LED display has the advantages of high brightness, high contrast, and bright colors. It has been widely used in advertising media, stage performances, sports events, monitoring and command and other fields. However, due to the discreteness of LED light-emitting tubes and circuit components, LED display screens often face the problem of inconsistent brightness and chromaticity.
If there is no debugging and correction at the factory, it will seriously affect the display quality. In order to effectively solve this problem, point-by-point correction technology came into being, among which cabinet correction technology is more important. SightLED will introduce you to the LED display cabinet correction technology.
The root cause of LED display quality problems
LED display screens are composed of a large number of LED light-emitting tubes. These light-emitting tubes are inevitably discrete during the production process. There are differences in the luminous efficiency, wavelength and other parameters of different LEDs, resulting in different brightness and chromaticity of each LED under the same driving current.
In addition, with the increase of use time, the LED light-emitting tube will decay, and the decay rate of different LEDs is also different, which further aggravates the inconsistency of brightness and chromaticity. At the same time, circuit components such as resistors and capacitors are also discrete, which will also affect the driving current of the LED, thereby affecting the display effect.
Under the combined effect of these factors, the LED display screen may have obvious brightness and chromaticity differences after splicing, causing problems such as mottled and uneven color blocks on the screen.
Classification and characteristics of point-by-point correction technology
In order to overcome LED display screens problem of non-uniform brightness and chromaticity, LED display manufacturers have introduced point-by-point correction technology. According to different application, point-by-point correction technology is mainly divided into two types: cabinet correction on the production line and on-site correction.
On-site correction technology allows the LED display screen to be corrected after it is installed at the actual application site. This correction method can fully consider on-site environmental factors, such as ambient light, viewing angle, etc., so as to ensure that the LED display screen achieves a satisfactory display effect.
However, on-site correction also faces many difficulties. Complex and changeable on-site environments, such as different spatial layouts, lighting conditions, etc., will bring difficulties to the correction work.
Moreover, for some long-distance orders, the cost and difficulty will be greatly increased. Because this often requires professional technicians to go to the site for operation, increasing the investment of manpower, material resources and time.
In contrast, cabinet calibration technology has more advantages. It is to calibrate the cabinet of the LED display on the production line. LED video wall manufacturers can complete it before the product leaves the factory, making the LED screen more uniform and reducing the subsequent technical support costs.
Introduction to LED display cabinet calibration
Definition and purpose of cabinet calibration
Cabinet calibration is an important form of production line calibration. It requires LED display manufacturers to add this link to the production line. Usually, cabinet calibration is arranged as the last link before leaving the factory. Its main purpose is to eliminate the brightness and chromaticity differences between the cabinet and the cabinet, and improve the uniformity of the LED display after splicing.
Follow-up of calibration effect in the production link
In the production link, in addition to adding the cabinet calibration link, LED screen manufacturers generally need to follow up on the calibration effect. There are three common practices:
All splicing observation method:
Splice all cabinets together and directly observe the display effect. Although this method can most intuitively understand the overall display after splicing, the workload of splicing is relatively large. It is inconvenient to implement, especially the number of cabinets is large.
Random sampling splicing method:
Randomly select some cabinets for splicing and observe the correction effect. This method is relatively simple and can reflect the overall correction effect to a certain extent. However, due to the sampling inspection, it may not be able to fully cover the situation of all cabinets, and there are certain limitations.
Simulation evaluation method:
Use the measurement data recorded by the correction system to simulate and evaluate the correction effect of all cabinets. This method does not require the actual splicing all cabinets. Through data analysis and simulation, the correction effect can be evaluated quickly and efficiently, greatly improving production efficiency.
Environment and equipment requirements for cabinet calibration
In order to ensure the accuracy of the measurement results, cabinet calibration usually needs to be carried out in a darkroom.
The darkroom needs to be equipped with a planar array imaging device and a colorimeter to measure the brightness and colorimetric information of each cabinet.
The planar array imaging device can quickly and accurately obtain the luminous conditions of each LED on the cabinet;
The colorimeter can accurately measure the colorimetric parameters. In order to ensure that the calibration process of all cabinets is carried out without being affected by external environmental conditions and achieve the goal of brightness and chromaticity consistency.
The darkroom is required to be completely sealed, and the temperature and humidity are constant. During the calibration process, the position of the cabinet and the calibration instrument must be fixed. The cabinet must be placed on the base to avoid the influence of ground reflection.
Basic process of cabinet calibration
Similar to on-site calibration, for each cabinet, the cabinet calibration process includes data acquisition, data analysis, target value setting, correction coefficient calculation and coefficient upload, and also requires the cooperation of the control system.
- Data acquisition is to obtain the brightness and chromaticity information of each LED on the cabinet through the array imaging device and the colorimeter;
- Data analysis is to process and analyze the collected data to find out the differences in brightness and chromaticity;
- Target value setting is to let each LED reach the target value of brightness and chromaticity according to the calibration standard;
- Correction coefficient calculation is to calculate the corresponding correction coefficient based on the actual measured value and the target value;
- Coefficient upload is to send the calculated correction coefficient to the receiving card of the corresponding cabinet. The display control system will adjust the LED current according to the correction coefficient, so that the brightness and chromaticity of all LEDs in the cabinet are consistent.
Key technologies and difficulties of cabinet correction
Uniformity between pixels inside the cabinet
The uniformity correction between pixels inside the cabinet is basically similar to the on-site correction. The technology is relatively mature. It mainly includes brightness and chromaticity uniformity correction and light and dark line correction.
Brightness and chromaticity uniformity correction:
The brightness and chromaticity information of each LED lamp in the LED cabinet is measured by measuring equipment. The measurement method involves photometry, chromaticity and digital image processing related knowledge.
After obtaining the point-by-point brightness and chromaticity information, the corresponding correction coefficient is calculated according to the corresponding correction standard and sent to the receiving card of the corresponding cabinet.
After the cabinet is lit, the LED display control system will adjust the current of the LED according to the correction coefficient, so that the brightness and chromaticity of all LEDs in the cabinet are consistent.
Brightness correction is to adjust the brightness of the fluctuating LED to a consistent level. In the process of adjusting the brightness, it is necessary to appropriately reduce the maximum brightness value of most LEDs to ensure the uniformity of the overall brightness.
Chroma correction is based on the RGB color matching principle, and solves the problem of chromaticity deviation by changing the color coordinates of the three RGB colors.
For example, in the color gamut of the display screen before correction, the color coordinates of the three RGB colors are discretely distributed, while in the color gamut of the display screen after correction, the color coordinates of the three RGB colors are more consistent, which significantly improves the chromaticity display effect.
Correction of bright and dark lines:
Due to the limitations of machining accuracy, assembly accuracy and other process reasons, there is a slight inconsistency in the spacing of the spliced light boards. After the low-pass filtering process of the human visual system, bright lines or dark lines will appear during display.
Due to the existing mechanical process limitations, small-pitch LED display screens generally require correction of bright and dark lines to significantly improve the uniformity of the cabinet.
The bright and dark line correction technology adjusts the driving current of the corresponding LED through accurate measurement and analysis of the spacing between the light boards, eliminates the bright and dark line phenomenon, and makes the picture smoother and more uniform.
Brightness and chromaticity consistency between different cabinets
There is a significant difference between cabinet calibration and on-site calibration. The cabinet is not spliced during calibration, and there is a lack of surrounding areas as a reference during calibration.
After calibration, it is necessary to ensure that the cabinet is spliced arbitrarily and there is no difference in brightness and chromaticity.
More importantly, as a bandpass filter, the human visual system is not sensitive to the difference in brightness with gentle gradient or the difference in detail with very small angular resolution, but it is extremely sensitive to the edge step signal with medium and low frequency components.
For LED display screens, it is reflected in that the human eye can only distinguish the brightness difference of more than 4-5% between LED pixels, but can easily identify the 1% difference in brightness and chromaticity of the cabinet.
In other words, the human eye has low requirements for the consistency of pixels inside the cabinet, but high requirements for the consistency between cabinets. Therefore, the consistency of brightness and chromaticity between cabinets is a key technology unique to cabinet correction.
The inconsistency of brightness and chromaticity between cabinets is mainly reflected in two aspects:
There are differences in the average brightness and chromaticity between cabinets:
When the cabinets are spliced, obvious boundary lines will appear. This can be achieved by adjusting the color gamut and setting appropriate target values.
For example, during the correction process, according to the actual brightness and chromaticity of each cabinet, the color gamut range is adjusted so that the brightness and chromaticity of different cabinets can be better matched.
If necessary, a higher accuracy colorimeter is to improve the accuracy of the measurement, so as to more accurately adjust the brightness and chromaticity differences between cabinets.
The brightness and chromaticity distribution of the cabinet is a gradient distribution:
This is caused by the gradient distribution phenomenon of the cabinet measurement data. Since the visual system is not sensitive to low-frequency, i.e., smooth and gradual brightness differences, this problem is difficult to be found when calibrating a single cabinet.
However, when the cabinets are spliced together, the brightness at the splicing point will jump greatly, forming an obvious splicing line. This requires the correction system to detect and solve the gradient distribution problem of the measurement data.
For example, by analyzing and processing the measurement data, the gradient distribution area is identified. The corresponding algorithm is used for correction to make the brightness and chromaticity transition between cabinets smoother.
Conclusion
The LED diplay cabinet correction technology is an effective means to improve the display quality. It has important application value in the manufacturing process of LED display screens.
It can solve the problem of inconsistent brightness and chromaticity inside and between cabinets, and significantly improve the uniformity and display quality of LED display screens.
With the continuous development of LED display technology and the continuous improvement of display quality requirements, cabinet correction technology will continue to improve and develop.
As a professional LED display manufacturer, we strictly implement relevant standards to fully guarantee the uniformity of LED screens. If you are looking for a high quality LED screen, feel free to contact us.
