Hey, everyone! I came here and did a quick search for a problem I was having, and found a lot of unresolved threads: https://www.onedesigns.com/support/search/featured+image+blurry
Like these OPs, I was uploading HUGE featured images in the Media Library (widths of >1000px), but when I assigned them as a featured image, they suddenly became super blurry.
However, I have another site that uses Pinboard, and it displays featured images of all sizes (even small width, such as 400×400) just fine, and I couldn’t suss out why.
I still don’t know EXACTLY why, but in isolating what was different about my new Pinboard vs. my working-Featured-Image old Pinboard, and I discovered the following hack:
The featured image will be blurry in the default layout ( Appearance > Theme Options > Layout > Content/Sidebar w/ 3 content columns.)
The blurriness appears to be solved if you simply select “Full Width” as the layout, instead of Content/Sidebar.
This might be a “duh” to the template designer and savvy coders, but I saw so many open threads, I thought I could offer this solution to n00bs like me π (Plus, if you’re really set on 2 content columns instead of 3, the issue persists, and unfortunately, I can’t help there!)