Screens flicker when filmed with another screen due to the difference in refresh rate frequency of the two screens. The interference between these frequencies causes this phenomenon visible to the human eye.
Each screen displays images at a certain frequency, meaning the number of times per second it refreshes (usually between 50 and 144 times per second). When you film a screen with another device, it also has its own shooting frequency. If these two frequencies do not match perfectly, they give rise to those infamous unsightly flickers. Essentially, the filmed screen is captured at different moments of its refresh cycle, which explains why you sometimes perceive bands or rather annoying visual pulses. The further apart or misaligned the respective frequencies are from each other, the more visible the phenomenon will be.
The shutter speed determines how long the camera sensor is exposed to light. With a fast speed, your sensor captures a very brief moment, often revealing the flicker or scan of the filmed screen, as it doesn't have time to smooth out light variations. At a slower speed, the variations blend naturally, and this flickering phenomenon becomes less noticeable. In practice, choosing a shutter speed that matches that of the screen helps achieve a pleasing image without the annoying effect of dark scan lines that spoil your videos.
The moiré effect occurs when two repetitive patterns overlap, like the pixels of your screen filmed by those of your camera. This causes strange visual interferences, sort of waves or flickering lines that move oddly. Essentially, two grids that are not quite aligned create a third interfering pattern that can become quite distracting to look at. Your screen has a very fine grid of pixels; when you film it with the sensor matrix of your camera, their two structures intertwine and generate this disturbing visual effect. The more similar the patterns are in size and alignment, the stronger and more visible the moiré effect becomes.
The different types of screens (LCD, LED, OLED, etc.) do not all manage their display in the same way. Some screens, like CRT cathode-ray tube displays or certain LED panels, refresh their image through rapid scanning or regular light modulation, which can cause very noticeable flickering effects when filmed. Settings such as refresh rate (60 Hz, 120 Hz, etc.) or even brightness also greatly influence these flickering phenomena or distracting banding. A well-calibrated screen or one designed specifically for filming (like some professional monitors or HDR screens for shooting) will have much less of this annoying side effect compared to a standard basic screen.
When there is a lot of light around your screen, the reflections and contrasts change the way your camera perceives the image. Basically, the brighter the room, the more complicated it is for the camera to clearly capture what appears on the screen. This often amplifies the effects of flickering or scanning, as the camera struggles to stabilize the image with competing ambient lighting. Conversely, filming your screen in a rather dark room or with soft lighting generally reduces this problem. A dark environment allows your camera to better manage exposure and thus significantly reduces these annoying visual effects.
To avoid distracting flickering when filming a screen, you can adjust your camera's shutter speed to a multiple of the screen's refresh rate (for example, 1/60 or 1/120 second).
Older cathode ray tube (CRT) screens exhibited a much more noticeable flicker than today, as they refreshed the image line by line, unlike modern screens that typically refresh the entire image at once.
The moiré effect, a strange visual interference pattern that you sometimes see when filming certain screens, is caused by the overlay of two grids or fine patterns (such as the pixels and the sensor of your camera) that are slightly misaligned.
Some screens use a method called pulse-width modulation (PWM) to adjust brightness. It is this rapid modulation of the backlight that can create a visible flickering effect when filmed.
The effect strongly depends on the type of screen (LCD, OLED, CRT) and its refresh technology, as well as its specific settings such as refresh rate or brightness.
Sure! Here is the translation: "Yes, artificial lighting (neon, LED, or low energy) can produce additional interference due to their own flicker frequencies, thus visually amplifying the flickering effect."
The moiré effect is a visual interference created by the superposition of two slightly offset repetitive patterns or frequencies. In the case of a camera filming a screen, this occurs when the pixel grid of the screen visually interacts with the camera's digital sensor.
Our eyes perceive very rapid changes as constant, while cameras capture these variations in screen refresh rates more sensitively, resulting in the visual phenomenon of flickering or shimmering.
You can adjust the shutter speed of your camera or smartphone to better match the refresh rate of your screen (for example, setting it to 1/50 or 1/60 second).
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