The functioning of global shutter sensors corresponds to the classical clapperboard: all pixels are exposed simultaneously.

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1 Rolling effect unavoidable? Using rolling with global start Capturing moving objects with rolling sensors produces bizarre results. Helicopters fly with bended propellers or vehicles are distorted along their direction of travel. Is a rolling sensor unsuitable for capturing moving objects? The answer is no, thanks to special operating modes such as the global start mode of the 18 MPi AR1820HS sensor from Aptina. Background Basically, the requirements for an image capture are always the same: recording of an event or subject with a recognizable and distortion-free result. The eposure duration is controlled via an electronic, that is, how long light falls on the photosensitive surface. The image is recorded in the sensor in four phases: Reset piels of the rows to be eposed Eposure of piel rows Charge transfer on the sensor Data readout There are two different methods: First, the global simultaneous recording using global, which is mostly used in CCD sensors. Second, the time-rolling recording using rolling which is used in CMOS sensors. Functioning of global and rolling Global The functioning of global sensors corresponds to the classical clapperboard: all piels are eposed simultaneously. Global First, all piel rows are reset. Afterwards the eposure starts. At the end of the eposure, all rows are simultaneously moved to a darkened area of the sensor. The piels are then read out row by row and transferred as digital values. All ueye CCD sensors as well as some CMOS sensors use the global method. 1

2 Advantages Disadvantages All rows are eposed simultaneously Smallest piel size 3.45 µm No compromises on applications No distortions of captured objects Requires comple and epensive sensor technology Occuring of hot piels at high temperature and long eposure time Rolling The rolling works like a camera with a focal-plane, that means the rows are not simultaneously but sequentially eposed and read-out from top to bottom. Rolling On a rolling sensor, the piel rows are reset and eposed one row after another. At the end of the eposure, the lines are read out sequentially. As this results in a time delay between the eposure of the first and the last sensor rows, captured images of moving objects are distorted or stretched. Advantages Very high resolution with small optical format More noise-free compared to global No memory cell: simple piel structure, allows very small piels up to 0.9 µm Disadvantages Moving objects causes artefacts during image recording The moves from top to bottom Rolling effect: positional error when capturing moving objects 2

3 Avoiding the rolling effect Global eposure window To counteract the disadvantages of the rolling, especially the rolling effect, you can use a global eposure window in ueye Cockpit. This allows implementing a global flash functionality which eposes all rows of a rolling sensor simultaneously like a global sensor. Keep in mind the following items: Your application supports flashing Make sure that no ambient light falls in. Rolling with global eposure window For the global eposure window, you set a delay time by which the flash activation is delayed. You can also specify the flash duration. Global eposure window in ueye Cockpit If you set the global eposure window, the driver calculates automatically the right flash timing. If the set eposure time is too short you will get a hint with the minimum eposure time. It may take a few images until the flash timing is adjusted. 3

4 Rolling with global start A further possibility offers rolling sensors with a special mode, the global start mode. Rolling with global start The global start mode ensures that the eposure of all rows starts simultaneously. For best results, use a flash for this mode. No light is allowed to fall on the sensor outside the flash period because otherwise the image brightness will be distributed unevenly. Summary Due to the huge progress in CMOS technology, the problems like limited long eposure or rolling effect have hardly any effect on applications. As CMOS sensors have a different design, they have a higher piel density and thus a greater resolution than CCD sensors. Shutter modes of CMOS sensors Camera Global shut- Rolling Rolling with ter global start UI-122/UI-322/UI-522 UI-124/UI-324/UI-524 UI-125/UI-325/UI-525 UI-146/UI-546 UI-148/UI-348/UI-548 UI-149/UI-549 UI-154/UI-554 UI-155/UI-555 UI-158/UI-358/UI-558 UI-164/UI-564 UI-3013XC 4

5 Camera Global shut- Rolling Rolling with ter global start UI-306 UI-336/UI-536 UI-337/UI-537 UI-359 For more information on configuring and using the different modes, refer to the ueye manual at Authors Patrick Schick, Product Management Marion Gentele, Technical Documentation Contact IDS Imaging Development Systems GmbH Dimbacher Straße Obersulm Germany Phone: marketing@ids-imaging.com Web: IDS Imaging Development Systems GmbH More TechTips and case studies can be found on our website. 5