When shooting some dense objects, such as architectural decoration, textiles, display screens, etc., we can see that there are some inexplicable color stripes that seriously affect the image effect of the proof. This kind of color stripes appearing on the proof with dense and repeated details is the so-called moire. How does this moire come into being? How can we avoid these moire patterns in the sample? Let's go into science.
A common explanation of moire is that on the sensitive elements of some digital cameras, scanners and other equipment, high-frequency interference is encountered during shooting and scanning, and color and irregular shape stripes appear on the pictures. The principle is to stack two equal amplitude sine waves with similar frequencies, and the amplitude of the composite signal will change according to the difference between the two frequencies. If the spatial frequency of the pixel in the sensor is close to the spatial frequency of the stripe in the image, it is easy to produce moire. If you want to avoid these moire patterns on the hardware level, you should use the lens resolution that is far less than the spatial frequency of the sensor to avoid the generation of moire patterns.
But not all cameras on the market have such a large unit pixel area, so some middle and low end cameras using Bayer array sensors often choose to add a low-pass filter in front of the sensor to reduce the generation of moire patterns. However, there are both advantages and disadvantages. The addition of low-pass filter will affect detail imaging. Although the impact on SLR is not very serious, the Maoist Party and Sharpness Party are unhappy.
In addition, some camera manufacturers are also developing some photosensitive components that can avoid this kind of moire, such as Sigma X3 and Fuji X - Trans sensors. Another article about this was also edited《 》It was mentioned that there was no introduction at that time because I missed the point a little. It's just here to introduce.
The structure of Shima's X3 sensor is completely different from that of the traditional Bayer array sensor. The traditional Bayer array sensor is designed with one layer of RGBG filter, while Shima's X3 is similar to the three-layer structure of film, which is overlaid with three layers of BGR pixels, just like the three-layer emulsion on the film, It's just that film doesn't have pixels. Each pixel of the X3 sensor can sense the RGB three colors, thus completing the color matching data on the same pixel, and it is no longer necessary to use the "color guessing" (anti mosaic operation) technology like Bayer array to fill in the colors of adjacent pixels. Since the process of "color guessing" is omitted directly, Sigma X3 has no interference between pixel colors, and it will be better for the accuracy of color restoration. However, due to the superposition of three pixel filters, the attenuation of light is also a problem, especially the red pixel filter at the bottom will suffer a lot, but it seems that the problem is not too big for the color from the photos taken by many netizens, and many people will choose post-processing after shooting. The color adjustment depends on your own preference.
The other is the X - Trans sensor developed by Fuji. It is an innovative sensor based on the traditional Bayer array sensor. The traditional Bayer sensor is arranged in 2 × 2 RGBG, while the X - Trans sensor is arranged in 6 × 6 pixels. Among them, the RGB pixel filter arrangement order of the X - Trans sensor is inspired by the disorder of silver salt particles in the film. The color filter array of the sensor is modified, and the simulated disorder arrangement is added. In fact, it is impossible to see a certain regular order when it comes to disorder, but the repetition frequency of the 6 × 6 array with large spacing and regular direction is much smaller than that of the Bayer array, so this array can also greatly reduce the generation of moire patterns. There are more green filters in the X - Trans sensor. Officially, the human eye is the most sensitive to green, so add more spots of green to make the color more realistic (that is, more beautiful, more suitable for the human eye).
The two new sensors described above directly eliminate the low-pass filter, which makes the details of the sample more sharp. The application of new technology can also reduce or even eliminate the generation of moire.
Taking Canon 70D as an example, even if a low-pass filter is added, there will still be obvious moire patterns when shooting the screen, because the RGB backlight pixels on the screen are more uniform, repetitive and dense. It is also possible to solve the problem. It is just a little defocusing, so that the focus is slightly inaccurate on the pixel, which can reduce the moire. Of course, the details of the proof are not clear enough, but it is slightly better than the full screen moire in terms of appearance. This technique is not limited to cameras. It is also effective for mobile phones, especially those that support manual focusing.
In addition to this way, you can also change the angle of the camera and tilt the camera to reduce moire patterns. Also, change the position of the camera, and walk several more places to observe the moire pattern. You can take pictures of the positions where the moire pattern is few and can accept the composition.
In addition, if you have money, you'd better directly consider choosing a new camera without low-pass filter or a full frame camera to reduce the generation of moire.
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