How to make images not resize in kivy?

Question

Python

from kivy.uix.scrollview import ScrollView
from kivy.core.window import Window
from kivy.app import runTouchApp
from kivy.uix.image import AsyncImage
from kivy.uix.gridlayout import GridLayout
from kivy.uix.label import Label

from main import getPhotos


layout = GridLayout(cols=1, spacing=10, size_hint= (1,None))
layout.bind(minimum_height=layout.setter('height'), minimum_width = layout.setter('width'))
photos = getPhotos()

for i in photos:
    image = AsyncImage(source = i, size_hint = (1, None))
    layout.add_widget(image)

root = ScrollView(size_hint=(1, None), size=(Window.width, Window.height))
root.add_widget(layout)

runTouchApp(root)

getPhotos returns a list of photo links.
it turns out that's it,
but I would like that the pictures were full-sized or decreased when the screen width was not enough.