fix transforms for scale and rotation

packages/imageviewer/src/widget.ts

@@ -81,7 +81,7 @@ class ImageViewer extends Widget implements DocumentRegistry.IReadyWidget {
     this._scale = value;
     let scaleNode = this.node.querySelector('div') as HTMLElement;
     let transform: string;
-    transform = `scale(${value})`;
+      transform = `translate(-50%,-50%) scale(${value}) rotate(${this._rotation}deg)`;
     scaleNode.style.transform = transform;
   }
 
@@ -98,7 +98,7 @@ class ImageViewer extends Widget implements DocumentRegistry.IReadyWidget {
     this._rotation = value;
     let rotNode = this.node.querySelector('div') as HTMLElement;
     let transform: string;
-      transform = `translate(-50%,-50%) rotate(${value}deg)`;
+      transform = `translate(-50%,-50%) scale(${this._scale}) rotate(${value}deg)`;
     rotNode.style.transform = transform;
   }