What Kind Of Shooting Skills Can Eliminate The Moiréeffect Of LED Screen Taken By Mobile Phone?

Compared with other displays, LED display has great advantages in brightness, size and so on. However, in the long-term use process, we will find that when the mobile phone or other shooting equipment is aimed at the LED screen, there will occasionally appear strange water wave like stripes and strange colors, as well as strange faults. The same is true for the photos taken. Many people think that the current is unstable, but it is not caused by this.

Some people call the streaks like water waves, but in fact he learned to call them "Moiréeffect". The explanation is that if there are dense streaks in the scenes taken with digital cameras, there are often inexplicable water waves like streaks. In short, Moore pattern is an expression of beat principle. Mathematically speaking, when two equal amplitude sine waves with similar frequency are superimposed, the amplitude of the synthesized signal will change according to the difference between the two frequencies.

The reason for the overflow of Moiréeffect is that the refresh rate of LED screen is not enough, and some lines on the LED screen are not lit up at the moment of taking a picture, resulting in a series of moire phenomenon. Refresh rate is commonly known as the hertz of the screen.

Now most of the liquid crystal displays are 60 Hz by default. Because the screen doesn't always glow, it will refresh once every other period of time. For example, the 60Hz represents 60 times of refresh per second. But the human eye has visual delay, so the human eye can't detect any flicker on the screen.

When the mobile phone takes pictures of the screen, most of them also have relatively fast shutter speed. When the shutter speed is faster than the refresh rate, we can capture the screen refresh process that we can't see with the naked eye, which will produce "stripes".

Taking a screen with 1 / 4 scan, equipped with ordinary cross flow drive IC and refresh rate of 1000Hz as an example, set the exposure time of the camera to 1 / 1000s, 1 / 500s, 1 / 800s and 1 / 2000s, the following situations will occur.

Only when the shutter speed is 1 / 500 second, all lines are lit twice, and the brightness is the same. When the shutter speed is 1 / 800 s and 1 / 1000 s, some lines are lit up once more, resulting in different degrees of moire. At the shutter speed of 1 / 2000 second, half of the lines are not lit up, so we can imagine the number of Moire lines.

Only when the refresh rate is more than twice the shutter speed of the camera, the LED screen will not appear moire.

Under the general camera shutter speed of 1 / 2000 second, the refresh rate of 1000 Hz of the common crossflow driver IC and 1920hz of the dual latch driver IC are not enough to avoid moire. Only the high-definition high-order PWM driver IC with a refresh rate above 3840hz can ensure that the LED screen does not appear Moiréeffect when taking photos.

What kind of shooting techniques can reduce or eliminate this kind of interference?

1)         Change the camera angle of the mobile phone. Because the angle between the mobile phone and the LED screen will cause moire, slightly changing the angle of the mobile phone camera (by rotating the mobile phone) can reduce or eliminate Moiréeffect.

2)         Change the camera position of the phone. By moving left and right or up and down to change the angle relationship, we can reduce the moire.

3)         Change the focus. Too clear focus and detail on the detailed pattern may cause Moiréeffect. Slightly changing the focus can change the clarity and help eliminate moire.

4)         Change the focal length of the lens. Use different lens or focal length settings to change or eliminate moire.

5)         Using software processing, using Photoshop plug-ins, etc., to eliminate any Moiréeffect on the final image.

6)         The filter in front of the CCD is directly installed in front of the CCD to make its exposure conditions meet the spatial frequency. The high spatial frequency part of the image is thoroughly filtered to reduce the chance of Moiréeffect, but it will also reduce the sharpness of the image