Method for measuring contrast sensitivity based on augmented reality display device

Abstract

The invention discloses a method for measuring contrast sensitivity based on augmented reality display equipment, which can obtain contrast thresholds when virtual images with different spatial frequencies can be just distinguished under different environmental illuminations by measuring a human eye contrast sensitivity function curve when the augmented reality display equipment is used. The optimization of the contrast sensitivity can ensure that the user can obtain clear and accurate visual experience under different illumination conditions and visual environments. According to the method for measuring the contrast sensitivity based on the augmented reality display equipment, reference is provided for improvement of the display quality of the augmented reality display equipment, and the immersion and comfort of a user during use are improved.

Description

Technical Field

[0001] The invention relates to a method for measuring contrast sensitivity based on an augmented reality display device, and belongs to the technical field of augmented reality. Background Art

[0002] The rapid progress of science and technology has led to the widespread application of augmented reality (AR) in many fields. This technology relies on tracking and registration technology, display technology, interactive technology, etc. to integrate real environment information and virtual information, allowing the two to overlap in the same screen and space, thereby expanding and enhancing the content of the real environment, enabling people to have richer and deeper exchanges with the real world and the digital world, and thus gain sensory experiences beyond the real world.

[0003] Optical See-Through Augmented Reality (OST-AR) displays use beam splitters or waveguides to add the light emitted by the display to natural light, so the color produced is a mixture of display light and ambient light. In some cases, virtual objects appear transparent and indistinguishable. While improving software and hardware technology, it is crucial to improve the user's subjective experience. In the human visual system space, contrast sensitivity (CS) is a very important indicator, which refers to the reciprocal of the contrast threshold that the visual system can perceive. The contrast sensitivity function (CSF) reflects the relationship between contrast sensitivity and spatial frequency under different conditions. Contrast sensitivity is a measure of the human eye's ability to distinguish object details under different contrasts and spatial frequencies.

[0004] In the process of developing augmented reality display devices, the measurement of contrast sensitivity is one of the important indicators for evaluating the advantages and disadvantages of display technology. By measuring the contrast sensitivity of different display technologies, we can understand the performance of various technologies under different visual conditions, and then guide the R&D team to optimize and improve the display technology. In addition, by measuring the contrast sensitivity of different users under different environmental conditions, we can understand the visual needs of different users in various scenarios, so as to design more flexible and adjustable display parameters and setting options. However, the existing methods for measuring contrast sensitivity are all based on flat display devices. Since the imaging principles and display effects of flat display devices and augmented reality display devices are quite different, the contrast sensitivity parameters measured by flat displays cannot be directly transferred to augmented reality display devices for use. At the same time, traditional measurement methods are not applicable to AR devices, resulting in the lack of relevant data references for contrast sensitivity in the current technology improvement of augmented reality display devices. Therefore, this method for measuring contrast sensitivity based on augmented reality display devices is proposed to provide a reference for the optimization and improvement of augmented reality display technology. Summary of the invention

[0005] Purpose: In order to overcome the shortcomings of the prior art, the present invention provides a method for measuring contrast sensitivity based on an augmented reality display device, so as to achieve the measurement of contrast sensitivity when using a near-eye display, broaden the measurement range of contrast sensitivity, and achieve near-eye display contrast sensitivity measurement with simple operation and low measurement cost. This method can provide a reference for improving the display quality of augmented reality display devices and improve the immersion and comfort of users when using them.

[0006] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A method for measuring contrast sensitivity based on an augmented reality display device comprises the following steps:

[0008] Step S1: determining a value set of a preset spatial frequency of grating stripes, and the number of different direction angles of grating stripes with different spatial frequencies.

[0009] Step S2: Select a spatial frequency value from the value set, and select the number of different directional angles of the grating stripes according to the spatial frequency value, display the grating stripes of different directional angles in the near-eye display device according to the spatial frequency value of the grating stripes and the number of corresponding different directional angles, and increase the grating stripe contrast uniformly from 0 to 1. The user judges that the grating stripes can be just distinguished according to the directional angle of the displayed grating stripes and presses the corresponding confirmation button.

[0010] Step S3: Acquire the grating fringe image at the time when the confirmation button is pressed, obtain the maximum grayscale value and the minimum grayscale value of the pixels corresponding to the grating fringe image, and calculate the contrast threshold.

[0011] Step S4: Replace the value of the spatial frequency of the grating stripes from the value set, and execute steps S2 to S3.

[0012] Step S5: Repeat step S4 until all values ​​in the value set are traversed, all grating stripes are judged, and the contrast thresholds of the grating stripes at different spatial frequencies are obtained. The contrast thresholds of the grating stripes at different directions and angles of the same spatial frequency are averaged to obtain the contrast sensitivity at the spatial frequency.

[0013] As a preferred solution, the number of different direction angles of the grating stripes with different spatial frequencies in step S1 is 3.

[0014] As a preferred solution, the values ​​of the spatial frequencies and the different direction angles in step S2 are randomly selected.

[0015] As a preferred solution, different directional angles of the grating stripes include 0°, 30° and 150°.

[0016] As a preferred solution, the confirmation key is set as a keyboard direction key, and a total of four direction keys are used on the keyboard, among which the "up" key represents the grating stripe direction of 0°, the "right" key represents the grating stripe direction of 30°, the "left" key represents the grating stripe direction of 150°, and the "down" key represents that the grating stripe direction is invisible.

[0017] As a preferred solution, the step S2 further includes: if the error confirmation button is pressed, the grating stripe stimulation will be repeated at the end of the entire grating stripe stimulation sequence until all grating stripe stimulations are judged correctly.

[0018] As a preferred solution, the contrast threshold calculation formula is as follows:

[0019]

[0020] in, is the contrast threshold, is the maximum gray value, is the minimum gray value.

[0021] As a preferred solution, the calculation formula for contrast sensitivity under the spatial frequency is as follows:

[0022]

[0023] in, is contrast sensitivity, is the average value of the contrast threshold of grating fringes at different directions and angles under the spatial frequency.

[0024] As a preferred solution, step S2 further includes: changing the brightness of the lighting in the environment to change the ambient illumination, and replacing the background wall with different colors and textures to measure the contrast sensitivity.

[0025] As a preferred solution, the near-eye display device adopts an augmented reality display device.

[0026] Beneficial effects: The present invention provides a method for measuring contrast sensitivity based on an augmented reality display device. This method can measure the contrast sensitivity function curve of the human eye when the augmented reality display device is used to obtain the contrast threshold at which virtual images of different spatial frequencies can be just distinguished under different ambient illuminations. Optimizing the contrast sensitivity can ensure that users can obtain clear and accurate visual experiences under different lighting conditions and visual environments.

[0027] According to the contrast threshold measured by this method, the augmented reality display device can more accurately adjust the integration degree between virtual objects and the real world, so that the virtual information can be more naturally and realistically integrated into the real scene, thereby enhancing the user's sense of immersion. In the research and development process of augmented reality display devices, the measurement of contrast sensitivity is one of the important indicators for evaluating the advantages and disadvantages of display technology. By measuring the contrast sensitivity of different display technologies, we can understand the performance of various technologies under different visual conditions, and then guide the R&D team to optimize and improve the display technology. In addition, by measuring the contrast sensitivity of different users under different environmental conditions, we can understand the visual needs of different users in various scenarios, so as to design more flexible and adjustable display parameters and setting options. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A flow chart of a method for measuring contrast sensitivity based on an augmented reality display device provided by the present invention.

[0029] Figure 2 Schematic diagram of grating stripes at three different angles in the method for measuring contrast sensitivity of an augmented reality display device provided by the present invention. Figure 2 (a) is the stimulus image with direction 0°. Figure 2 (b) is the stimulus image with a direction of 30°. Figure 2 (c) is the stimulus image with a direction of 150°.

[0030] Figure 3 A group of human eye contrast sensitivity test data of an embodiment of a method for measuring contrast sensitivity of an augmented reality display device provided by the present invention.

[0031] Figure 4A human eye contrast sensitivity curve according to a group of embodiments of a method for measuring contrast sensitivity of an augmented reality display device provided by the present invention. DETAILED DESCRIPTION

[0032] The following is a clear and complete description of the technical solutions in the examples of the present invention in conjunction with the accompanying drawings in the examples of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present invention.

[0033] The present invention will be further described below in conjunction with specific embodiments.

[0034] Embodiment 1:

[0035] This embodiment introduces a method for measuring contrast sensitivity based on an augmented reality display device, such as Figure 1 As shown, the following steps are included:

[0036] Step S1: determining a value set of a preset spatial frequency of grating stripes, and the number of different direction angles of grating stripes with different spatial frequencies.

[0037] Step S2: Select a spatial frequency value from the value set, and select the number of different directional angles of the grating stripes according to the spatial frequency value, display the grating stripes of different directional angles in the near-eye display device according to the spatial frequency value of the grating stripes and the number of corresponding different directional angles, and increase the grating stripe contrast uniformly from 0 to 1. The user judges that the grating stripes can be just distinguished according to the directional angle of the displayed grating stripes and presses the corresponding confirmation button.

[0038] Step S3: Acquire the grating fringe image at the time when the confirmation button is pressed, obtain the maximum grayscale value and the minimum grayscale value of the pixels corresponding to the grating fringe image, and calculate the contrast threshold.

[0039] Step S4: Replace the value of the spatial frequency of the grating stripes from the value set, and execute steps S2 to S3.

[0040] Step S5: Repeat step S4 until all values ​​in the value set are traversed, all grating stripes are judged, and the contrast thresholds of the grating stripes at different spatial frequencies are obtained. The contrast thresholds of the grating stripes at different directions and angles of the same spatial frequency are averaged to obtain the contrast sensitivity at the spatial frequency.

[0041] Furthermore, in step S1, the number of different direction angles of the grating stripes with different spatial frequencies is 3.

[0042] Furthermore, different directional angles of the grating stripes include 0°, 30° and 150°.

[0043] Furthermore, the values ​​of the spatial frequencies and the different direction angles in step S2 are randomly selected.

[0044] Furthermore, to facilitate the test process, the method defines the confirmation key as a keyboard arrow key to represent whether the tester can perceive the grating and the direction of the grating after perception. There are four arrow keys on the keyboard, where the "up" key represents the grating stripe direction of 0°, the "right" key represents the grating stripe direction of 30°, the "left" key represents the grating stripe direction of 150°, and the "down" key represents the grating stripe direction is invisible.

[0045] Therefore, when the user can judge that the grating direction is 0°, the "up" key needs to be pressed; when it is 30°, the "right" key needs to be pressed; when it is 150°, the "left" key needs to be pressed; if after waiting for a long time, the user still feels that the grating is not perceived or the direction of the grating is indistinguishable, the "down" key needs to be pressed to treat it as invisible;

[0046] Furthermore, the step S2 also includes: if the wrong confirmation button is pressed due to accidental touch or other reasons, the grating stripe stimulation will be repeated at the end of the entire grating stripe stimulation sequence until all grating stripe stimulations are judged correctly.

[0047] Furthermore, after obtaining the maximum grayscale value and the minimum grayscale value of the pixel in step S3, according to the formula The contrast threshold is calculated as is the contrast threshold, ranging from 0 to 1, is the maximum gray value, is the minimum gray value.

[0048] Furthermore, in step S5, the gratings of each spatial frequency appear three times at different directions and angles, and their contrast thresholds are respectively recorded as , find its average , and then take its reciprocal as the contrast sensitivity at this spatial frequency .

[0049] Furthermore, step S2 also includes: if the parameters of the augmented reality display device used permit, the method can change the brightness of the lighting in the experimental environment to change the ambient illumination, and replace the background walls of different colors and textures to change the real environment background to measure the contrast sensitivity, thereby obtaining the sensitivity difference of the same augmented reality device under different environmental factors.

[0050] Furthermore, this method can be used not only for augmented reality display devices, but also for all near-eye display devices to measure contrast sensitivity.

[0051] Embodiment 2:

[0052] This embodiment introduces the experimental process of the present invention. Before the test begins, the number of pixels and other parameters of the grating stripes are determined according to the contrast sensitivity test conditions for the "Spatial Standard Observer (SSO)" specified by the ModelFest organization established by the American Optical Society OSA and the parameters of the augmented reality display device used. In the contrast sensitivity function, the unit of spatial frequency is usually "cycles / degree (CPD)", that is, the number of ripples contained in each degree of viewing angle.

[0053] Assume that the number of sinusoidal fringe periods contained in the grating fringe range is , the field of view formed by the grating fringe range is , then the spatial frequency ( ) is calculated as:

[0054]

[0055] In the contrast sensitivity test of human eyes, a sine wave grating is usually used as a stimulus image. In order to make the grating edge blend with the background more naturally, this method uses a sine wave grating modulated by a Gaussian envelope as a visual stimulus image. Figure 2 The sine wave gratings in different directions are shown, with the directions being 0°, 30°, and 150° (vertical direction is 0°, increasing in clockwise direction). The number of pairs of light and dark fringes per unit viewing angle is the spatial frequency, which is represented by Indicates that its unit is cycle per degree (CPD).

[0056] After the test started, a sine wave grating modulated by a Gaussian envelope gradually appeared in the center of the augmented reality display screen. Its size and shape were fixed, but the spatial frequency was The direction of the grating stripes is random, and the contrast increases evenly from 0 to 1 over time. The subjects need to press the key of the corresponding direction when they can just distinguish the direction of the grating stripes. If the direction is 0°, press the "up" key, if it is 30°, press the "right" key, if it is 150°, press the "left" key; if after waiting for a long time, they still feel that they cannot perceive the grating or the direction of the grating is indistinguishable, press the "down" key and regard it as invisible; if the wrong key is pressed due to accidental touch or other reasons, the stimulus will be repeated at the end of the entire stimulus sequence until all stimuli are judged correctly.

[0057] Each time you press the correct key, the program will obtain the image at that moment and get the maximum and minimum grayscale values ​​of the pixels in the image. According to the formula The contrast threshold is calculated as is the contrast threshold, ranging from 0 to 1, is the maximum gray value, is the minimum gray value.

[0058] In order to eliminate the influence of the grating stripe direction on the contrast sensitivity value, the grating of each spatial frequency appeared three times, and the grating stripe directions were 0°, 30° and 150° (vertical direction was 0°, increasing in clockwise direction), and their contrast thresholds were recorded as After all images are judged, the three contrast thresholds for each spatial frequency are averaged. , and then take its reciprocal as the contrast sensitivity at this spatial frequency . Set contrast sensitivity The corresponding spatial frequency By plotting on the same coordinate axis, we can get the curve of the contrast sensitivity function. Figure 3 : is the human eye contrast sensitivity test data of a group of embodiments under the same ambient illumination. As the spatial frequency increases, the contrast sensitivity shows a common rule of rapidly increasing from low to peak value and then slowly decreasing to zero. Repeat the test under different ambient illuminations to obtain the average contrast sensitivity curve of a group of embodiments under two ambient illuminations as shown in FIG. Figure 4 As shown in Figure 2, the contrast sensitivity under dark conditions is higher than that under bright conditions overall, and the spatial frequency at which the maximum contrast sensitivity occurs shifts toward higher frequencies from dark environments (1.5 CPD) to bright environments (2.0 CPD).

[0059] After the Fourier transform, the image is presented as a Fourier spectrum. In this space, frequency is an indicator of the intensity of the gray value change of the image, and is the gradient of the gray value in the plane space. Low-frequency information refers to information with slow gray value change frequency, including brightness and color. It represents the area in the image where the brightness or gray value changes slowly, contains most of the energy of the image, and describes the main part of the image. High-frequency information generally defines the boundaries and texture features of objects, and the grayscale changes are relatively large. Therefore, the spatial frequency of the image determines the imaging quality of the image in the human eye, so this method is very necessary.

[0060] In this method, a sine wave grating is used as the stimulus object because the grating image can simply reflect the change of spatial frequency and is widely used in visual perception related experiments. The spatial frequency is characterized by grating stripes, and the relationship between spatial frequency and contrast sensitivity is established. At the same time, the different contrast sensitivities in bright and dark environments are studied and the results are compared, which has important guiding significance for the parameter adjustment of AR display devices in different environments. Unlike previous studies, this method is applied to AR device testing rather than normal flat-panel displays.

[0061] By measuring the contrast sensitivity function curve of the human eye when the augmented reality display device is used, the present invention can obtain the contrast threshold at which virtual images of different environments and different spatial frequencies can be distinguished. Optimizing the contrast sensitivity can ensure that users can obtain a clear and accurate visual experience under different lighting conditions and visual environments. According to the measured contrast threshold, the augmented reality display device can more accurately adjust the degree of integration of virtual objects and the real world, so that virtual information can be more naturally and realistically integrated into the real scene, thereby enhancing the user's sense of immersion.

[0062] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for measuring contrast sensitivity based on an augmented reality display device, characterized in that: The following steps are involved: Step S1: determining a value set of a preset spatial frequency of grating stripes, and the number of different direction angles of grating stripes with different spatial frequencies; Step S2: selecting a spatial frequency value from the value set, and selecting the number of different direction angles of the grating stripes according to the spatial frequency value, displaying the grating stripes of different direction angles in the near-eye display device according to the spatial frequency value of the grating stripes and the number of corresponding different direction angles, and uniformly increasing the grating stripe contrast from 0 to 1, and the user presses the corresponding confirmation button when judging that the grating stripes can be just distinguished according to the direction angle of the displayed grating stripes; Step S3: acquiring the grating fringe image at the time of pressing the confirmation button, obtaining the maximum grayscale value and the minimum grayscale value of the pixels corresponding to the grating fringe image, and calculating the contrast threshold; Step S4: changing the value of the spatial frequency of the grating fringes from the value set, and executing steps S2 to S3; Step S5: Repeat step S4 until all values ​​in the value set are traversed, all grating stripes are judged, and the contrast thresholds of the grating stripes at different spatial frequencies are obtained. The contrast thresholds of the grating stripes at different directions and angles of the same spatial frequency are averaged to obtain the contrast sensitivity at the spatial frequency.

2. The method for measuring contrast sensitivity based on an augmented reality display device according to claim 1, characterized in that: In step S1, the number of different direction angles of the grating stripes with different spatial frequencies is 3.

3. The method for measuring contrast sensitivity based on an augmented reality display device according to claim 2, characterized in that: The different orientation angles of the grating stripes include 0°, 30° and 150°.

4. The method for measuring contrast sensitivity based on an augmented reality display device according to claim 3, characterized in that: The confirmation button is set as a keyboard direction key. There are four direction keys on the keyboard, among which the "up" key represents the grating stripe direction of 0°, the "right" key represents the grating stripe direction of 30°, the "left" key represents the grating stripe direction of 150°, and the "down" key represents that the grating stripe direction is invisible.

5. The method for measuring contrast sensitivity based on an augmented reality display device according to claim 1, characterized in that: The values ​​of the spatial frequencies and the different direction angles in step S2 are randomly selected.

6. The method for measuring contrast sensitivity based on an augmented reality display device according to claim 1, characterized in that: The step S2 also includes: if the error confirmation button is pressed, the grating stripe stimulation will be repeated at the end of the entire grating stripe stimulation sequence until all grating stripe stimulations are judged correctly.

7. The method for measuring contrast sensitivity based on an augmented reality display device according to claim 1, characterized in that: The contrast threshold calculation formula is as follows: ； in, is the contrast threshold, is the maximum gray value, is the minimum gray value.

8. The method for measuring contrast sensitivity based on an augmented reality display device according to claim 1, characterized in that: The calculation formula of contrast sensitivity at the spatial frequency is as follows: ； in, is contrast sensitivity, is the average value of the contrast threshold of grating fringes at different directions and angles under the spatial frequency.

9. The method for measuring contrast sensitivity based on an augmented reality display device according to claim 1, characterized in that: The step S2 also includes: changing the brightness of the lighting in the environment to change the ambient illumination, and replacing the background wall with different colors and textures to measure the contrast sensitivity.

10. The method for measuring contrast sensitivity based on an augmented reality display device according to claim 1, characterized in that: The near-eye display device adopts an augmented reality display device.

Images