CONTINUOUS SLANTED EDGE FOCUS MEASUREMENTS SYSTEM
A continuous slanted edge focus measurement system characterizes focus of a camera lens. The measurement system may be used to measure effects on focus on caused by factors such as thermal focal shift, humidity focal shift, focal shift caused by changing parts in the camera, and focal shift by changing the camera design. An accurate measurement system enables camera designers to optimize focus under a variety of different conditions and ensure consistency in the products.
This application is a continuation of U.S. application Ser. No. 16/330,222, filed on Mar. 4, 2019, which is a 371 National Stage Application of International Application No. PCT/US2017/048510, filed Aug. 24, 2017, which claims priority to and the benefit of U.S. Provisional Application No. 62/383,374 filed on Sep. 2, 2016, the entire disclosures of which are hereby incorporated by reference.
TECHNICAL FIELDThis application relates generally to a camera testing system and more particularly, to a focus measurement system.
BACKGROUND Description of the Related ArtFixed focus cameras are common in devices such as mobile phones and action cameras. Such cameras are desirable because they can be produced relatively inexpensively compared to adjustable focus cameras and have fewer points of failure. In order to ensure that fixed focus cameras can produce sufficiently focused images, a precise testing system for use during production is desirable.
The disclosed embodiments have other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:
The figures and the following description relate to preferred embodiments by way of illustration only. It should be noted that from the following discussion, alternative embodiments of the structures and methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of what is claimed.
Reference will now be made in detail to several embodiments, examples of which are illustrated in the accompanying figures. It is noted that wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. The figures depict embodiments of the disclosed system (or method) for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein.
Configuration OverviewA measurement system characterizes focus of a camera. The measurement system comprises a unit under test holder, a slanted edge target sub-system, an illumination device, a fixture, and an enclosure. The unit under test holder holds a camera at a fixed position and orientation. The slanted edge target sub-system has a slanted edge target surface with a target pattern for capturing as an image by the camera. The target pattern comprises a line having a slanted edge positioned to intersect a center of the image when captured by the camera. The slanted edge may be oriented at an acute angle relative to the optical axis of the camera. Furthermore, the target pattern may comprise a plurality of fiducials including lines that are substantially horizontal in the image when captured by the camera. The plurality of fiducials may be at varying distances from the camera. The illumination device may be positioned under the slanted edge target sub-system and may have an illuminating surface for illuminating the target pattern. The fixture may support the unit under test holder, the slanted edge target sub-system, and the illumination device. The enclosure may enclose the unit under test holder, the slanted edge target sub-system, the illumination device, and the fixture.
Beneficially, the measurement system enables the camera to capture images of the target pattern in a highly repeatable manner. The pattern in the captured image can be analyzed using an image processing algorithm to measure a focal quality at varying distances from the camera. This information can be used to calibrate the camera focus.
Measurement SystemA continuous slanted edge focus measurement system characterizes focus of a camera lens. The measurement system may be used to measure effects on focus on caused by factors such as thermal focal shift, humidity focal shift, focal shift caused by changing parts in the camera, and focal shift by changing the camera design. An accurate measurement system enables camera designers to optimize focus under a variety of different conditions and ensure consistency in the products.
An embodiment of the measurement system 100 for characterizing focus of a camera is illustrated in
The unit holder 206 is designed to hold the UUT (e.g., camera 208) and provides a highly repeatable mechanical location that ensures the camera 208 is mounted in the same position and orientation in each test. The unit holder 206 is furthermore designed to enable access to all buttons and connectors on the camera 208. The unit holder 206 may be removable from the holder base 202 and different unit holders 206 may be swapped in and out that each are structured to hold cameras 208 with different form factors.
The relay lens 204 is positioned between the camera 208 and the slanted edge target described in further detail below. The relay lens 204 beneficially enables a slanted edge target having a shortened length (relative to what would be needed without the relay lens 204) while maintaining the same magnification. The relay lens 204 may also be removable from the holder base 202 in one embodiment, in order to enable relay lenses 204 of different optical characteristics to be swapped in and out of the holder base 202 depending on the camera 208 being tested and the type of test being performed.
Slanted Edge Target Sub-SystemThe fiducials 304 enable self-calibration features. Given the known distances from each fiducial line 304 to the relay lens 204, the distance of different regions of interest along the slanted edge 302 can be accurately determined. Therefore, this feature may mitigate any misalignment errors between the camera 208 and the slanted edge target sub-system 120.
Illumination Sub-SystemThe illumination sub-system 130 comprises an illuminating panel (e.g., an LED panel) positioned under the slanted edge target sub-system 120 to provide a uniform backlit illumination on the slanted edge target panel 350 seen by the camera 208. The illumination uniformity measured directly on the slanted edge plane with a meter may be different compared to the uniformity seen by the camera 208 because of the relative angle between them. Therefore, the illumination sub-system 130 may be positioned to maximize the intensity uniformity as seen by the camera 208. Since Fiducial #1 of the target pattern 300 is closer to the camera 208, less illumination in the adjacent area may be sufficient compared to an area adjacent to Fiducial #6 of the target pattern 300 that is further from the camera 208. This condition can be optimized by configuring the illumination sub-system 130 as illustrated in
In an embodiment, the illumination panel 402 has LED arrays installed on its long sides. Typically, the light intensity on the area along the long sides is higher than the area in the middle. Therefore, both long edges of the illumination panel may be covered (e.g., by 1.5″ black gaffer tape). This prevents the light from these areas from affecting the intensity uniformity on the slanted edge metal target plane.
The uniformity as seen at the camera 208 may be 85% or better.
As illustrated in
After capturing an image of the slanted edge target pattern 300 by the camera, an image processing algorithm is applied to the image to determine a focal quality measurement. As illustrated in
Throughout this specification, some embodiments have used the expression “coupled” along with its derivatives. The term “coupled” as used herein is not necessarily limited to two or more elements being in direct physical or electrical contact. Rather, the term “coupled” may also encompass two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other, or are structured to provide a thermal conduction path between the elements.
In addition, use of the “a” or “an” are employed to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general sense of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.
Finally, as used herein any reference to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
Upon reading this disclosure, those of skill in the art will appreciate still additional alternative structural and functional designs for the described embodiments as disclosed from the principles herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those skilled in the art, may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the scope defined in the appended claims.
Claims
1. A measurement system, comprising:
- a holder configured to secure a camera;
- a first sub-system having a slanted edge target surface with a target pattern configured to capture an image by the camera, the target pattern comprising a slanted edge positioned to intersect a center of the image; and
- a second sub-system beneath the first sub-system, the second sub-system having an illuminating surface configured to illuminate the target pattern.
2. The measurement system of claim 1, wherein the slanted edge is at an acute angle relative to an optical axis of the camera.
3. The measurement system of claim 1, wherein the target pattern further comprises fiducials comprising horizontally-oriented lines in the image when captured by the camera.
4. The measurement system of claim 3, wherein the horizontally-oriented lines have equal width and different lengths.
5. The measurement system of claim 4, wherein the fiducials are at varying distances from the camera.
6. The measurement system of claim 4, wherein the fiducials have varying lengths that decrease with distance from the camera.
7. The measurement system of claim 4, wherein the fiducials have approximately equal width.
8. The measurement system of claim 1, wherein the second sub-system extends past the first sub-system at an edge of the measurement system opposite the holder.
9. The measurement system of claim 8, wherein the edge is a far edge.
10. The measurement system of claim 1, further comprising:
- a fixture to support the holder, the first sub-system, and the second sub-system; and
- an enclosure to enclose the holder, the first sub-system, the second sub-system, and the fixture.
11. The measurement system of claim 1, wherein the slanted edge target surface slopes upward at a first angle with respect to a horizontal ground plane with increasing distance from the camera.
12. The measurement system of claim 11, wherein the illuminating surface slopes upward at a second angle with respect to the horizontal ground plane with increasing distance from the camera.
13. The measurement system of claim 1, wherein the first sub-system comprises:
- a slanted edge target panel including the slanted edge target surface;
- a diffuser layer configured to diffuse light emitted from the second sub-system; and
- a support layer configured to provide structural support for the diffuser layer and the slanted edge target panel.
14. The measurement system of claim 1, wherein the holder comprises:
- a unit holder configured to hold the camera at a fixed position and orientation; and
- a relay lens positioned along an optical axis of the camera between the camera and the first sub-system.
15. A system, comprising:
- a holder configured to secure a camera;
- a target surface with a pattern configured to capture an image by the camera, the pattern including a slanted edge positioned to intersect a center of the image; and
- an illuminating surface configured to illuminate the target pattern.
16. The system of claim 15, wherein the target surface comprises:
- a slanted edge target panel;
- a first layer configured to diffuse light emitted from the illuminating surface; and
- a second layer configured to support for the first layer and the slanted edge target panel.
17. The system of claim 15, wherein the holder secures the camera at a fixed position and orientation and includes a relay lens.
18. The system of claim 15, wherein the pattern includes fiducials comprising lines in the image when captured by the camera.
19. A slanted edge target system, comprising:
- a panel having a slanted edge target surface; and
- a target pattern in the slanted edge target surface, the target pattern comprising a slanted edge positioned to intersect a center of an image when captured by a camera.
20. The slanted edge target system of claim 19, wherein the target pattern further comprises fiducials comprising lines in the image when captured by the camera.
Type: Application
Filed: May 10, 2021
Publication Date: Aug 26, 2021
Inventors: Yin-Min Huang (Hayward, CA), Mark Schnittker (San Jose, CA), Robert Hoffman (Fremont, CA), Emilio Graff (Belmont, CA)
Application Number: 17/316,046