GIMP Panorama Projection Filter for 360 Images

This article explains the function of the GEGL Panorama Projection filter in GIMP, specifically detailing how it enables users to view, navigate, and edit spherical equirectangular panoramas. You will learn how the filter reprojects distorted 2D panoramic maps into standard perspective views, how panning controls work, and how this process facilitates seamless retouching of 360-degree photography.

Understanding the Equirectangular Format

A spherical panorama is typically stored as an equirectangular projection with a 2:1 aspect ratio. In its raw 2D state, the image suffers from extreme distortion, particularly at the north and south poles (the zenith and the nadir), while straight lines appear curved. Because of this distortion, directly painting, cloning, or retouching specific areas—such as removing a tripod from the ground—is nearly impossible using standard image manipulation tools.

The Core Function of Panorama Projection

The GEGL Panorama Projection filter (Filters > Map > Panorama Projection) solves this problem by mapping the flat 2D image onto a virtual 3D sphere and projecting a perspective-corrected viewpoint back onto the canvas. Instead of seeing the stretched, unwrapped panorama, the user sees a natural, rectilinear view similar to what a human eye or a standard camera lens would capture from the center of the scene.

Panning Around the Sphere

The primary interactive function of the filter is allowing directional navigation across the sphere using three main coordinate controls:

  • Pan (Yaw): Rotates the virtual camera horizontally 360 degrees, allowing you to scan left and right across the horizon.
  • Tilt (Pitch): Tilts the camera up toward the sky (zenith) or down toward the ground (nadir) by up to 90 degrees in either direction.
  • Spin (Roll): Rotates the camera along its viewing axis to level horizons or adjust the tilt.
  • Field of View (Zoom): Adjusts the virtual focal length, allowing you to zoom in on fine details or widen the perspective to see more of the environment.

The Round-Trip Retouching Workflow

Beyond simple viewing, the primary utility of the Panorama Projection filter in GIMP is enabling localized image editing through a two-step transformation:

  1. Reprojection: Apply the filter with a specific tilt and pan value (for example, setting Pitch to -90 degrees to point the camera directly at the ground where a tripod shadow sits). The polar stretching vanishes, presenting the ground as a flat, undistorted surface.
  2. Editing: Use standard GIMP tools—such as the Clone tool, Heal tool, or Inpainting—to remove artifacts, blemishes, or camera equipment on the undistorted plane.
  3. Inverse Reprojection: Open the Panorama Projection filter again, check the Inverse option, and apply the exact same coordinate settings used in step one. The filter warps the rectilinear edit back into the equirectangular format, seamlessly integrating the fix without visible seams or alignment errors.