What is the best way to resize 4k HDR -> 1080p HDR? Are there gotchas?

[Msuix]

All of the post I've seen regarding this talk about 4k HDR -> 1080p SDR w/ tonemapping, etc. I'd like to avoid tonemapping and just shrink down the 4k to 1080p while retaining HDR, but I'm unsure of the effects (if any) on the actual luminance / color after the resize. I read somewhere about "converting the HDR to linear before resizing" to prevent unintended dimming in certain regions, but unsure if its actually a necessary step or how to do that correctly.

I'm aware that I should be reverse upscaling when resizing a 4k source that was originally just upscaled, but for native 4k shot material what are the top few resizers I should be using? I've been using Bicubic for awhile but I've also seen Spline64 recommended on here before.

I'm resizing and encoding with avisynth+ and x265, and passing through the proper master-display info, max-cll, etc. I'm just concerned about unintended mistakes before I start spending these cpu cycles

[davexnet]

This is what I used in Vidcoder. Why don't you run some tests and see?

[ProWo]

You can also try my clever FFmpeg-GUI (x265 encoder only):


[Attachment 57581 - Click to enlarge]