diff --git a/02.recognize_digits/README.cn.md b/02.recognize_digits/README.cn.md
index 0f1e91a904f2152e3a9228292734f1bb3132c8ec..0d4d8c474bb2e4fbef3a41458f071f111c3b67cb 100644
--- a/02.recognize_digits/README.cn.md
+++ b/02.recognize_digits/README.cn.md
@@ -321,7 +321,7 @@ def load_image(file):
     im = Image.open(file).convert('L')
     im = im.resize((28, 28), Image.ANTIALIAS)
     im = np.array(im).astype(np.float32).flatten()
-    im = im / 255.0
+    im = im / 255.0 * 2.0 - 1.0
     return im
 
 test_data = []
diff --git a/02.recognize_digits/README.md b/02.recognize_digits/README.md
index 494a0292ce5ea00386d38bc28ec49aa4ccda5740..6292be0df2f99e75f5d6c74e70e526552d14d36b 100644
--- a/02.recognize_digits/README.md
+++ b/02.recognize_digits/README.md
@@ -325,7 +325,7 @@ def load_image(file):
     im = Image.open(file).convert('L')
     im = im.resize((28, 28), Image.ANTIALIAS)
     im = np.array(im).astype(np.float32).flatten()
-    im = im / 255.0
+    im = im / 255.0 * 2.0 - 1.0
     return im
 
 test_data = []
diff --git a/02.recognize_digits/index.cn.html b/02.recognize_digits/index.cn.html
index 737af444a2be1678fb7eee7a97e658bde3b8d93f..2a8fed233c64bea117fcc014e507f4cb2a2ccbb9 100644
--- a/02.recognize_digits/index.cn.html
+++ b/02.recognize_digits/index.cn.html
@@ -363,7 +363,7 @@ def load_image(file):
     im = Image.open(file).convert('L')
     im = im.resize((28, 28), Image.ANTIALIAS)
     im = np.array(im).astype(np.float32).flatten()
-    im = im / 255.0
+    im = im / 255.0 * 2.0 - 1.0
     return im
 
 test_data = []
diff --git a/02.recognize_digits/index.html b/02.recognize_digits/index.html
index 7b9e75a5934854038352f678dea88965d80eb3fc..edfee1053aedea203ea703a3db4149aeed772046 100644
--- a/02.recognize_digits/index.html
+++ b/02.recognize_digits/index.html
@@ -367,7 +367,7 @@ def load_image(file):
     im = Image.open(file).convert('L')
     im = im.resize((28, 28), Image.ANTIALIAS)
     im = np.array(im).astype(np.float32).flatten()
-    im = im / 255.0
+    im = im / 255.0 * 2.0 - 1.0
     return im
 
 test_data = []
diff --git a/02.recognize_digits/train.py b/02.recognize_digits/train.py
index 536ff0a0d64f168b0786956b93b422f702b4af8d..af7d000640b850b90012470c01f163253de228ed 100644
--- a/02.recognize_digits/train.py
+++ b/02.recognize_digits/train.py
@@ -112,7 +112,7 @@ def main():
         im = Image.open(file).convert('L')
         im = im.resize((28, 28), Image.ANTIALIAS)
         im = np.array(im).astype(np.float32).flatten()
-        im = im / 255.0
+        im = im / 255.0 * 2.0 - 1.0
         return im
 
     test_data = []