feat(android): remove background of images using mlkit selfie segmenter

android/src/main/java/com/backgroundremover/BackgroundRemoverModule.kt

@@ -1,22 +1,103 @@
 package com.backgroundremover
 
+import android.graphics.Bitmap
+import android.graphics.Canvas
+import android.graphics.Color
+import android.graphics.ImageDecoder
+import android.graphics.Paint
+import android.graphics.PorterDuff
+import android.graphics.PorterDuffXfermode
+import android.net.Uri
+import android.os.Build
+import android.provider.MediaStore
+import com.facebook.react.bridge.Promise
 import com.facebook.react.bridge.ReactApplicationContext
 import com.facebook.react.bridge.ReactContextBaseJavaModule
 import com.facebook.react.bridge.ReactMethod
-import com.facebook.react.bridge.Promise
+import com.google.mlkit.vision.common.InputImage
+import com.google.mlkit.vision.segmentation.Segmentation
+import com.google.mlkit.vision.segmentation.Segmenter
+import com.google.mlkit.vision.segmentation.selfie.SelfieSegmenterOptions
+import java.io.File
+import java.io.FileOutputStream
+import java.net.URI
+import kotlin.math.pow
+
 
 class BackgroundRemoverModule(reactContext: ReactApplicationContext) :
   ReactContextBaseJavaModule(reactContext) {
+  private var segmenter: Segmenter? = null
 
   override fun getName(): String {
     return NAME
   }
 
-  // Example method
-  // See https://reactnative.dev/docs/native-modules-android
   @ReactMethod
-  fun multiply(a: Double, b: Double, promise: Promise) {
-    promise.resolve(a * b)
+  fun removeBackground(imageURI: String, promise: Promise) {
+    val segmenter = this.segmenter ?: createSegmenter()
+    val image = getImageBitmap(imageURI)
+
+    val inputImage = InputImage.fromBitmap(image, 0)
+
+    segmenter.process(inputImage).addOnFailureListener { e ->
+      promise.reject(e)
+    }.addOnSuccessListener { result ->
+      val maskBuffer = result.buffer
+      val mask = Bitmap.createBitmap(result.width, result.height, Bitmap.Config.ARGB_8888)
+
+      for (y in 0 until result.height) {
+        for (x in 0 until result.width) {
+          val alpha = maskBuffer.getFloat().pow(4)
+          mask.setPixel(x, y, Color.argb((alpha * 255).toInt(), 0, 0, 0))
+        }
+      }
+
+      val paint = Paint(Paint.ANTI_ALIAS_FLAG)
+      paint.setXfermode(PorterDuffXfermode(PorterDuff.Mode.DST_IN))
+      val canvas = Canvas(image)
+      canvas.drawBitmap(mask, 0f, 0f, paint)
+
+      val fileName = URI(imageURI).path.split("/").last()
+      val savedImageURI = saveImage(image, fileName)
+      promise.resolve(savedImageURI)
+    }
+  }
+
+  private fun createSegmenter(): Segmenter {
+    val options =
+      SelfieSegmenterOptions.Builder()
+        .setDetectorMode(SelfieSegmenterOptions.SINGLE_IMAGE_MODE)
+        .build()
+
+    val segmenter = Segmentation.getClient(options)
+    this.segmenter = segmenter
+
+    return segmenter
+  }
+
+  private fun getImageBitmap(imageURI: String): Bitmap {
+    val uri = Uri.parse(imageURI)
+
+    val bitmap = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
+      ImageDecoder.decodeBitmap(
+        ImageDecoder.createSource(
+          reactApplicationContext.contentResolver,
+          uri
+        )
+      ).copy(Bitmap.Config.ARGB_8888, true)
+    } else {
+      MediaStore.Images.Media.getBitmap(reactApplicationContext.contentResolver, uri)
+    }
+
+    return bitmap
+  }
+
+  private fun saveImage(bitmap: Bitmap, fileName: String): String {
+    val file = File(reactApplicationContext.filesDir, fileName)
+    val fileOutputStream = FileOutputStream(file)
+    bitmap.compress(Bitmap.CompressFormat.JPEG, 100, fileOutputStream)
+    fileOutputStream.close()
+    return file.toURI().toString()
   }
 
   companion object {