LED display screens have been used in various fields such as studios, control centers, malls, exhibitions, indoor meetings, and more to attract audiences and drive sales since their inception. Due to their advantages in brightness, clarity, color, and dynamic displays, LED display screens have become popular backgrounds for photography and videography. However, a common issue encountered by photographers and videographers when shooting LED screens is the moiré effect. The moiré effect can ruin an otherwise perfect shot and image, but with the right techniques, it can be easily eliminated.
In this article, we will discuss what the moiré effect is, why it occurs when shooting LED screens, and how to effectively remove it from photography.
What is the Moiré Effect?
“Moiré” is a French word that means “a pattern with a wavy or rippled surface”. When two similar or slightly different patterns overlap or superimpose, unusual visual distortions such as rainbow patterns, waves, or stripes appear on the screen, which is known as the moiré effect.
The moiré effect is sometimes intentionally created in photography to capture a special effect, but more commonly, it interferes with the overall or specific parts of the clarity of the underlying image, text, or video, causing visual confusion. To fully utilize LED display screens, it is crucial to avoid the moiré effect at all costs.
Why Does the Moiré Effect Appear in LED Screen Photography?
The moiré effect is a manifestation of the aliasing principle. Mathematically speaking, when two closely matched sinusoidal waves are superimposed, the amplitude of the composite signal will change according to the difference between the two frequencies.
One of the main reasons for the moiré effect is the inadequate refresh rate of the LED display screen. LED screens are composed of thousands of pixels that emit light to generate images and videos. When a camera captures an LED screen, individual pixels can create an interference pattern on the camera’s sensor. In other words, at the moment the camera captures the image, if certain rows of pixels on the LED screen are not illuminated, it will create a series of moiré patterns in the captured image.
LED displays do not emit light continuously; instead, they refresh at regular intervals. For example, if your display screen has a refresh rate of 60Hz, it means the screen refreshes 60 times per second. Because the human eye has visual latency, we cannot perceive the screen’s changes. However, when using a phone or camera to capture images, if the shutter speed is faster than the screen’s refresh rate, it can capture the screen’s refresh process that is imperceptible to the naked eye, resulting in “stripes”.
Furthermore, when shooting LED displays, conflicts between the pixel structure of the LED panel and the pixel structure of the photo or video can also lead to the moiré effect. This is especially common when the camera and screen are not perfectly aligned, or when the screen is captured from a certain distance or angle. This can pose significant challenges when trying to market LED display screens. Fortunately, there are methods to combat moiré patterns accordingly.
How to Remove the Moiré Effect in LED Screen Photography?
There are several techniques that can be used to eliminate the moiré effect in images captured from LED screens. These techniques range from simple camera adjustments to more advanced post-processing methods.
- Change the Camera Angle
When capturing an LED screen, changing the shooting angle can help reduce the moiré effect. By adjusting the relative position of the camera to the screen or rotating the phone, you can minimize the interference between pixels and the camera sensor. This is particularly effective when shooting from a distance or from angles where the moiré effect is most pronounced.
- Adjust the Camera’s Focal Length
Adjust the resolution of the photo by changing the focal length of the camera when taking pictures of the LED screen to change or eliminate moiré.
- Adjust the Focus to Different Areas
Excessive sharpness and detail in intricate patterns can lead to moiré patterns. Slightly changing the focus when capturing an LED screen can alter the clarity and help eliminate the moiré pattern.
- Use Polarizing Filters
Polarizing filters are useful tools for reducing the moiré effect when capturing LED display screens. By rotating the filter, you can adjust the polarization angle to minimize the interference between the pixels on the screen and the camera sensor. This helps reduce the moiré effect, resulting in clearer and more refined images.
- Use Anti-Aliasing Filters
Anti-aliasing filters are designed to reduce the moiré effect by smoothing the interference pattern between the pixels on the screen and the camera sensor. These filters work by slightly blurring the image to minimize interference, resulting in a cleaner and more natural effect.
- Lower the shutter speed
Lowing the shutter speed helps compensate for the low refresh rate of LED screens, thereby reducing the moiré effect.
Let’s take the example of an LED display with a refresh rate of 1000Hz. If we set the camera’s exposure time to 1/500 second, 1/800 second, 1/1000 second, and 1/2000 second, different situations will occur. Only when the camera’s shutter speed is set to 1/500 second will the image of the LED display come out clear and perfect, as all the pixels on the screen are lit up twice. At shutter speeds of 1/800 second and 1/1000 second, some rows of pixels on the LED display will be lit up more than once, resulting in varying degrees of moiré patterns. At a shutter speed of 1/2000 second, half of the rows of pixels will not be lit up, leading to a significant amount of moiré patterns in the captured image.
At a shutter speed of 1/2000 second, LED displays with a typical horizontal scanning drive IC with a refresh rate of nearly 1000Hz and a dual latch drive IC with a 1920Hz refresh rate are not sufficient to avoid moiré patterns. Only high-definition and high-end PWM drive ICs with a refresh rate of over 3840Hz can better ensure that LED screens do not exhibit moiré patterns when photographed.
Therefore, moiré patterns will not appear in images only when the refresh rate of the display screen is more than twice the camera’s shutter speed.
- Post-Editing Images
If moiré patterns still exist in the image after using the above techniques, several post-processing methods can be used to eliminate them. A common method is to use software such as Adobe Photoshop or Lightroom to apply moiré pattern removal filters. These filters are specifically designed to target and eliminate unwanted interference patterns caused by moiré effects.
Another photo editing option is to overlay the original digital image. If you are fortunate enough to have access to the original image displayed on the screen at the time of capture (i.e., a screen capture of the original video), you can overlay that image to align with the affected image. Using the “Free Transform” tool in Photoshop (CMD+T on Mac or CTRL+T on Windows), hold CMD/CTRL and align the four corners.
Another post-processing technique involves using a method called frequency separation, which separates high-frequency details (where moiré patterns are most prominent) from low-frequency details. By processing these two layers separately, moiré patterns can be effectively eliminated without affecting the overall quality of the image.
When capturing LED screens, adjusting camera settings, lowering the shutter speed, using filters, changing shooting angles, and employing post-processing methods can effectively reduce and eliminate the moiré effect in LED screen photography. With these techniques, you can capture stunning images and videos to share with your clients, free from unnecessary interference patterns.
If you have further questions about the moiré effect in LED screen photography, feel free to consult RIGARD LED. RIGARD LED is a professional LED screen manufacturer, providing high-quality LED display screens with high definition, high brightness, and refresh rates up to 3840 Hz, which can perfectly present the details of your image or video to your users.