allow to scan inverted image

example/lib/main.dart

@@ -55,6 +55,7 @@ class _DemoPageState extends State<DemoPage> {
               onScan: (value) {
                 showMessage(context, 'Scanned: ${value.textString ?? ''}');
               },
+              tryInverted: true,
             ),
             ListView(
               children: [

lib/src/logic/camera_stream.dart

@@ -11,9 +11,15 @@ Future<void> startCameraProcessing() async {
 /// Stops reading barcode from the camera
 void stopCameraProcessing() => isolateUtils?.stopReadingBarcode();
 
-Future<CodeResult> processCameraImage(CameraImage image,
-    {int format = Format.Any, double cropPercent = 0.5}) async {
-  final IsolateData isolateData = IsolateData(image, format, cropPercent);
+Future<CodeResult> processCameraImage(
+  CameraImage image, {
+  int format = Format.Any,
+  double cropPercent = 0.5,
+  bool tryHarder = false,
+  bool tryInverted = false,
+}) async {
+  final IsolateData isolateData =
+      IsolateData(image, format, cropPercent, tryHarder, tryInverted);
   final CodeResult result = await _inference(isolateData);
   return result;
 }

lib/src/ui/reader_widget.dart

@@ -18,6 +18,8 @@ class ReaderWidget extends StatefulWidget {
     required this.onScan,
     this.onControllerCreated,
     this.codeFormat = Format.Any,
+    this.tryHarder = false,
+    this.tryInverted = false,
     this.showCroppingRect = true,
     this.scannerOverlay,
     this.showFlashlight = true,
@@ -33,6 +35,8 @@ class ReaderWidget extends StatefulWidget {
   final Function(CodeResult) onScan;
   final Function(CameraController?)? onControllerCreated;
   final int codeFormat;
+  final bool tryHarder;
+  final bool tryInverted;
   final bool showCroppingRect;
   final ScannerOverlay? scannerOverlay;
   final bool showFlashlight;
@@ -167,6 +171,8 @@ class _ReaderWidgetState extends State<ReaderWidget>
           image,
           format: widget.codeFormat,
           cropPercent: widget.showCroppingRect ? widget.cropPercent : 0,
+          tryHarder: widget.tryHarder,
+          tryInverted: widget.tryInverted,
         );
         if (result.isValidBool) {
           widget.onScan(result);

lib/src/utils/image_converter.dart

@@ -57,3 +57,11 @@ imglib.Image convertYUV420(CameraImage image) {
 
   return img;
 }
+
+Uint8List invertImage(Uint8List bytes) {
+  final Uint8List invertedBytes = Uint8List.fromList(bytes);
+  for (int i = 0; i < invertedBytes.length; i++) {
+    invertedBytes[i] = 255 - invertedBytes[i];
+  }
+  return invertedBytes;
+}

lib/src/utils/isolate_utils.dart

@@ -16,10 +16,14 @@ class IsolateData {
     this.cameraImage,
     this.format,
     this.cropPercent,
+    this.tryHarder,
+    this.tryInverted,
   );
   CameraImage cameraImage;
   int format;
   double cropPercent;
+  bool tryHarder;
+  bool tryInverted;
 
   SendPort? responsePort;
 }
@@ -63,16 +67,33 @@ class IsolateUtils {
           final Uint8List bytes = await convertImage(image);
           final int cropSize =
               (min(image.width, image.height) * cropPercent).round();
+          final bool tryHarder = isolateData.tryHarder;
+          final bool tryInverted = isolateData.tryInverted;
 
-          final CodeResult result = readBarcode(
+          CodeResult result = readBarcode(
             bytes,
             width: image.width,
             height: image.height,
             format: isolateData.format,
             cropWidth: cropSize,
             cropHeight: cropSize,
+            tryHarder: tryHarder,
           );
 
+          if (result.isValid == 0 && tryInverted) {
+            // try to invert the image and read again
+            final Uint8List invertedBytes = invertImage(bytes);
+            result = readBarcode(
+              invertedBytes,
+              width: image.width,
+              height: image.height,
+              format: isolateData.format,
+              cropWidth: cropSize,
+              cropHeight: cropSize,
+              tryHarder: tryHarder,
+            );
+          }
+
           isolateData.responsePort?.send(result);
         } catch (e) {
           isolateData.responsePort?.send(e);