Flutter: Unblocking UI thread with Isolates compute function

I do something different which is exporting the created pdf into png files which takes a heavy toll on the main thread. Do you know if there is a way to compute the below?

if (!isPdf) {
  int pageIndex = 1;

  await for (var page in Printing.raster(pdf.save(), dpi: 300)) {
    final image = await page.toPng();

    final String pageQty =
        (pagesToPrint > 1) ? '$pageIndex-$pagesToPrint' : '1-1';

    file = File("${output.path}/$fileName--$pageQty.png");

    await file.writeAsBytes(image);

    imageList.add(file);

    pageIndex++;
  }
} else {
  file = File("${output.path}/$fileName.pdf");

  await file.writeAsBytes(pdf.save());

  imageList.add(file);
}