Replaced the Stackblur algorithm with RenderScripts native blur for better performance. Only issue yet is, that it seems to cause a memory leak.

app/src/main/java/com/kabouzeid/gramophone/util/ImageUtil.java

@@ -22,4 +22,29 @@ public class ImageUtil {
         }
         return resizedBitmap;
     }
+
+    public static int calculateInSampleSize(int width, int height, int reqWidth) {
+        // setting reqWidth matching to desired 1:1 ratio and screen-size
+        if (width < height) {
+            reqWidth = (height / width) * reqWidth;
+        } else {
+            reqWidth = (width / height) * reqWidth;
+        }
+
+        int inSampleSize = 1;
+
+        if (height > reqWidth || width > reqWidth) {
+            final int halfHeight = height / 2;
+            final int halfWidth = width / 2;
+
+            // Calculate the largest inSampleSize value that is a power of 2 and keeps both
+            // height and width larger than the requested height and width.
+            while ((halfHeight / inSampleSize) > reqWidth
+                    && (halfWidth / inSampleSize) > reqWidth) {
+                inSampleSize *= 2;
+            }
+        }
+
+        return inSampleSize;
+    }
 }