Common ways to reduce the moiré of LED display

Figure 1 LED display moiré phenomenon

How to avoid or reduce moiré phenomenon? There are generally the following types of methods:

CCD pixel bias technology

In recent years, the moiré phenomenon has received more and more attention from camera manufacturers. Panasonic Corporation of Japan has adopted CCD pixel bias technology to reduce the occurrence of moiré.

Since the target surface of the CCD is arranged in a lattice, not a continuous surface, when the spatial frequency of the image (for example, the spatial frequency of the large screen of the LED) exceeds the spatial frequency of the CCD, the moiré phenomenon is likely to occur. Simply put, it is because the image details are smaller than the spacing between each image sensor. Space offset is a method used to increase the horizontal resolution of CCD camera brightness. This method can use the number of pixels in the CCD array as much as possible to achieve a higher resolution than the theoretical value. The pixel arrangement is shown in Figure 3. The red and blue CCDs are fixed on the prism module, and their spacing is horizontally offset by half the green. It doubles the number of samples in the scan line for making a luminance signal, which results in a higher resolution.

Figure 3 CCD biasing technology (P-Pitch: pitch, mechanical engineering quantifier, arc length between the same side flank)

FIG. 4 is a schematic diagram of the effect of improving the resolution by using the CCD pixel offset technique, and the frequency of the subject reflects the details of the image. When the pixel biasing technique is adopted, the green CCD and the red and blue CCD will obtain image information at different points. After the DSP digital signal processing, the image information of the red curve can be obtained (if the object has higher details than the red line, the image information cannot be obtained. Instead of using the pixel offset technique, only image information such as the blue curve can be obtained. Obviously, the actual output image details are much less. However, even with this method, the moiré cannot be completely eliminated because the CCD still has a certain spatial frequency and cannot be continuously formed into one surface.

Figure 4 CCD offset indication

Camera adjustment

The following methods can be used to reduce or eliminate moiré interference during TV shooting:

(1) Change the camera angle. Since the angle between the camera and the LED display causes moiré, slightly changing the angle of the camera (by rotating the camera) can reduce or eliminate moiré.

(2) Change the camera position. The moiré can be reduced by changing the angular relationship by moving left and right or up and down.

(3) Change the focus. Excessively sharp focus and detail on the detailed pattern can lead to moiré, and a slight change in focus can change the sharpness, which in turn helps eliminate moiré.

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

(5) Processing with software to eliminate the moiré that appears on the final image.

However, the above method can be applied in some specific situations, but there are practical operational problems for television cameras, especially television live programs.