Method and apparatus for testing camera flicker

Abstract

The present invention relates to a light-directing apparatus for directing light toward a device under test (DUT) including an image sensor equipped with an LED flicker mitigation (LFM) function, the light-directing apparatus being characterized by comprising: (a) at least one adjustable LED light source capable of emitting light in a pulse width modulation (PWM) signal manner by adjusting frequency or duty cycle; (b) a fixed light source capable of emitting light; and (c) a background means for reflecting or transmitting light emitted from the adjustable LED light source and the fixed light source, wherein the fixed light source is arranged such that the emitted light does not directly strike the device under test, and the background means is arranged such that the reflected or transmitted light is directly received by the device under test.

Description

Method and apparatus for testing camera flicker phenomenon

[0001] The present invention relates to a method and apparatus for testing camera flicker phenomena.

[0002] Currently, widely used LED lighting features the characteristic of controlling brightness using Pulse Width Modulation (PWM). PWM enables relatively precise and efficient brightness control by adjusting the duty cycle of a digital signal to control average power. However, this PWM method can be operated at various frequencies and duty cycles other than standard power frequencies (50Hz or 60Hz), resulting in a flicker phenomenon that is not easily detected by the human eye. Particularly when the frequency is low or the duty cycle is set to an extreme, this flickering becomes clearly visible in image or video systems and is a major cause of image or video quality degradation and perception errors.

[0003] Such flicker phenomena can pose a serious problem for automotive ADAS (Advanced Driver Assistance System) cameras. ADAS camera sensors are capable of detecting various light-based objects, such as traffic lights, road signs, and the headlights and taillights of other vehicles. However, if LED light sources cause flicker, objects may become distorted or momentarily disappear within the image or video, potentially leading to vehicle malfunctions or failure of driver warnings. To address this issue, LED Flicker Mitigation (LFM) features are being introduced in recent image sensors. LFM analyzes changes in light intensity within an image or video and corrects them to reduce distortion caused by flicker. However, the inclusion of LFM features does not guarantee effective operation, as their performance depends on various factors such as sensor structure, exposure method, and frequency conditions.

[0004] Since the performance of the LFM (LED Flicker Mitigation) function of a camera image sensor to prevent flicker caused by LED lighting has been evaluated only qualitatively or verified according to different standards by manufacturer, the present invention aims to provide a systematic test method that can quantitatively and objectively evaluate the effectiveness of the LFM function.

[0005] In addition, there was a limitation in that it was difficult to precisely verify differences in LFM performance according to specific exposure conditions or sensor structures. Therefore, the present invention aims to provide various evaluation environments by comparing flicker responses under various PWM conditions, positions, and viewing angles.

[0006] In one embodiment of the present invention, a light alignment device for a device to be tested may be provided. The light alignment device for a device to be tested may include at least one controllable LED light source capable of emitting light in a Pulse Width Modulation (PWM) signal manner by adjusting the frequency or duty cycle, a fixed light source capable of emitting light, and background means for reflecting or transmitting light emitted from the controllable LED light source and the fixed light source.

[0007] In one embodiment of the present invention, the light alignment device for a test target device may be such that the control LED light source is adjustable to a PWM signal frequency of 10 Hz or higher and 65,000 Hz.

[0008] In one embodiment of the present invention, the light alignment device for a test target device may be such that the control LED light source is controllable with a PWM signal duty cycle of 0 to 100%.

[0009] In one embodiment of the present invention, the PWM signal frequency or duty cycle of each of the control LED light sources may be the same or different.

[0010] In one embodiment of the present invention, the light alignment device for a test target device may be such that the control LED light source is positioned between the center and the edge within the shooting field of view of the test target device.

[0011] In one embodiment of the present invention, the shooting field of view of the test target device may have a horizontal angle of view of 40 to 180°.

[0012] In one embodiment of the present invention, the light alignment device for a test target device may include the background means as an evaluation chart of a single color patch or an evaluation chart composed of at least two or more color-separated patches.

[0013] In one embodiment of the present invention, the light alignment device for a test target device may further include a shield that blocks light emitted from the fixed light source from being directly irradiated onto the test target device.

[0014] In one embodiment of the present invention, the light alignment device for a test target device may be equipped with a rotational driving unit so that the test target device can rotate.

[0015] In one embodiment of the present invention, a method for evaluating the flicker response performance of a device under test may be provided. The method may include: a light emission step of generating a flicker phenomenon using at least one controllable LED light source capable of emitting light in a Pulse Width Modulation (PWM) manner by adjusting the frequency or duty cycle; a step of directing the emitted light to a device under test; a step of capturing and collecting at least an image or video by the device under test; a step of checking whether any one of a stripe phenomenon, a breathing phenomenon, and a blinking phenomenon caused by the flicker phenomenon occurs in the image or video; and a step of evaluating the LFM function of an image sensor within the device under test according to the occurrence or absence of the occurrence.

[0016] In one embodiment of the present invention, each control LED light source can emit light to the test target device at a different location within the shooting field of view of the test target device.

[0017] In one embodiment of the present invention, step (c) may involve rotating the test target device to position the control LED light source between the center and the edge within the shooting field of view of the test target device, while capturing and collecting an image or video.

[0018] The present invention can provide a systematic test method capable of quantitatively and objectively evaluating the effectiveness of the LFM (LED Flicker Mitigation) function.

[0019] The present invention can analyze flicker response under various frequency, duty cycle, and viewing angle conditions at once, and thus allows for multi-faceted evaluation of flicker response performance according to sensor structure or exposure method.

[0020] FIG. 1 shows an example of use of a light alignment device (1) for a test target device according to an embodiment of the present invention.

[0021] FIG. 2 shows a schematic diagram of each configuration of a light alignment device (1) for a test target device according to an embodiment of the present invention.

[0022] FIG. 3 shows an example of a cross-sectional component of a background means (30) and a flicker phenomenon evaluation chart (31) according to an embodiment of the present invention.

[0023] Hereinafter, a method for testing a camera flicker phenomenon and a light alignment device (1) for a test target device according to an embodiment of the present invention will be described in detail with reference to the attached drawings. The attached drawings are merely examples to aid in understanding an embodiment of the present invention, and the scope according to an embodiment of the present invention is not limited to the specific form of the drawings.

[0024] [Example] Light alignment device (1) for a device to be tested

[0025] FIG. 1 shows an example of use of a light alignment device (1) for a test target device according to an embodiment of the present invention. FIG. 2 shows a schematic diagram of each configuration of a light alignment device (1) for a test target device according to an embodiment of the present invention. FIG. 3 shows an example of a component of one cross-section of a background means (30) and a flicker phenomenon evaluation chart (31) according to an embodiment of the present invention.

[0026] Referring to FIGS. 1 and 2, the light alignment device (1) for a test target device may include an adjustable LED light source (10), a fixed light source (20), a background means (30), and a shield (40). The light alignment device (1) for a test target device may additionally include a rotary drive unit (50). Additionally, the test target device (T) may be located on one side of the light alignment device (1) for a test target device.

[0027] Referring to FIG. 3, the background means (30) may include an evaluation reference plane (31) and an evaluation chart (32) in one cross section.

[0028] In one embodiment of the present invention, the light alignment device (1) for a test target device can test the flicker phenomenon for a test target device (T) including an image sensor equipped with an LFM (LED Flicker Mitigation) function.

[0029] Adjustable LED light source (10)

[0030] In one embodiment of the present invention, the control LED light source (10) can generate conditions for a flicker phenomenon to occur in the light alignment device (1) for a test target device. Specifically, the control LED light source (10) can induce a flicker response under various conditions by controlling the frequency and duty cycle using a Pulse Width Modulation (PWM) signal method. Specifically, the control LED light source (10) can be adjusted to a PWM signal frequency of 10 Hz or more and 65,000 Hz or less, and a duty cycle of 0% or more and 100%. At this time, the PWM signal is a form of digital signal, and the average voltage or power applied to the LED of the control LED light source (10) can be controlled by adjusting the ratio of the time the digital signal is in a HIGH (ON) state and the time it is in a LOW (OFF) state within a certain period.

[0031] According to one embodiment of the present invention, the frequency of the PWM signal refers to how many times the digital signal is repeated in one second. In addition, the duty cycle refers to the ratio of the time during which the signal remains in the ON state within one cycle.

[0032] In one embodiment of the present invention, the control LED light source (10) may be positioned within the shooting field of view (T2) of the test target device (T). Specifically, the control LED light source (10) may be positioned between the center and the edge within the shooting field of view (T2) of the test target device (T). Additionally, the control LED light source (10) may irradiate a control light (10-1) for testing the flicker phenomenon.

[0033] According to one embodiment of the present invention, at least one control LED light source (10) may be placed at various locations. Additionally, when two or more control LED light sources (10) are used, each control LED light source (10) may have the same or different flicker conditions.

[0034] Fixed light source (20)

[0035] In one embodiment of the present invention, the fixed light source (20) can provide a reference illuminance for the light alignment device (1) for the device to be tested to perform a flicker test.

[0036] In one embodiment of the present invention, the fixed light source (20) can irradiate a uniform fixed light (20-1) to uniformly illuminate the background means (30). That is, unlike the adjustable LED light source (10), the fixed light source (20) can irradiate a uniform light to uniformly illuminate the background means (30) using a PWM signal method.

[0037] In one embodiment of the present invention, the fixed light source (20) can irradiate a separate fixed light (20-1) that is distinct from the control light (10-1) for creating a flicker test environment generated from the control LED light source (10).

[0038] As illustrated in FIG. 1, the light alignment device (1) for the device under test may include at least one fixed light source (20).

[0039] In one embodiment of the present invention, at least one of the light conditions (light intensity (lux) or color temperature (K), etc.) of the fixed light source (20) may be changed during the flicker test. Additionally, the fixed light source (20) may be installed together with a shield (40) to prevent the fixed light (20-1) from being directly incident on the device (T) to be tested.

[0040] Background means (30)

[0041] According to one embodiment of the present invention, the background means (30) corresponds to a structure in which the test target device (T) is positioned within the shooting field of view (T2) in the light alignment device (1) for the test target device. Additionally, the background means (30) may reflect or transmit the controlled light (10-1) and the fixed light (20-1) emitted from the controlled LED light source (10) or the fixed light source (20). Additionally, one cross-section of the background means (30) may be composed of an evaluation reference plane (31) and an evaluation chart (32).

[0042] Evaluation criteria surface (31)

[0043] In one embodiment of the present invention, the evaluation reference surface (31) can cause distortion phenomena such as stripe phenomena, breathing phenomena, and blinking phenomena caused by flicker to be visually displayed in an image or video captured by the test target device (T) in the background means (30). Additionally, the evaluation reference surface (31) can serve as a reference surface for detecting distortion phenomena caused by flicker in an image or video captured by the test target device (T).

[0044] In an embodiment of the invention, the evaluation reference surface (31) can serve as a reference surface for detecting the aforementioned stripe phenomenon. In this case, the stripe phenomenon mainly occurs in a Rolling Shutter type image sensor, and stripes may be generated by flicker. Additionally, the evaluation reference surface (31) can serve as a reference surface for detecting the aforementioned breathing phenomenon. In this case, the breathing phenomenon mainly occurs in a Global Shutter type image sensor, and an image or video may repeatedly become brighter and darker periodically due to flicker. Additionally, the evaluation reference surface (31) can serve as a reference surface for detecting the aforementioned blinking phenomenon. In this case, the blinking phenomenon refers to the phenomenon in which the control light (10-1) irradiated from the control LED light source (10) is periodically turned off and on.

[0045] Evaluation chart (32)

[0046] In one embodiment of the present invention, the background means (30) may form an evaluation chart (32) within the evaluation reference plane (31). The evaluation chart (32) may provide visual information for quantitatively analyzing whether a flicker phenomenon occurs and the degree thereof in an image or video captured by the test target device (T).

[0047] In one embodiment of the present invention, the controlled light (10-1) and fixed light (20-1) emitted from the controlled LED light source (10) and fixed light source (20) can be reflected or transmitted through the evaluation chart (32) to reach the test target device (T). Additionally, the evaluation chart (32), together with the evaluation reference surface (31), can serve as a reference surface through which the controlled light (10-1) and fixed light (20-1) emitted from the controlled LED light source (10) and fixed light source (20) can be reflected or transmitted. That is, the evaluation chart (32) can assist in more clearly identifying distortion phenomena such as striping, breathing, and blinking phenomena within an image or video caused by the flicker phenomenon.

[0048] In one embodiment of the present invention, FIG. 3(a) and FIG. 3(b) illustrate examples of a flicker evaluation chart (32) according to one embodiment of the present invention. Specifically, FIG. 3(a) illustrates an evaluation chart (32) composed of a single color patch used in a linear mode shooting method. FIG. 3(b) illustrates an evaluation chart (32) composed of a plurality of patches of various brightness used in an HDR (High Dynamic Range) mode shooting method.

[0049] According to one embodiment of the present invention, the linear mode shooting method illustrated in FIG. 3(a) is a method in which a test target device (T) and an image sensor (T1) linearly output a brightness value in proportion to the amount of light input under a single exposure time. Since only one exposure condition is applied in the linear mode shooting method, if a flicker phenomenon occurs, stripes or brightness blinking within the image or video can be reflected sensitively and directly. In addition, the linear mode shooting method can quickly identify the aforementioned distortion phenomenon caused by the flicker phenomenon.

[0050] In one embodiment of the present invention, when shooting in HDR mode of FIG. 3, the entire area may be composed of a single color patch as shown in the evaluation chart (32) of (a).

[0051] In one embodiment of the present invention, the aforementioned distortion phenomenon can be confirmed through the evaluation chart (32) of FIG. 3 (a) captured by the test target device (T) during linear mode shooting. Specifically, when a flicker phenomenon occurs caused by the control light (10-1) emitted from the control LED light source (10), the aforementioned distortion phenomenon can be confirmed in the single color patch area of ​​the evaluation chart (32) of FIG. 3 (a).

[0052] According to one embodiment of the present invention, the evaluation chart (32) of FIG. 3 (a) can evaluate the flicker mitigation performance of a test target device (T) equipped with an image sensor (T1) to which an LFM (LED Flicker Mitigation) function is applied by checking an image or video showing the aforementioned distortion phenomenon.

[0053] According to one embodiment of the present invention, the HDR mode shooting method illustrated in FIG. 3(b) is a shooting method that combines multiple images acquired by an image sensor under different exposure conditions to enable clear expression of both dark and bright areas simultaneously, even in scenes with large differences in brightness. Specifically, there are two types of HDR mode shooting methods. First, the Split Pixel method means that pixels for long exposure and pixels for short exposure are physically separated to collect different amounts of light. Second, the Interleaved Exposure method means that a single pixel alternately performs long exposure and short exposure at short time intervals. In the case of flickering, the HDR mode shooting method may result in brightness inconsistency, pattern loss, or distortion in the HDR composite result due to changes in lighting brightness between exposures.

[0054] According to one embodiment of the present invention, when shooting in HDR mode, a chart composed of a plurality of patches composed of various brightness levels, such as the evaluation chart (32) of FIG. 3 (b), can be used.

[0055] According to one embodiment of the present invention, the evaluation chart (32) of FIG. 3 (b) may be composed of two or more patches having various brightness levels.

[0056] According to one embodiment of the present invention, the evaluation chart (32) of FIG. 3(b) can be configured to check for flicker phenomena that may occur in HDR mode. Specifically, when a flicker phenomenon occurs caused by the control light (10-1) emitted from the control LED light source (10), the evaluation chart (32) of FIG. 3(b) may not show patches of various brightness sequentially, or a specific area may appear as a single color.

[0057] According to one embodiment of the present invention, the evaluation chart (32) of FIG. 3 (b) can evaluate the flicker mitigation performance of a test target device (T) equipped with an image sensor (T1) to which an LFM (LED Flicker Mitigation) function is applied by checking an image or video in which a specific area appears as a single color.

[0058] Screen (40)

[0059] In one embodiment of the present invention, the shield (40) can block fixed light (20-1) emitted from a fixed light source (20) from being directly irradiated onto the test target device (T).

[0060] In one embodiment of the present invention, the shield (40) can purify the light environment so that only the flicker phenomenon caused by the control light (10-1) emitted from the control LED light source (10) can be measured. Additionally, the shield (40) can be formed as a fixed structure or a variable structure. Furthermore, the shield (40) can be applied to various test conditions by adjusting the light blocking angle, height, position, etc., as needed.

[0061] Rotation drive unit (50)

[0062] In one embodiment of the present invention, the rotary drive unit (50) is coupled with the test target device (T) and can be rotated at a predetermined angle.

[0063] In one embodiment of the present invention, the rotation drive unit (50) can assist in providing an image or video of a flicker phenomenon under the shooting field of view (T2) conditions of the test target device (T). Specifically, the rotation drive unit (50) can position the control LED light source (10) between the center and the edge within the shooting field of view (T2) of the test target device (T) by rotating the test target device (T).

[0064] In one embodiment of the present invention, the rotational drive unit (50) can be controlled for driving speed, direction, and rotation range. Additionally, the rotational drive unit (50) can be controlled to enable repeated testing for a plurality of flicker conditions or various positions within the shooting field of view (T2) of the test target device (T). Furthermore, the rotational drive unit (50) can reflect the flicker phenomenon caused by camera movement or viewpoint change in a real environment.

[0065] Test target device (T) and image sensor (T1)

[0066] In one embodiment of the present invention, the device to be tested (T) may include an image sensor (T1).

[0067] In one embodiment of the present invention, the image sensor (T1) may be a sensor equipped with an LFM (LED Flicker Mitigation) function. Additionally, the test target device (T) may capture an image or video under flicker conditions according to the light alignment device (1) for the test target device. Specifically, the test target device (T) may receive control light (10-1) emitted under flicker conditions from a control LED light source (10). Subsequently, the test target device (T) may acquire image or video data through the image sensor (T1). At this time, the image sensor (T1) may convert and process the image or video information captured by the test target device (T) into a digital signal.

[0068] In one embodiment of the present invention, the test target device (T) records an image or video through a control light (10-1) irradiated from a control LED light source (10) under flicker conditions, and can confirm distortion reactions such as stripe phenomenon, breathing phenomenon and blinking phenomenon that occur according to the flicker phenomenon.

[0069] In one embodiment of the present invention, the image sensor (T1) may have high-speed response characteristics capable of responding to light changes in short time units caused by flicker phenomena.

[0070] In one embodiment of the present invention, the test target device (T) can be coupled with the rotational drive unit (50) of the light alignment device (1) for the test target device. Through this, the test target device (T) can be photographed in a stationary state according to the flicker test environment, and can be photographed while the rotational drive unit (50) rotates.

[0071] Example of installing a light alignment device (1) for a device under test

[0072] In one embodiment of the present invention, the background means (30) is arranged in a planar structure on one side and may be positioned within the field of view to be captured by the test target device (T). Specifically, the cross-section of the background means (30) facing the test target device (T) has an evaluation reference plane (31) and may have an evaluation chart (32) attached thereto.

[0073] In one embodiment of the present invention, the fixed light source (20) may be configured to be positioned on each side of the background means (30) so as to irradiate the fixed light (20-1) toward the background means (30). Additionally, the shield (40) may be positioned in an inclined shape between each fixed light source (20) and the test target device (T). This prevents the light emitted from the fixed light source (20) from being directly incident on the test target device (T).

[0074] In one embodiment of the present invention, the control LED light source (10) may be placed in the central area between the background means (30) and the test target device (T). Thereby, the test target device (T) may be configured so that the control light (10-1) is irradiated within the shooting field of view (T2).

[0075] In one embodiment of the present invention, the test target device (T) is located on the opposite side of the background means (30) and may be positioned to enable image or video capture toward the background means (30). The arrangement and configuration of the light alignment device (1) for the test target device described above is an example and is not limited thereto.

[0076] The scope of rights according to one embodiment of the present invention is not limited to the embodiments described above, but may be implemented in various forms of embodiments within the scope of the appended claims. It is deemed that various modifications are possible by anyone with ordinary knowledge in the technical field to which the invention pertains, without departing from the gist of the one embodiment of the present invention claimed in the claims, and are considered to be within the scope of the claims according to one embodiment of the present invention.

[0077] [Explanation of the symbol]

[0078] 1: Optical alignment device for the device under test

[0079] 10: Adjustable LED light source

[0080] 10-1: Controlled Light

[0081] 20: Fixed light source

[0082] 20-1: Fixed Light

[0083] 30: Background Means

[0084] 31: Evaluation Criteria

[0085] 32: Evaluation Chart

[0086] 40: Screen

[0087] 50: Rotary drive unit

[0088] T: Device Under Test (DUT)

[0089] T1: Image sensor

[0090] T2: Shooting field of view

Claims

1. A light alignment device for aligning light to a Device Under Test (DUT) including an image sensor equipped with an LFM (LED Flicker Mitigation) function, (a) at least one adjustable LED light source capable of emitting light in a Pulse Width Modulation (PWM) signal manner by adjusting the frequency or duty cycle; (b) a fixed light source capable of emitting light; and (c) Background means for reflecting or transmitting light emitted from the above-mentioned adjustable LED light source and the above-mentioned fixed light source Includes, The above fixed light source is positioned so that the emitted light is not directly irradiated onto the device under test, and the background means is positioned so that the reflected or transmitted light can be directly received by the device under test. Characterized by, Optical alignment device for a device under test.

2. In Paragraph 1, The above-described adjustable LED light source is adjustable to a PWM signal frequency of 10 Hz or higher and 65,000 Hz, Optical alignment device for a device under test.

3. In Paragraph 1, The above-described adjustable LED light source is capable of being controlled by a PWM signal duty cycle of 0 to 100%. Optical alignment device for a device under test.

4. In Paragraph 1, In the case where there are two or more of the above-mentioned control LED light sources, the PWM signal frequency or duty cycle of each of the above-mentioned control LED light sources may be the same or different. Optical alignment device for a device under test.

5. In Paragraph 1, The above-mentioned adjustable LED light source is such that the test subject device is positioned between the center and the edge within the shooting field of view. Optical alignment device for a device under test.

6. In Paragraph 5, The shooting field of view of the above-mentioned test device is, with a horizontal angle of view of 40 to 180°, Optical alignment device for a device under test.

7. In Paragraph 1, The above background means comprises an evaluation chart of a single color patch or an evaluation chart composed of at least two or more color-separated patches. Optical alignment device for a device under test.

8. In Paragraph 1, The above-mentioned test target device is, A shield further comprising a blocking device that prevents light emitted from the fixed light source from being directly irradiated onto the device under test. Optical alignment device for a device under test.

9. In Paragraph 1, The above-mentioned test subject device is one that has a rotary drive unit attached to enable rotation, Optical alignment device for a device under test.

10. A method for evaluating the flicker mitigation performance of a Device Under Test (DUT) including an image sensor equipped with an LFM (LED Flicker Mitigation) function, (a) A light emission step that generates a flicker phenomenon using at least one controllable LED light source capable of emitting light in a Pulse Width Modulation (PWM) manner by adjusting the frequency or duty cycle; (b) a step of directing the emitted light to the device under test; (c) a step of capturing and collecting at least an image or video by the above-mentioned test target device; (d) a step of checking whether any one of the stripe phenomenon, breathing phenomenon and blinking phenomenon resulting from the flicker phenomenon occurs in the image or video; and (e) a step of evaluating the LFM function of the image sensor in the test target device according to whether the above occurs; including, Method for evaluating flicker response performance of a device under test.

11. In Paragraph 10, If there are two or more of the above-mentioned adjustable LED light sources, each of the adjustable LED light sources emits light to the test target device at a different location within the shooting field of view of the test target device. Camera Flicker Test Method 12. In Paragraph 10, The above step (c) is to rotate the device under test to position the control LED light source between the center and the edge within the shooting field of view of the device under test, and to capture and collect an image or video. Camera Flicker Test Method

Images