This technique was initially patented by US7907154B2 1 for measuring individual LED pixels in large-format outdoor screens, where measurements are conducted over long time periods and multi-image measurement of a single display is common. Pixel-level measurement depends first and foremost on pixel registration, a technique of dynamically locating and setting a region of interest (ROI) around each pixel in the measurement image. Using multiple images to measure a display can improve the effective imaging resolution per pixel, but single-image measurement is key for correcting a display at reduced takt times, supporting efficient high-volume production processes and the commercialization of new types of displays. However, covering and isolating each display pixel while utilizing multiple image sensor pixels is demanding, certainly when the high quantity of pixels in the display relatively limits the sensor resolution of the measurement system. In all measurement scenarios, image-based display measurement systems must apply several image sensor pixels across each display pixel to improve the repeatability and accuracy of measured pixel-level luminance values. The latest smartphones can consist of anywhere from two to over four million pixels per display (with the number of subpixels three or four times greater) at 400 to over 500 pixels per inch (PPI).
Guaranteeing precise measurements for qualification and correction at the pixel level becomes more of a challenge as the resolution of emissive displays increases and pixels become smaller, more numerous, and closer together. This procedure – known as pixel uniformity correction, or ‘demura’ – depends on the precision of pixel-level luminance measurement for the purpose of calculating accurate correction coefficients for each pixel. Automated visual inspection of displays has been proven for identification of imperfections such as non-uniformity-while maintaining rapid cycle times, quantitative pass-fail results, and decreased operational costs necessary for commercialization and mass production.įor emissive displays, pixel and subpixel measurement techniques have enabled calibration of display uniformity by measuring, identifying, and correcting the luminance output of each pixel. This variability appears as non-uniformity or mura across the display, leading to low yield of high-quality displays as well as rejection of costly components and expensive rework. As such, these displays may exhibit variability in luminance and color output from pixel to pixel. Pixels in OLED (organic light-emitting diode), miniLED, and microLED displays are individual emitters, each producing their own light. Sponsored by Radiant Vision Systems Oct 12 2020
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