Commodore amiga thumbnail size

[i30817]

I was thinking of adding some thumbnails to this repository but i'm getting a bit confused.

Several screenshot and title thumbnails have 640x480 size, some images have 320x256, and the emulator can 'crop' the image too, or move it around.

I can do either, 512x720 (720 is default with 512, doesn't affect height of final image) or 640x480 (often looks better in titles, circles are circles, triangles are triangles etc).

After this i can often crop the remaining black borders with image magic, which gives a nice full image without blur artifacts. Only it's smaller than 640 or 512 width.

Finally i can zoom up those images to 512 or 640 width preserving aspect ratio. However, this introduces a ugly blur. Still i suspect that retroarch will also introduce the blur when it zooms in or resizes the image to 512 width (or whatever it is).

What's the right approach?

I'm thinking if the 640 images are persona non-gratas, to fix retroarch to 512, mess around with libretro-puae crop and alignment options so the image is 'as centered and as large as possible' and don't crop the borders externally later (so retroarch never zooms, assuming 512 width is the preferred case). Is this right? What about the zoom in widget in retroarch, is it a multiplier from 512 to 1024 width or something?

The only thing i'm not sure above is the images that look better with 640x480 fixed resolution, of which i've seen some.