People often mistakenly think that the water ripple is the scanning line, which is a big mistake.
1 Difference between water ripple and scanning line phenomenon
Water ripple generally presents an irregular arc diffusion state. The scanning line is a horizontal black stripe line, which is mainly caused by the low refresh of the display screen and is captured and presented by the camera!
2 The scientific name of "water ripple" is "Moir effect"
If there is a dense texture in the scene taken with a digital camera, inexplicable water wave like stripes often appear. In short, the moire pattern is a manifestation of the beat difference principle. Mathematically speaking, when two equal amplitude sine waves with similar frequencies are superimposed, the amplitude of the synthetic signal will change according to the difference between the two frequencies.
3 The process of molar striation
1. Two stripes with slightly different spatial frequencies have the same black line position at the left end. Due to different spacing, the lines gradually to the right can not coincide.
2. As a result of the overlapping of the two stripes, the white line can be seen on the left because the black line coincides. The right side is gradually misaligned, the white line faces the black line, and the overlapping result becomes completely black. There are white lines and all black changes, forming molar patterns.
3. If the two groups of stripes in Fig. 2 completely coincide, you can see the typical molar pattern.
4 Process of moire phenomenon on display screen
As shown in the figure above: the LED display screen is composed of RGB three-color units, which are evenly distributed on the display screen.
Note: if the pixel distribution density of LED display screen is just between the intervals that can be distinguished by CCD, it is inevitable that the digital camera will still interpret some recognizable results, but it will also add unrecognizable gray-scale areas. The sum of the two will form regular lines, which is visually periodic ripples.
1. Change the camera angle. Since the camera does not the angle of the object will cause molar ripple, slightly changing the angle of the camera (by rotating the camera) can eliminate or change any molar ripple.
2. Change the camera position. In addition, the molar ripple can be reduced by changing the angular relationship by moving left and right or up and down.
3. Change focus. Too clear focus and height details on detailed patterns may lead to molar ripple. Slightly changing the focus can change the clarity, which helps to eliminate molar ripple.
4. Change the lens focal length. Different lens or focal length settings can be used to change or eliminate molar ripple.
5. The front filter is directly installed in front of the CCD to make its exposure conditions meet the spatial frequency, thoroughly filter the high spatial frequency part of the image, and reduce the chance of moire, but it will also synchronously reduce the sharpness of the image.
6. Process with software. Use Photoshop plug-ins, etc. to eliminate any molar ripples on the final image.
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