In the lightbox, my images look great, but just the thumbnails look grainy. Is there a way to fix this?

Dear Chelsea,

Thanks for contacting us.

Can you please send us your gallery page URL, to check the thumbnails?

www.mcwebsiteonline2.com/press-kit/press-kit-pictures/

Dear Chelsea,

The original sizes of thumbnails are set to 300x300px max. Probably images were imported from WordPress Media Library, which by default cuts thumbnails to that size.

You may change thumb size in WordPress working area. Or alternatively you may set higher resolution for Photo Gallery images; to do so go to Photo Gallery Plugin > Options > Thumbnail options > Generated thumbnail dimensions. And if you upload images using the plugin's uploader, it shall create thumbnails of that size.

To fix your gallery images, you can upload them again with larger thumbnail size.

Let us know if that helps.
Thank you!