SUMMARY As the title says Gwenview doesn't show HDR images as HDR but as if they are in SDR. Tested with these: https://github.com/MishaalRahmanGH/Ultra_HDR_Samples/tree/main/Originals Coincidentally windows photo app can't do this either.
(In reply to Matej Mrenica from comment #0) Would you consider https://krita-artists.org/t/hdr-pngs-are-rendered-by-all-but-krita-at-50-opacity/92058?u=beedellrokejulianloc to be an example of this?
The images are loaded by the Qt plugin. It must be the first to support the HDR format in JPGs. I tried to load the JPGs you indicated with Qt 6.8 and the plugin returns 8-bit images (therefore SDR). The only Qt plugin that supports* HDR images I believe is TIFF (FP). The EXR, HDR, JXR and PFM formats from KImageFormats will support HDR images when MR !232 is merged (https://invent.kde.org/frameworks/kimageformats/ -/merge_requests/232). (*) "supports" means that FP data outside the 0-1 range is loaded and saved correctly and ICC conversions are possible. Not having an HDR monitor I have no idea if this is enough.