A distortion correction method

Abstract

The present invention provides a distortion correction method. First, basic optical indicators of a projection optical system, namely, original parameters of a projection lamp, are obtained. Then, a spatial relationship between a projection lens and a target image on an inclined projection surface, namely, parameters of an application scenario, is established. Then, basic optical parameters of the projection imaging optical system are calculated or simulated. Then, the projection source inclination angle and an actual mapping image of the target image corrected for lens distortion and inclined projection distortion are calculated based on a derivation formula using the optical parameters of the first three steps. The source image is then set as a projection source image. The method is not restricted by an environment in which system parameters are unknown. The method is simple and easy to understand, does not require repeated adjustments, has clear physical meaning, is easy to operate, and can achieve distortion-free, clear projection imaging with a large depth of field for inclined projections with a large field of view.

Description

Technical Field

[0001] The invention relates to the field of automobile welcome light projection, and particularly discloses a distortion correction method. Background Art

[0002] Projection lamps with images are widely used in commercial advertising, entertainment, and automotive applications. In recent years, the use of car welcome lights has become increasingly widespread, serving as auxiliary parking lights at night or for welcoming guests. Automotive projector lamps consist of components such as an imaging lens, film, collimating lens, and light source.

[0003] Many applications involve oblique projection, such as under a car door frame, creating a long, welcoming "red carpet" effect. This application is called a light carpet. Optical lenses have a limited depth of field, and the projection distance of a light carpet is long, so a lens with a large depth of field is required to achieve clear ground image clarity. Furthermore, the projection lens requires a large aperture to achieve high energy efficiency and ultimately meet ground illumination requirements. However, lenses with large apertures generally have a shallow depth of field. Consequently, during oblique projection, depending on the focus, only a certain area of ​​the image is clearly visible, while clarity in other areas rapidly decreases.

[0004] It is easy to associate it with the Scheimpflug Principle in photography, which is a photography technique that can be used to clearly image inclined planes, such as Figure 1 As shown in Figure 1, when photographing, the image plane is tilted at a certain angle so that the image plane and the object plane intersect at the same position on the lens plane. In a projection system, tilting the projection image source (such as film, DMD chip, LCD screen, etc.) according to Schaum's law can also improve the clarity of the image plane during tilted projection.

[0005] However, tilted projection inevitably introduces trapezoidal distortion. Projection systems generally have built-in trapezoidal distortion correction capabilities, such as the invention patent publication number CN1582459A, entitled "System and Method for Correcting Projected Image Distortion," which discloses the following technical content: The distortion is caused when a projector lens projects an input image onto a projection screen that is not orthogonal to the projector's projection axis. Projection parameters are first acquired, including the focal length of the projector lens and angle values ​​representing the projector's pan, tilt, and roll angles. Next, a projection area and an optimal visible rectangular area within the projection area are determined. The distortion caused by the projection is then characterized using a distortion transformation corresponding to the transformation between the vertices of the optimal visible rectangular area and the corresponding vertices of the projection area. Finally, the distortion transformation is flipped and applied to the input image to obtain a distortion-free projected image. Another example is the Chinese patent publication number CN104062831A, and the invention name is "Projection Device and Projection Method", which discloses the following technical content: The projector includes a light source unit and a micro-mirror element having a rectangular element range. The light emitted from the light source unit is modulated by the micro-mirror element and projected into the projection range of the projected object through the projection lens. The comparison unit included in the trapezoidal distortion correction unit of the projector compares the size relationship between the aspect ratio of the rectangular input image and the aspect ratio of the element range. Based on the above size relationship, the projection range determination unit determines the effective projection range that is included in the projection range and becomes a rectangle on the projected object. The element range determination unit determines the effective element range in a manner that the relationship of the effective projection range relative to the projection range corresponds to the relationship of the effective element range relative to the element range. The geometric transformation unit projects the input image into the effective element range in a manner that the input image is projected without distortion into the effective projection range of the projected object.

[0006] Both of the aforementioned prior arts describe methods for distortion correction during non-orthogonal projection. However, these methods primarily target projection equipment systems, specifically those used in environments where system parameters are unknown. Because these methods are complex, involve multiple steps, require repeated adjustments, and are often based on image feedback, they are not suitable for relatively simple automotive projector lamps. Furthermore, the projection source of these projection systems is typically perpendicular to the optical axis, which does not conform to Schaum's law. Optical lenses designed for front projection are generally required to exhibit no barrel or pincushion distortion.

[0007] In actual application, distortion is caused by the fact that the projection source plane is not orthogonal to the optical axis, and the intersection line with the tilted projection receiving surface intersects the main plane of the optical lens. The current distortion correction method of the projector is not completely suitable for the relatively simple lens with barrel distortion or pincushion distortion of tilted projection. Due to the cost limit of automotive projector lamps, there are fewer optical parts, and the distortion may not be completely eliminated if the lens is designed. In addition, it is known from geometric optics that the primary optical distortion is proportional to the cube of the object height, which means that when the field of view is increased, the optical distortion will increase rapidly. Therefore, when a large field of view projector lamp is used at an angle, there will be both trapezoidal distortion and optical distortion. Therefore, it is necessary to invent a simple and convenient correction method that can be used for clear, distortion-free (trapezoidal distortion, pincushion distortion or barrel distortion) tilted projection of a large field of view. Summary of the Invention

[0008] Based on this, it is necessary to provide a distortion correction method to address the existing technical problems, which can achieve distortion-free and clear projection imaging with a large depth of field for oblique projections with a larger field of view. The method is simple and easy to understand, has clear physical meaning, and is easy to operate.

[0009] To solve the problems of the prior art, the present invention discloses a distortion correction method, comprising the following steps:

[0010] (a) Obtain the basic optical specifications of the projection lens;

[0011] (b) establishing a spatial relationship between the projection lens and the target image on the tilted projection surface;

[0012] (c) calculating or simulating basic optical parameters of the projection imaging optical system; the basic optical parameters are the image distance of the projection source;

[0013] (d) Calculating the projection source inclination angle and the corrected source image of the target image using a derivation formula based on the optical parameters in steps (a), (b), and (c); the calculation process of the derivation formula is as follows:

[0014] Establish a spatial three-dimensional coordinate system Oxyz, with the optical axis as the z-axis, the corresponding object-image points as Ot and point O', the object distance as l, the image distance as l', and the vertical axis plane passing through point Ot as plane S0; the inclined pattern receiving surface is set as plane Si, and its plane coordinate system is O'x'y'. Take an arbitrary point on plane Si as M', and the plane coordinates of M' are (x', y'); the inclined projection source plane is set as plane St, and its plane coordinate system is Oxtyt. According to the law of refraction and Sham's law, M' on plane Si can find the corresponding mapping point on plane St, which is set as point M4 (x4, y4, z4). If the plane coordinates of point M4 on plane St are (xt, yt), it is the position of the projection source corresponding to point M';

[0015] The coordinate expression of the image point M of M' in Oxyz space is as follows:

[0016]

[0017] The expression for the oblique projection source plane St is as follows:

[0018] B·y+C·z+D=0 (2)

[0019] Given a plane St passing through points P(0,y0,0), point Ot(0,0,l),

[0020] Therefore, the expression of plane St can be obtained as:

[0021]

[0022] and

[0023] y0=-l′·tanα (4)

[0024] When the distortion is set to 0, the image point M is set to M1 on the inclined plane of the projection source, the straight line MM1 passes through the point O, and the intersection point of the straight line MM1 and the vertical axis plane S0 passing through the on-axis object image point Ot is set to M2;

[0025] When the distortion is set to non-zero, the corresponding point on the vertical plane S0 will change and become M3. The vertical projection source image height is set to M3Ot, and the ideal vertical image height is set to M2Ot. M3Ot and M2Ot are determined by the distortion amount.

[0026] The expression of the straight line M2M is:

[0027]

[0028] The expression of plane S0 is:

[0029] z=l (6)

[0030] From equations (5) and (6), we can get the coordinates of point M2 as:

[0031]

[0032] Assuming that the relationship between the distortion and image height on the vertical axis of the optical system is known to be dist, the actual vertical axis image height can be obtained as:

[0033] M3Ot=(1+dist)×M2Ot (8)

[0034] Get the coordinates of point M3 (x3, y3, z3);

[0035] The point M4 corresponding to point M3 on plane St is the intersection of line M3O and plane St;

[0036] The expression of the straight line M3O is:

[0037]

[0038] Combining equations (9) and (3) we can obtain the coordinates of point M4 (x4, y4, z4);

[0039] In addition, the angle β between plane St and plane S0 can be obtained as follows:

[0040]

[0041] The coordinates of point M4 (x4, y4, z4) are points on the spatial coordinate system Oxyz, which are converted into plane coordinates (xt, yt) on the plane St. The expression is:

[0042]

[0043] By traversing the target image point by point, the actual mapping image on the projection source with the lens distortion and tilt projection distortion corrected can be obtained;

[0044] (e) The actual mapping image obtained in step (d) on the projection source, which has been corrected for lens distortion and tilt projection distortion, is set as the projection source image.

[0045] Furthermore, in step (a), the basic optical indicators include the focal length of the projection lens, the full image height of the lens, the field of view angle of the lens, and the distortion coefficient.

[0046] Furthermore, in step (b), the target image spatial relationship includes the projection distance and inclination angle of the projection optical system.

[0047] Furthermore, the basic optical parameter in step (c) is the image distance of the projection source, which is calculated using the full image height of the lens in step (a) and the projection distance of the projection optical system in step (b).

[0048] Furthermore, the projection source is configured as a film, a DMD chip, or a liquid crystal screen.

[0049] The beneficial effects of the present invention are as follows: the present invention discloses a distortion correction method, which first obtains the basic optical indicators of the projection optical system, namely the original parameters of the projection lamp, then establishes the spatial relationship between the projection lens and the target image on the inclined projection surface, namely the parameters of the application scenario, and then calculates or simulates the basic optical parameters of the projection imaging optical system, and then calculates the projection source inclination angle and the actual mapping image of the target image corrected for lens distortion and inclined projection distortion according to the derivation formula based on the optical parameters of the first three steps, and then sets the source image as the projection source image, which is not restricted by the environment in which the system parameters are unknown. The method is simple and easy to understand, does not require repeated adjustments, has clear physical meaning, is easy to operate, and can achieve clear projection imaging with no distortion and a large depth of field for inclined projections with a large field of view. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Schematic diagram of Schaam's law for oblique imaging.

[0051] Figure 2 Schematic diagram of the distortion correction method of the present invention.

[0052] Figure 3 Schematic diagram of the object-image mapping relationship for tilted clear imaging of the optical lens containing distortion of the present invention.

[0053] Figure 4 Schematic diagram of the spatial relationship between the projection lens and the target image on the inclined projection surface established in step (b) of the present invention.

[0054] Figure 5 This is a light path diagram of a projection optical lens according to a first embodiment of the present invention.

[0055] Figure 6 Schematic diagram of the relationship between distortion and image height of a projection optical lens according to an embodiment of the present invention.

[0056] Figure 7 FIG. 1 is a schematic diagram of a projection source after distortion correction according to a first embodiment of the present invention. DETAILED DESCRIPTION

[0057] In order to further understand the features, technical means, specific objectives and functions achieved by the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0058] refer to Figures 2 to 4 .

[0059] The present invention discloses a distortion correction method, comprising the following steps:

[0060] (a) obtaining basic optical specifications of the projector; the basic optical specifications include the focal length of the projection lens, the full image height of the lens, the field of view angle of the lens, and the distortion coefficient;

[0061] (b) establishing a spatial relationship between the projection lens and the target image on the inclined projection surface; the target image spatial relationship includes the projection distance and the inclination angle of the projection optical system;

[0062] (c) calculating or simulating basic optical parameters of the projection imaging optical system; the basic optical parameters being the image distance of the projection source, the image distance of the projection source being calculated by applying the basic optical indicators in step (a) and the target image spatial relationship in step (b);

[0063] (d) Calculating the projection source inclination angle and the corrected source image of the target image using a derivation formula based on the optical parameters obtained in steps (a), (b), and (c). The calculation process of the derivation formula is as follows:

[0064] Establish a spatial coordinate system Oxyz, with the optical axis as the z-axis, the corresponding object-image points as Ot and O', the object distance as l, the image distance as l', and the perpendicular plane through point Ot as plane S0; the inclined pattern receiving surface is plane Si, whose plane coordinate system is O'x'y'. Take an arbitrary point on plane Si as M', and the plane coordinates of M' are (x', y');

[0065] The tilted projection source plane is set as plane St, and its plane coordinate system is Oxtyt. According to the law of refraction and Sham's law, M' on plane Si can find the corresponding mapping point on plane St, which is set as point M4 (x4, y4, z4). If the plane coordinates of point M4 on plane St are calculated (xt, yt), it is the position of the projection source corresponding to point M'.

[0066] The coordinate expression of the image point M of M' in Oxyz space is as follows:

[0067]

[0068] The expression for the oblique projection source plane St is as follows:

[0069] B·y+C·z+D=0 (2)

[0070] Given a plane St passing through points P(0,y0,0), point Ot(0,0,l),

[0071] Therefore, the expression of plane St can be obtained as:

[0072]

[0073] and

[0074] y0=-l′·tanα (4)

[0075] When the distortion is set to 0, the image point M is set to M1 on the inclined plane of the projection source, the straight line MM1 passes through the point O, and the intersection point of the straight line MM1 and the vertical axis plane S0 passing through the on-axis object image point Ot is set to M2;

[0076] When the distortion is set to non-zero, the corresponding point on the vertical plane S0 will change and become M3. The vertical projection source image height is set to M3Ot, and the ideal vertical image height is set to M2Ot. M3Ot and M2Ot are determined by the distortion amount.

[0077] The expression of the straight line M2M is:

[0078]

[0079] The expression of plane S0 is:

[0080] z=l (6)

[0081] From equations (5) and (6), we can get the coordinates of point M2 as:

[0082]

[0083] Assuming that the relationship between the distortion and image height on the vertical axis of the optical system is known to be dist, the actual vertical axis image height can be obtained as:

[0084] M3Ot=(1+dist)×M2Ot (8)

[0085] Get the coordinates of point M3 (x3, y3, z3);

[0086] The point M4 corresponding to point M3 on plane St is the intersection of line M3O and plane St;

[0087] The expression of the straight line M3O is:

[0088]

[0089] Combining equations (9) and (3) we can obtain the coordinates of point M4 (x4, y4, z4);

[0090] In addition, the angle β between plane St and plane S0 can be obtained as follows:

[0091]

[0092] The coordinates of point M4 (x4, y4, z4) are points on the spatial coordinate system Oxyz, which are converted into plane coordinates (xt, yt) on the plane St. The expression is:

[0093]

[0094] By traversing the target image point by point, the actual mapping image on the projection source with the lens distortion and tilt projection distortion corrected can be obtained;

[0095] (e) The actual mapping image obtained in step (d) on the projection source, which has been corrected for lens distortion and tilt projection distortion, is set as the projection source image.

[0096] As a preferred embodiment, the projection source is configured as a film, a DMD chip, or a liquid crystal screen.

[0097] Example 1, reference Figures 5 to 7 The target projection image is HELLO. According to the above steps,

[0098] The first step is to obtain the basic optical indicators of the projection optical system; this embodiment adopts the following Figure 5 The projection lens shown has a field of view of 30°, a full image height of 6.2mm, a focal length of 11.4mm, and optical distortion as shown below. Figure 6 The corresponding relationship shown.

[0099] The second step is to establish the spatial relationship between the projection lens and the target image on the tilted projection surface, such as Figure 4 As shown, the projection distance of the projection optical system is 500 mm and the inclination angle α=45°.

[0100] The third step is to calculate or simulate the basic optical parameters of the projection imaging optical system, and obtain the image distance of the projection image source as 11.14 mm and the projection distance |l'| = 500 mm, which are applied to the image height corresponding to the full field of view.

[0101] In the fourth step, the projection source inclination angle and the corrected source image of the target image are calculated using the above 11 derivations and the optical parameters in the first three steps. It can be calculated that the projection source inclination angle is 1.28 degrees.

[0102] In the fifth step, the actual mapping image on the projection source that has been finally obtained and has corrected the lens distortion and the tilt projection distortion is set as the projection source image.

[0103] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A distortion correction method, characterized in that: The method comprises the following steps: (a) obtaining basic optical indicators of the projection lens, wherein the basic optical indicators include the focal length of the projection lens, the full image height of the lens, the field of view angle of the lens, and the distortion coefficient; (b) establishing a spatial relationship between the projection lens and the target image on the tilted projection surface; (c) calculating or simulating basic optical parameters of the projection imaging optical system; the basic optical parameters are the image distance of the projection source; (d) Calculating the projection source inclination angle and the corrected source image of the target image using a derivation formula based on the optical parameters obtained in steps (a), (b), and (c). The calculation process of the derivation formula is as follows: Establish a spatial three-dimensional coordinate system Oxyz, with the optical axis as the z-axis, the corresponding object-image points as Ot and point O', the object distance as l, the image distance as l', and the vertical axis plane passing through point Ot as plane S0; the inclined pattern receiving surface is set as plane Si, and its plane coordinate system is O'x'y'. Take an arbitrary point on plane Si as M', and the plane coordinates of M' are (x', y'); the inclined projection source plane is set as plane St, and its plane coordinate system is Oxtyt. According to the law of refraction and Sham's law, M' on plane Si can find the corresponding mapping point on plane St, which is set as point M4 (x4, y4, z4). If the plane coordinates of point M4 on plane St are (xt, yt), it is the position of the projection source corresponding to point M'; α is the inclination angle between the projection lens and the inclined projection surface; The coordinate expression of the image point M of M' in Oxyz space is as follows: The expression for the oblique projection source plane St is as follows: B·y+C·z+D=0 (2) Given a plane St passing through points P(0,y0,0), point Ot(0,0,l), Therefore, the expression of plane St can be obtained as: and y0=-l′·tanα (4) When the distortion is set to 0, the image point M is set to M1 on the inclined plane of the projection source, the straight line MM1 passes through the point O, and the intersection point of the straight line MM1 and the vertical axis plane S0 passing through the on-axis object image point Ot is set to M2; When the distortion is set to non-zero, the corresponding point on the vertical plane S0 will change and become M3. The vertical projection source image height is set to M3Ot, and the ideal vertical image height is set to M2Ot. M3Ot and M2Ot are determined by the distortion amount. The expression of the straight line M2M is: The expression of plane S0 is: z＝l (6) From equations (5) and (6), we can get the coordinates of point M2 as: Assuming that the relationship between the distortion and image height on the vertical axis of the optical system is known to be dist, the actual vertical axis image height can be obtained as: M3Ot=(1+dist)×M2Ot (8) Get the coordinates of point M3 (x3, y3, z3); The point M4 corresponding to point M3 on plane St is the intersection of line M3O and plane St; The expression of the straight line M3O is: Combining equations (9) and (3) we can obtain the coordinates of point M4 (x4, y4, z4); In addition, the angle β between plane St and plane S0 can be obtained as follows: The coordinates of point M4 (x4, y4, z4) are points on the spatial coordinate system Oxyz, which are converted into plane coordinates (xt, yt) on the plane St. The expression is: By traversing the target image point by point, the actual mapping image on the projection source with the lens distortion and tilt projection distortion corrected can be obtained; (e) The actual mapping image obtained in step (d) on the projection source, which has been corrected for lens distortion and tilt projection distortion, is set as the projection source image.

2. The distortion correction method according to claim 1, wherein: In the step (b), the spatial relationship of the target image includes the projection distance and the inclination angle of the projection optical system.

3. The distortion correction method according to claim 2, wherein: The basic optical parameter in step (c) is the image distance of the projection source, which is calculated using the basic optical indicators of the lens in step (a) and the projection distance of the projection optical system in step (b).

4. The distortion correction method according to claim 1, wherein: The projection source is configured as a film, a DMD chip, or a liquid crystal screen.

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