How do I erase a section from custom paint on flutter?

Question

So I have this custom paint which gets ui.Image of a mask and an image both drawn on canvas. Now I made the mask be painted blue for this example but my goal is to save the canvas after I manage to completely delete the blue masked area (see example image) by making it transparent and saving it as a png image with just the body. Is this possible to achieve with custom painter? So far I cant seem to make anything on the canvas completely transparent even with blendmode.clear shapes.

import 'dart:ui' as ui;

import 'package:body_detection/models/pose_landmark_type.dart';
import 'package:flutter/material.dart';

class SegmentationPainter extends CustomPainter {
  SegmentationPainter(
      {required this.mask, required this.imageSize, this.image});

  final ui.Image? mask;
  final ui.Image? image;
  final Size imageSize;
  final pointPaint = Paint()..color = const Color.fromRGBO(255, 255, 255, 0.8);
  final leftPointPaint = Paint()..color = const Color.fromRGBO(223, 157, 80, 1);
  final rightPointPaint = Paint()
    ..color = const Color.fromRGBO(100, 208, 218, 1);
  final linePaint = Paint()
    ..color = const Color.fromRGBO(255, 255, 255, 0.9)
    ..strokeWidth = 3;
  final maskPaint = Paint()
    ..colorFilter = const ColorFilter.mode(Colors.blue, BlendMode.srcOut);

  @override
  void paint(Canvas canvas, Size size) {
    Paint background = Paint()..color = Colors.red;
    Rect rect = Rect.fromLTWH(0, 0, size.width, size.height);
    canvas.drawRect(rect, background);
    canvas.clipRect(rect);
    if (image != null) canvas.drawImage(image!, Offset.zero, Paint());
    canvas.saveLayer(Rect.fromLTWH(0, 0, size.width, size.height), Paint());
    canvas.restore();
    _paintMask(canvas, size);
  }

  void _paintMask(Canvas canvas, Size size) {
    if (mask == null) return;

    canvas.drawImageRect(
        mask!,
        Rect.fromLTWH(0, 0, mask!.width.toDouble(), mask!.height.toDouble()),
        Rect.fromLTWH(0, 0, size.width, size.height),
        maskPaint);
  }
enter image description here
  @override
  bool shouldRepaint(SegmentationPainter oldDelegate) {
    return oldDelegate.mask != mask || oldDelegate.imageSize != imageSize;
  }