diff --git a/lib/qr.ts b/lib/qr.ts
index b868097..c881c5d 100644
--- a/lib/qr.ts
+++ b/lib/qr.ts
@@ -48,6 +48,8 @@ class QrcodeDecoder {
     }
 
     this.gCtx!.clearRect(0, 0, width, height);
+    this.gCtx!.fillStyle = "#ffffff";
+    this.gCtx!.fillRect(0, 0, width, height);
     this.gCtx!.drawImage(target, 0, 0, width, height);
 
     const imageData = this.gCtx!.getImageData(