First, we need to know what is moire. Here is the moire definition: When taking photos or videos to the LED screen by using digital equipment like cellphones, cameras, etc, there would be some irregular patterns like water ripples. This is called moire phenomenon or moire effect. Just refer to the photo below:
What causes moire effect?
First, we would like to introduce the CCD image sensor of a digital camera. There are many photodiodes in alignment on the CCD image sensor. They could sense the light, and turn the light signal into the electric signal. For these photodiodes, they are called CCD pixels, just like the LED lamps are the LED screen pixels.
Below is a photo of these two kinds of pixels (the distance between two pixels is shown with grid shape):
When the camera is directed at the LED screen, we use the pixels photo above to simulate and it comes out as below:
The above explains what causes moire effect. Then how to remove moire?
Here we need to know one optics word: spatial frequency. It means in the unit view, the periodicity of image bright and dark lines repeated emergence. Here is a photo:
In this photo, the distance between the digital camera and the LED screen is fixed. From the view of the eye, if the pixels quantities of CCD and the LED screen are the same, then we could say the spatial frequency is the same for CCD and LED screen. A similar spatial frequency could cause moire lines easily.
Here are 5 tips to remove moire generally:
☛ Change the angle of the digital camera. As the angle of the camera could cause moire, then change the angle of the camera could remove moire.
☛ Change the focal point. A too-clear focal point may cause moire. So it could remove moire by changing the focal point.
☛ Change the lens or focal length. Different lens or focal length could be used to remove moire.
☛ Use the filter lens and put it in front of the CCD, and make its exposure to meet the requirement of the spatial frequency, so as to reduce the chance of moire coming out.
☛ Add one kind of optical processing screen in front of the screen. This kind of screen is made of special materials. It could amplify to display every pixel on the LED screen, remove the grid effect, and it could remove moire.
After the above description of moire, you may have some idea now of this common phenomenon when taking photos of the LED screen. Anyway, if you adjust the angle of the camera when taking photos, you could avoid it. Maybe you also note that there is another kind of black line occurring during taking images or videos of the LED screen. For such black lines, they are called scan lines. This is different from moire lines. And such black lines are caused because of the low refresh rate. This could be eliminated with the high refresh rate drive IC.
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