Choose the shutter architecture after measuring target motion

Source facts: motion blur and rolling-shutter distortion are different

Axis Communications’ July 2026 white paper, Global shutter vs rolling shutter, explains that a rolling-shutter sensor exposes its pixel rows at slightly different times. A global-shutter sensor exposes all pixels simultaneously and stores the result before row-by-row readout. The timing offset in a rolling shutter can distort fast motion: a passing vehicle may tilt, a golf club may appear bent, or rotating blades may lose their true shape.

This distortion is not the same as motion blur. Exposure duration causes blur; the offset between row exposures causes rolling-shutter distortion. A longer exposure can smear the distortion until it is less obvious, but it does not remove it. Conversely, a very short exposure can freeze the object while revealing the rolling-shutter shape error more clearly.

Axis notes that modern rolling-shutter sensors produce clean results in most ordinary surveillance scenes. The effect becomes important when objects move very quickly across the image, rotate rapidly, or must be measured by their true shape. Resolution and sensor readout time also affect the amount of distortion. A global shutter is therefore a use-case decision, not an automatic quality upgrade.

Source facts: a global shutter does not remove the need for light

Global-shutter benefits depend on an exposure short enough to control motion blur. Short exposures collect fewer photons, so fast-motion work commonly requires more visible or infrared illumination. Axis describes approximately 1/1000 second as common in traffic applications and even shorter exposure for rapidly spinning equipment, while emphasizing that the actual requirement belongs to the scene.

A global shutter can synchronize a short, high-intensity light pulse with the whole frame. A rolling shutter exposed row by row may record that pulse only across a band. Mixed installations also need attention: a strobe serving one camera can create bands or split images in another. Global-shutter sensors may cost more and can introduce more noise than rolling-shutter designs, especially under limited light.

DSE recommendation: specify the event before the sensor

Define the evidence or machine decision first. Record the target type, fastest expected speed, direction through the field of view, distance, required shape or marking, and whether a human, analytic, or industrial process will use the image. A parking overview, a vehicle classification lane, and a conveyor inspection point have different tolerances even when all contain fast motion.

1. Measure the installed geometry. Motion across the sensor can be more demanding than motion toward the camera. Test the planned height, angle, focal length, target distance, and crop.
2. Set an exposure range deliberately. Verify the camera can hold the necessary exposure under both daylight and the darkest required condition without unacceptable gain, noise, or blur.
3. Design the illumination with the camera. Confirm wavelength, beam, intensity, duty cycle, synchronization, power, reflections, and effects on nearby cameras. Never assume a strobe is invisible to another sensor.
4. Record real-speed passes. Use the production stream, codec, frame rate, VMS, and playback client. Review consecutive frames rather than selecting one favorable still.
5. Compare failure modes. Look separately for blur, tilted objects, bent edges, bright bands, split exposures, missed analytic events, and low-light noise.

DSE recommendation: preserve a repeatable acceptance record

Document camera model, firmware, sensor type, lens, resolution, exposure limit, gain, frame rate, illumination, target speed, weather, test direction, and result. Retain short clips from the hardest passing and failing conditions. If a rolling shutter meets the written requirement, it may be the more economical and lower-noise choice. If it changes the shape or position needed for a decision, specify global shutter and the supporting light.

Repeat the test after changes to the camera, lens, exposure policy, illumination, mounting angle, encoder profile, or analytic. The durable outcome is not “global shutter installed.” It is a recorded sequence that preserves the required information while the target moves at the speed the system was designed to handle.

Official references

• Axis Communications, Global shutter vs rolling shutter, July 2026.