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Cull Direct from a Memory Card: Rate Before You Import

By Ingo D ·

You come home from a shoot with a memory card full of 1,400 RAW frames. The standard routine kicks in: copy everything to a drive, open Lightroom, wait for previews, start flagging. By the time you have made your first keep/reject decision, an hour has passed and you have not even touched a slider.

What if you could cull before the copy, straight from the card?

The memory card that just came out of your camera is a USB drive. It reads at the same speed as an external SSD on a modern card reader. Plug it into your iPad on the train home, open a culling app, and you can finish the entire first pass before the card ever touches your desktop. Ratings are written to XMP sidecar files alongside your RAW frames on the card itself. When you later copy the folder to your NAS or SSD, the sidecars come with it. Lightroom, Capture One, and Darktable pick them up as if you had rated them at your desk.

Why would you cull from a memory card instead of copying first?

The conventional order of operations — copy everything, import everything, cull at the desk, edit the survivors — is safe and familiar. It is also the slowest possible sequence. The cull happens at the end of the chain, after every frame has already been committed to your storage and your catalogue. By that point, you have invested time in files you intend to delete.

Culling from the card flips the sequence. You make the keep/reject decision at the source, before the frames ever touch your permanent storage. The time you spend culling is the same either way, but you save the import-and-preview-build step for the rejects. On a 1,200-frame shoot where only 160 survive, that is roughly 85 per cent of the preview-generation overhead eliminated. For a wedding photographer who shoots 45MP RAWs, the time saving is tangible: those full-size Lightroom previews for 1,000 rejected frames take several minutes to build. By culling from the card first, you never build them at all.

The workflow also untethers the cull from your desk. You can plug the card into your iPad on a train, in a cafe, or on the sofa, and finish the entire rating pass before you sit down at your editing machine. When you do sit down, you copy only the folder — RAWs and their XMP sidecars together — and import only the keepers.

What do you need to cull from a memory card?

The hardware requirement is minimal: a card reader that plugs into your device, and a device that can read the filesystem. Most modern iPads and iPhones with USB-C will mount an SD or CFexpress card through a standard card reader just as a Mac does. The card appears in the Files app on iOS and iPadOS, or as a mounted volume on macOS. Any app that can open a local folder can now reach every RAW frame on the card.

CullKit reads local folders natively. Point it at the mounted card, and it browses the folder structure exactly as the camera wrote it. Full-resolution RAW previews render progressively. Nothing is copied to the device’s internal storage. Nothing is uploaded anywhere. The card stays in the reader, the files stay on the card, and every rating you assign is written to an XMP sidecar in the same directory as the RAW it belongs to. (More on the local-only model in the privacy FAQ.)

CullKit is an independent product. It is not affiliated with or endorsed by any camera manufacturer, memory card brand, or Adobe (Lightroom). It reads from mounted volumes via standard file-system access, the same way any other app does.

How to cull straight from an SD or CFexpress card: step by step

1. Connect the card reader to your device. On an iPad or iPhone with USB-C, plug the reader directly into the port. On a Mac, use a built-in SD slot or a USB reader. The card mounts automatically. In the Files app on iOS or iPadOS, you will see it listed under Locations. On macOS, it appears as a mounted volume in Finder.

2. Open CullKit and choose Local Folder. CullKit presents you with a file browser. Navigate to the mounted card. Camera cards typically have a DCIM folder at the root; inside that, one or more subfolders named by the camera (for example 100CANON or 103NIKON). Select the folder that holds your shoot.

3. Browse the grid before you commit to a culling session. CullKit shows a photo grid you can pinch to resize. Zoom out for an overview of the whole shoot, or zoom in to see individual frames. Thumbnails load progressively. You can spot whole sequences — burst runs, candids, setup shots — before entering the full-screen review, which helps you decide where to start.

4. Start a culling session. Choose from the three start modes: review all frames (the full card), unrated frames only (fresh card, no prior ratings), or a filtered subset (if you have already rated some and want to pick up where you left off). The session opens full-screen with the first frame.

5. Rate with gestures or keyboard. On iPhone and iPad, swipe right to keep a frame, swipe left to reject it. Tap the star icon to assign a rating from 1 to 5. The quick-access bar at the bottom gives you colour labels (the Lightroom palette: red, yellow, green, blue, purple). Configure swipe actions to match your most common decisions: one direction for a 5-star rating, another for a reject flag. On Mac, the keyboard drives the workflow: number keys for star ratings, P to pick, X to reject, 0 to clear, arrow keys to move through frames. Auto-advance carries you to the next frame after each action.

6. Complete the session. When you have rated the last frame, CullKit presents the batch-review summary. Confirm your selects. The app writes XMP sidecar files — one per RAW, a few kilobytes each — directly onto the card alongside the original frames. RAW and JPEG pairs share a single sidecar, following the Lightroom convention.

7. Eject the card safely. Once the session is complete and all sidecars are written, eject the card from your device the standard way (tap the eject icon next to the card in the Files app on iOS, or right-click and Eject on macOS). The card is now ready to be copied to your permanent storage, sidecars and all.

How do my ratings survive when I copy the card to my NAS or SSD?

Every star rating, reject flag, colour label, and tag you assigned during the culling session is stored in an XMP sidecar file. A sidecar is a small plain-text XML file with the same base name as the RAW, plus a .xmp extension. If your frame is IMG_4521.CR3, its sidecar is IMG_4521.CR3.xmp. Both live in the same folder on the card.

When you copy the card’s folder to your NAS, external SSD, or working directory, the sidecars come with it. They are files in the same directory as the images, so any file copy — Finder, File Explorer, rsync, a terminal cp command — carries them along. There is no export step, no metadata sync tool, no database migration. The ratings travel because the sidecar is a file in the folder.

When you later open the copy destination in Lightroom, Capture One, or Darktable, the editor reads the XMP sidecars and populates the star ratings, flags, and colour labels automatically. In Lightroom, use the Import dialog and the ratings appear during preview. If the folder is already in your catalogue, run Library -> Synchronize Folder or Metadata -> Read Metadata from Files and the ratings populate. In Capture One, the sidecars are read when you import into a session or catalogue. In Darktable, the sidecars load as part of the folder import.

Does this work with all memory card formats and camera RAW types?

CullKit reads from any mounted volume, so the memory card format does not matter: SD, SDHC, SDXC, CFexpress Type A or B, CFast, XQD — as long as your device’s operating system can mount the filesystem, CullKit can browse it. ExFAT, FAT32, and APFS-formatted cards all work.

On the RAW support side, CullKit handles the major camera systems: Canon CR2 and CR3, Nikon NEF, Sony ARW, Fuji RAF, Olympus ORF, Panasonic RW2, and Pentax PEF. HEIC files from iPhones and mirrorless cameras, standard JPEGs, common video formats, and Live Photos are all supported. Proprietary or brand-new RAW formats from recently released cameras may need a CullKit update to render previews, as the app relies on the operating system’s RAW decoder plus its own fallback renderer.

RAW and JPEG pairs — where the camera records both formats for every frame — are automatically grouped and reviewed as a single frame during the culling session. You see one image per shot, not two, and the single XMP sidecar applies to both files in the pair. This follows the Lightroom convention and prevents you from double-culling the same composition.

Is it safe to write XMP sidecars onto a memory card?

XMP sidecar files are tiny. A full metadata sidecar with ratings, flags, colour labels, and tags is typically under 10 kilobytes. Writing a few thousand sidecars to a card adds a negligible amount of data — far less than a single RAW frame. The card’s filesystem handles the writes the same way the camera does when saving an image.

CullKit does not modify the original RAW files. The sidecar is a separate file written alongside the RAW. Your original camera files remain byte-for-byte as the camera produced them. The sidecar approach is non-destructive, which is the same reason Lightroom and Capture One use sidecars for RAW metadata.

The one practical consideration is card speed. Older SD cards with slow write speeds (U1 or Class 10) may take a few seconds to commit a batch of several hundred sidecars at the end of a session. A modern UHS-II SD or CFexpress card handles this without perceptible delay. The culling pass itself — browsing and rating frames — reads from the card, which is much faster than writing, so the rating experience stays fluid even on older cards.

Memory card culling vs copying first: which workflow is faster?

Both paths end the same way: a folder full of rated RAWs with XMP sidecars, ready for your desktop editor. The difference is when the import and preview-generation tax gets paid.

With the traditional sequence (copy everything, import everything, cull in Lightroom), you pay the full import cost upfront for every frame, including the 80 to 85 per cent you will reject. With the memory-card-first sequence (cull on the card, copy only what survived, import only keepers), you pay the import cost only for the frames worth editing. On a 1,200-frame wedding with 180 keepers, that saves approximately 1,000 frames’ worth of Lightroom preview generation.

The culling time itself is roughly equivalent. Swiping through 1,200 frames takes around 40 minutes at 2 seconds per frame, whether those frames are on a card or a NAS. The speed difference comes from what happens before and after the cull: no waiting for a copy to finish before you can begin, and no import tax on rejects.

A practical hybrid: if you regularly shoot on multiple cards across a long event, begin your cull on the first card while the second card copies to your NAS in the background. By the time the copy finishes, card one is rated and ready to join it.

Troubleshooting memory card culling

  • Card does not appear in the file browser. Confirm the card is mounted and readable in Finder (Mac) or the Files app (iPad/iPhone). If the device prompts you to format the card, the filesystem may not be compatible with your OS; reformat the card in the camera, not on the device.
  • RAW previews do not render. CullKit relies on the operating system’s RAW decoder for rendering. A brand-new camera body released after the latest OS update may require you to wait for an OS-level RAW support update or a CullKit app update that adds a fallback renderer for that format. JPEG and HEIC always render.
  • Culling session feels slow on a large card. The culling interface reads full-resolution previews on demand. On an older U1 SD card, preview loading may lag slightly behind your swiping. A UHS-II or CFexpress card paired with a USB 3.2 reader provides a responsive experience.
  • Sidecars did not survive the copy. If you moved the files (cut and paste) rather than copied them, and the operation failed partway through, sidecars may be lost. Always copy the folder rather than move it, so you can verify the sidecars are present before formatting the card.
  • Ratings do not appear in Lightroom. Confirm the XMP sidecar files are in the same folder as the RAWs after the copy. Then run Metadata -> Read Metadata from Files on the folder in Lightroom. Also check Catalog Settings -> Metadata to confirm Lightroom is set to read XMP.

How do I import only my keepers after culling?

Once the card is copied to your NAS or SSD with sidecars intact, open Lightroom’s Import dialog and point it at the folder. Because Lightroom reads XMP sidecars during import, the grid shows every frame with its rating already visible. Use the Attribute filter bar to show only frames at, say, 3 stars and above, or only flagged picks. Uncheck everything below your threshold and import only what you intend to edit. The rejected frames stay on disk, untouched, but never enter your catalogue.

The same principle works in Capture One (filter the import by star rating) and Darktable (import only your picks). The sidecar is the universal handover format, and the filtering step is the same regardless of your editor.

A note on what CullKit does not do

CullKit is a culling, rating, and organising app. It does not edit or develop photos. There are no exposure adjustments, no crop tools, no colour grading. That work belongs in Lightroom, Capture One, or Darktable. CullKit handles the first pass: the sorting decision that turns your memory card’s worth of frames into the ones worth editing. It replaces the slow, desk-bound culling step, not the editing step that follows it.

Try it on your next shoot

CullKit runs on iPhone, iPad, and Mac. It is available exclusively on Apple platforms; there is no Android or Windows version. The free tier lets you browse any connected card, NAS, or local folder and view your images at full resolution.

The Pro tier (7-day free trial, then monthly or yearly) unlocks the full culling and rating workflow: star ratings, reject flags, colour labels, tags, XMP sidecar writing, and folder organisation. A built-in demo mode with seeded sample data lets you try the entire swipe and keyboard culling experience before you connect a real memory card.

You already carry a card reader and an iPad or iPhone to every shoot. Next time, do the cull on the way home. Your editor will thank you.

Download CullKit on the App Store

CullKit is an independent product. It is not affiliated with or endorsed by any camera manufacturer, memory card brand, or Adobe (Lightroom). Compatibility claims only.

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