markmccaughrean, 
Interesting 🤔
Was able to build a huge (21,000 x 14,400 pixels) colour composite of five different #JWST filter mosaics in PhotoShop & export fine to a PNG.
Importing to LightRoom for some post-processing all fine too, as was the tweaking.
But now exporting the final image from LR is taking f o r e v e r . . . 😱
p.s. hopefully you’ll agree that the image is amazing … if it ever saves 😬