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Resolution and frequency of line scan cameras

With a line scan camera, the resolution in the X direction is physically determined by the sensor. The resolution in the Y direction is variable and is determined by the line frequency. Ideally, the user chooses a line frequency that produces a distortion-free image in both the X and Y directions.

These calculations are used to determine the correct resolution and line frequency of a line scan camera. Both specifications are important when purchasing the correct line scan camera.

Tip:

An online wizard to calculate the line scan frequency can be found in the Service section.

Example calculation for a line scan camera

  • With a bandwidth of 550mm (camera field of view in X direction)
  • and a conveyor speed of 4 metres per second,
  • an accuracy of 0.3 mm per pixel should be
    should be achieved.

Calculation of the resolution in lateral direction:

    • Bandwidth = 550mm
    • Resolution X= 0.3 pixels/mm
    • Pixels required = 550mm / (0.3mm/pixel)=1833 pixels

    A minimum of 1833 pixels is therefore required to meet the specification. Typical resolutions for line scan cameras in machine vision are 1024, 2048, 4096, 8192 or 12288 pixels. The 2K line scan camera therefore slightly exceeds our specification of 0.27 mm accuracy per pixel.

     

    Line scan frequency calculation:

    For practical software reasons, the generated image should normally be undistorted. Of course, it would be possible to generate a much higher resolution in the transport direction. This is only determined by the frequency of image acquisition of a single line.

    • Undistorted image: resolution in X-direction = resolution in Y-direction
    • Resolution = 0.27 pixels
    • Transport speed T = 4000 mm/sec
    • Sampling rate F = T / A = 14800 Hz

    Result:

    In our example, a line scan camera with a resolution of 2K and a line frequency of approx. 14.8KHz can solve the task.

    Important: Please use an incremental encoder on the conveyor belt. This is the only way to ensure that an undistorted image with the same resolution in the direction of travel can be recorded when the belt speed changes (acceleration, deceleration, synchronisation fluctuations).

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