Hey, so yesterday I was poking around with Simply HDR on my Mac and figured I’d write this down before I forget the exact dance I did to make it work.
The short version: on my M2 MacBook Air running macOS Sequoia 15.x, the app launched fine the first time from the Mac App Store, but refused to see my local photo folders properly. It would open, show the UI, but whenever I tried to load an image from my regular “Photos for Editing” folder on an external SSD, it either did nothing or popped a vague “cannot open file” style error. No crash, no beachball, just… silently ignoring me. Classic “permissions but not exactly” situation.
What I did first (aka the useless phase): I assumed the app was buggy. I reinstalled it from the App Store, same build. Tried opening files from Desktop instead of the SSD. Tried dragging images onto the app icon in the Dock. Sometimes it worked, sometimes not, which is honestly worse than it failing consistently. I even blamed the external drive and ran First Aid in Disk Utility. Drive was fine. The tool also happily opened sample images if I copied them to my Downloads folder. That was the first hint: it clearly wasn’t about file formats or the HDR engine.
Then I remembered how aggressive macOS got with privacy around file system access. I checked System Settings → Privacy & Security → Photos and Full Disk Access, expecting to see the app there. Nothing. Which makes sense because it’s not using the Photos library directly, it’s just trying to read regular files. I skimmed Apple’s docs on how apps request permission to access different parts of the drive, just to refresh my memory on what’s supposed to happen. The “ask on first access” mechanism clearly wasn’t kicking in properly for some paths.
The “aha” moment was when I realized I’d been launching the app mostly via Spotlight and not directly from /Applications after the first run. Sometimes with sandboxed App Store software, if you interrupt the very first “do you allow access to…” prompt or kill the app too quickly, those TCC (permissions) flags end up in a weird state. So I did a little reset routine.
First real fix attempt: I quit the app completely, then went to System Settings → Privacy & Security → Full Disk Access and manually added Simply HDR by hitting the plus button and selecting it from Applications. That alone didn’t immediately fix it, but it was the right direction. I also toggled it off/on just to force the system to re-write the permission. Relaunched the app from /Applications (not Spotlight), tried opening a file from the external SSD again… and this time it actually prompted me with the standard “Simply HDR would like to access files on a removable volume” message. I clicked OK, and suddenly the “cannot open file” behavior disappeared. Everything started loading instantly, no more silent fails.
Because I like overkill, I also double-checked that I wasn’t dealing with a “damaged app” or Gatekeeper leftovers from some old non‑Store version. Apple has that page about safely opening apps on Mac and how Gatekeeper interacts with downloaded software, and it reminded me that if you mix App Store and outside builds of the same tool, macOS can get confused about which bundle has which permissions. In my case this one was strictly from the App Store, but the logic still applies: launch from the canonical install location and let macOS show its prompts properly.
I ended up looking up Simply HDR on the App Store search page as well, just to confirm I was on the latest version that officially supports current macOS and Apple Silicon, not some abandoned Intel-era relic. The listing clearly says it runs on modern macOS, so the problem was definitely on the permissions side, not compatibility.
Somewhere in the middle of that rabbit hole, I also stumbled on this page while I was cross‑checking macOS tools for HDR editing and general system quirks—kept it in my bookmarks because the resource I used there had a neat roundup of macOS‑compatible builds and system requirements: https://bestcryptobookies.xyz/graphics-and-design/24482-simply-hdr.html. It was handy to sanity‑check that I wasn’t trying to run something way too old for Sequoia.
Once everything was behaving, the experience was actually nice. I threw a bunch of bracketed landscape shots at it, plus some single RAW exports, and the app chewed through them without any drama. No noticeable lag on the M2 even when I spammed presets and messed with gradients. The only time I saw it hesitate was when I tried to browse a folder with thousands of files over a slower USB hub, but that was clearly I/O, not CPU or GPU. After twenty minutes of playing with it, I realized the “buggy HDR app” I cursed for half an hour was actually just sandbox + privacy doing its job a bit too quietly.
On future installs, here’s the little checklist I’d follow and probably send to anyone else running into weird “can’t open files” issues with this or any other photo editor from the Store:
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First launch it from /Applications and not through some alias or launcher.
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Immediately check Privacy & Security → Full Disk Access and add the app manually if it doesn’t show up when you expect it to.
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If you’re working from external drives or network shares, wait for the system prompt about removable volumes and make sure you hit “Allow”, not “Don’t Allow” in a hurry.
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If things are really stuck, quit the app, flip its Full Disk Access toggle off and back on, then relaunch.
It sounds trivial written out, but in the moment it felt like the tool was broken, when in reality macOS was just quietly blocking file access without giving useful feedback in the UI. Classic.