feat: Ability to scan both normal codes and inverted codes

android/src/main/kotlin/dev/steenbakker/mobile_scanner/MobileScanner.kt

@@ -1,11 +1,13 @@
 package dev.steenbakker.mobile_scanner
 
+import android.annotation.SuppressLint
 import android.app.Activity
 import android.content.Context
 import android.graphics.Bitmap
 import android.graphics.Matrix
 import android.graphics.Rect
 import android.hardware.display.DisplayManager
+import android.media.Image
 import android.net.Uri
 import android.os.Build
 import android.os.Handler
@@ -58,6 +60,8 @@ class MobileScanner(
 
     /// Configurable variables
     var scanWindow: List<Float>? = null
+    var shouldConsiderInvertedImages: Boolean = false
+    private var invertCurrentImage: Boolean = false
     private var detectionSpeed: DetectionSpeed = DetectionSpeed.NO_DUPLICATES
     private var detectionTimeout: Long = 250
     private var returnImage = false
@@ -77,7 +81,17 @@ class MobileScanner(
     @ExperimentalGetImage
     val captureOutput = ImageAnalysis.Analyzer { imageProxy -> // YUV_420_888 format
         val mediaImage = imageProxy.image ?: return@Analyzer
-        val inputImage = InputImage.fromMediaImage(mediaImage, imageProxy.imageInfo.rotationDegrees)
+
+        // Invert every other frame.
+        if (shouldConsiderInvertedImages) {
+            invertCurrentImage = !invertCurrentImage // so we jump from one normal to one inverted and viceversa
+        }
+
+        val inputImage = if (invertCurrentImage) {
+            invertInputImage(imageProxy)
+        } else {
+            InputImage.fromMediaImage(mediaImage, imageProxy.imageInfo.rotationDegrees)
+        }
 
         if (detectionSpeed == DetectionSpeed.NORMAL && scannerTimeout) {
             imageProxy.close()
@@ -244,11 +258,13 @@ class MobileScanner(
         mobileScannerErrorCallback: (exception: Exception) -> Unit,
         detectionTimeout: Long,
         cameraResolution: Size?,
-        newCameraResolutionSelector: Boolean
+        newCameraResolutionSelector: Boolean,
+        shouldConsiderInvertedImages: Boolean,
     ) {
         this.detectionSpeed = detectionSpeed
         this.detectionTimeout = detectionTimeout
         this.returnImage = returnImage
+        this.shouldConsiderInvertedImages = shouldConsiderInvertedImages
 
         if (camera?.cameraInfo != null && preview != null && textureEntry != null) {
             mobileScannerErrorCallback(AlreadyStarted())
@@ -462,6 +478,45 @@ class MobileScanner(
         }
     }
 
+    /**
+     * Inverts the image colours respecting the alpha channel
+     */
+    @SuppressLint("UnsafeOptInUsageError")
+    fun invertInputImage(imageProxy: ImageProxy): InputImage {
+        val image = imageProxy.image ?: throw IllegalArgumentException("Image is null")
+
+        // Convert YUV_420_888 image to NV21 format
+        // based on our util helper
+        val bitmap = Bitmap.createBitmap(image.width, image.height, Bitmap.Config.ARGB_8888)
+        YuvToRgbConverter(activity).yuvToRgb(image, bitmap)
+
+        // Invert RGB values
+        invertBitmapColors(bitmap)
+
+        return InputImage.fromBitmap(bitmap, imageProxy.imageInfo.rotationDegrees)
+    }
+
+    // Helper function to invert the colors of the bitmap
+    private fun invertBitmapColors(bitmap: Bitmap) {
+        val width = bitmap.width
+        val height = bitmap.height
+        for (x in 0 until width) {
+            for (y in 0 until height) {
+                val pixel = bitmap.getPixel(x, y)
+                val invertedColor = invertColor(pixel)
+                bitmap.setPixel(x, y, invertedColor)
+            }
+        }
+    }
+
+    private fun invertColor(pixel: Int): Int {
+        val alpha = pixel and 0xFF000000.toInt()
+        val red = 255 - (pixel shr 16 and 0xFF)
+        val green = 255 - (pixel shr 8 and 0xFF)
+        val blue = 255 - (pixel and 0xFF)
+        return alpha or (red shl 16) or (green shl 8) or blue
+    }
+
     /**
      * Analyze a single image.
      */

android/src/main/kotlin/dev/steenbakker/mobile_scanner/MobileScannerHandler.kt

@@ -124,6 +124,7 @@ class MobileScannerHandler(
             "setScale" -> setScale(call, result)
             "resetScale" -> resetScale(result)
             "updateScanWindow" -> updateScanWindow(call, result)
+            "setShouldConsiderInvertedImages" -> setShouldConsiderInvertedImages(call, result)
             else -> result.notImplemented()
         }
     }
@@ -143,6 +144,7 @@ class MobileScannerHandler(
         } else {
             null
         }
+        val shouldConsiderInvertedImages: Boolean = call.argument<Boolean>("shouldConsiderInvertedImages") ?: false
 
         val barcodeScannerOptions: BarcodeScannerOptions? = buildBarcodeScannerOptions(formats)
 
@@ -209,10 +211,20 @@ class MobileScannerHandler(
             },
             timeout.toLong(),
             cameraResolution,
-            useNewCameraSelector
+            useNewCameraSelector,
+            shouldConsiderInvertedImages,
         )
     }
 
+    private fun setShouldConsiderInvertedImages(call: MethodCall, result: MethodChannel.Result) {
+        val shouldConsiderInvertedImages = call.argument<Boolean?>("shouldConsiderInvertedImages")
+
+        if (shouldConsiderInvertedImages != null)
+            mobileScanner?.shouldConsiderInvertedImages = shouldConsiderInvertedImages
+
+        result.success(null)
+    }
+
     private fun stop(result: MethodChannel.Result) {
         try {
             mobileScanner!!.stop()

ios/Classes/MobileScanner.swift

@@ -48,6 +48,12 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
 
     var detectionSpeed: DetectionSpeed = DetectionSpeed.noDuplicates
 
+    var shouldConsiderInvertedImages: Bool = false
+    // local variable to invert this image only this time,
+    // it changes based on [shouldConsiderInvertedImages] and
+    // it defaults as false
+    private var invertCurrentImage: Bool = false
+
     private let backgroundQueue = DispatchQueue(label: "camera-handling")
 
     var standardZoomFactor: CGFloat = 1
@@ -120,6 +126,14 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
     func requestPermission(_ result: @escaping FlutterResult) {
         AVCaptureDevice.requestAccess(for: .video, completionHandler: { result($0) })
     }
+
+    private func convertCIImageToCGImage(inputImage: CIImage) -> CGImage? {
+        let context = CIContext(options: nil)
+        if let cgImage = context.createCGImage(inputImage, from: inputImage.extent) {
+            return cgImage
+        }
+        return nil
+    }
 
     /// Gets called when a new image is added to the buffer
     public func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
@@ -136,10 +150,19 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
 
             nextScanTime = currentTime + timeoutSeconds
             imagesCurrentlyBeingProcessed = true
-
-            let ciImage = latestBuffer.image
 
-            let image = VisionImage(image: ciImage)
+            // Invert every other frame.
+            let uiImage : UIImage
+            if (shouldConsiderInvertedImages) {
+               invertCurrentImage = !invertCurrentImage
+            }
+            if (invertCurrentImage) {
+                uiImage = self.invertInputImage(image: latestBuffer.image)
+            } else {
+                uiImage = latestBuffer.image
+            }
+
+            let image = VisionImage(image: uiImage)
             image.orientation = imageOrientation(
                 deviceOrientation: UIDevice.current.orientation,
                 defaultOrientation: .portrait,
@@ -163,14 +186,15 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
                     }
                 }
 
-                mobileScannerCallback(barcodes, error, ciImage)
+                mobileScannerCallback(barcodes, error, uiImage)
             }
         }
     }
 
     /// Start scanning for barcodes
-    func start(barcodeScannerOptions: BarcodeScannerOptions?, cameraPosition: AVCaptureDevice.Position, torch: Bool, detectionSpeed: DetectionSpeed, completion: @escaping (MobileScannerStartParameters) -> ()) throws {
+    func start(barcodeScannerOptions: BarcodeScannerOptions?, cameraPosition: AVCaptureDevice.Position, shouldConsiderInvertedImages: Bool, torch: Bool, detectionSpeed: DetectionSpeed, completion: @escaping (MobileScannerStartParameters) -> ()) throws {
         self.detectionSpeed = detectionSpeed
+        self.shouldConsiderInvertedImages = shouldConsiderInvertedImages
         if (device != nil || captureSession != nil) {
             throw MobileScannerError.alreadyStarted
         }
@@ -355,6 +379,10 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
             device.unlockForConfiguration()
         } catch(_) {}
     }
+
+    func setShouldConsiderInvertedImages(_ shouldConsiderInvertedImages: Bool) {
+        self.shouldConsiderInvertedImages = shouldConsiderInvertedImages
+    }
 
     /// Turn the torch on.
     private func turnTorchOn() {
@@ -434,16 +462,41 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
     /// Analyze a single image
     func analyzeImage(image: UIImage, position: AVCaptureDevice.Position,
                       barcodeScannerOptions: BarcodeScannerOptions?, callback: @escaping BarcodeScanningCallback) {
-        let image = VisionImage(image: image)
-        image.orientation = imageOrientation(
+        let uiImage: UIImage
+        if (invertCurrentImage) {
+            uiImage = self.invertInputImage(image: uiImage)
+        } else {
+            uiImage = image
+        }
+        let visionImage = VisionImage(image: uiImage)
+        visionImage.orientation = imageOrientation(
             deviceOrientation: UIDevice.current.orientation,
             defaultOrientation: .portrait,
             position: position
         )
 
         let scanner: BarcodeScanner = barcodeScannerOptions != nil ? BarcodeScanner.barcodeScanner(options: barcodeScannerOptions!) : BarcodeScanner.barcodeScanner()
 
-        scanner.process(image, completion: callback)
+        scanner.process(visionImage, completion: callback)
+    }
+
+    private func invertInputImage(image: UIImage) -> UIImage {
+        let ciImage = CIImage(image: image)
+
+        let filter: CIFilter?
+
+        if #available(iOS 13.0, *) {
+            filter = CIFilter.colorInvert()
+            filter?.setValue(ciImage, forKey: kCIInputImageKey)
+        } else {
+            filter = CIFilter(name: "CIColorInvert")
+            filter?.setValue(ciImage, forKey: kCIInputImageKey)
+        }
+
+        let outputImage = filter?.outputImage
+        let cgImage = convertCIImageToCGImage(inputImage: outputImage!)
+
+        return UIImage(cgImage: cgImage!, scale: image.scale, orientation: image.imageOrientation)
     }
 
     var barcodesString: Array<String?>?

ios/Classes/MobileScannerPlugin.swift

@@ -117,6 +117,8 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin {
             resetScale(call, result)
         case "updateScanWindow":
             updateScanWindow(call, result)
+        case "setShouldConsiderInvertedImages":
+            setShouldConsiderInvertedImages(call, result)
         default:
             result(FlutterMethodNotImplemented)
         }
@@ -128,6 +130,7 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin {
         let facing: Int = (call.arguments as! Dictionary<String, Any?>)["facing"] as? Int ?? 1
         let formats: Array<Int> = (call.arguments as! Dictionary<String, Any?>)["formats"] as? Array ?? []
         let returnImage: Bool = (call.arguments as! Dictionary<String, Any?>)["returnImage"] as? Bool ?? false
+        let shouldConsiderInvertedImages: Bool = (call.arguments as! Dictionary<String, Any?>)["shouldConsiderInvertedImages"] as? Bool ?? false
         let speed: Int = (call.arguments as! Dictionary<String, Any?>)["speed"] as? Int ?? 0
         let timeoutMs: Int = (call.arguments as! Dictionary<String, Any?>)["timeout"] as? Int ?? 0
         self.mobileScanner.timeoutSeconds = Double(timeoutMs) / Double(1000)
@@ -139,7 +142,7 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin {
         let detectionSpeed: DetectionSpeed = DetectionSpeed(rawValue: speed)!
 
         do {
-            try mobileScanner.start(barcodeScannerOptions: barcodeOptions, cameraPosition: position, torch: torch, detectionSpeed: detectionSpeed) { parameters in
+            try mobileScanner.start(barcodeScannerOptions: barcodeOptions, cameraPosition: position, shouldConsiderInvertedImages: shouldConsiderInvertedImages, torch: torch, detectionSpeed: detectionSpeed) { parameters in
                 DispatchQueue.main.async {
                     result([
                         "textureId": parameters.textureId,
@@ -167,6 +170,19 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin {
         }
     }
 
+    /// Sets the zoomScale.
+    private func setShouldConsiderInvertedImages(_ call: FlutterMethodCall, _ result: @escaping FlutterResult) {
+        let shouldConsiderInvertedImages = call.arguments as? Bool
+        if (shouldConsiderInvertedImages == nil) {
+            result(FlutterError(code: "MobileScanner",
+                                message: "You must provide a shouldConsiderInvertedImages (bool) when calling setShouldConsiderInvertedImages",
+                                details: nil))
+            return
+        }
+        mobileScanner.setShouldConsiderInvertedImages(shouldConsiderInvertedImages!)
+        result(nil)
+    }
+
     /// Stops the mobileScanner and closes the texture.
     private func stop(_ result: @escaping FlutterResult) {
         do {

lib/src/method_channel/mobile_scanner_method_channel.dart

@@ -288,6 +288,14 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
     );
   }
 
+  @override
+  Future<void> setShouldConsiderInvertedImages(bool shouldConsiderInvertedImages) async {
+    await methodChannel.invokeMethod<void>(
+      'setShouldConsiderInvertedImages',
+      {'shouldConsiderInvertedImages': shouldConsiderInvertedImages},
+    );
+  }
+
   @override
   Future<void> stop() async {
     if (_textureId == null) {

lib/src/mobile_scanner_controller.dart

@@ -25,6 +25,7 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
     this.formats = const <BarcodeFormat>[],
     this.returnImage = false,
     this.torchEnabled = false,
+    this.shouldConsiderInvertedImages = false,
     this.useNewCameraSelector = false,
   })  : detectionTimeoutMs =
             detectionSpeed == DetectionSpeed.normal ? detectionTimeoutMs : 0,
@@ -82,6 +83,17 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
   /// Defaults to false, and is only supported on iOS, MacOS and Android.
   final bool returnImage;
 
+  /// Whether the scanner should try to detect color-inverted barcodes in every other frame.
+  ///
+  /// When this option is enabled, every odd frame from the camera preview has its colors inverted before processing.
+  /// This is useful if barcodes can be both black-on-white (the most common) and white-on-black (less common).
+  /// Usage of this parameter can incur a performance cost, as some frames need to be altered further during processing.
+  ///
+  /// Defaults to false and is only supported on Android and iOS.
+  ///
+  /// Defaults to false.
+  final bool shouldConsiderInvertedImages;
+
   /// Whether the flashlight should be turned on when the camera is started.
   ///
   /// Defaults to false.
@@ -278,6 +290,7 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
       returnImage: returnImage,
       torchEnabled: torchEnabled,
       useNewCameraSelector: useNewCameraSelector,
+      shouldConsiderInvertedImages: shouldConsiderInvertedImages,
     );
 
     try {

lib/src/mobile_scanner_platform_interface.dart

@@ -111,6 +111,11 @@ abstract class MobileScannerPlatform extends PlatformInterface {
     throw UnimplementedError('updateScanWindow() has not been implemented.');
   }
 
+  /// Set inverting image colors in intervals (for negative Data Matrices).
+  Future<void> setShouldConsiderInvertedImages(bool shouldConsiderInvertedImages) {
+    throw UnimplementedError('setInvertImage() has not been implemented.');
+  }
+
   /// Dispose of this [MobileScannerPlatform] instance.
   Future<void> dispose() {
     throw UnimplementedError('dispose() has not been implemented.');

lib/src/objects/start_options.dart

@@ -15,6 +15,7 @@ class StartOptions {
     required this.returnImage,
     required this.torchEnabled,
     required this.useNewCameraSelector,
+    required this.shouldConsiderInvertedImages,
   });
 
   /// The direction for the camera.
@@ -23,6 +24,9 @@ class StartOptions {
   /// The desired camera resolution for the scanner.
   final Size? cameraResolution;
 
+  /// Whether the scanner should try to detect color-inverted barcodes in every other frame.
+  final bool shouldConsiderInvertedImages;
+
   /// The detection speed for the scanner.
   final DetectionSpeed detectionSpeed;
 
@@ -58,6 +62,7 @@ class StartOptions {
       'timeout': detectionTimeoutMs,
       'torch': torchEnabled,
       'useNewCameraSelector': useNewCameraSelector,
+      'shouldConsiderInvertedImages': shouldConsiderInvertedImages,
     };
   }
 }