diff --git a/assets/init.js b/assets/init.js
index b9d68cd..932590c 100644
--- a/assets/init.js
+++ b/assets/init.js
@@ -224,7 +224,25 @@ let Convert = {
             key: key,
             isEncode: false
         });
-    }
+    },
+    /** Encode bytes to hex string
+     * @param bytes {ArrayBuffer}
+     * @return {string}
+     */
+    hexEncode: (bytes) => {
+        const hexDigits = '0123456789abcdef';
+        const view = new Uint8Array(bytes);
+        let charCodes = new Uint8Array(view.length * 2);
+        let j = 0;
+
+        for (let i = 0; i < view.length; i++) {
+            let byte = view[i];
+            charCodes[j++] = hexDigits.charCodeAt((byte >> 4) & 0xF);
+            charCodes[j++] = hexDigits.charCodeAt(byte & 0xF);
+        }
+
+        return String.fromCharCode(...charCodes);
+    },
 }
 
 /**
@@ -1064,26 +1082,28 @@ class Image {
     }
 
     /**
-     * Create a new image based on the current image without copying the data.
-     * Modifying the new image will affect the current image.
+     * fill [image] with range(srcX, srcY, width, height) to this image at (x, y)
      * @param x
      * @param y
+     * @param image
+     * @param srcX
+     * @param srcY
      * @param width
      * @param height
-     * @returns {Image|null}
      */
-    subImage(x, y, width, height) {
-        let key = sendMessage({
+    fillImageRangeAt(x, y, image, srcX, srcY, width, height) {
+        sendMessage({
             method: "image",
-            function: "subImage",
+            function: "fillImageRangeAt",
             key: this.key,
             x: x,
             y: y,
+            image: image.key,
+            srcX: srcX,
+            srcY: srcY,
             width: width,
             height: height
         })
-        if(key == null) return null;
-        return new Image(key);
     }
 
     get width() {
diff --git a/lib/foundation/app.dart b/lib/foundation/app.dart
index 056cfc7..e1456b6 100644
--- a/lib/foundation/app.dart
+++ b/lib/foundation/app.dart
@@ -10,7 +10,7 @@ export "widget_utils.dart";
 export "context.dart";
 
 class _App {
-  final version = "1.0.1";
+  final version = "1.0.2";
 
   bool get isAndroid => Platform.isAndroid;
 
diff --git a/lib/foundation/image_provider/base_image_provider.dart b/lib/foundation/image_provider/base_image_provider.dart
index cdc1797..57dd120 100644
--- a/lib/foundation/image_provider/base_image_provider.dart
+++ b/lib/foundation/image_provider/base_image_provider.dart
@@ -87,17 +87,16 @@ abstract class BaseImageProvider<T extends BaseImageProvider<T>>
         return await decode(buffer);
       } catch (e) {
         await CacheManager().delete(this.key);
-        Object error = e;
         if (data.length < 2 * 1024) {
           // data is too short, it's likely that the data is text, not image
           try {
             var text = const Utf8Codec(allowMalformed: false).decoder.convert(data);
-            error = Exception("Expected image data, but got text: $text");
+            throw Exception("Expected image data, but got text: $text");
           } catch (e) {
             // ignore
           }
         }
-        throw error;
+        rethrow;
       }
     } catch (e) {
       scheduleMicrotask(() {
diff --git a/lib/network/images.dart b/lib/network/images.dart
index ea887bd..29c9005 100644
--- a/lib/network/images.dart
+++ b/lib/network/images.dart
@@ -3,6 +3,7 @@ import 'dart:typed_data';
 import 'package:venera/foundation/cache_manager.dart';
 import 'package:venera/foundation/comic_source/comic_source.dart';
 import 'package:venera/foundation/consts.dart';
+import 'package:venera/utils/image.dart';
 
 import 'app_dio.dart';
 
@@ -27,8 +28,8 @@ class ImageDownloader {
       configs = comicSource?.getThumbnailLoadingConfig?.call(url) ?? {};
     }
     configs['headers'] ??= {};
-    if(configs['headers']['user-agent'] == null
-        && configs['headers']['User-Agent'] == null) {
+    if (configs['headers']['user-agent'] == null &&
+        configs['headers']['User-Agent'] == null) {
       configs['headers']['user-agent'] = webUA;
     }
 
@@ -120,11 +121,22 @@ class ImageDownloader {
       buffer = configs['onResponse'](buffer);
     }
 
-    await CacheManager().writeCache(cacheKey, buffer);
+    var data = Uint8List.fromList(buffer);
+    buffer.clear();
+
+    if (configs['modifyImage'] != null) {
+      var newData = await modifyImageWithScript(
+        data,
+        configs['modifyImage'],
+      );
+      data = newData;
+    }
+
+    await CacheManager().writeCache(cacheKey, data);
     yield ImageDownloadProgress(
-      currentBytes: buffer.length,
-      totalBytes: buffer.length,
-      imageBytes: Uint8List.fromList(buffer),
+      currentBytes: data.length,
+      totalBytes: data.length,
+      imageBytes: data,
     );
   }
 }
diff --git a/lib/pages/comic_source_page.dart b/lib/pages/comic_source_page.dart
index 5710473..d6ff26e 100644
--- a/lib/pages/comic_source_page.dart
+++ b/lib/pages/comic_source_page.dart
@@ -161,71 +161,76 @@ class _BodyState extends State<_Body> {
     for (var item in source.settings!.entries) {
       var key = item.key;
       String type = item.value['type'];
-      if (type == "select") {
-        var current = source.data['settings'][key];
-        if (current == null) {
-          var d = item.value['default'];
-          for (var option in item.value['options']) {
-            if (option['value'] == d) {
-              current = option['text'] ?? option['value'];
-              break;
+      try {
+        if (type == "select") {
+          var current = source.data['settings'][key];
+          if (current == null) {
+            var d = item.value['default'];
+            for (var option in item.value['options']) {
+              if (option['value'] == d) {
+                current = option['text'] ?? option['value'];
+                break;
+              }
             }
           }
+          yield ListTile(
+            title: Text((item.value['title'] as String).ts(source.key)),
+            trailing: Select(
+              current: (current as String).ts(source.key),
+              values: (item.value['options'] as List)
+                  .map<String>(
+                      (e) => ((e['text'] ?? e['value']) as String).ts(source.key))
+                  .toList(),
+              onTap: (i) {
+                source.data['settings'][key] = item.value['options'][i]['value'];
+                source.saveData();
+                setState(() {});
+              },
+            ),
+          );
+        } else if (type == "switch") {
+          var current = source.data['settings'][key] ?? item.value['default'];
+          yield ListTile(
+            title: Text((item.value['title'] as String).ts(source.key)),
+            trailing: Switch(
+              value: current,
+              onChanged: (v) {
+                source.data['settings'][key] = v;
+                source.saveData();
+                setState(() {});
+              },
+            ),
+          );
+        } else if (type == "input") {
+          var current =
+              source.data['settings'][key] ?? item.value['default'] ?? '';
+          yield ListTile(
+            title: Text((item.value['title'] as String).ts(source.key)),
+            subtitle: Text(current, maxLines: 1, overflow: TextOverflow.ellipsis),
+            trailing: IconButton(
+              icon: const Icon(Icons.edit),
+              onPressed: () {
+                showInputDialog(
+                  context: context,
+                  title: (item.value['title'] as String).ts(source.key),
+                  initialValue: current,
+                  inputValidator: item.value['validator'] == null
+                      ? null
+                      : RegExp(item.value['validator']),
+                  onConfirm: (value) {
+                    source.data['settings'][key] = value;
+                    source.saveData();
+                    setState(() {});
+                    return null;
+                  },
+                );
+              },
+            ),
+          );
         }
-        yield ListTile(
-          title: Text((item.value['title'] as String).ts(source.key)),
-          trailing: Select(
-            current: (current as String).ts(source.key),
-            values: (item.value['options'] as List)
-                .map<String>(
-                    (e) => ((e['text'] ?? e['value']) as String).ts(source.key))
-                .toList(),
-            onTap: (i) {
-              source.data['settings'][key] = item.value['options'][i]['value'];
-              source.saveData();
-              setState(() {});
-            },
-          ),
-        );
-      } else if (type == "switch") {
-        var current = source.data['settings'][key] ?? item.value['default'];
-        yield ListTile(
-          title: Text((item.value['title'] as String).ts(source.key)),
-          trailing: Switch(
-            value: current,
-            onChanged: (v) {
-              source.data['settings'][key] = v;
-              source.saveData();
-              setState(() {});
-            },
-          ),
-        );
-      } else if (type == "input") {
-        var current =
-            source.data['settings'][key] ?? item.value['default'] ?? '';
-        yield ListTile(
-          title: Text((item.value['title'] as String).ts(source.key)),
-          subtitle: Text(current, maxLines: 1, overflow: TextOverflow.ellipsis),
-          trailing: IconButton(
-            icon: const Icon(Icons.edit),
-            onPressed: () {
-              showInputDialog(
-                context: context,
-                title: (item.value['title'] as String).ts(source.key),
-                initialValue: current,
-                inputValidator: item.value['validator'] == null
-                    ? null
-                    : RegExp(item.value['validator']),
-                onConfirm: (value) {
-                  source.data['settings'][key] = value;
-                  source.saveData();
-                  setState(() {});
-                  return null;
-                },
-              );
-            },
-          ),
-        );
+      }
+      catch(e, s) {
+        Log.error("ComicSourcePage", "Failed to build a setting\n$e\n$s");
       }
     }
   }
diff --git a/lib/pages/reader/scaffold.dart b/lib/pages/reader/scaffold.dart
index 537f2b0..c48c3b7 100644
--- a/lib/pages/reader/scaffold.dart
+++ b/lib/pages/reader/scaffold.dart
@@ -389,7 +389,7 @@ class _ReaderScaffoldState extends State<_ReaderScaffold> {
 
   Widget buildPageInfoText() {
     var epName = context.reader.widget.chapters?.values
-            .elementAt(context.reader.chapter - 1) ??
+            .elementAtOrNull(context.reader.chapter - 1) ??
         "E${context.reader.chapter}";
     if (epName.length > 8) {
       epName = "${epName.substring(0, 8)}...";
diff --git a/lib/utils/image.dart b/lib/utils/image.dart
index d8b1411..b7488b8 100644
--- a/lib/utils/image.dart
+++ b/lib/utils/image.dart
@@ -1,3 +1,4 @@
+import 'dart:ffi';
 import 'dart:isolate';
 import 'dart:typed_data';
 import 'dart:ui' as ui;
@@ -12,7 +13,12 @@ class Image {
 
   final int height;
 
-  Image(this._data, this.width, this.height);
+  Image(this._data, this.width, this.height) {
+    if (_data.length != width * height) {
+      throw ArgumentError(
+          'Invalid argument: data length must be equal to width * height.');
+    }
+  }
 
   Image.empty(this.width, this.height) : _data = Uint32List(width * height);
 
@@ -25,7 +31,7 @@ class Image {
       throw Exception('Failed to decode image');
     }
     var image = Image(
-      Uint32List.fromList(info.buffer.asUint32List()),
+      info.buffer.asUint32List(),
       frame.image.width,
       frame.image.height,
     );
@@ -34,6 +40,20 @@ class Image {
   }
 
   Image copyRange(int x, int y, int width, int height) {
+    if (width + x > this.width) {
+      throw ArgumentError('''
+        Invalid argument: x + width must be less than or equal to the image width.
+        x: $x, width: $width, image width: ${this.width}
+      '''
+          .trim());
+    }
+    if (height + y > this.height) {
+      throw ArgumentError('''
+        Invalid argument: y + height must be less than or equal to the image height.
+        y: $y, height: $height, image height: ${this.height}
+      '''
+          .trim());
+    }
     var data = Uint32List(width * height);
     for (var j = 0; j < height; j++) {
       for (var i = 0; i < width; i++) {
@@ -44,6 +64,20 @@ class Image {
   }
 
   void fillImageAt(int x, int y, Image image) {
+    if (x + image.width > width) {
+      throw ArgumentError('''
+        Invalid argument: x + image width must be less than or equal to the image width.
+        x: $x, image width: ${image.width}, image width: $width
+      '''
+          .trim());
+    }
+    if (y + image.height > height) {
+      throw ArgumentError('''
+        Invalid argument: y + image height must be less than or equal to the image height.
+        y: $y, image height: ${image.height}, image height: $height
+      '''
+          .trim());
+    }
     for (var j = 0; j < image.height && (j + y) < height; j++) {
       for (var i = 0; i < image.width && (i + x) < width; i++) {
         _data[(j + y) * width + i + x] = image._data[j * image.width + i];
@@ -51,6 +85,44 @@ class Image {
     }
   }
 
+  void fillImageRangeAt(
+      int x, int y, Image image, int srcX, int srcY, int width, int height) {
+    if (x + width > this.width) {
+      throw ArgumentError('''
+        Invalid argument: x + width must be less than or equal to the image width.
+        x: $x, width: $width, image width: ${this.width}
+      '''
+          .trim());
+    }
+    if (y + height > this.height) {
+      throw ArgumentError('''
+        Invalid argument: y + height must be less than or equal to the image height.
+        y: $y, height: $height, image height: ${this.height}
+      '''
+          .trim());
+    }
+    if (srcX + width > image.width) {
+      throw ArgumentError('''
+        Invalid argument: srcX + width must be less than or equal to the image width.
+        srcX: $srcX, width: $width, image width: ${image.width}
+      '''
+          .trim());
+    }
+    if (srcY + height > image.height) {
+      throw ArgumentError('''
+        Invalid argument: srcY + height must be less than or equal to the image height.
+        srcY: $srcY, height: $height, image height: ${image.height}
+      '''
+          .trim());
+    }
+    for (var j = 0; j < height; j++) {
+      for (var i = 0; i < width; i++) {
+        _data[(j + y) * this.width + i + x] =
+            image._data[(j + srcY) * image.width + i + srcX];
+      }
+    }
+  }
+
   Image copyAndRotate90() {
     var data = Uint32List(width * height);
     for (var j = 0; j < height; j++) {
@@ -62,28 +134,37 @@ class Image {
   }
 
   Color getPixel(int x, int y) {
+    if (x < 0 || x >= width) {
+      throw ArgumentError(
+          'Invalid argument: x must be in the range of [0, $width).');
+    }
+    if (y < 0 || y >= height) {
+      throw ArgumentError(
+          'Invalid argument: y must be in the range of [0, $height).');
+    }
     return Color.fromValue(_data[y * width + x]);
   }
 
   void setPixel(int x, int y, Color color) {
+    if (x < 0 || x >= width) {
+      throw ArgumentError(
+          'Invalid argument: x must be in the range of [0, $width).');
+    }
+    if (y < 0 || y >= height) {
+      throw ArgumentError(
+          'Invalid argument: y must be in the range of [0, $height).');
+    }
     _data[y * width + x] = color.value;
   }
 
-  Image subImage(int x, int y, int width, int height) {
-    var data = Uint32List.sublistView(
-      _data,
-      y * this.width + x,
-      width * height,
-    );
-    return Image(data, width, height);
-  }
-
   Uint8List encodePng() {
-    return lodepng.encodePng(lodepng.Image(
+    var data = lodepng.encodePngToPointer(lodepng.Image(
       _data.buffer.asUint8List(),
       width,
       height,
     ));
+    return Pointer<Uint8>.fromAddress(data.address).asTypedList(data.length,
+        finalizer: lodepng.ByteBuffer.finalizer);
   }
 }
 
@@ -166,16 +247,21 @@ class JsEngine {
           if (image2 == null) return null;
           image.fillImageAt(x, y, image2);
           return null;
-        case 'subImage':
+        case 'fillImageRangeAt':
           var key = message['key'];
           var image = images[key];
           if (image == null) return null;
           var x = message['x'];
           var y = message['y'];
+          var key2 = message['image'];
+          var image2 = images[key2];
+          if (image2 == null) return null;
+          var srcX = message['srcX'];
+          var srcY = message['srcY'];
           var width = message['width'];
           var height = message['height'];
-          var newImage = image.subImage(x, y, width, height);
-          return setImage(newImage);
+          image.fillImageRangeAt(x, y, image2, srcX, srcY, width, height);
+          return null;
         case 'getWidth':
           var key = message['key'];
           var image = images[key];
@@ -213,16 +299,18 @@ Future<Uint8List> modifyImageWithScript(Uint8List data, String script) async {
       jsEngine.runCode(script);
       var key = jsEngine.setImage(image);
       var res = jsEngine.runCode('''
-      let image = new Image($key);
-      let result = modifyImage(image);
-      return result.key;
-    ''');
+        let func = () => {
+          let image = new Image($key);
+          let result = modifyImage(image);
+          return result.key;
+        }
+        func();
+      ''');
       var newImage = jsEngine.images[res];
       var data = newImage!.encodePng();
-      return data;
+      return Uint8List.fromList(data);
     });
-  }
-  finally {
+  } finally {
     _tasksCount--;
   }
-}
\ No newline at end of file
+}
diff --git a/pubspec.lock b/pubspec.lock
index 8ef4e04..5f59f6f 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -461,7 +461,7 @@ packages:
     description:
       path: "."
       ref: HEAD
-      resolved-ref: "115b896a04c270a8d6d5d7bea09dcd04047bfad3"
+      resolved-ref: "5223cf4ce8aad1c2315db0093db3cc5c6c7191a8"
       url: "https://github.com/venera-app/lodepng_flutter"
     source: git
     version: "0.0.1"
diff --git a/pubspec.yaml b/pubspec.yaml
index 6bbdd3b..c77fc04 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -2,7 +2,7 @@ name: venera
 description: "A comic app."
 publish_to: 'none'
 
-version: 1.0.1+101
+version: 1.0.2+102
 
 environment:
   sdk: '>=3.5.0 <4.0.0'