Is there a way to change shape of an image in Kivy Python

Is there a way to change shape of an image that is used as button's background? First, I was using this .kv code:

Button:
    id: button
            
    size_hint: None, None
    background_color: (0, 0, 0, 0)
    pos: (root.width - self.width) / 2, (root.top - self.height) / 2 + self.height + 100
    size: 750, 500
    on_press: main.button_on_press()
    on_release: main.button_on_release()
    canvas.before:
        RoundedRectangle:
            pos: self.pos
            size: self.size
            radius: [100]
            source: "Button.png"

And the Python functions were:

def button_on_press(self):
    self.ids.button.source = "Button_pressed.png"

def button_on_release(self):
    self.ids.button.source = "Button.png"

But that didn't work. I didn't find any way to change the source from the Python code. If there is any way, please tell me.

Then I changed the .kv code to this:

Button:
    id: button
            
    size_hint: None, None
    background_color: (0, 0, 0, 0)
    pos: (root.width - self.width) / 2, (root.top - self.height) / 2 + self.height + 100
    size: 750, 500
    on_press: main.button_on_press()
    on_release: main.button_on_release()
    
    Image:
        id: image
        size: 750, 500
        source: "Button.png"
        pos: (root.width - self.width) / 2, (root.top - self.height) / 2 + self.height + 100

Now the Python functions looked like:

def button_on_press(self):
    self.ids.image.source = "Button_pressed.png"
    
def button_on_release(self):
    self.ids.image.source = "Button.png"

But can I now change the shape of the image? (Like RoundedRectangle)