Kivy: Quality of images

Question

i have programmed a little a Kivy/Python-program that opens an image and displays it. But it can cleary be seen, that there is a drop in image quality 2, when compared to the original image1. So i am wondering why this is the case. Is this normal with Kivy or do i need to change something in my code?

Code:

Kivy-file:

ImageExample:

<ImageExample>:
    orientation: "vertical"
    Image:
        source: "images/zdf.png"

python-file:

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout

class ImageExample(BoxLayout):
    pass

class TheLabApp(App):
    pass

TheLabApp().run()

Thanks for your time.