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How to Cull Photos on an iPhone: Rate and Reject Fast

By Ingo D ·

You finish a shoot. Your memory card has 1,200 frames on it. The laptop is back at home. But your iPhone is in your pocket. Most photographers do not think of their phone as a culling tool. It is a camera, a gallery, a messaging device. But it is also a fast, always-available screen connected to the same local network as your NAS or the same USB-C port as your external SSD. The hardware is ready. The missing piece has been software that can rate, reject, and write that metadata somewhere an editor understands.

CullKit turns the iPhone into a culling station that produces real XMP sidecar metadata. You connect to your Synology or QNAP NAS over Wi-Fi, plug in a USB-C SSD, or browse a local folder. You swipe through frames one-handed. You finish the session and every star rating, reject flag, and colour label you assigned is written to XMP sidecars alongside your RAW files, ready for Lightroom, Capture One, or Darktable on your desktop. The hour of desk culling disappears into the gaps in your day.

Why cull photos on an iPhone instead of a laptop?

The laptop is where editing happens. It is not necessarily where culling should happen. Three practical factors tip the balance towards the iPhone.

First, the iPhone is always with you. After a shoot, you copy your cards to a NAS or an SSD and you can start culling immediately: on the train, in a cafe, on the sofa while dinner cooks. You do not need to be at a desk. You do not need to open Lightroom. You do not need to wait for previews to generate for frames you will reject in the first pass anyway. The culling step moves into the spare minutes of your day rather than consuming a dedicated evening at the computer.

Second, the iPhone interface is direct. You touch the frame you are judging. Swipe right to keep, left to reject. There is no trackpad or mouse between your decision and the action. For a fast first pass that rejects obvious discards (blinks, misfires, the fourth near-identical frame in a burst), the thumb-swipe gesture on a phone is as fast as the keyboard shortcut P-to-pick on a laptop, and the physical posture is less fatiguing because you are not hunched forward at a screen.

Third, CullKit writes portable metadata. When you rate inside Lightroom, those ratings are locked to the catalogue. When you rate inside CullKit on your iPhone, the ratings go directly into XMP sidecar files in the same folder as your RAW images. Every desktop editor that reads XMP sees them. Your culling session produces metadata that belongs to the files, not to an app. That portability is what makes a phone culling session useful: it feeds the rest of your workflow rather than starting a separate silo.

CullKit is an independent product. It is not affiliated with or endorsed by Synology Inc., QNAP Technologies, Inc., TrueNAS / iXsystems, UGREEN Group, or Adobe (Lightroom). It connects via standard protocols: SMB for NAS shares, the Synology Photos API for Synology devices, and local file access for folders and SSDs.

How do I set up CullKit on my iPhone for culling?

The setup depends on where your photos live. CullKit works with four storage configurations on iPhone, and the initial connection takes under a minute.

Synology NAS (Synology Photos). Open CullKit and select Synology Photos as the source. Enter your QuickConnect ID or the local IP address of your DiskStation (for example, 192.168.1.50), plus your Synology account username and password. CullKit browses your Personal Space, Shared Space, and Albums, presenting your library the way Synology Photos organises it. Ratings are written both to the Synology database and to XMP sidecars on the NAS.

Any NAS over SMB (QNAP, TrueNAS, UGREEN, Asustor). Choose the SMB / NAS source type. Enter the share address manually (for example smb://192.168.1.100/Multimedia for a QNAP NAS or smb://192.168.1.200/photo for a TrueNAS share) or let Bonjour auto-discovery find it on your local network. Supply your NAS username and password. CullKit connects directly over the local network; no traffic goes through a cloud server.

External SSD or USB-C drive. Connect the drive to your iPhone’s USB-C port. CullKit detects it through the iOS file system. Select your shoot folder and start culling. This is the fastest setup because there is no network latency, and it works anywhere, including locations with no Wi-Fi or mobile signal.

Local folder on your Mac. If your workflow involves copying cards to a working directory on your Mac, point CullKit at that folder over the local network. The Mac and the iPhone must be on the same network and file sharing must be enabled on the Mac.

For first-time setup, CullKit saves your connection details. The next time you open the app, your NAS shares and recently used folders appear on the home screen. Connecting takes one tap.

How does the iPhone culling session actually work?

The culling session on iPhone is a full-screen, gesture-driven view designed for speed and minimal decision friction.

Start the session. Open your shoot folder. CullKit shows a thumbnail grid. Pinch to zoom the grid: zoom out to see many frames at once for a fast visual scan, zoom in to enlarge thumbnails for a closer look. Tap the culling button to enter the full-screen culling mode, which queues every unrated image in sequence.

Rate as you go. Each frame fills the iPhone display. Swipe right to keep. Swipe left to reject. Below the image, a quick-access bar holds star ratings (1 to 5), colour labels, a flag toggle, and a skip button. You can configure what each swipe direction does: one for a 1-star rating, another for reject, a third to clear. Auto-advance moves to the next frame the moment your gesture registers, so your thumb never needs to leave the rating zone.

Work in passes. A fast first pass rejects the obvious discards: blinks, lens-cap shots, test frames, duplicates. On an 800-frame folder, this pass takes about 20 minutes on iPhone, moving at roughly two to three seconds per frame. A second pass adds star ratings on the survivors, which takes another 10 to 15 minutes. You finish with a fully rated set of keepers.

Finish and write metadata. When you complete the session, CullKit writes an XMP sidecar alongside every rated RAW file on your NAS, SSD, or local folder. The sidecar contains your star rating, reject flag, colour label, and any tags. Rejected frames remain in place, unrated. Nothing is moved, nothing is deleted automatically, and nothing is uploaded.

If the session is interrupted (low battery, incoming call, app backgrounded), crash recovery restores your exact position when you return. No progress is lost, and no frame needs to be re-rated.

How does one-handed culling work on an iPhone?

The iPhone’s form factor makes one-handed use practical, and CullKit’s culling interface is designed around it. The swipe zone covers the centre of the screen, reachable with your thumb while holding the phone in one hand. The quick-access rating bar sits at the bottom of the display, within thumb reach. The controls are spatially stable: keep is always right, reject is always left, and the action bar is always at the bottom. You do not need to adjust your grip to reach different areas of the screen.

This one-handed design matters for real-world use. You can cull while standing on a crowded train holding a rail with your other hand. You can cull while holding a coffee. You can prop the phone on a table with a simple stand or a folio case and use one finger to swipe, without the arm fatigue that comes from holding a larger device at eye level for an hour.

For photographers who want more precision after the first pass, the star rating bar is designed for a tap, not a drag. Tap the star you want; the rating registers immediately. There is no slider to fumble with, no dropdown to open. The fewer interface elements between your decision and the action, the faster the session moves.

Can an iPhone handle RAW files for culling?

Yes. CullKit reads and displays RAW files from your NAS or SSD at full resolution on iPhone. Progressive loading shows a usable preview immediately while the full-resolution detail resolves over a second or two, depending on the file size and network speed. For culling decisions (sharpness, composition, exposure), the progressive preview is sufficient within moments, and the full detail follows quickly enough for critical sharpness checks.

RAW and JPEG pairs are grouped and reviewed as a single frame. If you shoot both formats simultaneously, you see one frame per shot, not two. The sidecar written after the session covers the pair. This follows the Lightroom convention: one sidecar for a RAW+JPEG pair, no conflicting ratings.

HEIC files, video files (.mp4, .mov), and Live Photos all render in the same culling session. A video preview plays inline in the grid and in the full-screen viewer. Live Photos show the key frame with the short video clip playing on tap. You can rate and reject video frames and Live Photos the same way you rate stills, and those ratings are written to sidecars alongside the files.

Where do my photos need to live for iPhone culling?

CullKit does not require your photos to be on the iPhone’s internal storage. It works as a remote viewer and rating tool, connecting to your library wherever it lives.

The storage options are the same as for iPad and Mac: Synology NAS (via Synology Photos API or SMB), any SMB-compatible NAS (QNAP, TrueNAS, UGREEN, Asustor), an external SSD plugged into the iPhone’s USB-C port, or a local folder on your Mac. The difference on iPhone is portability: you can connect to a NAS from your home Wi-Fi and cull in the next room, or you can take an SSD and the phone to a cafe and cull entirely offline.

For photographers who travel frequently, the SSD route is the most reliable. Copy your memory cards to a portable drive after the shoot, connect it to the iPhone over USB-C, and cull before you even check into your hotel. No Wi-Fi required. No cloud account needed. The sidecars are written directly to the drive. When you return to your Mac, the drive contains both the original files and the fully rated metadata.

How do my ratings get into Lightroom and Capture One from my iPhone?

This is the handoff that makes the iPhone session valuable. After you finish culling, CullKit writes an XMP sidecar file next to each rated RAW image. If your file is DSC_4821.NEF, the sidecar is DSC_4821.NEF.xmp. The sidecar contains your star rating, reject flag, colour label, and tags, all in the standard XMP namespace that every major desktop editor reads natively.

On your desktop, open Lightroom Classic. Import the folder that contains your RAW files and their sidecars. Lightroom reads the sidecars during import and applies the ratings. If the folder was already imported before the iPhone session, select the folder in the Library module and run Metadata > Read Metadata from Files. The ratings appear on every frame that has a sidecar.

Capture One works the same way: import the folder or use Synchronise Metadata on an existing catalogue entry. Darktable reads XMP sidecars on folder import as well. No format conversion. No ratings export step. No re-rating frames you already decided on.

A few technical details to be aware of:

  • Existing sidecars are merged. If a frame already has an XMP sidecar from Photo Mechanic or a previous editing session, CullKit downloads it, merges the new ratings in, and writes the merged file back. Nothing is overwritten.

  • RAW+JPEG pairs share one sidecar. One pair, one rating, one sidecar file. No duplicate metadata entries.

  • The sidecar stays with the image. Copy the folder to a backup drive, send it to a collaborator, move it to a different Mac. The ratings travel with the files because the sidecar lives in the same directory.

What is the battery and storage impact of iPhone culling?

CullKit does not copy or cache your photos on the iPhone’s internal storage during a culling session. The app streams previews from the source (NAS, SSD, or local folder) and displays them in memory. No large image files are stored on the device. A session culling 1,200 frames from a NAS over Wi-Fi uses roughly the same battery as streaming video for the same duration. On a recent iPhone (14 or later), a one-hour culling session consumes about 20 to 25 percent of a full charge.

If you are culling from an external SSD, the iPhone’s battery also powers the drive through USB-C. Bus-powered SSDs (the majority of portable drives) draw power from the phone. For long sessions, consider plugging the phone into a charger or using a powered USB-C hub that supplies power to both the phone and the SSD. Alternatively, cull in shorter bursts: a 20-minute session on the train, another 20 minutes while waiting for a meeting. The crash-recovery feature means you can stop and resume without losing progress.

For storage, the only files CullKit writes are the small XMP sidecars (typically 2 to 10 kilobytes each) back to the source location. Writing a few thousand sidecars to a NAS or SSD is a lightweight operation that has no measurable impact on the iPhone’s internal storage. The app itself is under 50 megabytes installed.

iPhone vs. iPad culling: which should I use?

Both work, and you can switch between them mid-session because both write to the same XMP sidecars in the same folder. The choice is about when and where you have time.

The iPhone is the device for speed and spontaneity. You have it with you. The one-handed swipe is fast for a first-pass cull that rejects the obvious discards. If you have 10 minutes on the bus or 15 minutes in a waiting room, that is a meaningful culling block. You will not judge critical sharpness on a 6.7-inch screen, but you can reject half the frames in a burst and mark the frame you want to keep. The second pass, where you add star ratings, works on iPhone too, though photographers who want the largest possible preview tend to save the rating pass for an iPad or a desktop session.

The iPad gives you a larger display for judging composition and exposure with more confidence during both passes. The 11-inch or 13-inch screen makes a difference when you are deciding between two near-identical frames or checking critical focus. The iPad also supports keyboard shortcuts if you pair a Bluetooth keyboard, which some photographers prefer for long sessions.

A practical rhythm that many photographers settle into: first pass on the iPhone (reject the discards, anywhere, any time), second pass on the iPad or desktop (star-rate the survivors with a larger view). Because both devices write to the same XMP sidecar location, there is no synchronisation step between them. The rejects from the phone session are already marked. The survivors are waiting in the same folder.

Troubleshooting iPhone culling

  • NAS not found on iPhone. Verify your iPhone is on the same Wi-Fi network as the NAS. Public or guest Wi-Fi networks (cafes, hotels) often block local device-to-device communication; use your own network or a travel router for NAS culling. If you are entering an IP address manually, check the NAS’s IP has not changed (assign a static IP or DHCP reservation on your router).

  • External SSD not appearing. Confirm the drive is formatted as exFAT or APFS and that it mounts in the Files app. The iPhone reads external drives through the Files system; if Files cannot see the drive, CullKit cannot either. Some high-draw SSDs need a powered USB-C hub rather than a direct connection.

  • Swipe gestures not registering reliably. Check that the iPhone’s display is clean and dry. A screen protector with a textured surface can reduce swipe sensitivity. In CullKit’s settings, you can adjust the swipe sensitivity threshold to match your touch style.

  • Ratings missing in Lightroom after the session. The most common cause is that the session was not finished. CullKit writes sidecars when you complete the session, not continuously as you rate. Return to the session and complete it. If the session is finished and sidecars are present in the folder (check with Finder or Files app), run Metadata > Read Metadata from Files in Lightroom on the relevant folder.

  • Connection drops during a long NAS session. The session state is saved locally on the iPhone. When the network reconnects, reopen the session and it resumes where you stopped. Ratings made before the drop are preserved in the session state and written to sidecars when you complete the session.

  • Unable to write sidecars to the NAS. Verify your NAS user account has read-write permissions on the photo share. If you can read the folder but not write to it, sidecar creation will fail silently. Check the share permissions in your NAS’s control panel.

Start culling from your pocket

The iPhone has been the most underused device in a photographer’s kit. It travels everywhere with you, it has a bright, colour-accurate display, and it connects to your storage over the same protocols your laptop uses. The only missing piece was software that could turn swipes and taps into usable metadata that survives the session.

CullKit is available on the App Store for iPhone, iPad, and Mac. The free tier lets you browse any connected library: Synology Photos, SMB NAS shares (QNAP, TrueNAS, UGREEN, Asustor), external SSDs, and local folders. The Pro tier (7-day free trial, then monthly or yearly) unlocks the full culling workflow: swipe-based rating, star ratings, reject flags, colour labels, XMP sidecar writing, and folder organisation.

A built-in demo mode with seeded sample data lets you try the full culling experience before connecting your own library or starting the trial.

Download CullKit on the App Store

CullKit is an independent product. It is not affiliated with or endorsed by Synology Inc., QNAP Technologies, Inc., TrueNAS / iXsystems, UGREEN Group, Adobe (Lightroom), Capture One, or Darktable. Compatibility claims only. Trademarks belong to their respective owners.

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