The five review lists in DeDup 1.0.1 on iPhone, and how each is built
DeDup 1.0.1 on iPhone has five review lists. Two find duplicates by comparing images. Three are simple filters on your library. This post says how each list is built and what the buttons do.
The five lists
Image Scanner (duplicate and similar photos). Each photo is shrunk to a 256-pixel thumbnail and turned into a 64-bit fingerprint. Photos with the same file size, resolution and fingerprint are grouped as exact copies. Others join the closest group when their fingerprints differ by no more than your Similarity Sensitivity (default 10, range 0 to 20). The keeper in each group is chosen in this order: favorited, better face-capture quality, higher resolution, sharper, larger file. With Enhanced AI Scan on, a photo-quality score comes in after "favorited".
Video Scanner (similar videos). Videos with the same size, resolution and duration are grouped as exact copies without opening them. For the rest, DeDup only compares videos whose lengths are within 1 second. It fingerprints a frame at 10%, 50% and 90% of the video, and groups videos when the biggest difference across those frames is within the same sensitivity setting. A video that isn't stored on the phone can only match as an exact copy. The keeper order is favorited, higher resolution, larger file.
Screenshots. Every item Photos marks as a screenshot. It's a plain list, with no image analysis.
Blurry Photos. DeDup measures how much edge detail a photo has. Photos scoring below 60 are listed. The code calls that threshold a heuristic. Screenshots are skipped. We found no check for camera shake, only this sharpness score.
Large File Review. Videos at or over your Large Video Size setting (default 100 MB), largest first.
What you can do with a list
- Open a list and tap Scan. Screenshots and Large File Review only need the library index. Blurry Photos uses the same scan as Image Scanner, and Video Scanner has its own.
- In the two duplicate lists, everything except each group's keeper starts selected. In the other three, nothing starts selected.
- Tap items to change the selection. The Select menu has Select Suggested and Deselect All. Press and hold to preview.
- Open Sort & Filter. Sort by largest, smallest, newest or oldest first, plus most copies first for duplicates. Filter by date (last 30 days, last 12 months, older than a year) and by minimum size (1, 10 or 100 MB). Hide Favorites is in every list's menu. Bursts Only shows only in Image Scanner.
- Tap Move to Trash.
What Move to Trash does
Items go to DeDup's Trash. They stay in your Photos library, but DeDup hides them from its results until you restore them or delete them permanently. Permanent deletion goes through the iOS confirmation. If you're a guest, DeDup asks you to sign in before it moves anything.
Scope of this post
Checked against: DeDup 1.0.1 source code (iOS).
Not tested on a device: how accurate any list is on a real library, how long a scan takes, and what the lists show for photos stored only in iCloud. The scan asks for images with network access off. No match rates or timings are claimed.