DE102019135222A1 - System for determining the field of view (FOV) of a camera - Google Patents

Abstract

A system (21) is provided for determining a field of view (FOV) of a camera, comprising: a light source (22); a pattern generator (23) which is adapted to generate a pattern from light emitted by the light source; wherein the pattern generator (23) comprises an optical element, the optical element being designed to direct the pattern to the lens of a camera in such a way that the FOV on the lens can be determined on the basis of the pattern.

Description

Field of invention

The present invention relates to a system for determining the field of view of a camera. In particular, it relates to a system that can be used to determine the field of view for cameras with both a wide and a narrow field of view.

General state of the art

The field of view of a camera or an optical system is the maximum extent of the visual area that is visible by the camera for a given positioning of the camera. Elements outside the camera's field of view, when the camera is in a given location, are not visible to the camera. Field of view is measured in degrees that indicate the size of the "angle" that objects in front of a camera are visible to the camera. Cameras are used in a wide variety of industrial applications, for example for detection in industrial processes and for taking pictures for assessment and analysis. It is therefore important that the field of view of the camera can be determined in order to assess its functionality and suitability for a given detection or recording task.

Typically, a method for measuring the field of view (FOV) of an optical system involves placing one or more targets a certain distance from the camera, with the camera fixed at a height (h). 1 shows how the field of view of a camera using trigonometry using a distance (X) on a perpendicular line from the camera to the plane of the target, the distance on the plane (Y) from the target to the perpendicular line (X) from the target Camera to the plane and the angle (α) between (X) and a straight line from the camera to the target can be determined. The field of view can be determined by the following formula $$\text{FOV}=2\mathrm{\alpha }=2\times \text{arctan}\left(\text{Y / X}\right).$$

The further the target is placed away from the camera, the more precisely the measurement of the field of view can be determined. As such, while large distances between a target and a camera can provide an accurate FOV determination, such distances generally tend to be impractical in an industrial setting, particularly when rapid field of view measurements are required. In addition, systems that provide a field of view determination without requiring long distance measurements are only accurate for cameras with a narrow field of view. Accordingly, it is desirable to create a system that can be used to determine the field of view for cameras with a wide as well as a narrow field of view.

Summary of the invention

The present invention provides a system for determining a field of view, FOV, of a camera comprising: a light source; a pattern generator configured to generate a pattern from light emitted by the light source; wherein the pattern generator comprises an optical element, wherein the optical element is designed to direct the pattern to the lens of a camera in such a way that the FOV on the lens can be determined on the basis of the pattern.

This is advantageous as it provides for determining the field of view of a camera without the requirement to take measurements over a long distance between a camera and a target. Furthermore, it provides that the field of view for cameras with both a wide and a narrow field of view can be determined. The optical element provides that a pattern is directed towards the lens of a camera in such a way that an image of the pattern can be obtained by the camera, whereby it is ensured that the field of view of the camera can be determined. With the image of the pattern, the field of view of the camera can be determined using the positions of elements of the pattern.

The light source can comprise a laser. This is beneficial as it helps avoid introducing light distortion into the system.

The pattern generator can comprise a refractive optical element. This is beneficial because it tends to spread a single beam of light into multiple beams, creating a "pattern" of light from a single source. Depending on the arrangement of the diffractive optical element, different light patterns can be generated.

The pattern generator can comprise a holographic optical element. This is advantageous as it provides an alternative means of spreading a single beam of light in multiple beams to again generate a "pattern" of light from a single source. Holographic optical elements provide additional versatility compared to diffractive optical elements and can be specifically tailored to spread a single light source over two perpendicular planes, ie, a a single holographic element can be cropped to create a series of vertical and horizontal lines from a single light source.

The generated pattern can include a series of dots, or the generated pattern can include a series of horizontal and vertical lines that form multiple square shapes. This is advantageous because it provides a periodic pattern from which the field of view of a camera can be determined.

The square shapes around the edges of the generated pattern can be clipped to form half squares or half rectangles. This is advantageous as it ensures that when the pattern is replicated there is no discontinuity in the dimensions of the pattern elements, for example when a half square is replicated on the edge of a pattern the replicated half square appears along the original half Square, creating a whole square from the two halves (the initial and replicated half).

The system can still have a replicator ( 31 ) for replicating the pattern from the pattern generator and is adapted so that the replicated pattern can be seen by a camera. The replicator ensures that a replicated pattern can be seen by a camera so that an image of the replicated pattern can be obtained by the camera. With the image of the replicated pattern, the field of view of the camera can be determined by utilizing the positions of elements of the replicated pattern. The degree of distortion can also be determined by comparing the distortion on the image to a known undistorted version of the replicated pattern. For example, if the generated pattern is known to be horizontal and vertical lines, and thus the replicated pattern is a series of horizontal and vertical lines that form multiple square shapes, distortion of the squares can easily be seen by the human eye. The degree of distortion can be determined by computer analysis or image processing of the obtained image.

The replicator may comprise a cube or parallelepiped-shaped box comprising: a first open side; a second closed side comprising a screen for receiving light propagated by the pattern generator; two or more sides comprising reflective surfaces, the reflective surfaces internally opposed within the box and adapted to reflect the pattern from the screen to create a replicated pattern within the box that can be seen through the first open side . This is advantageous as it ensures that a pattern can be replicated to infinity along at least one plane. When four sides include reflective surfaces, the reflective surfaces internally facing each other within the box, this allows a pattern to be replicated along two planes to infinity. This thus guarantees that the field of view of a camera lies within the replicated pattern and can be determined from the replicated element within the pattern. It also ensures that distortion within the camera lens can be detected, since distortion can be identified more easily on larger patterns.

The screen can comprise a transparent diffuser. This is advantageous as it provides a suitable surface for receiving light from the pattern generator on one side of the surface such that the pattern is visible to a camera on the other side of the surface. The diffuser ensures that the pattern “received” on one side of the diffuser is clearly “transmitted” to the other side for viewing by the camera.

The reflective surfaces can completely cover the internal surface of the box. This is advantageous because providing the reflective surfaces to cover the internal surface of the box in its entirety ensures that there are no gaps or discontinuities in the replicated pattern. Any such discontinuity would lead to inaccuracies in the field of view determination and would make it difficult to detect a distortion.

The system may further include a camera positioned on the first open side and configured to see the replicated pattern within the box. This is advantageous as it ensures that a camera to be tested can be placed relative to the system in order to determine the field of view of the camera. The system is thus adapted for use with any camera suitable for being positioned relative to the first open side of the box.

The invention further provides a method of determining the field of view of a camera using the system, the method comprising: generating at the pattern generator a pattern of light emitted by the light source; Obtaining via a camera an image of the generated pattern; Determining the field of view of the camera from the positions of the plurality of pattern elements in the obtained image of the generated pattern. This is advantageous as it ensures that the field of view can be precisely determined while there is no need to take physical measurements over large distances.

The method may further comprise: replicating, at a replicator, the pattern from the pattern generator, the replicated pattern comprising a plurality of pattern elements; Received through the camera ( 52 ), an image of the replicated pattern; Determining the field of view from the positions of the plurality of pattern elements in the obtained image of the replicated pattern. This is advantageous because it ensures that very wide field of view measurements can be precisely determined and furthermore ensures that a distortion of the camera lens can be detected in order to allow a calibration or additional corrective measures to be carried out.

Figure list

• 1 Figure 11 shows a distance method of obtaining a field of view measurement.
• 2A and 2 B Figure 12 shows a diagram of a system according to the invention comprising the light source and the pattern generator. 2A shows a DOE pattern generator, 2 B shows a HOE pattern generator.
• 3 Figure 3 shows a diagram of a system according to the invention further comprising the replicator.
• 4th Figure 13 shows an isometric view of the front of the replicator with a pattern from the pattern generator being spread onto the screen of the replicator.
• 5 Figure 3 shows an isometric view of the front of the replicator of the system of the invention.
• 6th Figure 3 shows an isometric view of the rear of the replicator of the system of the invention.
• 7A to 7C show the replication of a pattern appearing at the replicator for one, two and four sided reflective surfaces.
• 8th FIG. 13 shows the replication of a pattern using two sides with longer reflective surfaces than those in FIG 7A to 7C shown.
• 9 shows an exemplary “grid pattern” generated by the pattern generator.
• 10 shows an example of a distorted grid pattern with a "cylinder" distortion.
• 11 shows an example of a distorted grid pattern with a "pillow" distortion.
• 12th Figure 12 shows a sample image captured by a camera that is used to determine the camera's field of view.

Detailed description

The system of the invention will now be described with reference to the accompanying figures. 2 Figure 3 shows a diagram of a system 21 according to the invention, comprising the light source 22nd and the pattern generator 23 . A monochromatic light source such as a laser can be used as the light source so as not to introduce light distortion into the system. This is especially important as the system continues to ensure that any distortion of the camera's lens is detected. Accordingly, a gas laser can be used to minimize such light distortion and provide a collimated light source.

The system may include a pattern generator comprising a diffractive optical element (DOE) 24 or alternatively, a pattern generator comprising a holographic optical element (HOE) 25th include. 3A shows a pattern generator comprising a DOE, 3B Figure 10 shows a pattern generator that includes an HOE. 3A shows a laser light source that directs a collimated light beam onto a beam expander 26th emitted. The incident light beam is made by the beam expander 26th widened. Two diffractive optical elements in the form of two crossed diffraction gratings are placed behind the beam expanders 26th placed to light from the beam expander 26th to recieve.

The diffraction through the gratings is deterministic and thus the diffracted angles are known. The diffracted angle θ _{q of} the diffraction order q depends on the laser wavelength λ, the diffraction order q and the grating A. The angle θ _q is found from $$\text{sin}{\mathrm{\theta }}_{\text{q}}=\text{sense}{\mathrm{\theta }}_{\text{i}}=\text{s}\times \text{q}\mathrm{\lambda \; /\; \Lambda }$$

If the light source is monochromatic (a laser) then the only variable is the diffraction order q, which is an integer -n, -n + 1, ..., -2, -1, 0, +1, +2, .. ., + n (i.e. 1st order, 2nd order, 3rd order, etc.).

It is noted that where the incident beam is collimated, the diffraction orders also remain collimated.

A standard diffraction grating is designed to spread the light over a plane perpendicular to the lines of the grating. By doing If two gratings are used which are placed parallel to each other, but the lines of the first grating are perpendicular to the second grating, it is possible to spread the light over two perpendicular planes. As such, a single ray can form a pattern of rays 27 generated, separated by certain angles.

Alternatively, a holographic element (HOE) 25th can be used instead of a diffraction grating arrangement. 3B shows again a laser light source, which a collimated light beam on a beam expander 26th emitted. The incident light beam is passed through the beam expander 26th branched out. An optical element in the form of a holographic element (HOE) is placed behind the beam expander to remove light from the beam expander 26th to recieve. The holographic element generates a pattern of rays 27 , separated by certain angles. The optical elements are designed such that they direct the pattern to the lens of a camera in such a way that the field of view on the lens can be determined from the pattern.

The generated pattern can be in the form of a series of points. Alternatively, the generated pattern includes a series of horizontal and vertical lines that form multiple square or rectangular shapes. Such a square or "grid" type pattern can be formed, for example, as a result of using a scanning laser as the light source.

3 shows the system 21 who still have a replicator 31 includes. After the pattern is generated, it is then replicated by the replicator. 4th shows that the generated pattern 41 to the replicator 31 is projected. 5 and 6th show the replicator 31 even so that it encompasses a cube-shaped or cuboid-shaped box. The box includes a first open side 51 . The first open page 51 allowed a camera 52 for whom the field of view is to be determined can see the inside of the box and taking a picture of the inside of the box. The box further includes a second closed side that has a screen 53 for receiving from the pattern generator 23 includes spread light. This is how this is done by the pattern generator 23 generated patterns on the screen 53 of the box and displayed there. The screen 53 can be a transparent screen of the diffuser type. The screen 53 can furthermore be any suitable flat surface which can receive the light and which is sufficiently transparent that the light (and thus the pattern) can be transmitted into the box and thus be visible in the box.

The box further includes at least two sides that have reflective surfaces 54 with the reflective surfaces internally opposing each other within the box. The reflective surfaces can be mirrors. The reflective surfaces 54 are designed so that they match the pattern of the screen 53 reflect to create a replicated pattern within the box passing through the first open side 51 can be seen. If a camera 52 is placed on or around the first open side of the box, it is thus possible for the camera to see the replicated pattern and take a picture of the replicated pattern.

The way of replication is further related 7A to 7C described. 7A shows a generated grid-type pattern. Such a pattern can appear on the screen 53 of the replicator as described above. If the pattern than on the screen 53 generated as described above and the reflective surface shown 54 is viewed as the inner surface of one side of the box, then a camera positioned on the open side of the box will see the replicated pattern within the box as shown by A. A single reflective surface 54 in the replicator has the effect of "doubling" the original pattern generated inside the box.

In terms of 7B can return the pattern as on the screen 53 generated as described above. In this example, the two reflective surfaces shown are 54 considered to be the inner surfaces of the two sides of the box, the reflective surfaces internally opposing each other within the box. A camera positioned on the open side of the box will see the replicated pattern inside the box as shown by B. As such, two have reflective surfaces formed as shown in the replicator 54 the effect of repeating the generated original pattern in a vertical direction to infinity.

In terms of 7C can once again see the pattern as on the screen 53 generated as described above. In this example there are four reflective surfaces shown 54 considered to be the interior surfaces of four sides of the box, with the reflective surfaces internally opposing each other within the box. As such, the reflective surfaces entirely cover the interior sides of the box. A camera positioned on the open side of the box will see the replicated pattern inside the box as shown by C. As such, have four reflective surfaces formed as shown in the replicator 54 the effect of the Repeating the generated original pattern to infinity in both the vertical direction and a horizontal direction. This provides a 180 ° field of view for a camera oriented towards the pattern. This ensures that for a camera which is designed to see and record an image of the replicated pattern within the box, the field of view can be determined from the positions of the plurality of pattern elements in the recorded image of the replicated pattern.

8th shows the effect of using a longer reflective surface 54 , for example in the case of a cuboid box in the replicator. This has the effect of providing a greater number of multiples of the generated image compared to a reflective surface of shorter length over a given field of view within a replicated image.

Because the generated pattern 41 is to be replicated, the pattern should indicate a periodicity. The edges of the pattern should thus be designed to provide for reproducing the pattern without breaking the periodicity. For example, in the case where the generated pattern is a grid that forms a series of horizontal and vertical lines that form multiple square shapes, the shapes around the edges of the generated pattern should be clipped to form half squares (see Edges 91 of the grid in 9 ). This ensures that half a square of the generated original image is replicated by one of the reflective surfaces to form the "other half" of a full square. Thus, a full square is created in the grid from the original half square and the reflected half square. In this way the periodicity of the pattern is maintained in the replicated pattern.

Furthermore, the pattern replicated in the manner described ensures that a degree of distortion in the camera or the camera lens can be detected. For example shows 9 an undistorted image of an exemplary "grid" pattern generated by the pattern generator. The grid lines can be seen so that the horizontal lines of the grids are parallel to each other. Similarly, the vertical lines run parallel to each other. If there is distortion in the camera or camera lens, the lines will not appear parallel and the grid will appear to "bulge" in the center so that the lines in the center will be further apart compared to the outer ends of the pattern , known as "cylinder" distortion ( 10 ), or the grid will appear to "sink" in the center so that the lines are closer together in the center when compared to the outer ends of the pattern, known as "pillow" distortion ( 11 ). If such a distortion is detected on the camera, the camera can be adjusted or recalibrated so that the distortion is removed. If such a distortion is detected, it can also be taken into account in calculations in order to determine the field of view by assessing the position of the distorted pattern elements relative to the known positions of the elements for an undistorted image.

A method for determining the field of view of a camera will now be described. The method can be performed using the system described herein. A light source supplies light to a pattern generator. The pattern generator generates a pattern from light emitted by the light source. An image of the generated pattern is captured by a camera ( 52 ) receive. The camera's field of view ( 52 ) is determined on the basis of the positions of the plurality of pattern elements in the obtained image of the generated pattern. Alternatively, the pattern is replicated by the pattern generator to generate a replicated pattern comprising a plurality of pattern elements. As previously described, the pattern elements can be a series of points or grid lines. An optical system, such as a camera, for which the field of view is to be determined, is placed on the open side of the box of the replicator. The camera should be designed to face the open side and take a picture from inside the box. An image of the replicated pattern from inside the box is captured by the camera. The image can be captured and displayed on a computer screen or, alternatively, can be generated as a physical printout. The field of view of the camera is determined on the basis of the positions of the plurality of pattern elements in the obtained image of the replicated pattern. 12th Figure 12 shows a sample image captured by a camera that is used to determine the camera's field of view. In this example, the camera captured an image of a replicated dot pattern. The pattern carries the distortion of the camera. The center lines of the images provide a determination of the field of view, while the points indicate an angular position of incident light rays. The sample elements serve the same purpose as the "goals" as related to 1 described. Thus, the field of view can be determined in a similar manner on the basis of the recorded image. If, as above, distortion is detected in the image, it can be taken into account in calculations for determining the field of view by assessing the position of the distorted pattern elements relative to the known positions of the elements for an undistorted image.

The words "comprises" and the words "including" when used herein with reference to the present invention are used to specify the presence of identified features, integers, steps, or components, but include those The presence or addition of one or more other elements, integers, steps, components or groups thereof does not preclude.

It will be understood that certain features of the invention, which for the sake of clarity are described in the context of separate embodiments, can also be provided in combination in a single embodiment. Conversely, various features of the invention, which for the sake of brevity are described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

Claims (14)

A system (21) for determining a field of view (FOV) of a camera, comprising: a light source (22); a pattern generator (23) which is adapted to generate a pattern from light emitted by the light source; the system being characterized in that: the pattern generator (23) comprises an optical element, the optical element being adapted to direct the pattern to the lens of a camera in such a way that the FOV on the lens can be determined from the pattern . System according to Claim 1 wherein the light source (22) comprises a laser. System according to Claim 1 or 2 wherein the pattern generator (23) comprises a diffractive optical element (24). System according to Claim 1 or 2 wherein the pattern generator (22) comprises a holographic optical element (25). System according to one of the Claims 1 to 3 , further comprising a replicator (31) for replicating the pattern from the pattern generator and arranged so that the replicated pattern can be seen by a camera. System according to Claim 5 wherein the replicator (31) comprises a cube-shaped or cuboid-shaped box comprising: a first open side (51); a second closed side comprising a screen (53) for receiving light propagated by the pattern generator; at least two sides including reflective surfaces (54), the reflective surfaces internally opposing each other within the box and adapted to reflect the pattern from the screen (53) to create a replicated pattern within the box defined by the first open side (51) can be seen. System according to Claim 6 wherein the screen (53) comprises a transparent diffuser. System according to Claim 6 or 7th with the reflective surfaces covering the inner sides of the box in their entirety. System according to Claim 8 further comprising a camera (52) positioned on the first open side (53) and adapted to view the replicated pattern within the box. A system according to any preceding claim, wherein the generated pattern comprises a series of points. A system according to any preceding claim, wherein the generated pattern comprises a series of horizontal and vertical lines forming a plurality of square or rectangular shapes. System according to Claim 11 wherein the square shapes around the edges (91) of the generated pattern are clipped to form half squares or half rectangles. Method for determining the field of view of a camera using the system of FIG Claim 1 comprising: generating at the pattern generator (23) a pattern from light emitted from the light source (22); Obtaining via a camera (52) an image of the generated pattern; Determining the field of view of the camera (52) from the positions of the plurality of pattern elements in the obtained image of the generated pattern. Procedure according to Claim 13 further comprising: replicating, at a replicator (31), the pattern from the pattern generator (23), the replicated pattern comprising a plurality of pattern elements; Obtaining, via the camera (52), an image of the replicated pattern; Determining the field of view from the positions of the plurality of pattern elements in the obtained image of the replicated pattern.

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