diff --git a/book2/image.py b/book2/image.py
index 7389c3e..1c472b2 100644
--- a/book2/image.py
+++ b/book2/image.py
@@ -4,7 +4,13 @@
 
 
 class TextureImage:
+    '''
+    A tool class for loading image file.
 
+    Attributes:
+        filename: The image file.
+
+    '''
     def __init__(self, filename: str) -> None:
         self._load(filename)
 
@@ -12,18 +18,32 @@ def _load(self, filename: str) -> None:
         image = Image.open(filename)
         self.image_height = image.height
         self.image_width = image.width
-        self.data = [[0 for i in range(self.image_width)] for j in range(self.image_height)]
+        self.data = [[0 for i in range(self.image_width)]
+                     for j in range(self.image_height)]
         _data = image.load()
         for w in range(self.image_width):
             for h in range(self.image_height):
                 r, g, b = _data[w, h]
                 self.data[h][w] = (r, g, b)
-    
+
     def pixel_data(self, x: int, y: int) -> "Color":
+        '''
+        Find pixel :class:`Color` with given coordinate.
+
+        Args:
+            x: The x coord.
+            y: The y coord.
+
+        Returns:
+            Color: The color info.
+
+        '''
         x = self.clamp(x, 0, self.image_width)
         y = self.clamp(y, 0, self.image_height)
-        return Color(x=self.data[y][x][0], y=self.data[y][x][1], z=self.data[y][x][2])
-    
+        return Color(x=self.data[y][x][0],
+                     y=self.data[y][x][1],
+                     z=self.data[y][x][2])
+
     @staticmethod
     def clamp(x: int, low: int, high: int) -> int:
         if x < low:
@@ -36,7 +56,3 @@ def clamp(x: int, low: int, high: int) -> int:
 if __name__ == '__main__':
     ti = TextureImage('./earthmap.jpg')
     print(ti.data)
-
-
-
-
diff --git a/book2/interval.py b/book2/interval.py
index e5bc8b5..c855ee3 100644
--- a/book2/interval.py
+++ b/book2/interval.py
@@ -7,27 +7,32 @@
 
 class Interval:
     '''
-    Util class for detecting the relation between the target and two :type:`int`.
+    Util class for detecting the relation between the target and two
+    :type:`int`.
 
     Attributes:
         min: The minimum float.
         max: The maximum float.
-
+        a: One of :class:`Interval`s when it is made up by two
+            :class:`Intervals`.
+        b: Another :class:`Interval`.
     '''
 
-    def __init__(self, min: float=-INFINITY, max: float=INFINITY, 
-                 a: Optional["Interval"]=None, b: Optional["Interval"]=None) -> None:
+    def __init__(self, min: float = -INFINITY, max: float = INFINITY,
+                 a: Optional["Interval"] = None,
+                 b: Optional["Interval"] = None) -> None:
         self.min = min
         self.max = max
-        # NOTE: `a` and `b` will cover the `min` and `max` if both 
+        # NOTE: `a` and `b` will cover the `min` and `max` if both
         # assigned. Use dict parameters if you want to pass to `a` and `b`.
         if a is not None and b is not None:
             self.min = a.min if a.min < b.min else b.min
             self.max = a.max if a.max > b.max else b.max
-    
+
     def size(self) -> float:
+        '''The difference between the :arg:`max` and the :arg:`min`.'''
         return self.max - self.min
-    
+
     def contains(self, x: float) -> bool:
         '''
         Detect if the target is in the :class:`Interval` with edges included.
@@ -37,17 +42,18 @@ def contains(self, x: float) -> bool:
 
         '''
         return x >= self.min and x <= self.max
-    
+
     def surrounds(self, x: float) -> bool:
         '''
-        Detect if the target is out of the :class:`Interval` with edges excluded.
+        Detect if the target is out of the :class:`Interval` with edges
+        excluded.
 
         Args:
             x: The target.
 
         '''
         return x > self.min and x < self.max
-    
+
     def clamp(self, x: float) -> float:
         '''
         Return the clamped value of the target within the :class:`Interval`.
@@ -62,7 +68,7 @@ def clamp(self, x: float) -> float:
             return self.max
         else:
             return x
-    
+
     def expand(self, delta: float) -> "Interval":
         padding = delta / 2
         return Interval(self.min - padding, self.max + padding)
@@ -71,4 +77,4 @@ def expand(self, delta: float) -> "Interval":
 EMPTY = Interval(+INFINITY, -INFINITY)
 
 
-UNIVERSE = Interval(-INFINITY, +INFINITY)
\ No newline at end of file
+UNIVERSE = Interval(-INFINITY, +INFINITY)