Add live edge-detection overlay while aiming; v0.2.0

Bind a CameraX ImageAnalysis use case that runs EdgeDetector on downscaled
YUV frames (throttled ~6/s) and draw the detected document quad as a live
green overlay on the preview, mapped through the FILL_CENTER crop. Preview
switched to TextureView (COMPATIBLE) mode so the Compose overlay renders on
top. Bump versionCode 4 / versionName 0.2.0.

Fixes #4

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -1,6 +1,6 @@
 name: Build APK
 
-# Bouwt een getekende release-APK op elke versietag (v0.1.0, …) en op handmatige trigger.
+# Builds a signed release APK on every version tag (v0.1.0, …) and on manual trigger.
 on:
   push:
     tags:
@@ -9,26 +9,26 @@ on:
 
 jobs:
   build:
-    # Dedicated x86_64 runner (LXC op Proxmox) — de globale ARM64-runners hebben deze
+    # Dedicated x86_64 runner (LXC on Proxmox) — the global ARM64 runners don't have
-    # label niet, dus zij pikken deze job niet op.
+    # this label, so they won't pick up this job.
     runs-on: paperscan
-    # Laat het automatische Actions-token een release aanmaken + assets uploaden.
+    # Let the automatic Actions token create a release + upload assets.
     permissions:
       contents: write
-    # Image met Android SDK + JDK 17 + Gradle voorgeïnstalleerd.
+    # Image with Android SDK + JDK 17 + Gradle preinstalled.
     container:
       image: mingc/android-build-box:latest
     steps:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Herstel signing keystore uit secret
+      - name: Restore signing keystore from secret
         run: |
           echo "$SIGNING_KEYSTORE_BASE64" | base64 -d > "$GITHUB_WORKSPACE/release.jks"
         env:
           SIGNING_KEYSTORE_BASE64: ${{ secrets.SIGNING_KEYSTORE_BASE64 }}
 
-      - name: Genereer Gradle wrapper indien nodig
+      - name: Generate Gradle wrapper if needed
         run: |
           if [ ! -f gradle/wrapper/gradle-wrapper.jar ]; then
             gradle wrapper --gradle-version 8.11.1
@@ -44,7 +44,7 @@ jobs:
           SIGNING_KEY_ALIAS: ${{ secrets.SIGNING_KEY_ALIAS }}
           SIGNING_KEY_PASSWORD: ${{ secrets.SIGNING_KEY_PASSWORD }}
 
-      - name: Publiceer release met APK als download
+      - name: Publish release with APK as a download
         env:
           TOKEN: ${{ github.token }}
           TAG: ${{ github.ref_name }}
@@ -54,22 +54,22 @@ jobs:
           APK=$(ls app/build/outputs/apk/release/*.apk | head -1)
           AUTH="Authorization: token $TOKEN"
 
-          # Hergebruik een bestaande release voor deze tag, of maak 'm aan.
+          # Reuse an existing release for this tag, or create it.
           REL_ID=$(curl -sS -H "$AUTH" "$API/releases/tags/$TAG" | grep -oP '"id":\s*\K[0-9]+' | head -1 || true)
           if [ -z "$REL_ID" ]; then
             REL_ID=$(curl -sS -X POST "$API/releases" -H "$AUTH" -H "Content-Type: application/json" \
-              -d "{\"tag_name\":\"$TAG\",\"name\":\"PaperScan $TAG\",\"body\":\"Automatische build van $TAG.\"}" \
+              -d "{\"tag_name\":\"$TAG\",\"name\":\"PaperScan $TAG\",\"body\":\"Automated build of $TAG.\"}" \
               | grep -oP '"id":\s*\K[0-9]+' | head -1)
           fi
           echo "Release id: $REL_ID"
 
-          # Verwijder een eventueel bestaande asset met dezelfde naam (bij re-run/hertag).
+          # Remove any existing asset with the same name (on re-run/re-tag).
           ASSET_NAME="paperscan-$TAG.apk"
           OLD=$(curl -sS -H "$AUTH" "$API/releases/$REL_ID/assets" \
             | grep -oP "\"id\":\s*\K[0-9]+(?=[^}]*\"name\":\s*\"$ASSET_NAME\")" | head -1 || true)
           if [ -n "$OLD" ]; then curl -sS -X DELETE -H "$AUTH" "$API/releases/$REL_ID/assets/$OLD"; fi
 
-          # Upload de getekende APK als download-asset.
+          # Upload the signed APK as a downloadable asset.
           curl -sS -X POST "$API/releases/$REL_ID/assets?name=$ASSET_NAME" \
             -H "$AUTH" -H "Content-Type: application/octet-stream" \
             --data-binary @"$APK" | grep -oP '"browser_download_url":\s*"\K[^"]+' || true

README.md

@@ -1,110 +1,117 @@
 # PaperScan
 
-Een lokale, privacy-bewuste documentscanner voor Android. Scant papieren documenten
+A local, privacy-conscious document scanner for Android. Scan paper documents with your
-met de camera, detecteert automatisch de randen, corrigeert het perspectief en bundelt
+camera, automatically detect the edges, correct the perspective, and bundle multiple pages
-meerdere pagina's in één PDF. Die PDF kun je delen via Android of rechtstreeks uploaden
+into a single PDF. That PDF can be shared through Android or uploaded directly to your
-naar je zelf-gehoste **Paperless-ngx**.
+self-hosted **Paperless-ngx**.
 
-**Alles gebeurt op het toestel.** Camerabeelden, randdetectie (OpenCV) en PDF-creatie
+**Everything happens on the device.** Camera frames, edge detection (OpenCV) and PDF
-verlaten je telefoon niet. De enige netwerkverbinding is de optionele upload naar de
+creation never leave your phone. The only network connection is the optional upload to the
-Paperless-server die jij zelf configureert. Er is geen AI of cloud-verwerking.
+Paperless server you configure yourself. There is no AI or cloud processing.
 
-## Functies
+## Features
 
-- 📷 Camerapreview met multi-page vastleggen (pagina na pagina toevoegen)
+- 📷 Camera preview with multi-page capture (add pages one by one)
-- ✂️ Automatische randdetectie + perspectiefcorrectie (OpenCV), met handmatige hoekcorrectie
+- ✂️ Automatic edge detection + perspective correction (OpenCV), with manual corner adjustment
-- 🎨 Filters per pagina: kleur, grijstinten, zwart-wit (documentmodus)
+- 🎨 Per-page filters: color, grayscale, black & white (document mode)
-- 🔄 Pagina's draaien, herordenen en verwijderen
+- 🔄 Rotate, reorder and delete pages
-- 📄 Export naar multi-page PDF (A4 of originele grootte)
+- 📄 Export to a multi-page PDF (A4 or original size)
-- ☁️ Directe upload naar Paperless-ngx **of** delen via het Android-deelmenu
+- ☁️ Direct upload to Paperless-ngx **or** share via the Android share sheet
-- 🔐 API-token versleuteld opgeslagen (Android Keystore / EncryptedSharedPreferences)
+- 🔊 Capture feedback: shutter sound (only when the ringer isn't silenced) + a brief flash
+- 🔐 API token stored encrypted (Android Keystore / EncryptedSharedPreferences)
 
 ## Tech
 
 Kotlin · Jetpack Compose · CameraX · OpenCV (`org.opencv:opencv` via Maven) ·
 `PdfDocument` · OkHttp · DataStore. minSdk 26 (Android 8), target/compile SDK 35.
 
-## Lokaal bouwen
+## Building locally
 
-1. Open het project in **Android Studio** (Ladybug of nieuwer). Dit genereert automatisch
+1. Open the project in **Android Studio** (Ladybug or newer). This automatically generates
-   de Gradle wrapper (`gradlew` + `gradle-wrapper.jar`).
+   the Gradle wrapper (`gradlew` + `gradle-wrapper.jar`).
-2. Sluit een toestel aan of start een emulator en druk op **Run**.
+2. Connect a device or start an emulator and press **Run**.
 
-Of vanaf de command line (na `gradle wrapper` één keer):
+Or from the command line (after `gradle wrapper` once):
 
 ```bash
-./gradlew assembleDebug        # debug-APK, geen signing nodig
+./gradlew assembleDebug        # debug APK, no signing required
-./gradlew assembleRelease      # release-APK, vereist signing (zie onder)
+./gradlew assembleRelease      # release APK, requires signing (see below)
 ```
 
-De release-APK verschijnt in `app/build/outputs/apk/release/`.
+The release APK ends up in `app/build/outputs/apk/release/`.
 
-## Signing key aanmaken
+## Creating a signing key
 
-Nodig voor release-builds (en dus voor updates die elkaar kunnen overschrijven).
+Required for release builds (and therefore for updates that can overwrite each other).
 
 ```bash
 keytool -genkey -v -keystore release.jks -keyalg RSA -keysize 2048 \
         -validity 10000 -alias paperscan
 ```
 
-Bewaar `release.jks` **veilig en buiten git** (staat al in `.gitignore`).
+Keep `release.jks` **safe and out of git** (already in `.gitignore`).
 
-Voor lokale release-builds maak je een `keystore.properties` in de projectroot
+For local release builds, create a `keystore.properties` in the project root
-(zie `keystore.properties.example`):
+(see `keystore.properties.example`):
 
 ```properties
-storeFile=/pad/naar/release.jks
+storeFile=/path/to/release.jks
 storePassword=...
 keyAlias=paperscan
 keyPassword=...
 ```
 
-## Bouwen via Gitea Actions
+## Building via Gitea Actions
 
-De workflow `.gitea/workflows/build.yml` bouwt een getekende release-APK bij elke
+The workflow `.gitea/workflows/build.yml` builds a signed release APK on every version tag
-versietag (`git tag v0.1.0 && git push --tags`) of via een handmatige run.
+(`git tag v0.1.0 && git push --tags`) or via a manual run, and publishes it as a **Release**
+with the APK attached as a downloadable asset.
 
-Zet in je Gitea-repo onder **Settings → Actions → Secrets** deze secrets klaar:
+Add these secrets under **Settings → Actions → Secrets** in your Gitea repo:
 
-| Secret | Inhoud |
+| Secret | Contents |
 | --- | --- |
-| `SIGNING_KEYSTORE_BASE64` | `base64 -w0 release.jks` (de keystore als base64) |
+| `SIGNING_KEYSTORE_BASE64` | `base64 -w0 release.jks` (the keystore as base64) |
-| `SIGNING_STORE_PASSWORD` | wachtwoord van de keystore |
+| `SIGNING_STORE_PASSWORD` | keystore password |
-| `SIGNING_KEY_ALIAS` | bv. `paperscan` |
+| `SIGNING_KEY_ALIAS` | e.g. `paperscan` |
-| `SIGNING_KEY_PASSWORD` | wachtwoord van de sleutel |
+| `SIGNING_KEY_PASSWORD` | key password |
 
-De build gebruikt env-vars, dus er komt niets gevoeligs in de repo terecht. De APK
+The build uses env vars, so nothing sensitive ends up in the repo.
-komt als artifact `paperscan-release` beschikbaar bij de workflow-run.
 
-> Zorg dat je Gitea Actions-runner Docker-images kan trekken (`mingc/android-build-box`).
+> The build runs in a container (`mingc/android-build-box`), so the Actions runner must be
+> **x86_64** — the Android build tools (aapt2) are x86_64-Linux only and won't run natively
+> on an ARM64 runner.
 
-## Paperless-ngx instellen (in de app)
+## Setting up Paperless-ngx (in the app)
 
-1. Maak in Paperless een API-token aan: **Instellingen → profiel → API-token**
+1. Create an API token in Paperless: **Settings → profile → API token** (or via `/api/token/`).
-   (of via `/api/token/`).
+2. In PaperScan, open the gear icon → enter the **server URL** (e.g. `https://paperless.home.lan`)
-2. Open in PaperScan het tandwiel → vul **server-URL** (bv. `https://paperless.thuis.lan`)
+   and the **token** → **Test connection** → **Save**.
-   en het **token** in → **Verbinding testen** → **Opslaan**.
 
-Gebruik bij voorkeur **https**; bij `http://` waarschuwt de app dat token en documenten
+Prefer **https**; with `http://` the app warns that the token and documents travel over the
-onversleuteld over het netwerk gaan.
+network unencrypted.
 
-## Projectstructuur
+## Project layout
 
 ```
 app/src/main/java/eu/geyskens/pdfscan/
-├── PaperScanApp.kt          # Application; laadt OpenCV native libs
+├── PaperScanApp.kt          # Application; loads OpenCV native libs
-├── MainActivity.kt          # Compose host + navigatie
+├── MainActivity.kt          # Compose host + navigation
-├── ScanViewModel.kt         # scan-sessie, rendering, export, upload
+├── ScanViewModel.kt         # scan session, rendering, export, upload
-├── data/                    # Page-model, ScanFilter, SettingsRepository
+├── data/                    # Page model, ScanFilter, SettingsRepository
 ├── scan/                    # EdgeDetector, ImageProcessor, BitmapIo (OpenCV)
 ├── pdf/                     # PdfBuilder (multi-page PDF)
-├── paperless/               # PaperlessClient (OkHttp REST)
+├── paperless/               # PaperlessClient (OkHttp REST + task polling)
 └── ui/screens/              # Camera, Pages, Crop, Export, Settings
 ```
 
-## Roadmap / ideeën
+## Roadmap
 
-- Live randdetectie-overlay tijdens het richten (nu bij vastleggen)
+Tracked as issues in the repository:
-- OCR-tekstlaag (bv. Tesseract) volledig on-device
+
-- Batch-import van bestaande foto's uit de galerij
+- Live edge-detection overlay while aiming (like Microsoft Lens)
+- Internationalization: extract UI strings to resources + add translations
+- Batch import scans from the gallery
+
+> OCR is intentionally **not** done on-device: Paperless-ngx already runs OCR (via
+> OCRmyPDF/Tesseract) when it consumes the uploaded document.

app/build.gradle.kts

@@ -24,8 +24,8 @@ android {
         applicationId = "eu.geyskens.pdfscan"
         minSdk = 26
         targetSdk = 35
-        versionCode = 2
+        versionCode = 4
-        versionName = "0.1.1"
+        versionName = "0.2.0"
 
         // OpenCV native libs are large; ship only the ABIs real phones use.
         ndk {

app/src/main/java/eu/geyskens/pdfscan/ScanViewModel.kt

@@ -115,7 +115,7 @@ class ScanViewModel(app: Application) : AndroidViewModel(app) {
         val s = settings.value
         val token = settingsRepo.getToken()
         if (s.paperlessUrl.isBlank() || token.isNullOrBlank()) {
-            return PaperlessClient.Result.Failure("Paperless is nog niet ingesteld (URL + token).")
+            return PaperlessClient.Result.Failure("Paperless isn't set up yet (URL + token).")
         }
         return PaperlessClient(s.paperlessUrl, token).upload(pdf, title)
     }
@@ -133,7 +133,7 @@ class ScanViewModel(app: Application) : AndroidViewModel(app) {
 
     suspend fun testPaperless(url: String, token: String): PaperlessClient.Result {
         if (url.isBlank() || token.isBlank()) {
-            return PaperlessClient.Result.Failure("Vul eerst URL en token in.")
+            return PaperlessClient.Result.Failure("Enter a URL and token first.")
         }
         return PaperlessClient(url.trim(), token.trim()).testConnection()
     }

app/src/main/java/eu/geyskens/pdfscan/paperless/PaperlessClient.kt

@@ -1,12 +1,16 @@
 package eu.geyskens.pdfscan.paperless
 
 import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.NonCancellable
+import kotlinx.coroutines.delay
 import kotlinx.coroutines.withContext
 import okhttp3.MediaType.Companion.toMediaType
 import okhttp3.MultipartBody
 import okhttp3.OkHttpClient
 import okhttp3.Request
 import okhttp3.RequestBody.Companion.asRequestBody
+import org.json.JSONArray
+import org.json.JSONObject
 import java.io.File
 import java.util.concurrent.TimeUnit
 
@@ -28,7 +32,12 @@ class PaperlessClient(
     private val root = baseUrl.trim().trimEnd('/')
 
     sealed interface Result {
+        /** Document was consumed and created in Paperless. */
         data object Success : Result
+        /** Paperless rejected it as a duplicate of an existing document. */
+        data object Duplicate : Result
+        /** Upload was accepted but still processing when we stopped waiting. */
+        data object Pending : Result
         data class Failure(val message: String) : Result
     }
 
@@ -44,14 +53,18 @@ class PaperlessClient(
             client.newCall(request).execute().use { resp ->
                 when {
                     resp.isSuccessful -> Result.Success
-                    resp.code == 401 || resp.code == 403 -> Result.Failure("Ongeldig token (${resp.code}).")
+                    resp.code == 401 || resp.code == 403 -> Result.Failure("Invalid token (${resp.code}).")
-                    else -> Result.Failure("Server antwoordde met ${resp.code}.")
+                    else -> Result.Failure("Server responded with ${resp.code}.")
                 }
             }
-        }.getOrElse { Result.Failure(it.message ?: "Verbinding mislukt.") }
+        }.getOrElse { Result.Failure(it.message ?: "Connection failed.") }
     }
 
-    /** Uploads a PDF to the Paperless consume/inbox pipeline. */
+    /**
+     * Uploads a PDF and then waits for Paperless to actually consume it. The upload
+     * endpoint only queues the document and returns a task UUID; we poll the task so the
+     * user learns whether it was added, was a duplicate, or failed.
+     */
     suspend fun upload(pdf: File, title: String): Result = withContext(Dispatchers.IO) {
         val body = MultipartBody.Builder()
             .setType(MultipartBody.FORM)
@@ -66,11 +79,70 @@ class PaperlessClient(
             .header("Authorization", "Token $token")
             .post(body)
             .build()
+
+        // The POST runs NonCancellable so that "stop waiting" only skips the status poll —
+        // the document is always really queued. post_document returns the task UUID string.
+        val posted: kotlin.Result<String?> = withContext(NonCancellable) {
             runCatching {
                 client.newCall(request).execute().use { resp ->
-                if (resp.isSuccessful) Result.Success
+                    if (!resp.isSuccessful) error("Upload failed: ${resp.code} ${resp.message}")
-                else Result.Failure("Upload mislukt: ${resp.code} ${resp.message}")
+                    resp.body?.string()?.trim()?.trim('"')?.takeIf { it.isNotBlank() }
                 }
-        }.getOrElse { Result.Failure(it.message ?: "Upload mislukt.") }
+            }
+        }
+        val taskId = posted.getOrElse { return@withContext Result.Failure(it.message ?: "Upload failed.") }
+
+        // Older servers may not return a usable id; then we can only confirm acceptance.
+        if (taskId == null || taskId.equals("OK", ignoreCase = true)) return@withContext Result.Pending
+
+        pollTask(taskId)
+    }
+
+    /** Polls /api/tasks/ until the consume task finishes, or gives up after ~45s. */
+    private suspend fun pollTask(taskId: String): Result {
+        val deadline = System.currentTimeMillis() + 45_000
+        while (System.currentTimeMillis() < deadline) {
+            val task = runCatching {
+                val req = Request.Builder()
+                    .url("$root/api/tasks/?task_id=$taskId")
+                    .header("Authorization", "Token $token")
+                    .header("Accept", "application/json")
+                    .get()
+                    .build()
+                client.newCall(req).execute().use { resp ->
+                    if (resp.isSuccessful) firstTask(resp.body?.string()) else null
+                }
+            }.getOrNull()
+
+            when (task?.status?.uppercase()) {
+                "SUCCESS" -> return Result.Success
+                "FAILURE" -> {
+                    val msg = task.result.orEmpty()
+                    return if (msg.contains("duplicate", ignoreCase = true)) Result.Duplicate
+                    else Result.Failure(msg.ifBlank { "Paperless could not process the document." })
+                }
+                // PENDING / STARTED / RETRY / unknown → keep waiting.
+            }
+            delay(1500)
+        }
+        return Result.Pending
+    }
+
+    private data class Task(val status: String?, val result: String?)
+
+    /** Parses the first task object from the /api/tasks/ response (a plain array). */
+    private fun firstTask(json: String?): Task? {
+        if (json.isNullOrBlank()) return null
+        return runCatching {
+            val trimmed = json.trim()
+            val arr = if (trimmed.startsWith("[")) JSONArray(trimmed)
+            else JSONObject(trimmed).optJSONArray("results")
+            if (arr == null || arr.length() == 0) return null
+            val o = arr.getJSONObject(0)
+            Task(
+                status = o.optString("status").takeIf { it.isNotBlank() && it != "null" },
+                result = o.optString("result").takeIf { it.isNotBlank() && it != "null" },
+            )
+        }.getOrNull()
     }
 }

app/src/main/java/eu/geyskens/pdfscan/scan/BitmapIo.kt

@@ -21,7 +21,7 @@ object BitmapIo {
 
         val opts = BitmapFactory.Options().apply { inSampleSize = sample }
         val bitmap = BitmapFactory.decodeFile(file.absolutePath, opts)
-            ?: error("Kon afbeelding niet decoderen: ${file.name}")
+            ?: error("Could not decode image: ${file.name}")
 
         val orientation = ExifInterface(file.absolutePath)
             .getAttributeInt(ExifInterface.TAG_ORIENTATION, ExifInterface.ORIENTATION_NORMAL)

app/src/main/java/eu/geyskens/pdfscan/scan/DocumentAnalyzer.kt

@@ -0,0 +1,65 @@
+package eu.geyskens.pdfscan.scan
+
+import android.graphics.PointF
+import androidx.camera.core.ImageAnalysis
+import androidx.camera.core.ImageProxy
+import org.opencv.core.Core
+import org.opencv.core.CvType
+import org.opencv.core.Mat
+
+/**
+ * Runs [EdgeDetector] on live camera frames (throttled) and reports the detected document
+ * corners, normalized to a display-oriented frame, together with that frame's aspect ratio
+ * (width / height) so the overlay can map them onto the preview.
+ */
+class DocumentAnalyzer(
+    private val onResult: (corners: List<PointF>?, frameAspect: Float) -> Unit,
+) : ImageAnalysis.Analyzer {
+
+    @Volatile
+    private var lastRun = 0L
+
+    override fun analyze(image: ImageProxy) {
+        val now = System.currentTimeMillis()
+        if (now - lastRun < THROTTLE_MS) {
+            image.close()
+            return
+        }
+        lastRun = now
+        val result = try {
+            detect(image)
+        } catch (e: Throwable) {
+            android.util.Log.w("DocAnalyzer", "detect failed", e)
+            null
+        }
+        image.close()
+        if (result != null) onResult(result.first, result.second)
+    }
+
+    private fun detect(image: ImageProxy): Pair<List<PointF>?, Float> {
+        // The Y plane of the YUV frame is already a grayscale image.
+        val plane = image.planes[0]
+        val rowStride = plane.rowStride
+        val buffer = plane.buffer
+        val out = ByteArray(image.width * image.height)
+        for (row in 0 until image.height) {
+            buffer.position(row * rowStride)
+            buffer.get(out, row * image.width, image.width)
+        }
+        val gray = Mat(image.height, image.width, CvType.CV_8UC1)
+        gray.put(0, 0, out)
+
+        // Rotate the sensor-oriented frame to match how the preview is displayed.
+        when (image.imageInfo.rotationDegrees) {
+            90 -> Core.rotate(gray, gray, Core.ROTATE_90_CLOCKWISE)
+            180 -> Core.rotate(gray, gray, Core.ROTATE_180)
+            270 -> Core.rotate(gray, gray, Core.ROTATE_90_COUNTERCLOCKWISE)
+        }
+        val aspect = gray.cols().toFloat() / gray.rows()
+        return EdgeDetector.detectFromGray(gray) to aspect // detectFromGray releases gray
+    }
+
+    companion object {
+        private const val THROTTLE_MS = 150L
+    }
+}

app/src/main/java/eu/geyskens/pdfscan/scan/EdgeDetector.kt

@@ -22,17 +22,25 @@ object EdgeDetector {
     fun detect(bitmap: Bitmap): List<PointF>? {
         val src = Mat()
         Utils.bitmapToMat(bitmap, src)
-        try {
-            val scale = PROCESS_WIDTH / src.cols()
-            val work = Mat()
-            Imgproc.resize(src, work, Size(PROCESS_WIDTH, src.rows() * scale))
-
         val gray = Mat()
-            Imgproc.cvtColor(work, gray, Imgproc.COLOR_RGBA2GRAY)
+        Imgproc.cvtColor(src, gray, Imgproc.COLOR_RGBA2GRAY)
-            Imgproc.GaussianBlur(gray, gray, Size(5.0, 5.0), 0.0)
+        src.release()
+        return detectFromGray(gray)
+    }
+
+    /**
+     * Detects on a full-resolution single-channel grayscale [gray] Mat (e.g. a camera
+     * frame's Y plane). Corners are normalized to [gray]'s dimensions. Releases [gray].
+     */
+    fun detectFromGray(gray: Mat): List<PointF>? {
+        try {
+            val scale = PROCESS_WIDTH / gray.cols()
+            val work = Mat()
+            Imgproc.resize(gray, work, Size(PROCESS_WIDTH, gray.rows() * scale))
+            Imgproc.GaussianBlur(work, work, Size(5.0, 5.0), 0.0)
 
             val edges = Mat()
-            Imgproc.Canny(gray, edges, 50.0, 150.0)
+            Imgproc.Canny(work, edges, 50.0, 150.0)
             // Close small gaps so contours form a continuous loop.
             val kernel = Imgproc.getStructuringElement(Imgproc.MORPH_RECT, Size(5.0, 5.0))
             Imgproc.dilate(edges, edges, kernel)
@@ -65,7 +73,7 @@ object EdgeDetector {
             }
             return best
         } finally {
-            src.release()
+            gray.release()
         }
     }
 

app/src/main/java/eu/geyskens/pdfscan/ui/screens/CameraScreen.kt

@@ -1,9 +1,13 @@
 package eu.geyskens.pdfscan.ui.screens
 
 import android.Manifest
+import android.graphics.PointF
 import android.media.AudioManager
 import android.media.MediaActionSound
 import androidx.camera.core.CameraSelector
+import androidx.camera.core.ImageAnalysis
+import androidx.camera.core.resolutionselector.AspectRatioStrategy
+import androidx.camera.core.resolutionselector.ResolutionSelector
 import androidx.camera.core.ImageCapture
 import androidx.camera.core.ImageCaptureException
 import androidx.camera.core.Preview
@@ -11,6 +15,7 @@ import androidx.camera.lifecycle.ProcessCameraProvider
 import androidx.camera.view.PreviewView
 import androidx.compose.animation.core.Animatable
 import androidx.compose.animation.core.tween
+import androidx.compose.foundation.Canvas
 import androidx.compose.foundation.background
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
@@ -42,6 +47,7 @@ import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.platform.LocalLifecycleOwner
@@ -54,6 +60,7 @@ import com.google.accompanist.permissions.isGranted
 import com.google.accompanist.permissions.rememberPermissionState
 import eu.geyskens.pdfscan.Routes
 import eu.geyskens.pdfscan.ScanViewModel
+import eu.geyskens.pdfscan.scan.DocumentAnalyzer
 import kotlinx.coroutines.launch
 import java.io.File
 import java.util.concurrent.Executors
@@ -77,13 +84,13 @@ private fun PermissionRequest(onRequest: () -> Unit) {
     Box(Modifier.fillMaxSize().padding(32.dp), contentAlignment = Alignment.Center) {
         androidx.compose.foundation.layout.Column(horizontalAlignment = Alignment.CenterHorizontally) {
             Text(
-                "PaperScan heeft cameratoegang nodig om documenten te scannen. " +
+                "PaperScan needs camera access to scan documents. " +
-                    "Er wordt niets naar de cloud gestuurd.",
+                    "Nothing is sent to the cloud.",
                 color = Color.White,
                 textAlign = TextAlign.Center,
             )
             androidx.compose.foundation.layout.Spacer(Modifier.size(16.dp))
-            Button(onClick = onRequest) { Text("Toegang geven") }
+            Button(onClick = onRequest) { Text("Grant access") }
         }
     }
 }
@@ -96,12 +103,27 @@ private fun CameraContent(vm: ScanViewModel, navController: androidx.navigation.
     val pages by vm.pages.collectAsState()
 
     val executor = remember { Executors.newSingleThreadExecutor() }
+    // Same 4:3 aspect for preview and analysis so the live overlay lines up with the preview.
+    val resolutionSelector = remember {
+        ResolutionSelector.Builder()
+            .setAspectRatioStrategy(AspectRatioStrategy.RATIO_4_3_FALLBACK_AUTO_STRATEGY)
+            .build()
+    }
     val imageCapture = remember {
         ImageCapture.Builder()
             .setCaptureMode(ImageCapture.CAPTURE_MODE_MAXIMIZE_QUALITY)
             .build()
     }
+    val imageAnalysis = remember {
+        ImageAnalysis.Builder()
+            .setResolutionSelector(resolutionSelector)
+            .setBackpressureStrategy(ImageAnalysis.STRATEGY_KEEP_ONLY_LATEST)
+            .build()
+    }
     var capturing by remember { mutableStateOf(false) }
+    // Live document corners (normalized, display-oriented) + the analysis frame aspect ratio.
+    var liveCorners by remember { mutableStateOf<List<PointF>?>(null) }
+    var frameAspect by remember { mutableStateOf(0f) }
 
     // Capture feedback: system shutter sound + a brief white flash over the preview,
     // so there's clear confirmation even when the phone is on silent.
@@ -120,15 +142,27 @@ private fun CameraContent(vm: ScanViewModel, navController: androidx.navigation.
     }
 
     val previewView = remember {
-        PreviewView(context).apply { scaleType = PreviewView.ScaleType.FILL_CENTER }
+        PreviewView(context).apply {
+            scaleType = PreviewView.ScaleType.FILL_CENTER
+            // TextureView mode so the Compose overlay draws on top of the preview
+            // (SurfaceView mode composites on a separate layer that hides the overlay).
+            implementationMode = PreviewView.ImplementationMode.COMPATIBLE
+        }
     }
 
     androidx.compose.runtime.LaunchedEffect(Unit) {
         val provider = ProcessCameraProvider.getInstance(context).await()
-        val preview = Preview.Builder().build().also { it.setSurfaceProvider(previewView.surfaceProvider) }
+        val preview = Preview.Builder()
+            .setResolutionSelector(resolutionSelector)
+            .build()
+            .also { it.setSurfaceProvider(previewView.surfaceProvider) }
+        imageAnalysis.setAnalyzer(executor, DocumentAnalyzer { corners, aspect ->
+            liveCorners = corners
+            frameAspect = aspect
+        })
         provider.unbindAll()
         provider.bindToLifecycle(
-            lifecycleOwner, CameraSelector.DEFAULT_BACK_CAMERA, preview, imageCapture
+            lifecycleOwner, CameraSelector.DEFAULT_BACK_CAMERA, preview, imageCapture, imageAnalysis
         )
     }
 
@@ -138,12 +172,33 @@ private fun CameraContent(vm: ScanViewModel, navController: androidx.navigation.
             modifier = Modifier.fillMaxSize(),
         )
 
+        // Live edge-detection overlay, mapped onto the FILL_CENTER-cropped preview.
+        Canvas(Modifier.fillMaxSize()) {
+            val corners = liveCorners
+            if (corners != null && corners.size == 4 && frameAspect > 0f) {
+                val viewAspect = size.width / size.height
+                val dispW: Float
+                val dispH: Float
+                if (frameAspect > viewAspect) {
+                    dispH = size.height; dispW = size.height * frameAspect
+                } else {
+                    dispW = size.width; dispH = size.width / frameAspect
+                }
+                val offX = (size.width - dispW) / 2f
+                val offY = (size.height - dispH) / 2f
+                val pts = corners.map { Offset(offX + it.x * dispW, offY + it.y * dispH) }
+                for (i in pts.indices) {
+                    drawLine(Color(0xFF00E676), pts[i], pts[(i + 1) % 4], strokeWidth = 5f)
+                }
+            }
+        }
+
         // Top bar: settings.
         IconButton(
             onClick = { navController.navigate(Routes.SETTINGS) },
             modifier = Modifier.align(Alignment.TopEnd).statusBarsPadding().padding(8.dp),
         ) {
-            Icon(Icons.Filled.Settings, contentDescription = "Instellingen", tint = Color.White)
+            Icon(Icons.Filled.Settings, contentDescription = "Settings", tint = Color.White)
         }
 
         // Bottom controls.
@@ -204,7 +259,7 @@ private fun CameraContent(vm: ScanViewModel, navController: androidx.navigation.
             ) {
                 Icon(
                     Icons.Filled.Check,
-                    contentDescription = "Klaar",
+                    contentDescription = "Done",
                     tint = if (pages.isEmpty()) Color.Gray else Color.White,
                 )
             }

app/src/main/java/eu/geyskens/pdfscan/ui/screens/CropScreen.kt

@@ -135,9 +135,9 @@ fun CropScreen(vm: ScanViewModel, navController: NavController, pageId: String)
             Modifier.fillMaxWidth().padding(12.dp),
             horizontalArrangement = Arrangement.spacedBy(8.dp),
         ) {
-            FilterOption("Kleur", filter == ScanFilter.COLOR) { filter = ScanFilter.COLOR }
+            FilterOption("Color", filter == ScanFilter.COLOR) { filter = ScanFilter.COLOR }
-            FilterOption("Grijs", filter == ScanFilter.GRAYSCALE) { filter = ScanFilter.GRAYSCALE }
+            FilterOption("Grayscale", filter == ScanFilter.GRAYSCALE) { filter = ScanFilter.GRAYSCALE }
-            FilterOption("Zwart-wit", filter == ScanFilter.BLACK_WHITE) { filter = ScanFilter.BLACK_WHITE }
+            FilterOption("Black & white", filter == ScanFilter.BLACK_WHITE) { filter = ScanFilter.BLACK_WHITE }
         }
 
         Row(
@@ -145,7 +145,7 @@ fun CropScreen(vm: ScanViewModel, navController: NavController, pageId: String)
             horizontalArrangement = Arrangement.spacedBy(8.dp),
         ) {
             OutlinedButton(onClick = { vm.rotate(pageId) }, modifier = Modifier.weight(1f)) {
-                Text("Draaien")
+                Text("Rotate")
             }
             OutlinedButton(
                 onClick = {
@@ -153,7 +153,7 @@ fun CropScreen(vm: ScanViewModel, navController: NavController, pageId: String)
                     full.forEachIndexed { i, p -> corners[i].value = PointF(p.x, p.y) }
                 },
                 modifier = Modifier.weight(1f),
-            ) { Text("Herstel") }
+            ) { Text("Reset") }
             Button(
                 onClick = {
                     vm.updateCorners(pageId, corners.map { PointF(it.value.x, it.value.y) })
@@ -161,7 +161,7 @@ fun CropScreen(vm: ScanViewModel, navController: NavController, pageId: String)
                     navController.popBackStack()
                 },
                 modifier = Modifier.weight(1f),
-            ) { Text("Toepassen") }
+            ) { Text("Apply") }
         }
     }
 }

app/src/main/java/eu/geyskens/pdfscan/ui/screens/ExportScreen.kt

@@ -42,6 +42,8 @@ import eu.geyskens.pdfscan.Routes
 import eu.geyskens.pdfscan.ScanViewModel
 import eu.geyskens.pdfscan.paperless.PaperlessClient
 import eu.geyskens.pdfscan.pdf.PageSizeMode
+import kotlinx.coroutines.CancellationException
+import kotlinx.coroutines.Job
 import kotlinx.coroutines.launch
 import java.text.SimpleDateFormat
 import java.util.Date
@@ -61,12 +63,14 @@ fun ExportScreen(vm: ScanViewModel, navController: NavController) {
     var fileName by remember { mutableStateOf(defaultName) }
     var a4 by remember { mutableStateOf(true) }
     var busy by remember { mutableStateOf(false) }
+    var uploading by remember { mutableStateOf(false) }
+    var uploadJob by remember { mutableStateOf<Job?>(null) }
     var status by remember { mutableStateOf<String?>(null) }
 
     fun mode() = if (a4) PageSizeMode.A4 else PageSizeMode.ORIGINAL
 
     Scaffold(
-        topBar = { TopAppBar(title = { Text("Exporteren (${pages.size} pagina's)") }) },
+        topBar = { TopAppBar(title = { Text("Export (${pages.size} pages)") }) },
     ) { padding ->
         Column(
             Modifier.fillMaxSize().padding(padding).padding(16.dp),
@@ -75,7 +79,7 @@ fun ExportScreen(vm: ScanViewModel, navController: NavController) {
             OutlinedTextField(
                 value = fileName,
                 onValueChange = { fileName = it },
-                label = { Text("Bestandsnaam") },
+                label = { Text("File name") },
                 singleLine = true,
                 modifier = Modifier.fillMaxWidth(),
             )
@@ -85,12 +89,12 @@ fun ExportScreen(vm: ScanViewModel, navController: NavController) {
                     selected = a4,
                     onClick = { a4 = true },
                     shape = SegmentedButtonDefaults.itemShape(0, 2),
-                ) { Text("A4-pagina") }
+                ) { Text("A4 page") }
                 SegmentedButton(
                     selected = !a4,
                     onClick = { a4 = false },
                     shape = SegmentedButtonDefaults.itemShape(1, 2),
-                ) { Text("Originele grootte") }
+                ) { Text("Original size") }
             }
 
             Button(
@@ -109,9 +113,9 @@ fun ExportScreen(vm: ScanViewModel, navController: NavController) {
                                 putExtra(Intent.EXTRA_STREAM, uri)
                                 addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION)
                             }
-                            context.startActivity(Intent.createChooser(share, "PDF delen"))
+                            context.startActivity(Intent.createChooser(share, "Share PDF"))
                         } catch (e: Exception) {
-                            status = "Fout bij exporteren: ${e.message}"
+                            status = "Export failed: ${e.message}"
                         } finally {
                             busy = false
                         }
@@ -122,27 +126,36 @@ fun ExportScreen(vm: ScanViewModel, navController: NavController) {
             ) {
                 Icon(Icons.Filled.Share, contentDescription = null)
                 Spacer(Modifier.width(8.dp))
-                Text("Delen / opslaan")
+                Text("Share / save")
             }
 
             Button(
                 onClick = {
                     if (busy) return@Button
                     busy = true
+                    uploading = true
                     status = null
-                    scope.launch {
+                    uploadJob = scope.launch {
                         try {
                             val pdf = vm.exportPdf(fileName, mode())
                             when (val r = vm.uploadToPaperless(pdf, fileName)) {
                                 is PaperlessClient.Result.Success ->
-                                    status = "Geüpload naar Paperless ✓"
+                                    status = "Added to Paperless ✓"
+                                is PaperlessClient.Result.Duplicate ->
+                                    status = "Already in Paperless (duplicate) — not added again."
+                                is PaperlessClient.Result.Pending ->
+                                    status = "Uploaded — Paperless is still processing…"
                                 is PaperlessClient.Result.Failure ->
                                     status = r.message
                             }
+                        } catch (e: CancellationException) {
+                            // User tapped "Don't wait": the document was already sent.
+                            status = "Uploaded — Paperless will finish processing in the background."
                         } catch (e: Exception) {
-                            status = "Fout: ${e.message}"
+                            status = "Error: ${e.message}"
                         } finally {
                             busy = false
+                            uploading = false
                         }
                     }
                 },
@@ -156,21 +169,25 @@ fun ExportScreen(vm: ScanViewModel, navController: NavController) {
 
             if (!settings.paperlessUrl.isNotBlank() || !settings.hasToken) {
                 Text(
-                    "Configureer eerst Paperless (server-URL + token) in de instellingen om te kunnen uploaden.",
+                    "Configure Paperless (server URL + token) in settings first to upload.",
                     style = androidx.compose.material3.MaterialTheme.typography.bodySmall,
                     color = Color(0xFF9A9A9A),
                 )
                 OutlinedButton(
                     onClick = { navController.navigate(Routes.SETTINGS) },
                     modifier = Modifier.fillMaxWidth(),
-                ) { Text("Paperless instellen") }
+                ) { Text("Set up Paperless") }
             }
 
             if (busy) {
                 Row(verticalAlignment = androidx.compose.ui.Alignment.CenterVertically) {
                     CircularProgressIndicator(Modifier.height(24.dp))
                     Spacer(Modifier.width(12.dp))
-                    Text("Bezig…")
+                    Text(if (uploading) "Uploading…" else "Working…")
+                    if (uploading) {
+                        Spacer(Modifier.width(12.dp))
+                        OutlinedButton(onClick = { uploadJob?.cancel() }) { Text("Don't wait") }
+                    }
                 }
             }
             status?.let { Text(it, color = Color(0xFF1F6FEB)) }

app/src/main/java/eu/geyskens/pdfscan/ui/screens/PagesScreen.kt

@@ -53,12 +53,12 @@ fun PagesScreen(vm: ScanViewModel, navController: NavController) {
     Scaffold(
         topBar = {
             TopAppBar(
-                title = { Text("Pagina's (${pages.size})") },
+                title = { Text("Pages (${pages.size})") },
                 actions = {
                     IconButton(
                         onClick = { if (pages.isNotEmpty()) navController.navigate(Routes.EXPORT) },
                     ) {
-                        Icon(Icons.Filled.PictureAsPdf, contentDescription = "Exporteer PDF")
+                        Icon(Icons.Filled.PictureAsPdf, contentDescription = "Export PDF")
                     }
                 },
             )
@@ -67,7 +67,7 @@ fun PagesScreen(vm: ScanViewModel, navController: NavController) {
             ExtendedFloatingActionButton(
                 onClick = { navController.navigate(Routes.CAMERA) },
                 icon = { Icon(Icons.Filled.Add, contentDescription = null) },
-                text = { Text("Pagina toevoegen") },
+                text = { Text("Add page") },
             )
         },
     ) { padding ->
@@ -122,24 +122,24 @@ private fun PageRow(
             bitmap?.let {
                 Image(
                     bitmap = it.asImageBitmap(),
-                    contentDescription = "Pagina ${index + 1}",
+                    contentDescription = "Page ${index + 1}",
                     contentScale = ContentScale.Crop,
                     modifier = Modifier.fillMaxSize(),
                 )
             }
         }
         Spacer(Modifier.width(12.dp))
-        Text("Pagina ${index + 1}", style = MaterialTheme.typography.bodyLarge, modifier = Modifier.weight(1f))
+        Text("Page ${index + 1}", style = MaterialTheme.typography.bodyLarge, modifier = Modifier.weight(1f))
         Column {
             IconButton(onClick = onUp, enabled = !isFirst) {
-                Icon(Icons.Filled.ArrowUpward, contentDescription = "Omhoog")
+                Icon(Icons.Filled.ArrowUpward, contentDescription = "Move up")
             }
             IconButton(onClick = onDown, enabled = !isLast) {
-                Icon(Icons.Filled.ArrowDownward, contentDescription = "Omlaag")
+                Icon(Icons.Filled.ArrowDownward, contentDescription = "Move down")
             }
         }
         IconButton(onClick = onDelete) {
-            Icon(Icons.Filled.Delete, contentDescription = "Verwijderen", tint = Color(0xFFD32F2F))
+            Icon(Icons.Filled.Delete, contentDescription = "Delete", tint = Color(0xFFD32F2F))
         }
     }
 }

app/src/main/java/eu/geyskens/pdfscan/ui/screens/SettingsScreen.kt

@@ -59,10 +59,10 @@ fun SettingsScreen(vm: ScanViewModel, navController: NavController) {
         snackbarHost = { SnackbarHost(snackbarHostState) },
         topBar = {
             TopAppBar(
-                title = { Text("Instellingen") },
+                title = { Text("Settings") },
                 navigationIcon = {
                     IconButton(onClick = { navController.popBackStack() }) {
-                        Icon(Icons.AutoMirrored.Filled.ArrowBack, contentDescription = "Terug")
+                        Icon(Icons.AutoMirrored.Filled.ArrowBack, contentDescription = "Back")
                     }
                 },
             )
@@ -81,22 +81,22 @@ fun SettingsScreen(vm: ScanViewModel, navController: NavController) {
             OutlinedTextField(
                 value = url,
                 onValueChange = { url = it; testResult = null },
-                label = { Text("Server-URL (bv. https://paperless.thuis.lan)") },
+                label = { Text("Server URL (e.g. https://paperless.home.lan)") },
                 singleLine = true,
                 modifier = Modifier.fillMaxWidth(),
             )
             OutlinedTextField(
                 value = token,
                 onValueChange = { token = it; testResult = null },
-                label = { Text("API-token") },
+                label = { Text("API token") },
                 singleLine = true,
                 visualTransformation = PasswordVisualTransformation(),
                 modifier = Modifier.fillMaxWidth(),
             )
             if (url.startsWith("http://")) {
                 Text(
-                    "⚠ Je gebruikt http:// — je token en documenten gaan onversleuteld over het " +
+                    "⚠ You're using http:// — your token and documents travel unencrypted over the " +
-                        "netwerk. Gebruik https:// als het even kan.",
+                        "network. Use https:// when you can.",
                     color = Color(0xFFB26A00),
                     style = androidx.compose.material3.MaterialTheme.typography.bodySmall,
                 )
@@ -109,54 +109,55 @@ fun SettingsScreen(vm: ScanViewModel, navController: NavController) {
                         testResult = null
                         scope.launch {
                             testResult = when (val r = vm.testPaperless(url, token)) {
-                                is PaperlessClient.Result.Success -> "Verbinding OK ✓"
+                                is PaperlessClient.Result.Success -> "Connection OK ✓"
                                 is PaperlessClient.Result.Failure -> r.message
+                                else -> "Unexpected response from the server."
                             }
                             testing = false
                         }
                     },
                     enabled = !testing,
                     modifier = Modifier.weight(1f),
-                ) { Text("Verbinding testen") }
+                ) { Text("Test connection") }
 
                 Button(
                     onClick = {
                         scope.launch {
                             vm.savePaperless(url, token)
-                            snackbarHostState.showSnackbar("Instellingen opgeslagen ✓")
+                            snackbarHostState.showSnackbar("Settings saved ✓")
                         }
                     },
                     modifier = Modifier.weight(1f),
-                ) { Text("Opslaan") }
+                ) { Text("Save") }
             }
             if (testing) {
                 Row(verticalAlignment = Alignment.CenterVertically) {
                     CircularProgressIndicator(Modifier.width(20.dp))
                     Spacer(Modifier.width(8.dp))
-                    Text("Testen…")
+                    Text("Testing…")
                 }
             }
             testResult?.let { Text(it, color = Color(0xFF1F6FEB)) }
 
             Text(
-                "Standaardfilter",
+                "Default filter",
                 style = androidx.compose.material3.MaterialTheme.typography.titleMedium,
             )
             Row(horizontalArrangement = Arrangement.spacedBy(8.dp)) {
                 FilterChip(
                     selected = settings.defaultFilter == ScanFilter.COLOR,
                     onClick = { scope.launch { vm.setDefaultFilter(ScanFilter.COLOR) } },
-                    label = { Text("Kleur") },
+                    label = { Text("Color") },
                 )
                 FilterChip(
                     selected = settings.defaultFilter == ScanFilter.GRAYSCALE,
                     onClick = { scope.launch { vm.setDefaultFilter(ScanFilter.GRAYSCALE) } },
-                    label = { Text("Grijs") },
+                    label = { Text("Grayscale") },
                 )
                 FilterChip(
                     selected = settings.defaultFilter == ScanFilter.BLACK_WHITE,
                     onClick = { scope.launch { vm.setDefaultFilter(ScanFilter.BLACK_WHITE) } },
-                    label = { Text("Zwart-wit") },
+                    label = { Text("Black & white") },
                 )
             }
         }

keystore.properties.example

@@ -1,5 +1,5 @@
-# Kopieer naar keystore.properties (staat in .gitignore) voor lokale release-builds.
+# Copy to keystore.properties (gitignored) for local release builds.
-storeFile=/absoluut/pad/naar/release.jks
+storeFile=/absolute/path/to/release.jks
 storePassword=CHANGEME
 keyAlias=paperscan
 keyPassword=CHANGEME