ModularGrid serves the images in two resolutions depending if you have a "retina" high DPI screen or not.
All images are converted to png, maybe that is the step where loss in clarity occurs.
You can try to upload the image as png to prevent the conversion. Opacity will be preserved btw.
The module does not look too bad for me on my computer.
Beep, Bopp, Bleep: info@modulargrid.net