Analysis of Common Misunderstandings in Point by Point Correction Design of LED Display Screen

However, for the conditions, implementation, application fields and subsequent maintenance of point-to-point correction, there are still various misunderstandings and vague concepts in the industry. Some common misunderstandings are clarified and discussed below.

Myth 1: point by point correction requires the use of a special driver chip

As long as the control system supports, the general driver chip can also realize point by point correction!

Myth 2: point by point correction is done by the control system manufacturer, and the correction technology is bundled with the control system

The real necessary conditions for point by point correction are the following three points:

1. High precision and high efficiency light spot brightness acquisition equipment

2. Control system capable of point by point correction

3. Data docking of the above two

Point by point correction can be divided into two steps:

1. Accurately measure the brightness of each lamp / chip to obtain the point by point correction coefficient.

2. The correction coefficient data is fed back to the control system to realize the precise driving control point by point.

The point by point drive control has long been realized, and the general control systems in the market already have this function. However, for the acquisition of millions of light point data, some control system manufacturers have developed various tools, which are incompatible with other systems. This leads to the misunderstanding that the point by point correction and control system are bundled and integrated.

At present, there are several common acquisition methods, such as organic desktop point-to-point acquisition, digital camera acquisition, imported equipment acquisition and high-speed brightness measurement instrument Sv-1 system acquisition. Among them, Sv-1 system has realized data docking with most general control systems in the market. Display screen manufacturers can freely choose drive chips and control systems to complete convenient and efficient point-to-point correction by themselves.

Myth 3: as long as the spectral width is narrow enough, there is no need to correct it point by point

Even without considering the cost of fine segmentation, point-by-point correction is still very useful.

There are great limitations in using the light and color splitter to ensure the uniformity of the display screen. Firstly, the color separation accuracy of the light and color splitter can reach 1nm, which basically meets the requirements of chromaticity uniformity; However, the spectral accuracy is 10%! This means that even if the spectral width is 1:1.1, the actual brightness range of the lamp you get is about 1:1.3.

In the design and production process of display screen, circuit board design, mold shell design, box design, plug-in lamp, welding lamp, positive lamp and even assembly process will affect the display uniformity of final products. The display screen must undergo 72 hours of aging before leaving the factory, and the light attenuation of each light point is not consistent in the aging process. This leads to the uncontrollable uniformity of the finished display products to be delivered, which can not meet the design expectations at all. In addition, the use of light and color splitter to ensure the uniformity of the final product can not meet the needs of optimizing the display quality of the screen after a period of use.

So what can point by point correction do? Using high-precision acquisition equipment, such as Sv-1 system of zhongkeweiyou, can make great achievements in the following aspects:

1. As the last process before the display screen leaves the factory, the display uniformity is greatly improved. Using the Sv-1 system, even if the lamp with 1:1.1 light splitting is adopted, the accuracy of Sv-1 is enough to let you see the effect of improving the uniformity.

2. With the control system supporting chromaticity correction, Sv-1 can give the bright color correction coefficient matrix point by point, realize the color gamut space conversion, and improve the display uniformity and color fidelity.

3. Correct and maintain the display screen whose uniformity deteriorates after use for a period of time to improve the display quality.

However, the original spectral width is narrow, which is very valuable for point by point correction. Our experimental data show that:

a) The display screen with narrow original spectral width and good uniformity requires less brightness loss for correction.

According to the statistics of the measured data of Sv-1, it is also necessary to achieve about 3% of the pixel brightness mean square deviation after correction:

Original spectral width loss brightness ratio

b) The display screen with narrow original spectral width and good uniformity loses the same brightness proportion and smaller mean square error after correction.

According to the statistics of measured data of Sv-1, 10% brightness is also sacrificed:

Mean square error before original spectral width correction and mean square error after correction

Myth 4: chroma correction = chroma uniformity correction

The application of chromaticity correction is more the conversion of color gamut space.

Chromaticity correction can be divided into two main contents:

1. Gamut space correction: it solves the problem of full screen color fidelity.

2. Chromaticity uniformity correction: it solves the problem of color difference between pixels.

The application of gamut space correction is as follows:

1. Improve the color fidelity of the display screen and make the color restore more realistic: correct the color gamut space of the display screen to standard color spaces such as sRGB and NTSC.

2. Meet customers' special requirements for display gamut space: correct the display gamut space to the color space specified by customers.

3. Mixing of different batches of rental screen boxes: different batches of rental screen boxes correspond to different brightness and color gamut spaces. It is necessary to find a coincidence area and convert them to the same brightness and color space, so that there will be no brightness difference and chromaticity difference when they are used together.

4. Clean up the LED lights of different batches in inventory: as long as the LED lights of different batches are made into different boxes, the rental screen boxes of different batches are mixed with the same treatment method for correction, multiple batches of inventory lights of different batches can be used for the same display screen.

Under normal circumstances, after brightness correction, the bright color uniformity of the display screen can reach a very high level. With color gamut space correction, the color fidelity of the display screen can also reach a very high level.

5. Application of chromaticity uniformity correction

Due to the good color separation accuracy and stability of the light and color splitter and the effective process flow of lamp mixing and crystal mixing, the application occasions of chromaticity uniformity correction are quite limited, mainly as follows:

5.1 due to mistakes in the production process, lamps / chips of different wavelengths are mixed together and used on the same screen. Chromaticity uniformity correction can be used as a final remedy.

5.2 when clearing the inventory, be sure to mix a very small amount of lamps with scattered wavelengths on one screen. At this time, chromaticity uniformity correction is also the only choice.

Myth 5: chromaticity correction needs to measure color point by point

The color gamut space conversion needs the bright color correction coefficient point by point, but it is not necessary to measure the color point by point. Only the chromaticity uniformity correction must measure the color point by point.

Because the luminance ratio of RGB in each pixel is different, the color gamut space conversion needs to provide 3 for each pixel 3, but the calculation of the bright color correction coefficient only needs to provide the X and Y coordinate values of the regional color space, the X and Y coordinate values of the target color space, and the RGB brightness value of each light point.

Since the Sv-1 system can obtain the absolute brightness data (in CD / m2) of each lamp point, combined with the chromaticity data given by the conventional color coordinate measuring instrument, the target color space can be easily set by using the CCM (color correction module) software module in the system to obtain the bright color correction coefficient matrix of each pixel.

It should be noted that chromaticity correction needs the support of the control system. With the bright color correction data, the control system needs to be able to read correctly and use effectively in order to truly realize the bright color correction. Chromaticity correction puts forward higher requirements for gray scale depth, starting gray scale, operation resources and storage resources of the control system.

Myth 6: once the customer is satisfied after correction, everything will be fine

The subsequent maintenance of point by point correction requires professional tools.

At present, due to the popularization and generalization of point-to-point correction, many display manufacturers have not realized the necessity of subsequent maintenance tools after point-to-point correction. If this is ignored, it is likely to pay a heavy price.

Since the data of point-to-point correction must be strictly one-to-one corresponding to the light point, the subsequent maintenance of point-to-point correction is far more complex than expected, and strong engineering management is required, including many professional tools such as overall data, local data storage and reproduction, data segmentation, reorganization and replacement, fine tuning and so on.

Maintenance after point by point correction requires many considerations, such as:

1. What if the control card is replaced?

2. What if the module / unit board is replaced and repaired?

3. What about correcting data loss?

4. When the old and new batches of boxes are mixed, can the data of the old box not be collected again?