My featured images are blurry, even though I’ve been following the size guide (640x250). Images within my posts aren’t looking as sharp, either, although better than the featured image. How can I improve this? I’m using high-res images to start with.
Can you please share your page link with us so we can inspect this on your end?
If you were using some other theme, or some plugin for image optimization this can be the problem, and you should try this plugin in order to regenerate images to sizes defined by the theme https://wordpress.org/plugins/regenerate-thumbnails/.
Also since images will be re-sized to 640×250 you can try to use double the size ex. 1280x500px
Ah! Yes. The link is http://blog.seamly.co/. Thank you for the plugin rec.
I checked your page, and everything is fine, you can try to use double size of images, or sty with same size but use less compression when saving, or no compression at all. For example this image http://blog.seamly.co/wp-content/uploads/2015/08/Utility-Jacket-Featured-640x250.jpg is 28kb in size. It is quite compressed, you can use images up to 100kb and you should have no problem with page speed, and site performance.