Analysis Of The Meaning Of Professional Terms In LED Display
What is LED display gray scale
Grayscale, also known as gradation or grayscale, refers to the degree of brightness and darkness. For digital display technology, grayscale is the determinant of the number of displayed colors. Generally speaking, the higher the grayscale, the richer the colors displayed, the more delicate the picture, and the easier it is to express rich details.
The gray level mainly depends on the number of A/D conversion bits of the system. Of course, the video processing chip, memory and transmission system of the system must provide the support of the corresponding number of digits. At present, the domestic LED display mainly adopts an 8-bit processing system, that is, 256 (28) levels of gray. A simple understanding is that there are 256 brightness changes from black to white. Using RGB three primary colors can form 256×256×256=16777216 colors. That is commonly referred to as 16 trillion colors. The international brand display screen mainly adopts a 10-bit processing system, that is, 1024 gray levels, and the three primary colors of RGB can form 1.07 billion colors.
Although grayscale is the determining factor for the number of colors, it does not mean that the larger the limit, the better. Because first of all, the resolution of the human eye is limited, and the increase in the number of bits processed by the system will involve changes in system video processing, storage, transmission, scanning, etc., resulting in a sharp increase in cost and a decrease in cost performance. Generally speaking, 8-bit systems can be used for civilian or commercial-grade products, and 10-bit systems can be used for broadcast-grade products.
Grayscale Nonlinear Transformation
Grayscale nonlinear transformation refers to transforming grayscale data according to empirical data or some arithmetic nonlinear relationship and then providing it to the display screen for display. Since LED is a linear device, it is different from the nonlinear display characteristics of traditional displays. In order to make the LED display effect conform to the traditional data source without losing the gray level, the non-linear transformation of grayscale data is generally performed in the latter stage of the LED display system, and the number of data bits after the transformation will increase (to ensure that the grayscale is not lost). data). At present, the so-called 4096-level grayscale or 16384-level grayscale or higher of some domestic control system suppliers refers to the grayscale space size after nonlinear transformation. The 4096 level adopts the nonlinear transformation technology of 8-bit source to 12-bit space, and the 16384 level adopts the nonlinear transformation technology of 8-bit to 16-bit space. The non-linear transformation is performed by the 8-bit source, and the converted space must be larger than that of the 8-bit source. Usually at least 10. Like grayscale, this parameter is not as large as possible, generally 12 bits can do enough transformation.
What is the pixel runaway rate
Pixel runaway rate refers to the proportion of the smallest imaging unit (pixel) of the display screen that does not work normally (runaway). There are two modes of pixel out of control: one is blind spot, that is, blind spot, when it needs to be bright, it is not bright, which is called blind spot; the other is constant bright spot, when it needs to be off, it is always on, Call it a bright spot. In general, the composition of the pixel is 2R1G1B (2 red lights, 1 green light and 1 blue light, the same is the case below), 1R1G1B, 2R1G, 3R6G, etc., and the loss of control is generally not the same pixel in the red, Both green and blue lights are out of control at the same time, but as long as one of the lights is out of control, we consider this pixel out of control. For the sake of simplicity, we carry out the statistics and calculation of out-of-control pixels according to each primary color of the LED display (ie, red, green, and blue), and take the maximum value as the pixel out-of-control rate of the display.
The ratio of the number of out-of-control pixels to the total number of full-screen pixels is called the "full-screen pixel out-of-control rate". In addition, in order to avoid the concentration of out-of-control pixels in a certain area, we propose the "regional pixel out-of-control rate", which is the ratio of the number of out-of-control pixels to the total number of regional pixels (i.e. 10000) in a 100×100 pixel area. This indicator quantifies the requirement of "out-of-control pixels are discretely distributed" in "General Specification for LED Displays" SJ/T11141-2003, which is convenient and intuitive.
At present, the domestic LED display will be aged (baking machine) before leaving the factory, and the LED lights of the out-of-control pixels will be repaired and replaced. There is no problem within 3/104, and even the corporate standards of some individual manufacturers require that out-of-control pixels are not allowed before leaving the factory, but this will inevitably increase the manufacturer's manufacturing and maintenance costs and prolong the delivery time. In different applications, the actual requirements of the pixel runaway rate can be quite different. Generally speaking, when the LED display is used for video playback, it is acceptable and achievable to control the indicator requirements within 1/104; If it is used for simple character information release, it is reasonable to control the index requirement within 12/104.
What is Brightness Discrimination Level
The brightness discrimination level refers to the brightness level of the image that can be distinguished by the human eye from the darkest to the whitest. As mentioned earlier, the gray scale of the display screen is very high, which can reach 256 or even 1024. However, due to the limited sensitivity of the human eye to brightness, these gray levels cannot be fully recognized. That is to say, many adjacent levels of grayscale may look the same to the human eye. And the ability of the eyes to distinguish is different for each person. For the display screen, the higher the level of human eye recognition, the better, because the displayed image is for people to see after all. The more brightness levels the human eye can distinguish, the greater the color space of the display, and the greater the potential for rich colors. The brightness discrimination level can be tested with special software. Generally, if the display screen can reach level 20 or above, it is considered a good level.
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