How to add a 2D texture to an Equirectangular image - theory

Question

I have a 2D texture like some text and want to add it to an equirectangular image without it being distorted as it would be if I just paste it on top.
To clarify:
I have a 2D texture:
I have an equirectangular image (source):
if I just put the 2D texture on top in a 360 degree viewer it will look distorted so how do I get around this and convert it to an equirectangular texture? any help is greatly appreciated :)

Answer 1

I use this Windows Shell/DOS script, but there are some caveats, see below:
:: Parameters:
:: 1: source equirectangular image
:: 2: folder of the image
:: 3: yaw of the point of interest
:: 4: pitch of the point of interest
#set LOGL=error
Rem Inserts strings into the command environment. The set values
Rem can be used later by programs.
::----------- Extract image section ------------
#echo.
#echo Centering image on desired point...
ffmpeg -hide_banner -loglevel %LOGL% -i %2%1 -vf v360=e:e:yaw=-%3:pitch=-%4 -y %2test_equi_rotated-%1
#echo.
#echo Extracing region to edit...
ffmpeg -hide_banner -loglevel %LOGL% -i %2test_equi_rotated-%1 -vf v360=e:flat -y %2test_crop_flat-%1
#echo.
#echo Please write your text onto "test_crop_flat-%1"
#echo.
#set /p=Hit ENTER to continue...
::-------- Convert edited extracted section back to equirectangular ---------------
#echo.
#echo Converting crop+text back to equirectangular...
ffmpeg -hide_banner -loglevel %LOGL% -i %2test_crop_flat-%1 -vf v360=flat:e -y %2test_crop_equi-%1
#echo.
#echo Please save "%2test_crop_equi-%1" with transparency
#echo.
#set /p=Hit ENTER to continue...
::--------- Overlay edited extracted section on original image --------------
#echo.
#echo Merging edited crop into rotated image...
ffmpeg -hide_banner -loglevel %LOGL% -i %2test_equi_rotated-%1 -i %2test_crop_equi-%1 -filter_complex "overlay" -y %2test_merge_rotated-%1
#echo.
#echo Rotating the image back to original direction:
ffmpeg -hide_banner -loglevel %LOGL% -i %2test_merge_rotated-%1 -vf v360=e:e:yaw=%3:pitch=%4:roll=2.1 -y %2test_merge-%1
#del %2test_merge_rotated-%1
#echo.
#echo Output saved in "test_merge-%1"
Example usage:
overlay.bat test-base.png .\ 10 10
Script is divided in 3 parts:
Extract from original ER image the region of interest and convert to flat projection
After this part the script stops, waiting for user to edit the extracted image at wish.
Reproject the edited section into equirectangular
After this part the script stops, waiting for user to save the temporary output adding transparency to image (I don't know how to do it with ffmpeg).
Paste the section back on the original image
Warning: I had to add a small roll to the final image, else upon converting back to equirectangular it appears slightly rotated, don't know why.