GEGL Panorama Projection for 360 Images in GIMP

The GEGL Panorama Projection filter in GIMP is a dedicated tool designed to facilitate the viewing and editing of 360-degree equirectangular images. This article covers the primary purpose of the filter, how it converts distorted spherical projections into standard flat views, and the essential workflow for retouching panoramas without seam artifacts or optical warping.

The Problem with 360-Degree Equirectangular Images

Standard 360-degree photography produces images using an equirectangular projection, which maps a spherical surface onto a flat 2:1 aspect ratio canvas. While this format preserves full horizontal and vertical visual data, it creates severe stretching and distortion at the top (zenith) and bottom (nadir) of the image. Standard editing tools, such as the Clone tool or Healing brush, cannot be used accurately in these distorted regions because regular brush strokes become warped when the image is viewed back in a 360-degree spherical viewer.

The Core Purpose of GEGL Panorama Projection

The primary purpose of the GEGL Panorama Projection filter is to act as a bridge between the distorted equirectangular canvas and an undistorted, perspective-correct viewport. It allows you to:

  • Navigate the 360 Scene: Adjust parameters such as Pan (horizontal rotation), Tilt (vertical angle), and Field of View (zoom level) to look at any specific part of the sphere as a standard flat image.
  • Edit the Nadir and Zenith: Rotate the view straight down to remove tripods, shadows, or camera mounts, or straight up to fix sky defects and ceiling lights without distortion.
  • Maintain Visual Fidelity: Work with native GIMP painting and selection tools on a flat, rectilinear perspective.

How the Filter Workflow Operates

Using the filter involves a non-destructive round-trip process that lets you modify the image and return it to its original 360-degree format:

  1. Initial Projection: Apply the Panorama Projection filter to rotate and project the target area (such as the tripod at the nadir) into a standard flat perspective.
  2. Editing: Use GIMP's standard retouching tools—such as Heal, Clone, or Inpaint—directly on the flattened view.
  3. Inverse Projection: Re-apply the filter with the inverse settings to map the edited flat perspective back into the proper coordinates of the 2:1 equirectangular canvas.

By handling the complex mathematics of spherical coordinate transformation, the GEGL Panorama Projection filter ensures that all visual corrections seamlessly integrate back into 360-degree virtual tours and VR viewers without creating visible seams or alignment errors.