On Sun, Feb 24, 2019 at 8:30 AM Julien Hardelin wrote:

Hi devs,

I can't understand the Inverse Transform option in Little Planet and Panorama Projection filters, and can't find any explanation about that on the Internet.

UI pop help tells "useful for touching up zenith, nadir of other parts of panorama": how to manage that, I hardly recognize anything in the inverse transformed image.

Both of these operations only work on equirectangular panoramas that are 360x180 degrees. If you have an incomplete panorama, or want to edit out a tripod in nadir - straight down it is difficult directly on the panorama since the bottom is very distorted and distributed all along the bottom of the panorama image. To create a patch for the panorama image with retouched/edited content with the gegl:panorama-projection operation in GIMP you can do the following steps:

1. duplicate layer
2. panorama-projection, adjust it to point straight down with desired zoom (or in some other direction)
3. perform edits to the transformed view of the projection 4. panorama-projection, but this time recall the previous parameter settings from the history list in the operation dialog, and tick the "inverse transform" option
5. optional, merge/down, flatten image

This inverse transform in the panorama projection op the transform that happens from lens-normalized input images to merged panorama when creating a panorama with for example hugin. For little-planet it might be a little less useful; but having an inverse transform here serves a similar purpose.

/pippin