First is the original, second is how the 3DS scales it, in case you somehow can't tell lol. Both integer scaled to 1280x960 per screen to look nice for the Internet (5x for DS, 4x for 3DS)
In case you didn't know, if you hold Start or Select while opening a DS game on the 3DS, you can make it display without any blurry upscaling. It'll be smaller since it's mapping pixel-to-pixel, which is unusable on a small 3DS/2DS imo. But fun fact, a 3DS/2DS XL will actually display it bigger than any DS other than the DSi XL. So it's actually completely usable there
EDIT: If you're viewing this on your phone, please press on the pictures and put it in landscape (horizontal) mode! Try to replicate the size of a 3DS/DS screen as close as you can. I realize now I shouldn't have put the images next to each other horizontally, that was silly of me
EDIT 2: More comparisons here: https://www.reddit.com/r/3DS/s/VRItF6jMM3