HEIFs are about 1/3rd the file size of PNGs, which are the smallest lossless files Ultra Fractal can write.
I’m converting the PNGs to HEIFs with another app but it doesn’t batch-process very well. It’d be sweet to have lossless HEIF right from UF. Even better if the files are saved with the .heif extension not .heic because Final Cut Pro and other apps don’t recognize .heic files.
Edit for clarity: HEIF is a container which can hold various kinds of image data (even JPEG), but the objective here is a lossless HEIC/HEVC encoded image inside a .heif file.