This photo doesn’t look right when exported from Lightroom Classic

For some reason, this photo, which was shot on an iPhone 15 Pro Max, doesn’t look right when I export it as a JPG from Lightroom Classic (desktop) and view it again on an iPhone. It looks more flat and muted, and generally not as nice. In fact, if you view this image outside of Apple Photos, Camera, or Instagram, I’m not sure it will look right to you either (it depends).

Now, ideally I would carefully control for all variables, and try different experiments to see which variables matter. But I don’t have time for that (although I did try a few combinations willy-nilly).

Scientific method notwithstanding, my best guess is this related to Apple’s HDR features: that they encode HDR info in JPGs (presumably as metadata), and Instagram preserves this metadata, so viewing the image from Instagram still looks right (in addition to viewing it from Apple’s Camera or Photos apps). But viewing that same image in a mobile browser, Safari or Chrome (which shouldn’t matter since AFAIK Chrome uses Safari’s rendering engine), looks flat and muted as mentioned above. Which is weird because you’d think Apple’s web engine would support it, but maybe not.

This support page indicates that phones newer than iPhone 12 use HDR and it can’t be manually turned off anymore. And this Apple dev page describes an HDR Gain Map. It wasn’t clear from that page if Apple stores their metadata as EXIF, but when I check metadata using exiftool, I don’t see metadata keys for HDRGainMapVersion or MakerNote. I would have to try the Apple sample code to be sure.

That said, the EXIF metadata does suggest a number of HDR features via keys that are present in the Apple-generated JPG but not in the Lightroom-generated JPG (even when I enabled HDR editing and enable HDR output in the Lightroom JPG export). Whether these features are an HDR gain map, or another HDR functionality set, isn’t clear, but I would have to assume the latter.

The keys of interest are:

• Photometric Interpretation of Linear Raw
• HDR Headroom and HDR Gain values
• A number of keys related to MPF (Multi Picture Format), which indicate 3 images. I would presume those are the HDR images at different exposures rather than a gain map. But I could be wrong, maybe one of them is in fact a gain map.

These keys aren’t present in the Lightroom export JPGS (w/ or w/o HDR output enabled). Although, I’d have to check key by key to be absolutely sure.

Given the Photometric Interpretation is Linear Raw, that is, non-gamma corrected data, I wonder if the muted color comes from this. That is:

• The data is Linear Raw, even in the JPG produced by Apple from the DNG.
• Lightroom Classic sees the Photometric Interpretation key and correctly applies a gamma, so the image looks right in Lightroom.
• But, when the image is exported, it just exports the original data as-is, doesn’t apply any gamma correction, and loses the photometric interpretation key, so basically the ungamma corrected data is displayed henceforth and that’s why it looks all flat.

That seems plausible but I haven’t thought deeply about gamma correction in a while so I’d have to work through an example to make sure it all hangs together.

This post is basically raw notes, apologies if it’s hard to follow. Although this experience dissuades me from doing much more photography on an iPhone if the results are so finicky to get right, and so markedly inconsistent. Or rather, maybe I need to find a 3rd-party camera app that doesn’t do the HDR trickery.