Build a Document Scanner App with ML Kit on Android

Creating a document scanner app is an exciting project that allows you to delve into mobile app development while leveraging machine learning capabilities. In this article, we will explore how to build a document scanner app for Android using ML Kit, Google's powerful machine learning suite. The following sections will guide you through the necessary steps to make your own app. Setting Up Your Android Project Before diving into the code, ensure you have Android Studio installed. Start by creating a new project: 1. Open Android Studio and select "New Project." 2. Choose "Empty Activity" and click "Next." 3. Name your application, select Kotlin as the language, and set your desired API level. 4. Click "Finish" to create the project. Once your project is set up, you will need to add the necessary dependencies for ML Kit. Open the build.gradle file for your app module and add the following dependencies: groovy dependencies { implementation 'com.google.mlkit:document-scanning:16.1.0' implementation 'com.google.android.material:material:1.4.0' implementation 'androidx.camera:camera-core:1.0.2' implementation 'androidx.camera:camera-camera2:1.0.2' implementation 'androidx.camera:camera-lifecycle:1.0.2' implementation 'androidx.camera:camera-view:1.0.0-alpha27' } Sync your project to download the necessary libraries. Designing the User Interface Next, we need to design the user interface (UI) for the document scanning app. Open activitymain.xml and replace its content with the following XML layout: xml <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layoutwidth="matchparent" android:layoutheight="matchparent" tools:context=".MainActivity" <SurfaceView android:id="@+id/previewview" android:layoutwidth="matchparent" android:layoutheight="matchparent" / <Button android:id="@+id/capturebutton" android:layoutwidth="wrapcontent" android:layoutheight="wrapcontent" android:text="Capture Document" android:layoutalignParentBottom="true" android:layoutcenterHorizontal="true" / </RelativeLayout This layout includes a SurfaceView to display the camera preview and a button to capture the document. Implementing Camera Functionality With the UI set up, we can now implement the camera functionality. In your MainActivity.kt, add the following code to initialize the camera and handle the preview: kotlin import android.Manifest import android.content.pm.PackageManager import android.os.Bundle import android.view.SurfaceHolder import android.view.SurfaceView import android.widget.Button import androidx.activity.result.contract.ActivityResultContracts import androidx.appcompat.app.AppCompatActivity import androidx.camera.core. import androidx.camera.lifecycle.ProcessCameraProvider import com.google.common.util.concurrent.ListenableFuture class MainActivity : AppCompatActivity() { private lateinit var cameraProviderFuture: ListenableFuture<ProcessCameraProvider private lateinit var previewView: SurfaceView override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activitymain) previewView = findViewById(R.id.previewview) val captureButton: Button = findViewById(R.id.capturebutton) cameraProviderFuture = ProcessCameraProvider.getInstance(this) cameraProviderFuture.addListener(Runnable { val cameraProvider = cameraProviderFuture.get() startCamera(cameraProvider) }, ContextCompat.getMainExecutor(this)) captureButton.setOnClickListener { // Capture logic will go here } } private fun startCamera(cameraProvider: ProcessCameraProvider) { val preview = Preview.Builder().build().also { it.setSurfaceProvider(previewView.holder.surface) } val cameraSelector = CameraSelector.DEFAULTBACKCAMERA cameraProvider.bindToLifecycle(this, cameraSelector, preview) } } This code initializes the camera and binds it to the lifecycle of the activity. The SurfaceView will display the camera feed. Implementing Document Scanning Now that we have the camera set up, we can implement document scanning using ML Kit. Inside the setOnClickListener for the capture button, we will add the following code: kotlin private fun scanDocument(image: InputImage) { val scanner = DocumentScanner.getClient() scanner.process(image) .addOnSuccessListener { scannedDocument - // Handle the scanned document } .addOnFailureListener { e - // Handle the error } } To capture the image from the SurfaceView, you can modify the capture logic inside the button click event: kotlin private fun captureImage() { val holder: SurfaceHolder = previewView.holder val bitmap = holder.surface.lockCanvas(null).let { // Convert to InputImage InputImage.fromBitmap(bitmap, 0) } scanDocument(bitmap) } This code captures the current frame from the camera preview and processes it for document scanning. Handling Document Scanning Results When the document scanning is successful, you will receive a ScannedDocument object. You can extract the scanned text and display it to the user. For instance, you can modify the addOnSuccessListener like this: kotlin .addOnSuccessListener { scannedDocument - val text = scannedDocument.text // Display the scanned text in a TextView or another UI component } Conclusion By following these steps, you have built a functional document scanner app using ML Kit on Android. This app captures images from the camera, processes them to detect documents, and retrieves the text contained within them. The combination of Android's CameraX library and ML Kit's document scanning capabilities makes it straightforward to implement such features in your applications. For a visual guide and further details, you can refer to the video tutorial: Watch the full tutorial on YouTube(https://www.youtube.com/watch?v=1ehycqOv4CA). With this knowledge, you can enhance the app further by adding features like saving scanned documents or improving the user interface for a better experience. Happy coding!