Calculating Field of View (FoV) using distance settings

Owned by Henry Koren
Last updated: Feb 27, 2024 by Jackson Knappen
2 min read

Field of view (FoV) estimation is available in Imatest for SFRplus, eSFR ISO, and Checkerboard analyses.

Imatest’s FoV calculation requires the user to enter two physicals distances in the “More Settings” window.

checkerboard_FOV_settings.png
Checkerboard FoV calculation relies on the user-entered square size and lens-to-chart distance. FoV calculation also relies on the fitted distortion model.

For all chart analyses, the user must enter the lens-to-chart distance.

The user must also enter the size of a physical element on the chart, which varies depending on the type of chart:

  • For checkerboard analysis, the user must enter the size (spacing) of the squares on the chart.

  • For SFRplus analysis, the user must enter the bar-to-bar height (the black bars on the chart) which should be measured from the top of the top bar to the bottom of the bottom bar on the chart.

  • For eSFR ISO analysis, the user must enter the vertical distance between the registration marks on the chart.

Imatest’s FoV calculation uses the fitted distortion model in combination with the detected size of the physical chart element (e.g., for checkerboard, this is the size of a central checker measured in image space). The fitted distortion model is used to calculate the undistorted radius (in pixels) at the top/bottom, left/right sides, and corners of the image with respect to the numeric image center. These correspond to the vertical, horizontal, and diagonal FoV limits. Then, the size of the the physical chart element in image space is used to relate the undistorted radii to physical distance. Finally, using the two physical distances entered by the user, the FoV limits are converted into degrees by applying trigonometry.

  • Note: FoV results can vary depending on the selected distortion model (and the resulting fitted distortion model).

  • Note: FoV results can vary depending on the alignment of the chart in the image. The chart should be centered in the image and perpendicular to the camera’s optical axis.

  • Note: Imatest’s FoV calculation assumes that the distortion in the center of the image is near zero and that the optical distortion is radially symmetric.