Improve scaled Image aliasing in Canvas - flutter

Question

How can I improving the aliasing of Image objects painted on a scaled Canvas? For example, for the following:
import 'dart:async';
import 'dart:typed_data';
import 'dart:ui' as ui;
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
Future<ui.Image> loadUiImage(String imageAssetPath) async {
final ByteData data = await rootBundle.load(imageAssetPath);
final Completer<ui.Image> completer = Completer();
ui.decodeImageFromList(Uint8List.view(data.buffer), (ui.Image img) {
return completer.complete(img);
});
return completer.future;
}
void main() async {
WidgetsFlutterBinding.ensureInitialized();
final image = await loadUiImage("assets/thierry.png");
runApp(MyApp(image));
}
class MyApp extends StatelessWidget {
final ui.Image image;
const MyApp(this.image, {Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(
elevation: 0,
),
body: Container(
height: 300,
width: 300,
child: CustomPaint(
painter: CanvasPainter(this.image),
),
),
));
}
}
class CanvasPainter extends CustomPainter {
final ui.Image image;
CanvasPainter(this.image);
#override
void paint(Canvas canvas, Size size) {
canvas.save();
canvas.scale(size.width / image.width);
canvas.drawImage(
image,
Offset.zero,
ui.Paint()
..isAntiAlias = true
..filterQuality = ui.FilterQuality.high);
canvas.restore();
}
#override
bool shouldRepaint(CanvasPainter oldDelegate) => true;
}
This is what I see in the emulator:
If I scale the image in an image viewer to similar dimensions, I see this:
The original image is 5814 x 3828.
Notice that the long horizontal lines are more aliased in the version displayed on the emulator. If I don't scale, I don't see this level of aliasing.

Answer 1

To get the best image quality for my scenario, I had to use filterQuality = ui.FilterQuality.medium. According to the documentation, "when scaling down, medium provides the best quality especially when scaling an image to less than half its size". In my case the scale factor is less than half, so that explains why quality is better with medium.
For reference, here's what the above image looks like with medium: