The Study Of Luminance Uniformity Evaluation For LED Display Panel Based On HVS

LED Brightness, chroma, viewing angle, uniformity and processing capacity of gray scale etc. are the critical indexes of LED screens. The uniformity of a screen is one of the important factors determining the quality of screens, and the uniformity of brightness has become one of the most important indexes judging LED screens are superior or inferior. For the screens with bad uniformity, people may feel it not clean, even sometimes they can see dark spots, bright spots and mosaic on screens, which affect the display effect badly. Therefore, it is necessary to test and evaluate the brightness uniformity of LED screens during their development and production. The traditional evaluating methods of brightness uniformity of LED screens have nine-dot connected region method, mean squared deviation (MSD), histogram and subjective observation, all of which have their inherent defects. In the method of connected region, a few dots rather than all pixel points of the full screen are measured, so the measuring result is local and not enough to reflect the brightness uniformity of the full screen pixel. As a result, it is not scientific if use such result to represent the uniformity of the full screen. Although the sample space of histogram and MSD covers all pixels of LED screens, the principles of both methods are calculating statistical errors and the final observation results of image are measured by human eyes. So the results yielded from these two methods are usually different from the subjective evaluation of people. The wave of brightness value of some pixel points, veins and other details in image are often ignored, which leads to the brightness uniformity of the image can’t be reflected completely. Since the human eye visual characteristics are considered in the method of subjective observation, it better shows the true feeling of human eye. However, this method whose operation is quite complicated needs a large amount of manpower, material resources and time. Moreover, mathematical models can’t be applied to describe this method; the quantitative calculation also can’t be used for measurement and its stability is not good.This paper taking LED screens as the research subject and using CCD camera to obtain photo-electricity information, mainly researched human eye visual characteristics, thoroughly analyze the effects made by brightness, veins and space position information on people’s visual impression, formed a corresponding calculation method for these effects and established a vision model of evaluation of brightness uniformity of LED screens. This model divides the image into several sub-regions with same size and figures out brightness feature factor, veins detail factor and space position factor basing on HVS in every region. The feature integration of the three factors is regard as the evaluating parameter of every region and the dispersion degree value of each parameter of each region in the full screen is regarded as the index of uniformity evaluation of the full screen, which realizes an evaluation with subjective and objective ideas combining together upon the brightness evaluation of LED screens.An experiment about objective evaluation of brightness uniformity for typical images and LED screens was made by adopting the method put forward in this paper. Comparing with traditional evaluating methods, it shows that the evaluating result yielded from the method in this paper meets the subjective impression of people and has a good stability.