Why it is so difficult to photograph Ledwall screens well: what is the Moiré effect

When we take a photo of a Ledwall screen, especially with mobile phones, it is very common to encounter a typical visual phenomenon that manifests itself with the appearance of curves on the screen and color decomposition. This effect is called the Moiré Effect and is generated in the presence of repetitive details in the image, such as lines, dots and particular colors, and is considered a defect

The Moiré effect is a challenge for photographers, as it is difficult to remove it afterwards, in post-production, and therefore must necessarily be addressed during the shooting phase. Soft images with fewer details have less chance of moiré effects. The sharper the image, the greater the possibility of the moiré effect occurring.

In this article we will explore what the Moiré Effect is, how it forms and how to avoid it during video or photographic shooting.

How the Moiré effect forms

In the context of Ledwalls, the moiré effect mainly manifests itself due to the interaction between two grid structures:

1. The Ledwall structure: Each Ledwall is composed of a matrix of individual pixels arranged according to a specific pattern. This grid structure (pattern) is intrinsic to the technology.
2. The imaging sensor in the camera or video: the camera sensor is also composed of a set of pixels arranged in a grid and also forms a pattern.

When these two patterns interact as happens in a video-photographic shoot of a ledwall, a distortion, an artifact called the Moiré effect, is determined. The overlap angle, the spatial frequency of the two grids and their density are factors that influence the intensity and visibility of the effect.

In other words, two similar patterns, both in the captured object (the Ledwall) and in the camera's imaging chip, result in a third pattern called Moiré. This is the result of a random process and it is not possible to predict under what conditions it will form.

On television, this effect is often visible in sports footage with Ledwalls on the sidelines, in shots where the Ledwall occupies most of the frame.

How to reduce the LED display moiré effect

Eliminating this disturbance is not easy but it is certainly possible to greatly reduce it. The simplest solution is to avoid it during shooting, but the quality of the Ledwall can also help minimize it.

Avoiding the moiré effect during photographic and video shooting

Here are some of the simplest ways to reduce the moiré effect during image production

• Change focus
  If moiré is forming, it means that two patterns are overlapping. This can be solved by changing the focus. Changing the focus from the point where the distortion occurs will eliminate the overlap and thus the Moiré effect. Slightly blurring the image can also help. A less defined image (within acceptable limits, of course), softer, makes the distortion less evident until it often disappears.
• Change the camera angle
  Moiré is caused by the overlapping of two contrasting patterns. When distortion forms, it means that the shooting angle causes the patterns to overlap. The best way to solve this problem is to change or adjust the camera angle. Most problems will be solved by this adjustment.
• Adjust the camera's focal length
  Most of the Moiré effect can be solved simply by adjusting the camera's focal length. When you change the focal length, you adjust the image resolution. This reduces the possibility of Moiré patterns forming in large numbers. Another alternative to this is to change the distance.
  Moving closer or further away a bit helps to find the perfect distance. Once reached, the Moiré effect will eventually disappear. With mobile phones, the wide-angle function (x 0.5 on iPhones) can often be decisive.
• Adjust the shutter speed
  Slightly lowering the camera's shutter speed will help compensate for the LED display's refresh rate. This will lower the possibility of the artifact appearing.

Minimizing the moiré effect from the Ledwall side

• Careful content selection
  Avoid thin striped patterns or grids: When possible, it is preferable to use graphic and video content that does not present repetitive patterns with similar spatial frequencies.
• Optimizing Ledwall settings
  Use of advanced video processors: Professional video processors can offer scaling and de-interlacing functionalities that can help mitigate the moiré effect.
• Ledwall with specific characteristics
  Higher pixel pitch: For applications where the viewing distance is shorter, a higher pixel pitch can make the appearance of the Moiré effect less likely in the presence of certain types of content. However, this choice must be balanced with resolution and detail requirements.

Conclusion

The rainbow-like pattern you see in your photos and on TV screens is called the Moiré Effect. Eliminating it is one of the biggest challenges for photographers. However, there are techniques we can use to eliminate or at least reduce the Moiré effect on our images and LED displays.

The most reliable way to eliminate the moiré effect is to avoid it during production. If the problem persists, there are post-production methods and software that can reduce the Moiré effect. There are also some technologies such as optical processing and fine LED modules that can reduce the Moiré Effect on screens.