diff --git a/apng_library/src/main/java/oupson/apng/ImageUtils/PnnQuantizer.java b/apng_library/src/main/java/oupson/apng/ImageUtils/PnnQuantizer.java
index 5aff13e..1cea98c 100644
--- a/apng_library/src/main/java/oupson/apng/ImageUtils/PnnQuantizer.java
+++ b/apng_library/src/main/java/oupson/apng/ImageUtils/PnnQuantizer.java
@@ -9,9 +9,10 @@ Copyright (c) 2018 Miller Cy Chan
     https://github.com/mcychan/nQuant.android/blob/master/nQuant.master/src/main/java/com/android/nQuant/PnnQuantizer.java
  */
 
-import android.graphics.Color;
 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
+import android.graphics.Color;
+
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.HashMap;
diff --git a/apng_library/src/main/java/oupson/apng/Utils.kt b/apng_library/src/main/java/oupson/apng/Utils.kt
index 2ddb438..ccf71b6 100644
--- a/apng_library/src/main/java/oupson/apng/Utils.kt
+++ b/apng_library/src/main/java/oupson/apng/Utils.kt
@@ -18,13 +18,17 @@ class Utils {
          * @return True if is an APNG
          */
         fun isApng(byteArray: ByteArray) : Boolean {
+            if (!isPng(byteArray)) return false
             try {
-                val acTL = byteArrayOf(0x66, 0x63, 0x54, 0x4c)
-                loop@ for (i in 0 until byteArray.size) {
+                val acTL = byteArrayOf(0x61, 0x63, 0x54, 0x4c)
+                val IDAT = byteArrayOf(0x49, 0x44, 0x41, 0x54)
+                for (i in 0 until byteArray.size) {
                     val it = byteArray.copyOfRange(i, i + 4)
                     // if byteArray contain acTL
                     if (it.contentEquals(acTL)) {
                         return true
+                    } else if (it.contentEquals(IDAT)){
+                        return false
                     }
                 }
                 return false
diff --git a/app-test/src/main/java/oupson/apngcreator/Main2Activity.kt b/app-test/src/main/java/oupson/apngcreator/Main2Activity.kt
index 48ba203..048c9be 100644
--- a/app-test/src/main/java/oupson/apngcreator/Main2Activity.kt
+++ b/app-test/src/main/java/oupson/apngcreator/Main2Activity.kt
@@ -62,7 +62,13 @@ class Main2Activity : AppCompatActivity() {
             }
         } else {
             try {
-                animator.load(getImageRealPath(contentResolver, uri, null))
+                val bytes = contentResolver.openInputStream(uri).readBytes()
+                if (isApng(bytes)) {
+                    animator.load(bytes)
+                } else {
+                    imageView3.setImageBitmap(BitmapFactory.decodeFile(getImageRealPath(contentResolver, uri, null)))
+                    Snackbar.make(constraint, "Not an APNG", Snackbar.LENGTH_LONG).show()
+                }
             } catch (e: NotApngException) {
                 imageView3.setImageBitmap(BitmapFactory.decodeFile(getImageRealPath(contentResolver, uri, null)))
                 Snackbar.make(constraint, "Not an APNG", Snackbar.LENGTH_LONG).show()
diff --git a/app-test/src/main/java/oupson/apngcreator/MainActivity.kt b/app-test/src/main/java/oupson/apngcreator/MainActivity.kt
index 268d522..cbc1077 100644
--- a/app-test/src/main/java/oupson/apngcreator/MainActivity.kt
+++ b/app-test/src/main/java/oupson/apngcreator/MainActivity.kt
@@ -29,7 +29,7 @@ class MainActivity : AppCompatActivity() {
             load(imageUrl)
             onLoaded {
                 setOnAnimationLoopListener {
-                    Log.e("app-test", "onLoop")
+                    // Log.e("app-test", "onLoop")
                 }
             }
         }