Frame Rate, LED Refresh and Camera Exposure

Keep three clocks separate

Source frame rate describes how often new pictures arrive. LED refresh describes aspects of the panel's light-emission timing. Camera exposure describes the interval during which a sensor collects light. A high LED refresh number does not increase the number of unique frames in a low-frame-rate source.

Multiplexed LED drive addresses groups of pixels in sequence. Pulse-width modulation controls light output through timed pulses. The resulting waveform depends on the driver, scan architecture, grayscale settings and operating brightness. Request the exact panel and processor configuration instead of treating refresh rate as a standalone camera-compatibility certificate.

Calculate exposure time

For a camera using shutter angle α and frame rate f, exposure time is t = α/(360f). At 25 frames/s with a 180° shutter, t = 0.02 s = 1/50 s. At 50 frames/s with the same angle, exposure is 1/100 s. These relationships define exposure duration; they do not describe rolling-shutter readout or guarantee a compatible LED waveform.

Separate spatial and temporal artefacts

Moiré often changes with distance, focal length, focus and sensor sampling. Bands and partial exposures often respond to exposure duration, scan timing, phase and camera readout. Compression and image processing can add their own patterns. Change one parameter at a time and retain original camera files so that a correction can be repeated.

Genlock establishes a timing reference between compatible devices. Exposure alignment and panel timing still require configuration. Brompton's ShutterSync is a hardware-specific example of adjusting LED timing to camera exposure; support must be confirmed for the installed processor, receiving hardware and panel. Do not transfer a setting from one product family to another without its documentation.

Camera acceptance matrix

1. Record camera model, sensor mode, recording resolution, frame rate, shutter, gain, lens and focus distance.
2. Record source rate, processor reference/phase, panel mode and brightness.
3. Capture neutral fields, dark gradients, fine patterns and representative motion.
4. Repeat the required combinations of framing, viewing angle and camera movement.
5. Save an accepted preset and check it again after firmware or receiving-card changes.

Agree separate criteria for in-person viewing and recorded images. An installation used for conferences may need both, even when the principal content consists of slides. Include the intended phone or broadcast camera modes only where they are actual project requirements.