Also, just because there's a spec for using gainmaps with JPEG doesn't mean that it works well. With only 8 bits of precision, it really sucks for HDR, gainmap or no gainmap. You just get too much banding. JXL otoh is completely immune to banding, with or without gainmaps.
Also, just because there's a spec for using gainmaps with JPEG doesn't mean that it works well. With only 8 bits of precision, it really sucks for HDR, gainmap or no gainmap. You just get too much banding. JXL otoh is completely immune to banding, with or without gainmaps.