Industry Background and Problem Statement
With the increasing demands for visual presentation precision in film and television virtual production (XR), professional studios, and large-scale performances, LED displays have gradually replaced traditional green/blue screens, becoming the core carrier for virtual shooting backgrounds. Their "what you see is what you get" real-time compositing advantage significantly reduces post-production costs and improves shooting efficiency.
However, when using photographic equipment to shoot LED screens, two typical "fatal flaws" often appear: moiré patterns and "scanning patterns." The former manifests as irregular water ripple interference, while the latter appears as horizontal black stripes, directly damaging the image quality and even rendering the footage unusable. These have become key technical bottlenecks restricting the widespread adoption of LED virtual shooting.
Clarifying the core issue: The technical differences between moiré patterns and scanning patterns
In practice, the two are easily confused, but they are fundamentally different in terms of visual characteristics, formation mechanisms, and solution paths. A detailed comparison is shown in the table below：
|
Comparison Dimensions |
Moiré pattern (water ripple pattern) |
Scanning lines (horizontal black stripes) |
|
Visual features |
Irregular arc/grid-like diffusion, color varies with shooting angle/parameters |
Fixed horizontal black stripes, stripe spacing varies with refresh rate, with no color interference. |
|
Essential Mechanism |
Interference phenomenon between two periodic pixel arrays (LED screen pixels vs. camera sensor pixels) |
Synchronization deviation caused by mismatch between camera shutter speed and LED screen progressive scan frequency |
|
Core trigger |
1. Insufficient LED screen refresh rate; 2. Mismatch between camera parameters (aperture, object distance, focal length) and LED pixel density; 3. The angle between the pixel arrays of the two devices is close to 0°. |
1. LED screen refresh rate < 1000Hz (progressive scan drive); 2. Camera uses progressive shutter. |
|
Industry Misconceptions |
"It can be cured simply by adjusting the camera angle" (In reality, it can only alleviate the symptoms, not eliminate them). |
"Flickering is invisible to the human eye, meaning there is no scanning pattern" (the camera shutter sampling frequency and the LED scanning frequency are not synchronized, so the naked eye cannot perceive it, but the camera can capture it). |
Targeted Solutions: A Technological Path from "Relief" to "Cure"
Moiré Pattern Solution: Dual-End Optimization, with Display Screen as the Core
Shooting Equipment Side: Parameter Adjustment (Mitigation Measures)
Principle: By altering the relative grating relationship between the camera and the LED screen, the system seeks the parameter combination with the weakest interference, primarily by avoiding the resonance range of the two pixel array frequencies/angles. The specific operation method and technical logic are as follows:
|
Adjust parameters |
Operational suggestions |
Technical Logic |
|
Aperture |
Prioritize using large apertures (such as F2.8-F4.0) and avoid small apertures (F8.0 and above). |
A large aperture results in a shallow depth of field, blurring the edges of the LED pixels on the camera sensor and reducing periodic interference; a small aperture results in a deep depth of field, sharp pixel images, and increased interference. |
|
Object Distance |
Adjust the distance between the camera and the LED screen (e.g., increase from 4m to 6m) to avoid a fixed object distance. |
Changes in object distance alter the "imaging pixel pitch" of LED pixels on the sensor. When the pitch is not an integer multiple of the sensor pixel pitch, interference weakens. |
|
Focal Length |
Avoid using telephoto lenses (such as 105mm), and prioritize wide-angle to standard focal lengths (24mm-50mm). |
Telephoto lenses amplify the periodicity of the LED pixel array, exacerbating interference; wide-angle lenses offer a wider field of view, reducing the pixel density in the image and thus weakening interference. |
|
Shooting angle |
Make the angle between the camera's optical axis and the LED screen's normal 5°-15° (non-perpendicular shooting). |
By changing the angle between the two pixel arrays, the "parallel resonance" state is broken, reducing the generation of interference fringes with alternating light and dark areas. |
Limitations: This solution can only "alleviate" moiré patterns and imposes multiple limitations on shooting-such as the inability of a large aperture to meet depth-of-field requirements (foreground actors and background LED screens need to be clearly captured), and the non-perpendicular angle disrupts the perspective relationship of the virtual scene. It has low operability in actual shooting and cannot be used as a radical solution.
Display Screen: Technological Innovation (Root Cause Solution)
Principle: Starting from the source of moiré patterns (the periodicity and refresh rate of the LED screen itself), eliminating the "interference source" by increasing the refresh rate and optimizing the pixel structure is the industry-recognized solution.
The core technical requirements are as follows:
1. Ultra-high refresh rate: The LED screen refresh rate must be ≥7680Hz (industry term "shooting-grade refresh rate"). By increasing the signal output frequency of the driver IC, the on/off cycle of the LED pixels is made much faster than the camera shutter sampling cycle, weakening the basis for periodic interference.
2. Pixel density optimization: High-density packaging technologies such as MiniCOB (e.g., pixel pitch P1.2 and below) are used to reduce the LED pixel pitch, making the "periodic frequency" of the pixel array far away from the pixel frequency of the camera sensor (e.g., a full-frame camera with approximately 60 megapixels has a frequency of approximately 200dpi), thus avoiding resonance at the frequency level.
3. Flicker-free drive: "PWM (Pulse Width Modulation) flicker-free technology" is used to replace the traditional "duty cycle drive," ensuring continuous and stable LED pixel brightness output and avoiding increased moiré patterns due to brightness fluctuations.
Scanning Texture Solution: Focusing on "Refresh Rate + Shutter Synchronization"
The essence of scan lines is "synchronization deviation between camera shutter and LED progressive scan". The solution is more direct, focusing on "increasing the refresh rate" and "optimizing the synchronization mechanism".
Core Solution: Increasing the Refresh Rate of the LED Screen
1. When the LED screen refresh rate is ≥1000Hz, the "line switching time" of progressive scan is shortened to less than 1ms. The camera's progressive shutter speed (such as the common 1/50s or 1/60s) cannot capture the brightness difference between lines, and the scan lines naturally disappear.
2. For broadcast-grade cameras, it is recommended that the LED screen refresh rate be ≥7680Hz, which can match the camera's "global shutter" mode, completely eliminating scan lines and flicker..
Auxiliary Technology: Shutter-Refresh Synchronization
Some high-end LED control systems (such as Bangteng) support "camera shutter signal input". By adjusting the scanning frequency of the LED screen in real time to synchronize with the camera shutter speed (such as setting the LED refresh rate to an integer multiple of 500Hz when the shutter speed is 1/50s), scanning patterns are further avoided. This is suitable for high dynamic virtual shooting scenarios (such as fast camera zoom-in and zoom-out, and large-scale actor movements).
