看看图像包.以下是示例部分中提供的代码段，它将JPEG转换为PNG:

Take a look at the image package. The following is a snippet available in the examples section, which converts JPEG to PNG:

import 'dart:io';
import 'package:image/image.dart';
void main() {
  // Read a jpeg image from file.
  Image image = decodeImage(new File('test.jpg').readAsBytesSync());

  // Resize the image to a 120x? thumbnail (maintaining the aspect ratio).
  Image thumbnail = copyResize(image, 120);

  // Save the thumbnail as a PNG.
  new File('out/thumbnail-test.png')
    ..writeAsBytesSync(encodePng(thumbnail));
}