HDR Image Import

You're making major changes to the color space.

HDR formats have both a much bigger "volume" and range of color hues than is available in Rec.709/SDR work. Plus they have a much bigger dynamic range ... the difference between black and white. So the colors/hues and tones have to be remapped to fit within the Rec.709/SDR space as best as possible.

As a lot of colors of say the HLG/Rec2100 color space don't exist in SDR/Rec.709's sRGB color space, the changes will attempt to remap to the closest hue value.

And the app will also try to remap the wider dynamic range without loosing white or black data. But that of course reduces the total contrast 'range' from black to white, and often at first looks a lot less contrasty. So you may need to add some Contrast ... or alternatively, drop Shadows and/or lift Highlights controls a bit to get a better visual contrast.

Thankfully, once you've done this using the Color workspace's Lumetri panel, you can save that as a Preset then simply drag/drop from the Effects bin over similar clips in the project panel and 'fix' them all in one quick action.

And depending on what options you have set in Premiere for auto-tonemapping, and what those do with different clips from different sources, you should expect slightly to notable different views between clip types.

You might choose to turn off the HDR/HLG recording on the iPhone at this time though. Staying in SDR/Rec.709 is far simpler. HDR is still very much the Wild Wild West of video production. Most pro colorists have yet to deliver a single paid job of HDR, most screens out there don't handle it well if at all.

And it's got more competing "standards" between HLG, PQ, HDR-10, HDR-10+, DolbyVision and some others it seems ... than we had way back in the Betacam vs VHS "battle" days.

Neil