Cropping PNGs with Flutters Image package

Question

I am working on a Flutter project that involves PNGs with arbitrarily wide transparent margins. For example, consider this cat in a box. Cat in a box

I need a way to crop off the margins without knowing where the image will be positioned. This can be done with Flutter's Image package, but I feel like there should be a more elegant solution. Here is how I am currently doing it:

int top = _findHighestPixel(decodedImage);
int bottom = _findLowestPixel(decodedImage);
int left = _findLeftmostPixel(decodedImage);
int right = _findRightmostPixel(decodedImage);

decodedImage = img.copyCrop(decodedImage, x: left, y: top, width: right - left, height: bottom - top);
Uint8List croppedByteList = img.encodePng(decodedImage);

int _findHighestPixel(img.Image decodedImage) {
    for (int y = 0; y < decodedImage.height; y++) {
      for (int x = 0; x < decodedImage.width; x++) {
        if(decodedImage.getPixel(x, y).a != 0) {
          return y;
        }
      }
    }
    return 0;
  }

int _findLowestPixel(img.Image decodedImage) {
    for (int y = decodedImage.height - 1; y >= 0; y--) {
      for (int x = 0; x < decodedImage.width; x++) {
        if(decodedImage.getPixel(x, y).a != 0) {
          return y;
        }
      }
    }
    return decodedImage.height;
  }

int _findLeftmostPixel(img.Image decodedImage) {
    for (int x = 0; x < decodedImage.width; x++) {
      for (int y = 0; y < decodedImage.height; y++) {
        if(decodedImage.getPixel(x, y).a != 0) {
          return x;
        }
      }
    }
    return 0;
  }

int _findRightmostPixel(img.Image decodedImage) {
    for (int x = decodedImage.width - 1; x >= 0; x--) {
      for (int y = 0; y < decodedImage.height; y++) {
        if(decodedImage.getPixel(x, y).a != 0) {
          return x;
        }
      }
    }
    return decodedImage.width;
  }

I would love to know if there is a simpler/faster approach than tediously iterating through all the pixels until I hit the image wall. Thanks!