Re: [Gimp-developer] Inverse Transform option

On Sun, Feb 24, 2019 at 8:30 AM Julien Hardelin <jm hard wanadoo fr> 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

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.


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