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YUV -> RGB Conversion in Flutter

Full working example of YUV to RGB conversion in Dart with native code(Java)

Why is it needed?

Personally, I encountered a problem while making a real time recognition app, using a model i trained with the FastAI library.
Since the library requires an RGBA image type for prediction, and the Camera plugin produces YUV images, i got stuck for a few days searching for efficient conversion solution.
After reading a lot of half working examples of people stuck in the same situation as I, and with a lot of trial and error, I managed to get a decent solution for my purposes.

The solution in brief

After trying a few examples, the best solution seemed to be using native code(Java) to convert the image. A MethodChanel is being opened upon page init, allowing a direct connection for transferring the content of the frame forwards and backwards, to and from the conversion function.

Average conversion time:

The conversion speed depends on the phone itself + the quality you chose for the CameraController.
Here are the results for 2 different physical devices tested:

  • Redmi Note 4:

    • Low quality: ~0.03-0.06 Seconds.
    • Medium quality: ~0.1-0.14 Seconds.
    • High quality: ~0.2-0.24 Seconds.

  • Meizu 16:

    • Low quality: ~0.015-0.016 Seconds.
    • Medium quality: ~0.03-0.05 Seconds.
    • High quality: ~0.09-0.1 Seconds.

What does this example includes?

  • Permission handling for the camera(loop until the users accept).
  • Full screen of the live camera preview
  • Channeling camera frames for conversion
  • Optional response stream for the RGBA Jpeg image(Uint8List)

Important notes

  • The minimum SDK version of the application is 21 ( Required by the "Camera" package).
    • Action to preform: Open "android/app/build.gradle" and change minSdkVersion XX to minSdkVersion 21
  • Camera privileges need to be requested at the Manifest level.
    • Action to preform: Open "android/app/src/main/AndroidManifest.xml", add <uses-permission android:name="android.permission.CAMERA"/> to the <manifest> element.
    • Note: Do not insert the element to the <application>). It should be a direct child of the manifest element.

Camera resolution

When initializing the "CameraController" object, an enum called "ResolutionPreset" should be passed to define the camera quality.
Those are the values for each entry as shown in the official flutter site..

  • low → 352x288 on iOS, 240p (320x240) on Android
  • medium → 480p (640x480 on iOS, 720x480 on Android)
  • high → 720p (1280x720)
  • veryHigh → 1080p (1920x1080)
  • ultraHigh → 2160p (3840x2160)
  • max → The highest resolution available.