paper_scanner_android 0.1.0

Android implementation of paper_scanner, using OpenCV for document detection, perspective crop and filters.

paper_scanner_android

The Android implementation of paper_scanner, using OpenCV.

Apps should depend on paper_scanner (this package is pulled in automatically as the endorsed Android implementation).

How it works

Operation	OpenCV pipeline
Detect	cvtColor → GaussianBlur → Canny → dilate → findContours → approxPolyDP → largest convex 4-point quad
Crop	getPerspectiveTransform → warpPerspective
Filter	cvtColor (grayscale), adaptiveThreshold (black-and-white), CLAHE on Lab L-channel (enhance)

Realtime frames send only the Y/luminance plane (or BGRA on the rare Android BGRA stream), which is all edge detection needs, keeping the channel cheap.

Why OpenCV and not ML Kit?

ML Kit exposes no standalone document-quad detector — detection is locked inside the full-UI GmsDocumentScanner, whose camera/crop/review flow is rendered by Google Play services and cannot be restyled. To build a custom UI we need detection-only primitives, so this package uses OpenCV.

Native dependency

implementation "org.opencv:opencv:4.10.0"

OpenCV bundles prebuilt .so libraries per ABI (arm64-v8a, armeabi-v7a, x86, x86_64) — roughly 10 MB per ABI. Use ABI splits or an app bundle to avoid shipping all four to every device. minSdk 21.