Defishing Fisheye Images Excessively to Flatten the Curved Horizon

Defishing is a process for removing barrel distortions from fisheye images, producing rectilinear images that preserve straight lines. A different fisheye lens produces a different amount of distortion & needs a different defishing strength.

Flat-Earthers like to apply a stronger defishing parameter than necessary with the goal not to remove the distortions but to make the horizon flat. As a result, they not only remove barrel distortion from the image but also introduce pincushion distortion that straightens the curved horizon.

The horizon in the end image might appear flat. However, it is due to the distortion these flat-Earthers deliberately introduced to the image, not because the horizon is flat.

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Magnitude of Visible Earth’s Curvature in a Photograph

The magnitude of the curvature that appears in a photograph of Earth’s curvature depends on several factors:

  1. The observer’s altitude.
  2. The camera’s field of view or focal length.
  3. The distortion characteristics of the camera lens.

Flat-Earthers like to dismiss a photo of Earth’s curvature by comparing it to another photo showing a different amount of curvature. In reality, to compare the visible curvature, we need to ensure all the images were taken from the same altitude, same field of view, and account for the lens’ distortion.

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Fisheye Videos

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In images taken using a fisheye lens, a straight line will remain straight if it crosses the center of the image. We can use this attribute to determine if a line is straight in reality.

In any fisheye videos taken from a high altitude, there should be plenty of moments where the horizon crosses the center of the image, and we can use those to determine that the horizon line is curved in the real world.

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