When reencoding images with a maxWidth and maxHeight set, the picker plugin currently uses 100% for the JPEG quality level:

• (always passed quality:nil AFAICT) https://github.com/flutter/plugins/blob/master/packages/image_picker/ios/Classes/FLTImagePickerMetaDataUtil.m#L79
• https://github.com/flutter/plugins/blob/master/packages/image_picker/android/src/main/java/io/flutter/plugins/imagepicker/ImageResizer.java#L90

100% quality does not mean lossless compression, however; chroma subsampling and DCT coefficient rounding still occurs, so compression artifacts are still going to be introduced.

However, if the user wants to increase the compression level they then have to re-encode again which introduces yet more artifacting, besides being inefficient for multiple reasons.

This should be a good introductory issue for someone wanting to learn about the Flutter native bridge although it would touch both Android and iOS code.