convertYUV420ToImage static method

Implementation

static image_lib.Image convertYUV420ToImage(CameraImage cameraImage) {
  final imageWidth = cameraImage.width;
  final imageHeight = cameraImage.height;

  final yBuffer = cameraImage.planes[0].bytes;
  final uBuffer = cameraImage.planes[1].bytes;
  final vBuffer = cameraImage.planes[2].bytes;

  final int yRowStride = cameraImage.planes[0].bytesPerRow;
  final int yPixelStride = cameraImage.planes[0].bytesPerPixel!;

  final int uvRowStride = cameraImage.planes[1].bytesPerRow;
  final int uvPixelStride = cameraImage.planes[1].bytesPerPixel!;

  final image = image_lib.Image(imageWidth, imageHeight);

  for (int h = 0; h < imageHeight; h++) {
    int uvh = (h / 2).floor();

    for (int w = 0; w < imageWidth; w++) {
      int uvw = (w / 2).floor();

      final yIndex = (h * yRowStride) + (w * yPixelStride);

      // Y plane should have positive values belonging to [0...255]
      final int y = yBuffer[yIndex];

      // U/V Values are subsampled i.e. each pixel in U/V chanel in a
      // YUV_420 image act as chroma value for 4 neighbouring pixels
      final int uvIndex = (uvh * uvRowStride) + (uvw * uvPixelStride);

      // U/V values ideally fall under [-0.5, 0.5] range. To fit them into
      // [0, 255] range they are scaled up and centered to 128.
      // Operation below brings U/V values to [-128, 127].
      final int u = uBuffer[uvIndex];
      final int v = vBuffer[uvIndex];

      // Compute RGB values per formula above.
      int r = (y + v * 1436 / 1024 - 179).round();
      int g = (y - u * 46549 / 131072 + 44 - v * 93604 / 131072 + 91).round();
      int b = (y + u * 1814 / 1024 - 227).round();

      r = r.clamp(0, 255);
      g = g.clamp(0, 255);
      b = b.clamp(0, 255);

      // Use 255 for alpha value, no transparency. ARGB values are
      // positioned in each byte of a single 4 byte integer
      // [AAAAAAAARRRRRRRRGGGGGGGGBBBBBBBB]
      final int argbIndex = h * imageWidth + w;

      image.data[argbIndex] = 0xff000000 |
          ((b << 16) & 0xff0000) |
          ((g << 8) & 0xff00) |
          (r & 0xff);
    }
  }

  return image;
}