When LED display screen is used in control room, TV studio and other places, it will sometimes cause moire interference to the camera picture. This paper introduces the causes and solutions of moire, and focuses on how to select LED display screen to reduce or eliminate moire.
LED display screen has gradually become the mainstream display equipment in control room and TV studio. However, in the long-term use process, it will be found that when the camera lens is aimed at the LED display screen, stripes like water waves and strange colors (as shown in Figure 1) will occasionally appear, which is also known as Moir é pattern.
How did the moire come into being?
When two patterns with spatial frequency overlap, another new pattern is usually generated, which is usually called moire pattern (as shown in Figure 2).
The traditional LED display screen is arranged by independent luminous pixels, and there are obvious non luminous black areas between the pixels. At the same time, the sensitive element of the digital camera also has an obvious weak light sensing area when sensing light. When digital display and digital photography exist at the same time, the moire pattern is born.
Since the CCD (image sensor) target surface (photosensitive surface) of the camera is similar to the figure in the middle of Figure 2, while the traditional LED display screen is similar to the image on the left side of Figure 2. It is composed of lattice light emitting tubes arranged in a consistent manner. The entire display screen has a large non luminous area, forming a grid like pattern. The overlapping of the two forms a moire pattern similar to the right side of Figure 2.
How to eliminate or reduce moire?
Since the LED display grid structure interacts with the camera CCD grid structure to form moire patterns, changing the relative value and grid structure of the camera CCD grid structure and the LED display grid structure can theoretically eliminate or reduce moire patterns.
How to change the grid structure of camera CCD and LED display?
In the process of film recording, there is no pixel with regular distribution, so there is no fixed spatial frequency and no moire.
Therefore, the moire phenomenon is a problem caused by the digitalization of TV camera. To eliminate the moire, the resolution of the LED display screen image taken in the lens should be far less than the spatial frequency of the sensitive element. When this condition is met, no fringes similar to those of the sensor can appear in the image, and thus no moire will be generated.
In some digital cameras, a low-pass filter is installed to filter the higher spatial frequency part of the image in order to reduce moire, but this will reduce the image sharpness. Some digital cameras use higher spatial frequency sensing elements.
How to change the relative value of camera CCD and LED display grid structure?
1. Change the camera shooting angle. By rotating the camera and slightly changing the shooting angle of the camera, the moire ripple can be eliminated or reduced.
2. Change the camera shooting position. By moving the camera left and right or up and down, you can eliminate or reduce the mole ripple.
3. Change the focus setting on the camera. The focus and high detail that are too clear on the detailed drawings may cause mole ripples. Slightly changing the focus setting can change the clarity, thus helping to eliminate mole ripples.
4. Change the focal length of the lens. Different lenses or focal length settings can be used to eliminate or reduce molar ripple.
LED display screen is arranged by independent luminous pixels, and there are obvious non luminous black areas between pixels. Find a way to turn the non luminous black area into a luminous area, and reduce the brightness difference with independent luminous pixels, which can naturally reduce or even eliminate moire.
Is there a way to turn the non luminous black area into a luminous area on LED display?
COB packaging process LED display, it is easy to do this. If we have the opportunity to put the LED display of COB together with the LED display of SMD, we can easily find that: the LED display of COB emits soft light like a surface light source, while the LED display of SMD obviously feels that the luminous particles are independent luminous points. It can be seen from Figure 3 that the sealing method of COB packaging is significantly different from that of SMD. The sealing method of COB packaging is the overall light-emitting surface of many light-emitting pixels together. The sealing method of SMD packaging is a single luminous pixel, which is an independent luminous point.