kivy 相机应用与 android 中的 opencv 显示黑屏

Question

我正在尝试基于 Kivy 中的 OpenCv 构建相机 Android 应用程序：

主文件

import kivy
from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.camera import Camera
import cv2
from kivy.uix.image import Image
from kivy.clock import Clock
from kivy.graphics.texture import Texture
import numpy as np

class KivyCamera(Image):
    def __init__(self, capture, fps, **kwargs):
        super(KivyCamera, self).__init__(**kwargs)
        self.capture = capture
        Clock.schedule_interval(self.update, 1.0 / fps)

    def update(self, dt):
        ret, frame = self.capture.read()

        if ret:
            # convert it to texture
            buf1 = cv2.flip(frame, 0)
            buf = buf1.tostring()
            image_texture = Texture.create(size=(frame.shape[1], frame.shape[0]), colorfmt='bgr')
            image_texture.blit_buffer(buf, colorfmt='bgr', bufferfmt='ubyte')
            # display image from the texture
            self.texture = image_texture

class MainApp(App):
    def build(self):
        self.capture = cv2.VideoCapture(0)
        self.camera = KivyCamera(capture=self.capture, fps=30)
        return self.camera

if __name__== "__main__":
    MainApp().run()

buildozer.spec

[app]
title = Test_app
package.name = myapp
package.domain = org.test
source.dir = .
source.include_exts = py,png,jpg,kv,atlas,xml
version = 0.1
requirements = python3,kivy,numpy,opencv
orientation = portrait

# Android specific
fullscreen = 0
android.permissions = INTERNET, ACCESS_FINE_LOCATION, WRITE_EXTERNAL_STORAGE, CAMERA
android.arch = armeabi-v7a
[buildozer]
log_level = 2
warn_on_root = 1

代码在 windows 中成功运行。 然后我用 buildozer 为 android 构建了代码，当我打开 Android 应用程序时，它显示一个黑屏，屏幕左角有一个小方块。 我认为 cv2.VideoCapture() 工作不正常。所以我将 cv2.VideoCapture(0) 更改为 cv2.VideoCapture(-1) 和 cv2.VideoCapture(1)。 但两者都不起作用。

谁能帮我解决这个问题？

Answer 1

我有 2 个解决方案可以让它在 Android 上工作。

---

解决方案1：

我受到 kivy-for-android-opencv-demo 的启发，在 GitHub: link上找到，因为 Kivy 不再支持 Python2。 这是我对 Python3 的解决方案。

主文件

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.graphics.texture import Texture
from kivy.uix.camera import Camera
from kivy.lang import Builder
import numpy as np
import cv2

Builder.load_file("myapplayout.kv")

class AndroidCamera(Camera):
    camera_resolution = (640, 480)
    counter = 0

    def _camera_loaded(self, *largs):
        self.texture = Texture.create(size=np.flip(self.camera_resolution), colorfmt='rgb')
        self.texture_size = list(self.texture.size)

    def on_tex(self, *l):
        if self._camera._buffer is None:
            return None
        frame = self.frame_from_buf()
        self.frame_to_screen(frame)
        super(AndroidCamera, self).on_tex(*l)

    def frame_from_buf(self):
        w, h = self.resolution
        frame = np.frombuffer(self._camera._buffer.tostring(), 'uint8').reshape((h + h // 2, w))
        frame_bgr = cv2.cvtColor(frame, 93)
        return np.rot90(frame_bgr, 3)

    def frame_to_screen(self, frame):
        frame_rgb = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
        cv2.putText(frame_rgb, str(self.counter), (20, 50), cv2.FONT_HERSHEY_SIMPLEX, 1, (0, 255, 0), 2, cv2.LINE_AA)
        self.counter += 1
        flipped = np.flip(frame_rgb, 0)
        buf = flipped.tostring()
        self.texture.blit_buffer(buf, colorfmt='rgb', bufferfmt='ubyte')

class MyLayout(BoxLayout):
    pass

class MyApp(App):
    def build(self):
        return MyLayout()

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

我的应用程序.kv

<MyLayout>
    orientation: 'vertical'
    size: root.width, root.height

    AndroidCamera:
        index: 0
        resolution: self.camera_resolution
        allow_stretch: True
        play: True

在 buildozer.spec 中：

requirements = python3,kivy==2.0.0,opencv==4.5.2,numpy
android.permissions = CAMERA

---

解决方案2：

我从显示的相机图像的小部件中获取帧，每秒 4 次。 如果您不需要每一个框架，并且没有必要在框架顶部绘制文本或框等内容，那么这是一个简单的解决方案。

主文件

from kivy.app import App
from kivy.uix.camera import Camera
from kivy.uix.boxlayout import BoxLayout
from kivy.lang import Builder
from kivy.clock import Clock
import numpy as np
import cv2

Builder.load_file('myapplayout.kv')

class AndroidCamera(Camera):
    camera_resolution = (640, 480)
    cam_ratio = camera_resolution[0] / camera_resolution[1]

class MyLayout(BoxLayout):
    pass


class MyApp(App):
    counter = 0

    def build(self):
        return MyLayout()

    def on_start(self):
        Clock.schedule_once(self.get_frame, 5)

    def get_frame(self, dt):
        cam = self.root.ids.a_cam
        image_object = cam.export_as_image(scale=round((400 / int(cam.height)), 2))
        w, h = image_object._texture.size
        frame = np.frombuffer(image_object._texture.pixels, 'uint8').reshape(h, w, 4)
        gray = cv2.cvtColor(frame, cv2.COLOR_RGBA2GRAY)
        self.root.ids.frame_counter.text = f'frame: {self.counter}'
        self.counter += 1
        Clock.schedule_once(self.get_frame, 0.25)

if __name__ == "__main__":
    MyApp().run()

我的应用程序.kv

<MyLayout>:
    orientation: 'vertical'
    size: root.width, root.height

    GridLayout:
        rows: 2

        RelativeLayout:
            size_hint: 1, 0.8

            AndroidCamera:
                index: 0
                id: a_cam
                resolution: self.camera_resolution
                allow_stretch: True
                play: True
                canvas.before:
                    PushMatrix
                    Rotate:
                        angle: -90
                        origin: self.center
                    Scale:
                        x: self.cam_ratio
                        y: self.cam_ratio
                        origin: self.center
                canvas.after:
                    PopMatrix

        Label:
            size_hint: 1, 0.2
            id: frame_counter
            font_size: self.height * 0.4
            text: ''

buildozer.spec 与解决方案 1 中的相同。

---

最后，不要忘记在安装后为相机添加权限。 （我的代码中没有包含权限请求。）