CN110060625B - LED display screen acquisition vignetting compensation method - Google Patents
LED display screen acquisition vignetting compensation method Download PDFInfo
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Abstract
A method for compensating vignetting acquired by an LED display screen relates to the technical field of LED correction and solves the problem that the display uniformity of the corrected display screen is damaged due to vignetting of a camera in the existing display screen acquisition and correction process. The invention can ensure the authenticity of the data acquired under the condition of the same aperture focal length of the camera and can realize the uniform correction of absolute brightness. The invention can be applied according to different display screens, has universality and simple operation, and is suitable for engineering application.
Description
Technical Field
The invention relates to the technical field of LED correction, in particular to an LED display acquisition vignetting compensation method.
Background
With the continuous development of the LED display technology, the LED display screen gradually develops towards the directions of ultrahigh density, ultra-small spacing and ultra-large size, and higher requirements are provided for the display uniformity of the display screen. Since the LED brightness is discrete, a correction technique must be applied to ensure the display uniformity of the LED, so that each display pixel has uniform brightness after the collection correction technique is applied. The important factor for realizing the acquisition and correction technology is that the brightness of each display pixel of the LED display screen can be accurately obtained, so that how to accurately obtain the brightness of the display pixels of the display screen becomes one of the important factors for ensuring the uniformity.
At present, the brightness of display pixels of a display screen is mainly acquired by a camera, and the vignetting phenomenon exists in the camera due to the optical characteristics of the camera, and mainly means that the acquired data is large in the middle and small in the periphery; the acquired image is bright in the middle and dark at the periphery, which seriously influences the accuracy of acquiring the brightness of the display pixels of the display screen, so that the display screen after correction has the phenomena of dark in the middle and bright at the periphery, and the display uniformity is influenced. Meanwhile, due to the fact that the brightness of the LED display screen is discrete, each display pixel has brightness difference, the brightness difference and vignetting of the camera are mixed and overlapped, the difficulty of camera vignetting compensation is increased, and the uniformity of the corrected display screen is damaged more and more.
In order to solve the problems, the conventional main method is to calibrate the camera by using an integrating sphere and a uniform white board, but the calibration method is only suitable for a fixed aperture and a fixed focal length, when the focal length of the camera and the relative distance between the camera and a display screen are changed, the calibration is required to be carried out again, the price of the integrating sphere is high, the calibration process is complex, the integrating sphere is not universal, and the integrating sphere is not suitable for engineering practical application. Therefore, how to accurately obtain the vignetting curve acquired by the camera and compensate the vignetting acquired by the camera is a difficult problem of acquisition correction.
Disclosure of Invention
The invention provides a camera vignetting compensation method in the collection and correction of an LED display screen, which aims to solve the problem that the display uniformity of a corrected display screen is damaged due to the vignetting of a camera in the collection and correction process of the existing display screen.
A method for compensating vignetting acquired by an LED display screen is realized by the following steps:
setting k display screens, wherein the number of pixels displayed by each display screen is mxn, selecting one display screen and a camera for positioning and debugging, so that the optical axis of the camera is superposed with the normal of the display screen, and the display screen is positioned in the middle of a camera viewing frame; respectively fixing a camera and a display screen, adjusting the aperture and the focal length of the camera to clearly acquire each display pixel of the display screen, and fixing the aperture and the focal length of the camera; k is more than or equal to 10, m is the number of display screen row pixels, and n is the number of display screen column pixels;
step two, the camera sequentially collects the pixels of the k display screens in the step one to obtain the brightness data L of each display pixel of each display screeni(m×n)Respectively carrying out Gaussian two-dimensional filtering on the k brightness data to obtain the brightness data LG after the Gaussian two-dimensional filteringi(m×n)；
The k Gaussian two-dimensional Gaussian filtered luminance data LGi(m×n)The pixels at the same coordinate position are superposed to obtain the superposed pixels at the same coordinate position and Lsum(m×n)；
Step three, the pixel and the L which are obtained in the step two and are in the same coordinate position after being superposed are subjected to superpositionsum(m×n)Normalizing the pixels to obtain a vignetting surface Lo acquired by the camera(m×n)Expressed by the following formula:
in the formula, max (L)sum(m×n)) Is Lsum(m×n)Is measured.
Step four, obtaining the vignetting curved surface Lo obtained in the step three(m×n)Taking reciprocal to obtain a camera vignetting compensation curved surface Lo'(m×n)And then compensating the camera vignetting for a curved surface Lo'(m×n)Brightness data L of display pixels of k display screensi(m×n)And multiplying pixels at corresponding positions to obtain a brightness acquisition value after camera vignetting compensation, thereby realizing the vignetting compensation of the camera.
The invention has the beneficial effects that: according to the method, the approximate curved surface of the camera vignetting is obtained by utilizing a multi-time acquisition and superposition method according to the inherent discrete characteristics of the LED, and then the compensation curved surface is obtained, so that the vignetting compensation is realized. The integrating sphere calibration method before correction saves cost, can be applied according to different display screens, has universality and simple operation, and is suitable for engineering application.
The method utilizes the brightness fluctuation characteristic of the LED, adopts an iterative acquisition method, and eliminates the influence of the brightness fluctuation on the camera acquisition vignetting by processing the data acquired for many times, thereby obtaining the camera acquisition vignetting curved surface, compensating, obtaining the accurate and real brightness difference of the display screen, and ensuring the corrected display effect. The invention can ensure the authenticity of the data acquired under the condition of the same aperture focal length of the camera and can realize the uniform correction of absolute brightness.
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FIG. 1 is a schematic diagram of a positional relationship between a camera and a display screen;
FIG. 2 is a diagram illustrating the effect of data collected by a camera;
FIG. 3 is a camera-acquired vignetting curve effect diagram obtained by superimposing camera-acquired vignetting diagrams in the LED display screen acquisition vignetting compensation method according to the present invention;
FIG. 4 is a compensation curve effect diagram of a camera-collected vignetting diagram in the LED display screen-collected vignetting compensation method according to the present invention;
FIG. 5 is a graph showing the effect of brightness data of each display pixel of the LED display screen after vignetting compensation in the method for collecting the vignetting compensation of the LED display screen according to the present invention;
fig. 6 is a flowchart of a method for compensating vignetting collected by an LED display screen according to the present invention.
Detailed Description
In a first specific embodiment, the present embodiment is described with reference to fig. 1 to 6, and a method for compensating vignetting collected by an LED display screen is specifically implemented by the following steps:
step one, setting the number of display screens to be corrected of the same model as k, wherein i is 1,2,3. Numbering each display screen, setting one display screen as B, adjusting the relative position of the display screen and the camera to enable the discovery of the display screen to be coincident with the optical axis of the camera, and enabling the display screen to be located in the middle of the camera viewing frame. And fixing the position of the camera, adjusting the aperture and the focal length of the camera, and fixing the aperture and the focal length of the camera.
Step two, respectively placing the k display screens on the first display screen BiSequentially acquiring the brightness data L of each display pixel of each display screeni(m×n)For k L respectivelyi(m×n)And carrying out Gaussian two-dimensional filtering to eliminate high-frequency noise, wherein a two-dimensional Gaussian function is shown as a formula (1):
wherein x ∈ m, y ∈ n, (x, y) is Li(m×n)Coordinates of any point in the image. G (x, y) is a two-dimensional Gaussian convolution kernel. Let the brightness data after two-dimensional Gaussian filtering be LGi(m×n)。
LG (light emitting diode) with k display screens subjected to two-dimensional Gaussian filteringi(m×n)The pixels at the same coordinate position are superposed, as shown in formula (2):
wherein L issum(m×n)Is LGi(m×n)The sum of pixels at the same coordinate position.
Step three, to Lsum(m×n)All pixels are normalized to obtain a vignetting curved surface Lo acquired by a camera(m×n)As shown in equation (3):
step four, Lo(m×n)Taking reciprocal to obtain a vignetting compensation curved surface as shown in formula (4):
wherein Lo'(m×n)A camera vignetting compensation curved surface.
Step five, then compensating the camera vignetting to form a curved surface Lo'(m×n)L respectively corresponding to k display screensi(m×n)Multiplying the pixels at the corresponding positions to obtain a brightness acquisition value after camera vignetting compensation, as shown in formula (5):
L'i(m×n)＝Lo'(m×n)×Li(m×n)(5)
in a second embodiment, the present embodiment is described with reference to fig. 1 to 6, and the present embodiment is an example of a method for collecting and compensating vignetting of an LED display screen according to the first embodiment:
step one, as shown in fig. 1, k (k is larger than or equal to 10) square display screens with pixels of 320 × 320 are required to be collected and corrected, one display screen B is taken out to be positioned and debugged with a camera, the optical axis of the camera is perpendicular to the display screens and is superposed with the normal lines of the display screens, the distance between the optical axis of the camera and the normal lines of the display screens is adjusted to be 2 meters, the position is fixed, and the position of the display screens is also fixed. And then adjusting the aperture and the focal length of the camera to enable the camera to clearly acquire each display pixel of the display screen, and fixing the aperture and the focal length.
Step two, as shown in fig. 2, the k display screens are sequentially placed at the same position of the B display screen, and the k display screens are sequentially collected by a camera to obtain the brightness data L of each pixel of each display screeni(320×320)。
Step three, respectively aligning k Li(320×320)And carrying out Gaussian two-dimensional filtering to eliminate high-frequency noise, wherein a two-dimensional Gaussian function is shown as a formula (1):
wherein x ∈ m, y ∈ n, (x, y) is Li(320×320)Coordinates of any point in the image. G (x, y) is a two-dimensional Gaussian convolution kernel. Let the brightness data after two-dimensional Gaussian filtering be LGi(320×320). LG (light emitting diode) with k display screens subjected to two-dimensional Gaussian filteringi(320×320)The pixels at the same coordinate position are superposed, as shown in formula (2):
wherein L issum(320×320)Is LGi(320×320)The sum of pixels at the same coordinate position.
Step four, as shown in FIG. 3, apply Lsum(320×320)And carrying out normalization to obtain a camera acquisition vignetting curved surface. As shown in equation (3):
wherein Lo(320×320)The camera was acquired with vignetting curves of size 320 × 320, corresponding to the number of display screen pixels.
Step five, as shown in figure 4, Lo(m×n)Taking reciprocal to obtain a vignetting compensation curved surface, as shown in formula(4) Shown in the figure:
wherein Lo'(320×320)A camera vignetting compensation curved surface.
Step six, then compensating the curved surface Lo 'of camera vignetting'(320×320)L respectively corresponding to k display screensi(320×320)And multiplying pixels at corresponding positions to obtain a brightness acquisition value after camera vignetting compensation, namely real brightness data. As shown in equation (5):
L'i(320×320)＝Lo'(320×320)×Li(320×320)(5)
the method of the embodiment utilizes the brightness discrete characteristic of each display pixel of the LED display screen, obtains the camera acquisition vignetting curve by sequentially and independently acquiring data of the plurality of display screens and superposing and summing the display pixels corresponding to all the acquired data, compensates the camera acquisition vignetting curve, and is suitable for engineering application.
Claims (3)
1. A method for compensating vignetting acquired by an LED display screen is characterized by comprising the following steps:
setting k display screens, wherein the number of pixels displayed by each display screen is mxn, selecting one display screen and a camera for positioning and debugging, so that the optical axis of the camera is superposed with the normal of the display screen, and the display screen is positioned in the middle of a camera viewing frame; respectively fixing a camera and a display screen, adjusting the aperture and the focal length of the camera to clearly acquire each display pixel of the display screen, and fixing the aperture and the focal length of the camera; k is more than or equal to 10, m is the number of display screen row pixels, and n is the number of display screen column pixels;
step two, the camera sequentially collects the pixels of the k display screens in the step one to obtain the brightness data L of each display pixel of each display screeni(m×n)Respectively carrying out two-dimensional Gaussian filtering on the k brightness data to obtain brightness data LG after the two-dimensional Gaussian filteringi(m×n)；
Luminance data LG obtained by subjecting k display screens to two-dimensional Gaussian filteringi(m×n)The pixels at the same coordinate position are superposed to obtain the superposed pixels at the same coordinate position and Lsum(m×n)；
Step three, the pixel and the L which are obtained in the step two and are in the same coordinate position after being superposed are subjected to superpositionsum(m×n)Normalizing the pixels to obtain a vignetting surface Lo acquired by the camera(m×n)Expressed by the following formula:
in the formula, max (L)sum(m×n)) Is Lsum(m×n)Maximum value of (d);
step four, obtaining the vignetting curved surface Lo obtained in the step three(m×n)Taking reciprocal to obtain a camera vignetting compensation curved surface Lo'(m×n)And then compensating the camera vignetting for a curved surface Lo'(m×n)Brightness data L of display pixels of k display screensi(m×n)And multiplying pixels at corresponding positions to obtain a brightness acquisition value after camera vignetting compensation, thereby realizing the vignetting compensation of the camera.
2. The method for compensating the vignetting collected by the LED display screen according to claim 1, wherein the method comprises the following steps: in the second step, k pieces of the brightness data L are processedi(m×n)Two-dimensional Gaussian filtering is carried out to obtain brightness data LG after two-dimensional Gaussian filteringi(m×n)；
The two-dimensional gaussian function is represented by:
wherein x is not more than m, y is not more than n, and (x, y) is Li(m×n)G (x, y) is a two-dimensional gaussian convolution kernel;
LG (liquid Crystal display) with k display screens subjected to two-dimensional Gaussian filteringi(m×n)Is superimposed and expressed by the following formula:
wherein L issum(m×n)Is LGi(m×n)The sum of pixels at the same coordinate position.
3. The method for compensating the vignetting collected by the LED display screen according to claim 1, wherein the method comprises the following steps: in the fourth step, the vignetting curved surface Lo is formed(m×n)Taking reciprocal to obtain a vignetting compensation curved surface, and expressing the vignetting compensation curved surface by the following formula:
wherein Lo'(m×n)A camera vignetting compensation curved surface;
then camera vignetting compensation curved surface Lo'(m×n)L respectively corresponding to k display screensi(m×n)Multiplying the pixels at the corresponding positions to obtain a brightness acquisition value after camera vignetting compensation, and expressing the brightness acquisition value as follows by using a formula:
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