automatically clear the canvas when drawing over old digit

Author: xendke

src/canvas.py

@@ -20,18 +20,19 @@ def __init__(self, master, w=400, h=400):
         self.height = h
         self.file_name = "in.gif"  # name of the screenshot file that self.save uses
         self.create_text(self.width/2, self.height/2, text="Write Your Digit Here", anchor="center")
-        self.isNew = True
-        self.isEmpty = True
+        self.is_new = True
+        self.is_empty = True
+        self.has_been_predicted = False  # True when the canvas drawing has been sent through the Neural Network
         self.delay_id = None  # holds the id of the delay started since the pen has been lifted from canvas
         Pen(self)  # used draw on canvas
 
     def clear(self):
         self.delete(tk.ALL)  # deletes all items on the canvas
-        self.isEmpty = True
+        self.is_empty = True
 
     def grab(self):
         """ get current pixel data from canvas and save image to file"""
-        if not self.isEmpty:
+        if not self.is_empty:
             x = self.winfo_rootx()
             y = self.winfo_rooty()
             offset = self.border_w  # needed because of the canvas' border
@@ -52,28 +53,29 @@ def grab(self):
 
     def center_drawing(self):
         """ center drawing by calculating the center of mass https://stackoverflow.com/questions/37519238/"""
-        if self.isEmpty:
+        if not self.is_empty:
+            x = self.winfo_rootx()
+            y = self.winfo_rooty()
+            offset = self.border_w # needed because of the canvas' border
+            canvas_image = ImageGrab.grab((x+offset,y+offset,x+self.width+offset,y+self.height+offset)).convert('L')
+            immat = canvas_image.load()
+            m = np.zeros((self.width, self.height))
+            # calculate center of mass (cx, cy)
+            for x in range(0, self.width):
+                for y in range(0, self.height):
+                    m[x, y] = immat[(x, y)] != 255
+            m = m / np.sum(np.sum(m))
+            # marginal distributions
+            dx = np.sum(m, 1)
+            dy = np.sum(m, 0)
+            # expected values
+            cx = np.sum(dx * np.arange(self.width))
+            cy = np.sum(dy * np.arange(self.height))
+
+            self.move(tk.ALL, (self.width/2)-cx, (self.height/2)-cy)  # use center of mass to center
+            self.update()  # force the canvas to update immediately
+        else:
             raise ValueError('Canvas is empty.')
-        x = self.winfo_rootx()
-        y = self.winfo_rooty()
-        offset = self.border_w # needed because of the canvas' border
-        canvas_image = ImageGrab.grab((x+offset,y+offset,x+self.width+offset,y+self.height+offset)).convert('L')
-        immat = canvas_image.load()
-        m = np.zeros((self.width, self.height))
-        # calculate center of mass (cx, cy)
-        for x in range(0, self.width):
-            for y in range(0, self.height):
-                m[x, y] = immat[(x, y)] != 255
-        m = m / np.sum(np.sum(m))
-        # marginal distributions
-        dx = np.sum(m, 1)
-        dy = np.sum(m, 0)
-        # expected values
-        cx = np.sum(dx * np.arange(self.width))
-        cy = np.sum(dy * np.arange(self.height))
-
-        self.move(tk.ALL, (self.width/2)-cx, (self.height/2)-cy)  # use center of mass to center
-        self.update()  # force the canvas to update immediately
 
     def predict_timeout(self):
         """ cancel old and set a new single timeout until prediction begins """
@@ -103,11 +105,14 @@ def hovered(self, event):
     def draw(self, event):
         """ draw a line for straight brush strokes and a circle for rounded corners """
         self.canvas.predict_timeout()  # reset timeout
-        self.canvas.isEmpty = False
+        self.canvas.is_empty = False
         offset = self.width/2
-        if self.canvas.isNew:  # clear the initial text prompt
+        if self.canvas.is_new:  # clear the initial text prompt
+            self.canvas.clear()
+            self.canvas.is_new = False
+        elif self.canvas.has_been_predicted:
             self.canvas.clear()
-            self.canvas.isNew = False
+            self.canvas.has_been_predicted = False
         self.canvas.create_line(event.x, event.y, self.previous_x, self.previous_y, fill=self.color, width=self.width+1)
         self.canvas.create_oval(event.x-offset, event.y-offset, event.x+offset, event.y+offset, fill=self.color)
         self.set_previous(event.x, event.y)

src/main.py

@@ -23,7 +23,7 @@ def __init__(self, parent):
         self.cnv = None  # canvas widget
 
         self.build_ui()
-        self.bind_actions()
+        # self.bind_actions()
 
     def build_ui(self):
         # using grid system to set the widgets in the window
@@ -43,6 +43,7 @@ def predict(self):
         try:
             self.cnv.center_drawing()
             image_data = self.cnv.grab()
+            self.cnv.has_been_predicted = True
         except ValueError:
             print("Empty canvas. Will not predict.")
             return