a first image corresponding to the first lens 10a and a second image corresponding to the second lens 10b. One of the image sets (i.e., the aforementioned reference image set) will be described hereafter. The reference image set includes a first reference image corresponding to the first lens 10a and a second reference image corresponding to the second lens 10b. 
Next, the deformation detection module 126 detects whether the reference image set is deformed (step S203). The deformation detection module 126 may determine whether the reference image set is deformed according to an offset of an arbitrary feature point of the reference image set or a three-dimensional depth estimation on the reference image set, and yet the invention is not limited thereto.
To be specific, in one embodiment, the deformation detection module 126 may detect the arbitrary feature point of the reference image set according to a conventional feature detection algorithm, and determine whether the offset between image coordinates of the feature point respectively on the first reference image and the second reference image exceeds a threshold, so as to detect whether the reference image set is deformed. In the present embodiment, after the deformation detection module 126 detects the feature point, it may determine whether a vertical offset (i.e., a difference in Y-axis coordinate) between the image coordinates of the feature point respectively on the first reference image and the second reference image exceeds the threshold. When the deformation detection module 126 determines that the offset between the image coordinates of the feature point of the reference image set does not exceed the threshold, it indicates that the reference image set is not deformed. The image capturing device 100 may end the method for calibrating image deformation. Otherwise, when the deformation detection module 126 determines that the offset between the image coordinates of the feature point of the reference image set exceeds the threshold, it indicates that the reference image set is deformed, and the image capturing device 100 may continue to execute the method for calibrating image deformation.
From another perspective, before the reference image set is captured by the image capturing module 122, the focusing module 124 may control the focusing actuator 15 to move the first lens 10a and the second lens 10b to a focusing position by applying an autofocusing technique such as a hill-climbing algorithm, so as to adjust a distance between the first lens 10a and a object and a distance between the second lens 10b and the object, so as to obtain the capturing object with a maximum resolution. The object with the maximum resolution in the reference image set may be referred to as a “reference focus target”. In the present embodiment, the deformation detection module 126 may determine whether the reference image set is deformed according to depth information of the reference focus target. More specifically, the deformation detection module 126 may process the reference image set through a stereo vision technique to obtain the depth information of the reference focus target in a spatial domain, and obtain an object distance of the reference focus target (i.e., a focusing distance of the reference focus target) according to the depth information.
It should be noted that, the closer the object is to the image capturing device 100, the greater the number of steps that the focusing actuator 15 is required to move the first lens 10a and the second lens 10b to the focusing position is greater; the farther the object is from the image capturing device 100, the less the number of steps that the focusing actuator 15 is required to move the first lens 10a and the second lens 10b to the focusing position. Therefore, there exists a corresponding relation between the focusing distance of the capturing object and the number of steps to be moved by the focusing actuator 15, and such corresponding relation is referred to as a “first focusing step-to-focusing distance relation.” The first focusing step-to-focusing distance relation may be pre-stored in the storage unit 20 as a look-up table (LUT), where an input index of the look-up table is a focusing distance, and an output of the look-up table is a focusing step. However, when deformation or offset occurs on the first lens 10a, the second lens 10b and the focusing actuator 15, the first focusing step-to-focusing distance relation pre-stored in the storage unit 20 becomes unreliable.
Accordingly, the deformation detection module 126 may determine whether the focusing step and the focusing distance corresponding to the reference focus target satisfy the first focusing step-to-focusing distance relation pre-stored in the storage unit 20. In other words, the deformation detection module 126 may determine whether the focusing distance obtained according to the depth information and the number of steps that the focusing module 124 is required to move the first lens 10a and the second lens 10b for obtaining the reference image set satisfy the first focusing step-to-focusing distance relation. When the deformation detection module 126 determines that the focusing step and the focusing distance corresponding to the reference focus target satisfy the first focusing step-to-focusing distance relation, it indicates that the reference image set is deformed, and the image capturing device 100 may end the method for calibrating image deformation. Otherwise, when the deformation detection module 126 determines that the focusing step and the focusing distance corresponding to the reference focus target do not satisfy the first focusing step-to-focusing distance relation, it indicates that the reference image set is deformed, and the image capturing device 100 may continue to execute the method for calibrating image deformation.
When the deformation detection module 126 detects that the reference image set is deformed, the calibrating module 128 calibrates the first focusing step-to-focusing distance relation according to a focusing step and a focusing distance corresponding to a focus target in each of the image sets (step S205), so as to complete the calibration process. Herein, the calibrating module 128 may calibrate the first focusing step-to-focusing distance relation according to images with different focusing distances. Detailed steps regarding the above will be described along with embodiments hereafter.
FIG. 3 is a flowchart illustrating a method for calibrating image deformation of the image capturing device according to an embodiment of the invention. In the present embodiment, the image capturing device 100 further includes a condition detection module (not shown), configured to detect a focusing condition of the image capturing device 100 for calibrating the first focusing step-to-focusing distance relation in different manners.
Referring to both FIG. 1 and FIG. 3, first, the image capturing module 122 captures a plurality of image sets by utilizing the first lens 10a and the second lens 10b, where the image sets include a reference image set (step S301). Next, the deformation detection module 126 detects whether the reference image set is deformed (step S303). Descriptions for step S301 and step S303 may refer to the related descriptions in step S201 and step S203, which may not be repeated hereinafter. When the deformation detection module 126 detects that the reference image set is deformed, the image capturing device 100 may end the method for calibrating image deformation. Otherwise, when the deformation detection module 126 detects that the image deformation occurs on the reference image set, the condition detection module detects a focusing condition of the image capturing device 100 (step S305). Herein, the focusing condition includes a far focusing condition and a near focusing condition. To be specific, when the image capturing module 122 obtains, for example, a plurality of preview image sets by utilizing the first lens 10a and the second lens 10b, the condition detection module may detect whether content of the image sets captured by the image capturing device 100 is a far-scene image or a near-scene image. For example, the far scene may be an outdoor scene, and the near scene may be an indoor scene. The condition detection module may detect the brightness of an ambient light source, recognize a scene of image content by leveraging a pattern recognition algorithm, or use the parameters adopted by the first lens 10a and the second lens 10b for determining the focusing condition, and yet the invention is not limited thereto.
When the condition detection module determines that the focusing condition is the far focusing condition, the calibrating module 128 records the focusing step corresponding to a focus target in each of the image sets (step S307). To be specific, because each the image sets captured is captured by the image capturing module 122 under the far focusing condition, an object with a maximum resolution (referred to as a “focus object”) in each of the image sets is located at an infinity position with respect to the first lens 10a and the second lens 10b. In the present embodiment, the infinity position may be a position that is more than 5 meters away from the first lens 10a and the second lens 10b. The calibrating module 128 records the number of steps that the image capturing module 122 is required to move the first lens 10a and the second lens 10b for capturing the image with an infinity focusing distance.
When the focusing step corresponding to the focus target in each of the image sets reaches a convergent value, the calibrating module 128 obtains a minimum focusing step in the first focusing step-to-focusing distance relation (step S309), and calculates a difference value between the minimum focusing step and the convergent value for calibrating the first focusing step-to-focusing distance relation (step S311). To be specific, within a range of the focusing distance, a negative linear relationship is found in the first focusing step-to-focusing distance relation. When the focusing step corresponding to each of image sets with the far-scene image captured by image capturing module 122 converges to a minimum value, said convergent value represents the number of steps that the focusing actuator 15 is required to move for focusing the focus object at the infinity position. Subsequently, the calibrating module 128 may obtain a minimum focusing step in the first focusing step-to-focusing distance relation, and calibrate the first focusing step-to-focusing distance relation according to the difference value between the minimum focusing step and the convergent value.
For instance, Table 1 lists numbers of steps that focusing actuator 15 is required to move in order to capture ten sets of the far-scene image.

















TABLE 1





Image Sets
1
2
3
4
5
6
7
8
9
10







Focusing Step
308
310
300
303
307
301
303
300
301
300









In Table 1, the corresponding focusing steps of all the ten far-scene image sets captured by the image capturing module 122 converge to 300; namely, the convergent value is 300. The calibrating module 128 may calibrate the first focusing step-to-focusing distance relation by such convergent value.
FIG. 4 illustrates a schematic diagram of calibrating the first focusing step-to-focusing distance relation according to an embodiment of the invention.
Referring to FIG. 4, a straight line 41 represents a first focusing step-to-focusing distance relation with the focusing distance ranged from 0.2 meter to 5 meters, where the focusing step corresponding to the focusing distance of 0.2 meter is 600, and the focusing step corresponding to the focusing distance of 5 meters is 200. In other words, in the present embodiment, the minimum focusing step is 200. In the example of Table 1, since the focusing step corresponding to the image sets with the far-scene image captured by the image capturing module 122 converges to 300, the calibrating module 128 may determine that the focusing step is a focusing step corresponding to the focusing distance of 5 meters, which may be represented by a point 421. The calibrating module 128 may calibrate the first focusing step-to-focusing distance relation according to a shortest distance between the point 421 and the straight line 41. In brief, the shortest distance is a difference value between the minimum focusing step and the convergent value in the Y-axis direction, and the calibrating module 128 may calibrate the first focusing step-to-focusing distance relation according to the difference value.
Take FIG. 4 as an example, the calibrating module 128 may shift the straight line 41 towards Y-axis in the positive direction, so that the straight line 41 is moved upwardly until overlapping with the point 421. A final position of the straight line 41 is where a straight line 42 is located, where the straight line 42 represents a new focusing step-to-focusing distance relation. The calibrating module 128 may replace the first focusing step-to-focusing distance relation pre-stored in the storage unit 20 with the new focusing step-to-focusing distance relation to complete the calibration process.
When the condition detection module determines that the focusing condition is the near focusing condition, the calibrating module 128 performs a three-dimensional depth estimation on each of the image sets to generate depth information of the focus target in each of the image sets (step S313), and obtains the focusing distance corresponding to the focus target in each of the image sets according to each of the depth information (step S315). More specifically, the calibrating module 28 may process each of the image sets through the stereo vision technique to obtain the depth information of the focus target in each of the image sets in a spatial domain, and obtain an object distance of the focus target (i.e., a focusing distance of the focus target) according to the depth information.
Next, the calibrating module 128 performs a regression according to the focusing distance and the focusing step corresponding to the focus target in each of the image sets as well as calibrates the first focusing step-to-focusing distance relation according to a result of the regression calculation (step S317). In other words, the calibrating module 128 may perform a regression analysis on multiple sets of the focusing distance and the focusing step being collected. In the present embodiment, because a negative linear relationship is found in the first focusing step-to-focusing distance relation, the calibrating module 128 may fit a linear regression model to find a fitted regression line of the sets of the focusing distance and the focusing step for replacing the first focusing step-to-focusing distance relation.
For instance, FIG. 5A and FIG. 5B illustrate schematic diagrams of calibrating the first focusing step-to-focusing distance relation according to an embodiment of the invention. Referring to FIG. 5A, a straight line 51 represents a first focusing step-to-focusing distance relation with the focusing distance ranged from 0.2 meter to 5 meters, where the focusing step corresponding to the focusing distance of 0.2 meter is 600, and the focusing step corresponding to the focusing distance of 5 meters is 200. After eleven image sets are captured by the image capturing module 122, focusing distances and focusing steps of the eleven image sets are represented by points 521 to 531. In the present embodiment, the calibrating module 128 may perform a regression analysis on the points 521 to 531 by fitting a least square regression model. However, in other embodiment, the calibrating module 128 may perform the regression analysis by fitting other linear regression models. The invention is not limited herein. A fitted regression line computed by the calibrating module 128 after performing the regression analysis on the points 521 to 531 is a straight line 52 as illustrated in FIG. 5B, which represents a new focusing step-to-focusing distance relation. The calibrating module 128 may then replace the first focusing step-to-focusing distance relation pre-stored in the storage unit 20 with the new focusing step-to-focusing distance relation to complete to complete the calibration process.
Additionally, in another embodiment, when the image capturing unit 122 captures the image sets under both of the far focusing condition and the near focusing condition, the calibrating module 128 may first execute steps S313 to S317 for the images captured under the near focusing condition to calibrate the first focusing step-to-focusing distance relation, and then execute steps S307 to S311 for the images captured under the far focusing condition to further calibrate the new focusing step-to-focusing distance relation for a more precise result. In another embodiment, the calibrating module 128 may first execute steps S307 to S311 for the images captured under the far focusing condition to calibrate the first focusing step-to-focusing distance relation, and then execute steps S313 to S317 for the images obtained under the near focusing condition to further calibrate the new focusing step-to-focusing distance relation. The invention is not limited to the above.
In summary, according to the image capturing device and the method for calibrating the image deformation thereof as proposed by the invention, when a deformation or an offset occurs on a first lens, a second lens and the focusing actuator of the image capturing device, the image capturing module is capable of calibrating the first focusing step-to-focusing distance relation pre-stored in the image capturing device according to the focusing distance corresponding to the focus target in each of the image sets captured by the first lens and the second lens as well as the focusing step that the focusing actuator is required to move the first lens and the second lens to the focusing position. The image capturing device and the method for calibrating the image deformation thereof as proposed in the invention may allow for a simple and quick automatic calibration on the image capturing device without even being noticed by the user, so as to ensure a stable quality of the image capturing device and enhance user experience.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.

## Claims

1. A method for calibrating image deformation, adapted to an image capturing device having a first lens, a second lens, a focusing actuator, and a pre-stored first focusing step-to-focusing distance ratio, comprising:
capturing a plurality of image sets by utilizing the first lens and the second lens, wherein each of the image sets comprises a first image corresponding to the first lens and a second image corresponding to the second lens, and the image sets comprise a reference image set including a first reference image corresponding to the first lens and a second reference image corresponding to the second lens;
detecting whether the reference image set is deformed and detecting a focusing condition of the image capturing device;
when the reference image set is detected to be deformed and when the focusing condition of the image capturing device is a far focusing condition:
recording a focusing step corresponding to a focused target in each of the image set, wherein the focusing step corresponding to the focused target in each of the image sets is a number of steps that the focusing actuator is required to move the first lens and the second lens to a focusing position for generating each of the image sets;
when the focusing step corresponding to the focused target in each of the image sets reaches a convergent value, obtaining a minimum focusing step and calculating a difference value between the minimum focusing step and the convergent value; and
calibrating the first focusing step to focusing distance ratio according to the difference value; and
when the reference image set is detected to be defored and when the focusing condition of the image capturing device is a near focusing condition:
performing a three-dimensional depth estimation on each of the image sets to generate depth information of the focused target in each of the image sets;
obtaining the focusing distance corresponding to the focused target in each of the image sets according to each of the depth information;
performing a regression according to the focusing distance and the focusing step corresponding to the focused target in each of the image sets; and
calibrating the first focusing step-to-focusing distance ratio according to a result of the regression.

2. The method for calibrating image deformation of claim 1, wherein the step of detecting whether the reference image set is deformed comprises:
detecting image coordinates of a feature point respectively on the first reference image and the second reference image of the reference image set;
determining whether an offset between the image coordinates of the feature point respectively on the first reference image and the second reference image exceeds a threshold; and
if yes, determining that the reference image set is deformed.

3. The method for calibrating image deformation of claim 1, wherein the step of detecting whether the reference image set is deformed comprises:
performing a three-dimensional depth estimation on the first reference image and the second reference image to generate reference depth information of a reference focused target in the reference image set;
obtaining a focusing distance corresponding to the reference focused target according to the reference depth information;
determining whether a focusing step and the focusing distance corresponding to the reference focused target satisfy the first focusing step-to-focusing distance ratio; and
if no, determining that the reference image set is deformed.

4. image capturing device, comprising:
a first lens;
a second lens;
a focusing actuator, coupled to the first lens and the second lens;
a storage unit, recording a plurality of modules and a first focusing step-to-focusing distance ratio; and
one or more processing units, coupled to the first lens, the second lens, the focusing actuator and the storage unit, and accessing and executing the modules recorded in the storage unit, wherein the modules comprise:
an image capturing module, capturing a plurality of image sets by utilizing the first lens and the second lens, wherein each of the image sets comprises a tirst image corresponding to the first lens and a second image corresponding to the second lens, and the image sets comprise a reference image set including a first reference image corresponding to the first lens and a second reference image corresponding to the second lens;
a focusing module, controlling the focusing actuator to move the first lens and the second lens to a focusing position;
a deformation detection module, detecting whether the reference image set is deformed;
a condition detection module, detecting a focusing condition of the image capturing device, wherein the focusing condition comprises a far focusing condition and a near focusing condition;
a calibrating module, when the reference image set is detected to be deformed and when the focusing condition of the image capturing device is the far focusing condition:
the calibrating module records a focusing step corresponding to a focused target in each of the image set, wherein the focusing step corresponding to the focused target in each of the image sets is a number of steps that the focusing actuator is required to move the first lens and the second lens to a focusing position for generating each of the image sets: and
when the focusing step corresponding to the focused target in each of the image sets reaches a convergent value, the calibrating module obtains a minimum focusing step, calculates a difference value between the minimum focusing step and the convergent value, and calibrates the first focusing step to focusing distance ratio according to the difference value; and
when the reference image set is detected to be deformed and when the focusing condition of the image capturing device is the near focusing condition:
the calibrating module performs a three-dimensional depth estimation on each of the image sets to generate depth information of the focused target in each of the image sets, obtains the focusing distance corresponding to the focused target in each of the inage sets according to each of the depth information, performs a regression according to the focusing distance and the focusing step corresponding to the focused target in each of the image sets, and calibrates the first focusing step-to-focusing distance ratio according to a result of the regression.

5. The image capturing device of claim 4, wherein the deformation detection module detects image coordinates of a feature point respectively on the first reference image and the second reference image of the reference image set, determines whether an offset between the image coordinates of the feature point respectively on the first reference image and the second reference image exceeds a threshold, and if yes, the deformation detection module determines that the reference image set is deformed.

6. The image capturing device of claim 4, wherein the deformation detection module performs a three-dimensional depth estimation on the first reference image and the second reference image to generate reference depth information of a reference focused target in the reference image set, obtains a focusing distance corresponding to the reference focused target according to the reference depth information, determines whether a focusing step and the focusing distance corresponding to the reference focused target satisfy the first focusing step-to-focusing distance ratio, and if no, the deformation detection module determines that the reference image set is deformed.