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Kento: film your Go game, get the record, review it

Prop your phone in front of a real Go board and play. When the game is over, hand Kento the video: it finds the board, watches for the moment each stone lands, reads the moves in order and writes the game record for you. Then you review it with KataGo, all on the phone.

Open on Google Play Watch the intro

The iOS version is in App Store review.

What it does

Game record from a videoA fixed-camera video of a game becomes a move-by-move record. The rules of Go act as an error corrector; no illegal move gets in.
Live recordingPoint the phone at the board and the moves count themselves while you play.
Position from a photoPhotograph an unfinished game and have the position on the screen in seconds. Corners and board size are found for you.
Review in pointsEvery mistake is measured in points, the biggest one is a tap away; branch off at any move and try what you should have played.
70,000 professional games110 packs from Dosaku to AlphaGo; around 3,000 ship inside the app.
Nothing leaves the phoneThe board reader and the analysis engine both run on the device. No account needed; cloud backup is optional.

How it reads the board

The board reader is two small convolutional networks I trained myself. One finds the corners of the board (a coarse guess, then a per-corner refinement); the other reads each of the 361 intersections on the straightened board as empty, black or white. The training data is mine as well: synthetic boards, real photos I labelled by hand, and game videos labelled automatically by lining them up with their known records.

On 102 boards kept out of training entirely, the stone reader reaches 99.1% balanced accuracy. The weights ship inside the app; no image ever leaves the phone.

The analysis engine is KataGo: MIT-licensed, open source, compiled from source and running entirely on the device. The rest of Kento (the camera pipeline, the two networks, video and live recording, the interface) is my own work.

Pricing

Free: three full game reviews a day; re-reviewing the same game is always free. A single one-time purchase unlocks unlimited reviews. No subscription, no ads.