I am trying to figure out the optimal size for the 'small' images (the one that will appear on a category page) but no matter what size or resolution I make them, they appear as low resolution - I have tried them from as high as 2000 x 2000 px - down to 250 x 250 px and they are always saved as optimized for web through Photoshop
All images in the frontend are automatically resized based on theme settings. The sizes are defined in
etc/view.xml of the theme and are different for various areas, like the category grid.
For example: luma/etc/view.xml
<image id="category_page_grid-1" type="small_image"> <width>240</width> <height>300</height> </image>