You can clearly see the rendered image is blurred when compared to the original.
I think this might be due to the compression and optimization done to the images on upload. Your image is scaled and optimized to 30kb while my image, at the same image size, is 69kb. i think this makes all the difference.
Can you add an option in the plugin settings to choose either:
1. No optimizations.
2. Only scale image to plugin settings.
3. Scale and optimize (to reduce the kb of the file.)
I notice some plugin developers, even give options to choose the level of file optimization, 50%. 70%, 90% etc.