How to eliminate moire patterns and simplify them easily

For beginners of photography, one of the most common photographic problems is that when shooting dense objects such as architectural decoration, textiles and display screens, we often see some color stripes that affect the proofs. This hormone is called moire. Now let's go into science and learn how to eliminate moire, an annoying little thing!

moire

The common explanation of moire is that the photosensitive elements of some digital cameras, scanners and other equipment are disturbed by high frequency in the process of shooting and scanning, and stripes with irregular colors and shapes appear on the pictures. The principle is that when two sine waves with similar frequencies are superimposed, the amplitude of the synthesized signal will change according to the difference between the two frequencies. If the spatial frequency of pixels in the photosensitive element is close to the spatial frequency of stripes 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 far less than the spatial frequency of the photosensitive element to avoid moire patterns.

how to avoid moire

but not all cameras on the market have such a large unit pixel area, so some low-end cameras using Bayer array sensors often choose to add a low-pass filter in front of the sensor to reduce moire. However, there are advantages and disadvantages. The addition of low-pass filter will affect the detail imaging. Although the impact on the SLR is not quite serious, the number of hair parties and sharpness parties are just 1, unhappy.

In addition, some camera manufacturers are also developing some photosensitive elements that can avoid this moire pattern, such as X3 of Sigma and X-Trans sensor of Fuji. This point was also mentioned in my other article "Exploring the" W "of Sony's new RGBW sensor", but I didn't introduce it because I ran a little bit, so I just want to introduce it here.

avoiding moire

moire

Sigma's X3 sensor is completely different from the traditional Bayer array sensor in structure. The traditional Bayer array sensor is designed as a layer of RGBG filter, while Sigma's X3 is similar to the three-layer structure design of film, which is formed by overlaying BGR three layers of pixels on the sensor, just like the three-layer emulsion on the film, except that the film has no such thing as pixels. Each pixel of X3 photosensitive element can sense three colors of RGB, 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. Because the process of "color guessing" is directly omitted, Sigma X3 has no interference with pixel colors, and it will be better for the accuracy of color reproduction. However, because of the superposition of three pixel filters, the attenuation of light is also a problem, especially the red pixel filter at the bottom will suffer, but it seems that the color shot by netizens is not a big problem, and many people will choose post-processing after shooting, and the color adjustment depends on your own preferences.

X-Trans sensor

X-Trans

The other is the X-Trans sensor developed by Fuji, which is different from the 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 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. It is said that it is disordered, but in fact, a certain regular order can not be seen. It is just that the repetition frequency of 6 6, which is regularly arranged at large intervals, is indeed much smaller than that of Bayer array, so this array mode can also greatly reduce the occurrence of moire patterns. There will be more green filters in the X-Trans sensor. Officially, the human eye is the most sensitive to green, so add more green to make the color more realistic (that is, more gorgeous and more suitable for the human eye).

The two new sensors introduced above directly cancel the low-pass filter, which makes the details of the sample more sharp, and the application of new technology can also reduce or even eliminate the moire pattern.

moire pattern of Canon 7D

Moire pattern technique

Take Canon 7D as an example, even if a low-pass filter is added, there will still be obvious moire pattern when shooting the screen, because the RGB backlight pixels on the screen are more uniform, repetitive and dense. It is also possible to solve this problem, that is, slightly defocusing and making the focus slightly less accurate on the pixel point can alleviate this moire pattern, but of course, the details of the proof are not clear enough, but it will be slightly better than the full screen moire pattern in terms of perception. This technique is not limited to cameras, but also effective for mobile phones, especially those that support manual focusing.

in addition to this way, you can also reduce moire by changing the camera's angle and tilting the camera. Also, change the position of the camera, and take more positions to observe moire patterns. You can take pictures of any position where moire patterns are less and can accept this framing composition.