Vision Framework

# Vision Framework

Detect text, faces, barcodes, objects, and body poses in images and video using
on-device computer vision. Patterns target iOS 26+ with Swift 6.3,
backward-compatible where noted.

See [references/vision-requests.md](references/vision-requests.md) for complete code patterns and
[references/visionkit-scanner.md](references/visionkit-scanner.md) for DataScannerViewController integration.

## Contents

- [Two API Generations](#two-api-generations)
- [Request Pattern (Modern API)](#request-pattern-modern-api)
- [Text Recognition (OCR)](#text-recognition-ocr)
- [Face Detection](#face-detection)
- [Barcode Detection](#barcode-detection)
- [Document Scanning (iOS 26+)](#document-scanning-ios-26)
- [Image Segmentation](#image-segmentation)
- [Object Tracking](#object-tracking)
- [Other Request Types](#other-request-types)
- [Core ML Integration](#core-ml-integration)
- [VisionKit: DataScannerViewController](#visionkit-datascannerviewcontroller)
- [Common Mistakes](#common-mistakes)
- [Review Checklist](#review-checklist)
- [References](#references)

## Two API Generations

Vision has two distinct API layers. Prefer the modern API for new code.

| Aspect | Modern (iOS 18+) | Legacy |
|---|---|---|
| Pattern | `let result = try await request.perform(on: image)` | `VNImageRequestHandler` + completion handler |
| Request types | Swift types — structs and classes (`RecognizeTextRequest`, `DetectFaceRectanglesRequest`) | ObjC classes (`VNRecognizeTextRequest`, `VNDetectFaceRectanglesRequest`) |
| Concurrency | Native async/await | Completion handlers or synchronous `perform` |
| Observations | Typed return values | Cast `results` from `[Any]` |
| Availability | iOS 18+ / macOS 15+ | iOS 11+ |

The modern API uses the `ImageProcessingRequest` protocol. Each request type
has a `perform(on:orientation:)` method that accepts `CGImage`, `CIImage`,
`CVPixelBuffer`, `CMSampleBuffer`, `Data`, or `URL`. Most requests are
structs; stateful requests for video tracking (e.g., `TrackObjectRequest`,
`TrackRectangleRequest`, `DetectTrajectoriesRequest`) are final classes.

## Request Pattern (Modern API)

All modern Vision requests follow the same pattern: create a request struct,
call `perform(on:)`, and handle the typed result.

```swift
import Vision

func recognizeText(in image: CGImage) async throws -> [String] {
    var request = RecognizeTextRequest()
    request.recognitionLevel = .accurate
    request.recognitionLanguages = [Locale.Language(identifier: "en-US")]

    let observations = try await request.perform(on: image)
    return observations.compactMap { observation in
        observation.topCandidates(1).first?.string
    }
}
```

### Legacy Pattern (Pre-iOS 18)

Use `VNImageRequestHandler` with completion-based requests when targeting
older deployment versions.

```swift
import Vision

func recognizeTextLegacy(in image: CGImage) throws -> [String] {
    var recognized: [String] = []
    let request = VNRecognizeTextRequest { request, error in
        guard let observations = request.results as? [VNRecognizedTextObservation] else { return }
        recognized = observations.compactMap { $0.topCandidates(1).first?.string }
    }
    request.recognitionLevel = .accurate

    let handler = VNImageRequestHandler(cgImage: image)
    try handler.perform([request])
    return recognized
}
```

## Text Recognition (OCR)

### Modern: RecognizeTextRequest (iOS 18+)

```swift
var request = RecognizeTextRequest()
request.