Подробнее см. в примере.

Пример

main.py

from kivy.app import App
from kivy.uix.tabbedpanel import TabbedPanel
from kivy.properties import ObjectProperty
from PIL import Image


class RootWidget(TabbedPanel):
    manager = ObjectProperty(None)
    img = ObjectProperty(None)
    img3 = ObjectProperty(None)
    img4 = ObjectProperty(None)
    lab = ObjectProperty(None)

    def on_touch_up(self, touch):
        if not self.img3.collide_point(*touch.pos):
            return True
        else:
            self.lab.text = 'Pos: (%d,%d)' % (touch.x, touch.y)
            return True

    def switch_to(self, header):
        # set the Screen manager to load  the appropriate screen
        # linked to the tab head instead of loading content
        self.manager.current = header.screen

        # we have to replace the functionality of the original switch_to
        self.current_tab.state = "normal"
        header.state = 'down'
        self._current_tab = header

    def select_to(self, *args):
        try:
            print(args[1][0])
            iw = Image.open(args[1][0])
            iw.save('./phase.jpg')
            gray = iw.convert('1')
            gray.save('./gray_im.jpg')
            self.img3.source = './gray_im.jpg'
            self.img4.source = './gray_im.jpg'
            self.img.source = './phase.jpg'
            self.img.reload()
            self.img3.reload()
            self.img4.reload()
        except:
            pass

    def update_touch_label(self, label, touch):
        label.text = 'Pos:(%d, %d)' % (touch.x, touch.y)
        label.texture_update()
        label.pos = touch.pos
        label.size = label.texture_size[0] + 20, label.texture_size[1] + 20


class TestApp(App):
    title = 'Screen Widget'

    def build(self):
        return RootWidget()

    def on_pause(self):
        return True


if __name__ == '__main__':
    TestApp().run()

test.kv

#:kivy 1.10.1

<RootWidget>:
    manager: manager
    img: img
    img3: img3
    img4: img4
    lab: lab
    do_default_tab: False

    ScreenManager:
        id: manager

        Screen:
            id: sc1
            name:'Load img'

            FileChooserIconView:
                canvas.before:
                    Color:
                        rgb: 0.5, 0.4, 0.5
                    Rectangle:
                        pos: self.pos
                        size: self.size
                on_selection:
                    root.select_to(*args)

        Screen:
            id: sc2
            name: 'Image'

            FloatLayout:
                Button:
                    id: lab
                    pos_hint: {"right": 0.55, 'top': 1}
                    size_hint: .15,0.1

            RelativeLayout:
                Image:
                    id: img
                    on_touch_down:
                        str('Relative:{}'.format(args[1].pos))
                    pos_hint: {"left": 1, 'bottom': 1}
                    size_hint: 0.5, 1
                    allow_stretch: True

            RelativeLayout:
                Image:
                    id: img3
                    pos_hint: {"right": 1, 'bottom': 1}
                    size_hint: 0.5, 1
                    allow_stretch: True

        Screen:
            id: sc3
            name: 'Image_'

            FloatLayout:
                Image:
                    id: img4
                    keep_data: True
                    post: self.pos
                    size: self.size

    TabbedPanelHeader:
        text: sc1.name
        background_color: 1, 0, 0, 1
        screen: sc1.name

    TabbedPanelHeader:
        text: sc2.name
        background_color: 1, 1, 0, 1
        screen: sc2.name

    TabbedPanelHeader:
        text: sc3.name
        background_color: 1, 0, 1, 1
        screen: sc3.name

Выход