poor slide quality on thethe image slider

The quality of the images I am uploading changes when the images appear in the slider. I might, for example, upload a 100kb image that is crisp, and then the slider shows a slightly blurred version that is only taking up ~40kb. Does anyone know why this might be happening? Is there a way to stop it from happening?

Thanks!

https://www.ads-software.com/extend/plugins/thethe-image-slider/