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Photo Culling Undo, Rewind, and Crash Recovery Guide

By Ingo D ·

You come home from a wedding with 2,000 RAW frames on your NAS. You need to cut that down to 80 keepers before your editor can start. You open your culling app, settle into the sofa, and start swiping. Two hundred frames in, your thumb slips and you accidentally reject a shot the bride will love. Four hundred frames later, a phone call pulls you away. When you return, the app has restarted and your place in the session is gone. That fear of losing progress is why many photographers still cull at their desk, tethered to Lightroom, even though it is the slowest part of their workflow.

Photo culling undo, rewind, and crash recovery are not luxuries for high-volume shooters. They are trust mechanisms. Without them, every tap carries risk, and every interruption costs time. This guide explains how CullKit handles those risks so you can cull 2,000 frames without fear, whether you are on a Synology NAS, a QNAP share, or a local folder on your Mac.

Why does culling 2,000 frames feel so risky?

Long culling sessions are psychologically different from quick reviews. When you are working through a wedding, an event, or a week-long travel shoot, the session can last 30 to 60 minutes. During that time, accidents happen. You might tap the wrong button while holding the iPad at an angle. You might reject a frame because the thumbnail loaded slowly and you misread it. Or you might simply change your mind five frames later and want to walk back a decision without starting the whole session over.

The second risk is interruption. A message pops up. The battery warning appears. The app crashes because the OS reclaimed memory. On many culling tools, that means your session state is lost. You have to remember where you were, scroll back, and re-establish context. For a 2,000-frame wedding, that friction is enough to make you postpone the job until you are back at your desk.

The third risk is metadata loss. If ratings are stored only in a local app database that never syncs, a crash does not just cost time; it costs decisions. Every star, flag, and label you assigned vanishes. You are left with a folder of unmarked RAW files and a vague memory of what you intended to keep.

CullKit is built to remove all three risks. It treats undo, rewind, and crash recovery as core infrastructure, not afterthoughts.

How do I start a culling session in CullKit?

Before you can use undo or crash recovery, you need to enter a culling session. CullKit does not force you to rate one image at a time in a grid. Instead, it opens a dedicated full-screen session from any folder or album. The session isolates your work, tracks your progress, and creates the state that undo and recovery can restore.

Follow these steps to start:

  1. Open CullKit on your iPhone, iPad, or Mac and connect to your photo library. If you use a Synology NAS, browse to smb://diskstation.local/photo or enter your DiskStation IP directly. For a QNAP device, connect to \\<NAS-IP>\Multimedia or the equivalent SMB path. TrueNAS users can mount smb://<TrueNAS-IP>/photos, and UGREEN NAS owners typically use smb://<UGREEN-IP>/UGREEN. If your files are on a Mac folder or external SSD, simply choose the local folder instead.

  2. Navigate to the folder that contains your shoot. CullKit shows a grid with rating overlays and colour-label dots, so you can see what is already marked before you begin.

  3. Tap the Start Culling Session button. You will see three entry options: start from the beginning, start from a filtered view (for example, only unrated frames), or resume a previously interrupted session if one exists.

  4. The session opens in full-screen mode. On iOS, swipe right to keep or pick a frame, swipe left to reject it, and tap the star bar to assign 1 to 5 stars. On macOS, use the number keys for star ratings, P to pick, X to reject, and the arrow keys to move forward and back.

  5. As you rate, CullKit writes decisions to a local session log and, if you are on a NAS or local folder, begins writing XMP sidecar files in the background. Your progress is never held only in memory.

CullKit is an independent product. It is not affiliated with or endorsed by Synology Inc., QNAP Technologies, Inc., TrueNAS / iXsystems, UGREEN Group, Adobe, or Capture One. It connects to storage via standard SMB or local folder access, the same way any other file client does.

How does undo and rewind work in CullKit?

CullKit offers two ways to walk back a decision, depending on how far you need to go.

Immediate undo appears as a snackbar at the bottom of the screen for a few seconds after every action. If you accidentally reject a keeper, tap Undo before the snackbar disappears and the frame reverts to its previous state. The undo buffer covers the last action only, so it is perfect for slips and mis-taps. It does not require a network round-trip because the previous rating is held in the local session state.

Rewind is for bigger mistakes. If you realise you misjudged a sequence of ten frames five minutes ago, you can open the session timeline and scroll back to any previous decision. Tap a frame in the timeline and choose Rewind to here. CullKit restores every rating, flag, and label from that point forward to the state it was in before you reached it. You do not lose the work you did before the rewind point; only the subsequent decisions are cleared.

Both undo and rewind work offline. If you are culling on a train with no signal, or your NAS Wi-Fi drops briefly, the actions are queued locally and reconciled when the connection returns. Your session state is stored in the app’s local SwiftData cache, not on a remote server, so there is no latency and no risk of a network failure swallowing your undo history.

For a wedding photographer reviewing 2,000 frames, this means you can cull aggressively. Reject freely, star generously, and trust that a mistake costs one tap to fix, not an hour of re-review.

What happens if CullKit crashes mid-session?

Apps crash. iOS terminates background processes when memory runs low. macOS restarts after an update. The question is not whether an interruption will happen, but whether your work survives it.

CullKit persists culling session state automatically. Every rating, flag, label, and navigation position is written to a local recovery log at intervals of a few seconds. If the app is forced closed, if your iPad battery dies, or if the OS reclaims memory while you switch to answer a call, the session is not lost.

When you reopen CullKit, it checks for an interrupted session. If one exists, you see a Resume Session prompt that tells you the folder name, how many frames you have already rated, and the timestamp of the interruption. Tap Resume and you return to the exact frame you were reviewing, with every decision intact. Tap Discard only if you genuinely want to start over.

This crash recovery applies to all storage types. Whether you are culling from a Synology NAS at smb://diskstation.local/photo, a QNAP share at \\<NAS-IP>\Multimedia, a TrueNAS pool, a UGREEN device, or a local folder on your Mac, the recovery log lives on your device. Your NAS does not need to support session state; CullKit handles that locally.

One caveat: if you manually delete the app or clear its device data, the recovery log is removed. Ratings that were already written to XMP sidecars on your NAS or in your local folder are safe, but the session position itself is gone. For that reason, we recommend enabling XMP writing in Settings so every decision is persisted to your files as you go, not just to the session log.

How does CullKit compare to Photo Mechanic and Lightroom?

Photo Mechanic and Adobe Lightroom are the two tools most photographers know, so it is worth comparing how they handle undo, session safety, and NAS workflows.

Photo Mechanic is fast and keyboard-driven, and it offers an Ingest-and-Apply workflow that many pros rely on. However, it is desktop-only. You cannot run it on an iPhone or iPad, and it does not connect to a NAS without first copying files to a local working volume. It also does not have a dedicated session-resume feature for interrupted culls; if your Mac restarts, you reopen the folder and manually find your place. Photo Mechanic is a powerful tool, but it keeps you at your desk.

Lightroom Classic has flags, stars, and colour labels, and it can read XMP sidecars. However, it is not designed for NAS culling. To rate photos that live on a Synology or QNAP NAS, you must first import them into a Lightroom catalogue, which copies or references them from a local drive. There is no crash recovery for a culling session because Lightroom does not think in sessions; it thinks in catalogues. If Lightroom crashes, your ratings are safe in the catalogue, but you have already paid the import tax.

CullKit sits between your NAS and your editor. It is native on iPhone, iPad, and Mac. It reads directly from SMB shares and local folders with no import step. It writes XMP sidecars so Lightroom and Capture One inherit your ratings automatically. And it offers undo, rewind, and crash recovery as first-class features, not workarounds. For a photographer who wants to cull 2,000 frames on the sofa, on a train, or in a hotel room, CullKit is the only option that combines mobility, storage-neutrality, and session safety.

If you are curious how the Pro tier pricing works, you can see the current plans on our pricing page. Every subscription includes the full undo, rewind, and recovery stack.

How do my ratings get into Lightroom or Capture One?

Undo and crash recovery protect your session. XMP sidecars protect your metadata. Together they mean your decisions survive both app crashes and tool changes.

CullKit writes every star rating, reject flag, colour label, and tag to an XMP sidecar file stored alongside your RAW image. If you shoot RAW plus JPEG, CullKit follows the Lightroom convention and writes a single sidecar that covers both files. The XMP format is an open standard, which means Lightroom Classic, Lightroom CC, Capture One, and Darktable all read it natively.

To move your culls into your editor:

  1. Finish your CullKit session. You can confirm completion by tapping End Session and reviewing the batch summary, which shows how many frames were kept, rejected, and starred.

  2. Open Lightroom Classic and navigate to the same folder on your NAS or local drive. If the folder is already in your catalogue, select it and choose Metadata > Read Metadata from Files. Lightroom scans the XMP sidecars and updates each image with the ratings and flags you assigned in CullKit.

  3. In Capture One, import the folder or refresh the existing album. Capture One reads XMP sidecars on import and updates its rating fields automatically.

  4. If you use Darktable, the sidecars are read at startup or when you force a metadata rescan. Your star ratings appear in the image information panel.

Because the metadata lives in the sidecar, not in a proprietary database, you can switch between CullKit, Lightroom, and Capture One without losing decisions. Your culls are portable. For photographers who worry about vendor lock-in, this is a genuine advantage.

If you have questions about whether your photos are ever uploaded anywhere, see the FAQ. The short answer is no: CullKit is 100 percent local, and your files never leave your devices or your NAS.

Troubleshooting: undo, recovery, and XMP issues

Even with robust safeguards, occasional questions come up. Here is how to handle the most common ones.

The undo snackbar disappeared before I could tap it. Undo is designed for immediate slips and only covers the very last action. If you missed the window, use the session timeline to rewind instead. Open the timeline from the culling session toolbar, scroll to the frame you want to revert, and tap Rewind to here. This clears all decisions from that point forward, letting you re-rate the sequence.

CullKit did not offer to resume my session after a crash. This usually happens for one of three reasons. First, you may have opened a different folder or storage source than the one you were culling. Crash recovery is tied to the specific folder path. Second, if you were using Demo Mode, session state is not persisted across launches because demo data is regenerated each time. Third, if you force-quit the app and immediately reopened it, the OS may not have finished writing the recovery log to disk. Wait a few seconds before relaunching.

Lightroom does not see my ratings. Check three things. First, open CullKit Settings and confirm that XMP Writing is enabled and set to the correct scope (RAW only, all formats, or all formats with embedded updates). Second, in Lightroom Classic, ensure you have chosen Read Metadata from Files rather than expecting Lightroom to poll automatically. Third, verify that your NAS account has write permissions to the photo folder; if CullKit could not write the sidecar, there is nothing for Lightroom to read.

The rewind point is further back than I expected. Rewind restores the state at the chosen frame, which means all decisions after that frame are cleared. If you only want to change one frame deep in the session, it is often faster to exit the session, find that frame in the grid, and edit its rating directly rather than rewinding the entire tail of the session.

My NAS connection dropped during a session and some ratings seem missing. CullKit queues rating changes locally when the network is unavailable. If the connection does not return before the session ends, those queued changes are written as soon as the share is reachable again. If you manually disconnected or changed Wi-Fi networks, reopen the folder and wait a few moments for the sync indicator to clear before closing the app.

Your safety net for high-volume culls

When you are staring down a 2,000-frame wedding, the tool you choose is not just about speed. It is about trust. You need to know that a slip of the thumb will not cost you a keeper, that a phone call will not erase your place, and that a crash will not send you back to frame one.

CullKit gives you that trust. Undo catches the accident. Rewind fixes the sequence. Crash recovery brings you back exactly where you left off. And XMP sidecars make sure your decisions are waiting in Lightroom or Capture One when you are ready to edit.

Ready to cull without fear? Download CullKit from the App Store and try a 2,000-frame session with the safety of undo, rewind, and crash recovery built in. Your first seven days are free.

Download CullKit on the App Store

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