Traditional Culture Encyclopedia - Photography major - Why does it always flash when I shoot a computer screen with my mobile phone?
Why does it always flash when I shoot a computer screen with my mobile phone?
The refresh frequency is what we often call screen hertz. In fact, the screen is not always shining, but it will be refreshed every once in a while, such as 60hz, which means it will be refreshed 60 times a second, but the naked eye is completely unaware of what is flashing on the screen.
However, the shutter speed of the mobile phone is faster when shooting the screen. When the shutter speed is faster than the refresh frequency, we can capture the screen refresh process that we can't see with our naked eyes, which is why ripples occur.
Moire fringe is an interference image produced by two lines with similar spatial frequency interfering with each other and overlapping into two or more groups of different fringes. Moire fringe is the visual result of interference between two lines at a certain frequency. When the human eye can't distinguish these two lines or two objects, it actually magnifies the difference between stripes.
Extended data
If the spatial frequency of CCD(CMOS) pixels is close to the spatial frequency of fringes in the image, moire fringes will appear. In order to eliminate moire fringes, the resolution of the lens should be much smaller than the spatial frequency of the photosensitive element. If this condition is satisfied, it is impossible to have fringes similar to photosensitive elements in the image, so moire fringes will not appear.
In some digital cameras, in order to reduce moire fringes, a low-pass filter is installed to filter out the parts with high spatial frequency in the image, which will of course reduce the clarity of the image. In the future, if the pixel per inch can be greatly improved, far exceeding the resolution of the lens, moire fringes will not appear.
Reduce and eliminate the influence of moire fringe in photography
1, change the camera angle. Because the angle between the camera and the object will lead to moire fringes, any moire fringes can be eliminated or changed by slightly changing the camera angle (by rotating the camera).
2. Change the position of the camera. In addition, moire fringes can be reduced by changing the angular relationship by moving left and right or up and down.
3. change the focus. Too clear focus and height details on detail patterns may lead to moire fringes, and a slight change in focus can change the clarity, thus helping to eliminate moire fringes.
4. Change the focal length of the lens. Different lens or focal length settings can be used to change or eliminate moire fringes.
5. Use software to process. Such as Nikon capture or Photoshop plug-in, to eliminate any ripple on the final image. But you can't restore the original details.
References:
Baidu Encyclopedia: Moire Patterns
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