Detail, LED display gray level

6 min readApr 17, 2023

The gray level of LED display is the so-called color scale or gray scale, refers to the brightness of the degree of darkness. Generally speaking, the higher the gray level, the more colorful the display, the more delicate the picture, and the easier it is to show rich details. The gray level of LED display refers to the brightness level that can be distinguished from the darkest to the brightest in the same level of brightness of LED display. How to adjust the brightness and contrast of LED display?

The gray level mainly depends on the number of digital-to-analog (A/D) conversion bits of the system. Of course, the system’s video processing chip, memory and transmission system should provide the corresponding bits of support. Generally no gray level, 8 level, 16 level, 32 level, 64 level, 128 level, 256 level, 1024 level, LED display gray level, the higher the color is richer, the color is more beautiful; On the contrary, the display color is single and the change is simple. At present, the domestic LED display mainly uses 8-bit processing system, that is, 256 (28) level gray. The simple idea is that there are 256 variations in brightness from black to white. Using RGB three primary colors can constitute 256×256×256=16777216 colors. This is commonly referred to as 16 megabytes. International brand display screen mainly uses 10-bit processing system, namely 1024 level gray, RGB three primary colors can constitute 1.07 billion colors.

Grayscale, also known as the color scale or gray scale, refers to the degree of brightness. For digital display technology, gray is the determining factor of display color number. Generally speaking, the higher the gray level, the more colorful the display, the more delicate the picture, and the easier it is to show rich details.

The gray level depends mainly on the A/D conversion number of the system. Of course, the system’s video processing chip, memory and transmission system should provide the corresponding bits of support. At present, the domestic LED display mainly uses 8-bit processing system, that is, 256 (28) level gray. The simple idea is that there are 256 variations in brightness from black to white. Using RGB three primary colors can constitute 256×256×256=16777216 colors. This is commonly referred to as 16 megabytes. International brand display screen mainly uses 10-bit processing system, namely 1024 level gray, RGB three primary colors can constitute 1.07 billion colors.

Although grayscale is the determining factor in determining the number of colors, it does not mean that unlimited bigger is better. Because first of all, the resolution of the human eye is limited, and the improvement of the system processing digit will be involved in the system video processing, storage, transmission, scanning and other aspects of the change, the cost increases, the cost performance decreases. Generally speaking, 8-bit systems can be used for civil or commercial grade products, and 10-bit systems can be used for broadcast grade products.

Gray nonlinear transformation

Beijing led display manufacturers said gray nonlinear transformation refers to the gray data according to the empirical data or some arithmetic nonlinear relationship transformation and then provided to the display screen. Because LED is linear device, and traditional display nonlinear display characteristics are different. In order to make the LED display effect conform to the traditional data sources without loss of gray level, generally in the LED display system after the nonlinear transformation of gray data, the transformed data number will increase (to ensure no loss of gray data). At present, the so-called 4096 level gray or 16384 level gray or higher of some domestic control system suppliers refer to the size of gray space after nonlinear transformation. Class 4096 uses an 8-bit source to 12-bit space, and class 16384 uses an 8-bit to 16-bit nonlinear transform. When a nonlinear transformation is made from an 8-bit source, the converted space is definitely larger than that of an 8-bit source. It’s usually at least 10 bits. Like gray scale, this parameter is not the bigger the better, generally 12 bits can do enough transformation.

Pixel runaway rate

Pixel runaway rate is the percentage of a display’s smallest imaging unit (pixel) that doesn’t work properly (out of control). The pixel out of control has two modes: one is the blind spot, that is, the blind spot. When it is not bright when it needs to be bright, it is called the blind spot; The second is the usual bright spot, in the need not bright when it has been bright, called the usual bright spot. Generally speaking, pixels are composed of 2R1G1B (2 red lights, 1 green light and 1 blue light, the same as below), 1R1G1B, 2R1G, 3R6G, etc. Generally, the loss of control does not mean that all red, green and blue lights in the same pixel are out of control at the same time, but as long as one of the lights is out of control, we consider the pixel to be out of control. For simplicity, the statistics and calculation of out-of-control pixels were carried out according to each primary color of LED display (namely red, green and blue), and the maximum value was taken as the out-of-control pixel rate of the display.

The ratio of out-of-control pixels to the total number of pixels on the full screen is called the “pixel out of control ratio”. In addition, in order to avoid the concentration of out-of-control pixels in a certain area, we put forward the “out-of-control pixel rate of the area”, that is, the ratio of the number of out-of-control pixels to the total number of pixels of the area (i.e. 10000) in the area of 100×100 pixels. This index quantifies the requirement of “discrete distribution of out-of-control pixels” in General Specification for LED Display SJ/T11141–2003, which is convenient and intuitive.

At present, the domestic LED display will be aging (oven) before leaving the factory, and the LED lights with out-of-control pixels will be repaired and replaced. It is no problem to control the “pixel out of control rate of the whole screen” within 1/104 and the “pixel out of control rate of the region” within 3/104. Some enterprise standards of individual manufacturers even require that out-of-control pixels are not allowed before leaving the factory. But this is bound to increase the manufacturing and maintenance costs of manufacturers and extend the shipping time. In different applications, the actual requirements of pixel runaway rate can be quite different. Generally speaking, LED display screen is used for video playback, and the index requirement is controlled within 1/104, which is acceptable and achievable. If it is used for simple character information publishing, it is reasonable to require a limit of 12/104.

Brightness identification grade

The level of brightness discrimination refers to the level of brightness of an image that the human eye can distinguish from the blackest to the whitest. As mentioned above, the gray level of the display can be very high, up to 256 or even 1024 levels. However, due to the limited sensitivity of the human eye to brightness, it can not fully recognize these gray levels. That is to say, many adjacent levels of gray may look the same to human eyes. And eye resolution varies from person to person. When it comes to displays, the more the human eye recognizes, the better, because the image displayed is for people to see after all. The more levels of brightness the human eye can distinguish, the more color space the display has, and the more potential it has to display rich colors. Brightness identification level can be used to test the special software, the general display can reach more than 20 level is a good level.

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Detail, LED display gray level

Written by Chinaseoer