CN109632092A - A kind of luminance test system and method based on spatial light field - Google Patents

Abstract

The invention discloses a kind of luminance test system and method based on spatial light field, CCD is demarcated in advance using the scaling method of traditional luminance meter, using this calculated relationship as the corresponding relationship of image grayscale and brightness, and then the image on required focal plane is obtained by light field refocusing algorithm, the Luminance Distribution in respective planes is converted thereof into again, by adjusting the image and its Luminance Distribution of the available different focal planes of relevant parameter of refocusing, it does not need to focus when measuring brightness, it operates very easy, and it can be quick, real-time capture spatial brightness information, match different measurement demands.

Description

A brightness testing system and method based on spatial light field

technical field

The invention relates to a brightness testing system and method based on a spatial light field, and belongs to the field of display device measurement.

Background technique

With the rapid development of display, lighting and other technologies, the composition of the light environment is becoming more and more diverse, and the accurate measurement and evaluation of the light environment is also particularly important. The evaluation of light environment involves a variety of indicators, such as brightness, illuminance, spectrum, stroboscopic, etc. Among them, brightness, as an important indicator of light environment evaluation, has been widely concerned for a long time. How to measure brightness conveniently and accurately is a A very crucial question.

The research on luminance measurement has a long history, and some results have been achieved. Currently, there are many kinds of luminance meters available on the market. The more common photometers include shading tube photometer, aiming point photometer and CCD imaging photometer. Among them, the shading tube photometer is characterized by simple manufacture and convenient use. The disadvantage is that its measurement accuracy is not high, and the detection The receiving surface of the receiver is very small, and certain accuracy can be guaranteed only when the radius of the small hole of the cylinder is less than one-tenth of the length of the cylinder; Focusing, the measurement accuracy is high, but its measurement range is small, it can only measure the brightness at the aiming point, and the operation is cumbersome; the CCD imaging brightness meter allows simultaneous brightness measurement of multiple points related in space, It uses three-color filters matched with CIE for luminance and chromaticity measurement, which can display the CIE color coordinates and color temperature of each pixel in the image, and capture millions of luminance data information in seconds. Its principle is to use the corresponding characteristics of the spectrum The CCD photoelectric coupling device, which is consistent with the optical efficiency function of the observer, simultaneously obtains the light radiation intensity and image of the illuminant through the optical system, and then through the linear signal processing system, the brightness of the detected target in the measurement field of view can be obtained. CCD imaging The luminance meter has a large measurement range and high precision, but it still needs to be focused in advance during measurement, and cannot directly obtain the spatial luminance distribution information. At present, there is no corresponding solution for the measurement of full-spatial luminance distribution data, and the research done is few and lacks systematic.

SUMMARY OF THE INVENTION

Purpose of the invention: The present invention proposes a brightness testing system and method based on a spatial light field to measure full-space brightness distribution data.

Technical solution: The technical solution adopted in the present invention is a brightness test system based on a spatial light field, including an imaging module and a host, the imaging module includes a main lens with parallel optical axes and a microlens array, and the other side of the microlens array A photo-coupler is provided, and the signal data obtained by the photo-coupler is then calculated by the host to calculate the brightness of the spatial light field.

The microlens array is located at the focal plane of the main lens, and the optocoupler is located at the focal plane of the microlens array.

A method for measuring the brightness of a space light field based on a time-domain transformation method, comprising a main lens with parallel optical axes and a microlens array, and a CCD is arranged on the other side of the microlens array, comprising the following steps:

1) Use the point luminance meter to calibrate the image gray value and luminance value of the CCD;

2) Determine the distance relationship between the refocusing plane and the microlens array, and parameterize the light field coordinate biplane;

3) Establish the two-dimensional geometric relationship of the main lens plane, the CCD plane, and the refocusing plane;

4) Extend the above two-dimensional geometric relationship to a four-dimensional light field;

5) Integrate the four-dimensional light field on the main lens plane to obtain an image of the refocusing plane;

6) Reprocessing the obtained refocusing image according to the pre-calibrated correspondence between the grayscale and the brightness of the image, and converting it into a brightness distribution map on the required focal plane.

In the step 2), the main lens plane is regarded as the u-v plane, the CCD plane is regarded as the x-y plane, the distance F between the two planes is the focal length of the main lens, L represents the intensity of the incident light, and the incident light is recorded as L ( u,v,x,y).

In the step 3), the light passes through the main lens plane position (u, v), then reaches the CCD plane position (x, y), and finally reaches the refocusing plane. In the two-dimensional case, its geometric relationship is:

In the above formula, L _F (x, u) represents the plenoptic function, which refers to a certain ray in particular. L _αF represents the intersection of the same ray on the refocusing plane, F' is the distance from the main lens to the refocusing plane.

In the step 4), the conversion relationship in the two-dimensional case is extended to a four-dimensional light field:

where F' is the distance from the main lens plane to the refocusing plane.

In the step 5), the four-dimensional light field pair (u, v) is integrated to obtain the image E _αF (x, y) of the refocusing plane:

A method for testing the brightness of a space light field based on a Fourier slice algorithm, comprising a main lens with parallel optical axes and a microlens array, the other side of the microlens array is provided with a CCD, and includes the following steps:

1) Use the point luminance meter to calibrate the image gray value and luminance value of the CCD;

2) Parameterize the light field coordinate biplane;

3) Extract appropriate two-dimensional slices in the frequency domain;

4) Do two-dimensional inverse Fourier transform again to obtain the image on the refocusing plane;

5) After the refocusing image is finally obtained, the obtained refocusing image is reprocessed according to the pre-calibrated correspondence between image grayscale and brightness, and is converted into a brightness distribution map on the corresponding focal plane.

In the step 2), the main lens plane is regarded as the u-v plane, the refocusing plane is regarded as the x-y plane, the distance F between the main lens plane and the CCD plane is the focal length of the main lens, and the incident light is recorded as L (u ,v,x,y).

In the steps 3) and 4), let the distance between the refocusing plane and the main lens plane be F', that is, αF, the intersection of the light ray and the refocusing plane is (x, y), denoted as L _αF , then the light ray and the CCD plane The coordinates of the intersection point are (u+(xu)/α, v+(yv)/α);

Define P _α as the conversion factor of the light field from the CCD depth F to αF, then P _α [L _F ] means that P _α acts on the light field L _F and is projected from space to a two-dimensional plane:

According to the Fourier slice theorem, the above formula can be defined as:

in, is the integration factor, the last two dimensions of the four-dimensional function are integrated, and B _α is the four-dimensional transformation:

define slice factor And F ⁿ is the N-dimensional Fourier transform, F ^-n is the N-dimensional inverse Fourier transform, and the replace with Available:

make Available:

The calculation method of _βα is:

The refocused image is obtained by E _F = P _α [L _F ].

Beneficial effects: the present invention combines the light field measurement principle and the traditional luminance meter measurement principle, obtains the spatial light field distribution information in real time through the imaging module, and the collected data is more complete. The traditional luminance meter calibration method is used to calibrate the CCD in advance, and the calculated relationship is the corresponding relationship between the image grayscale and the brightness, and then the image on the required focal plane is obtained through the light field refocusing algorithm, and then converted into the corresponding The brightness distribution on the plane, by adjusting the relevant parameters of refocusing, the images of different focal planes and their brightness distribution can be obtained. When measuring the brightness, it is not necessary to focus, the operation is very simple, and the spatial brightness information can be quickly and real-time captured, matching different measurement needs.

Description of drawings

Fig. 1 is the structural representation of the test system of the present invention;

2 is a schematic structural diagram of an imaging module;

Fig. 3 is a schematic diagram of biplane parameterization of light field coordinates;

FIG. 4 is a diagram showing the positional relationship between the refocusing plane and the microlens array.

Detailed ways

Below in conjunction with the accompanying drawings and specific embodiments, the present invention will be further clarified. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Modifications of equivalent forms all fall within the scope defined by the appended claims of this application.

Example 1

A light field is a concept used to describe the radiative transfer characteristics of light in three-dimensional space. Generally speaking, a sampling point of the light field, that is, a ray, is represented by the coordinates of the intersection of the light and two planes and the intensity of the light.

As shown in FIG. 1 , the brightness testing system based on the spatial light field in this embodiment includes a host 2 and an imaging module 1 . The imaging module 1 further includes a main lens 3 and a microlens array 4 with coincident optical axes, and a photocoupler 5 perpendicular to the optical axis is also provided on the other side of the microlens array 4, that is, a CCD, as shown in FIG. 2 . . The resolution of the microlens array 4 is 434*625, the distance between adjacent microlenses is 14um, and the resolution of the optocoupler 5 is above 7000*5000. The microlens array 4 is located on the focal plane of the main lens 3 , and the optocoupler 5 is located on the focal plane of the microlens array 4 .

The photoelectric coupler 5 is calibrated with a point luminance meter for image grayscale value and luminance value before use. The grayscale value ranges from 0 to 255 and the luminance value ranges from 0 to 1000cd/m ² .

The imaging module 1 shoots the scene to be tested. Lights from different directions enter the camera through the main lens 3, converge on different microlenses of the microlens array 4, and then diverge into several light rays after passing through the microlens to reach the optocoupler 5 respectively. After being received by the photocoupler 5, it is converted into an electrical signal, and the electrical signal is sent to the host 2 for processing.

The host 2 processes the received signal according to the principle of light field refocusing. If the requirements for accuracy are high and the running time requirements are relatively low, the host 2 uses the time domain transformation method to refocus the original light field, and uses ray tracing to refocus the original light field. The principle of coordinate transformation is carried out, and the image on the corresponding focal plane is obtained by integrating on the new image plane. First, the distance relationship between the refocusing plane and the microlens array 4 is determined.

As shown in Figure 3, the light field coordinates are then parameterized in two planes, the main lens plane is regarded as the u-v plane, the CCD plane is regarded as the x-y plane, the distance F between the two planes is the focal length of the main lens, and the incident light Passing through the double plane, intersecting at the point (u, v, x, y), L represents the light intensity, then the light is recorded as L(u, v, x, y), where (x, y) represents the intersection of the light and the CCD plane The coordinates are also the position of each microlens (because the focal length of the microlens is small, the microlens array 4 and the optocoupler 6 are close to a negligible distance); (u, v) are the coordinates of the intersection of the light ray and the main lens plane.

Further, according to the geometric relationship between the main lens plane, the CCD plane, and the refocusing plane, the light passes through the main lens plane position (u, v), then reaches the CCD plane position (x, y), and finally reaches the refocusing plane. In the two-dimensional case The geometric relationship is as follows:

In the above formula, L _F (x, u) represents the plenoptic function, which refers to a certain ray in particular. L _αF represents the intersection of the same ray on the refocusing plane.

Further, the conversion relationship in the two-dimensional case is extended to the four-dimensional light field:

in F' is the distance from the main lens plane to the refocusing plane.

Finally, the four-dimensional light field is integrated on (u, v) to obtain the image E _αF (x, y) of the refocusing plane:

After obtaining the refocusing image E _αF (x, y), the host 2 reprocesses the obtained refocusing image according to the pre-calibrated correspondence between image grayscale and brightness, and converts it into the brightness distribution on the required focal plane. Figure, and record the relevant brightness data, and export the data according to the user's needs.

Example 2

If the running speed is required to be fast, but the accuracy requirements are relatively low, the host 2 uses the frequency domain Fourier slice algorithm to refocus the original light field. The principle is to first perform a four-dimensional Fourier transform on the original space light field, and then The appropriate two-dimensional slices are extracted in the frequency domain, and then the two-dimensional inverse Fourier transform is performed to obtain the image on the corresponding focal plane.

As shown in Figure 4, in this embodiment, the main lens plane is regarded as the u-v plane, the refocusing plane is regarded as the x-y plane, the distance F between the main lens plane and the CCD plane is the focal length of the main lens, and the light passes through the main lens. The plane and the refocusing plane intersect the four-dimensional space at the point (u,v,x,y), then this ray is recorded as L(u,v,x,y).

Next, let the distance between the refocusing plane and the main lens plane be F', namely αF, and the intersection of the ray and the refocusing plane be (x, y), denoted as L _αF . According to the triangle similarity theorem, the coordinates of the intersection of the ray and the CCD plane are (u+(xu)/α, v+(yv)/α).

Further, define P _α as the conversion factor of the light field from the CCD depth F to αF, then P _α [L _F ] means that P _α acts on the light field _LF , and the purpose is to calculate the photo that the light field camera focuses on at the corresponding depth, namely Project from space to a 2D plane:

According to the Fourier slice theorem, the above formula can be defined as:

in, is the integration factor, the last two dimensions of the four-dimensional function are integrated, and B _α is the four-dimensional transformation:

Further define the slice factor And F ⁿ is the N-dimensional Fourier transform, F ^-n is the N-dimensional inverse Fourier transform, and the replace with Available:

make Available:

The calculation method of _βα is:

The refocused image is obtained by E _F = P _α [L _F ].

After the refocusing image is finally obtained, the host 2 reprocesses the obtained refocusing image according to the pre-calibrated correspondence between image grayscale and brightness, converts it into a brightness distribution map on the corresponding focal plane, and records the relevant brightness Data, export data according to the needs of users.

Claims (10)

1. A brightness testing system based on a spatial light field, characterized in that it comprises an imaging module (1) and a host (2), the imaging module (1) comprising a main lens (3) and a microlens array with parallel optical axes (4), the other side of the microlens array (4) is provided with a photocoupler (5), and the signal data obtained by the photocoupler (5) is then used to calculate the brightness of the spatial light field by the host (2). 2. The brightness test system based on spatial light field according to claim 1, wherein the microlens array (4) is located at the focal plane of the main lens (3), and the optocoupler (5) is located at the microlens (3) focal plane. at the focal plane of the lens array (4). 3. a method for measuring the brightness of space light field based on time-domain transformation method, comprising the main lens and the microlens array that are parallel to the optical axis, and the other side of the microlens array is provided with a CCD, is characterized in that, comprises the following steps: 1) Use the point luminance meter to calibrate the image gray value and luminance value of the CCD; 2) Determine the distance relationship between the refocusing plane and the microlens array, and parameterize the light field coordinate biplane; 3) Establish the two-dimensional geometric relationship of the main lens plane, the CCD plane, and the refocusing plane; 4) Extend the above two-dimensional geometric relationship to a four-dimensional light field; 5) Integrate the four-dimensional light field on the main lens plane to obtain an image of the refocusing plane; 6) Reprocessing the obtained refocusing image according to the pre-calibrated correspondence between the grayscale and the brightness of the image, and converting it into a brightness distribution map on the required focal plane. 4. according to claim 3, it is characterized in that, in described step 2), main lens plane is regarded as u-v plane, CCD plane is regarded as x-y plane, two planes The distance F is the focal length of the main lens, L represents the intensity of the incident light, and the incident light is recorded as L(u, v, x, y). 5. according to claim 4, it is characterized in that, in described step 3), light passes through main lens plane position (u, v), then reaches CCD plane position (x ,y), and finally reach the refocusing plane. In the two-dimensional case, its geometric relationship is: In the above formula, L _F (x, u) represents the plenoptic function, which refers to a certain ray in particular. L _αF represents the intersection of the same ray on the refocusing plane, F' is the distance from the main lens to the refocusing plane. 6. according to claim 5, it is characterized in that, in described step 4), the conversion relation under the two-dimensional situation is extended to four-dimensional light field: where F' is the distance from the main lens plane to the refocusing plane. 7. The method for testing the brightness of space light field based on time domain transformation method according to claim 6, is characterized in that, in described step 5), four-dimensional light field is integrated to (u, v) to obtain the image of the refocusing plane E _αF (x,y): 8. A method for testing the brightness of space light field based on Fourier slice algorithm, comprising a main lens parallel to the optical axis and a microlens array, and the other side of the microlens array is provided with a CCD, and is characterized in that, comprising the following steps: 1) Use the point luminance meter to calibrate the image gray value and luminance value of the CCD; 2) Parameterize the light field coordinate biplane; 3) Extract appropriate two-dimensional slices in the frequency domain; 4) Do two-dimensional inverse Fourier transform again to obtain the image on the refocusing plane; 5) After the refocusing image is finally obtained, the obtained refocusing image is reprocessed according to the pre-calibrated correspondence between image grayscale and brightness, and is converted into a brightness distribution map on the corresponding focal plane. 9. the method for testing the brightness of space light field based on Fourier slice algorithm according to claim 8, is characterized in that, in the described step 2), the main lens plane is regarded as the u-v plane, and the refocusing plane is regarded as the x-y plane, The distance F between the main lens plane and the CCD plane is the focal length of the main lens, and the incident light is recorded as L(u, v, x, y). 10. The method for testing the brightness of space light field based on Fourier slice algorithm according to claim 9, wherein in described steps 3) and 4), the distance between the refocusing plane and the main lens plane is made to be F', that is, αF, the intersection of the ray and the refocusing plane is (x, y), denoted as L _αF , then the coordinates of the intersection of the ray and the CCD plane are (u+(xu)/α, v+(yv)/α); Define P _α as the conversion factor of the light field from the CCD depth F to αF, then P _α [L _F ] means that P _α acts on the light field L _F and is projected from space to a two-dimensional plane: According to the Fourier slice theorem, the above formula can be defined as: in, is the integration factor, the last two dimensions of the four-dimensional function are integrated, and B _α is the four-dimensional transformation: define slice factor And F ⁿ is the N-dimensional Fourier transform, F ^-n is the N-dimensional inverse Fourier transform, and the replace with Available: make Available: The calculation method of _βα is: The refocused image is obtained by E _F = P _α [L _F ].