I'm in the process of creating sprites for my game and this time I'm not using pixel art which were the size of 24x24ish but higher res 2d sprites created in Affinity Designer which can export hi-res images. I'm now in the process of gathering my sprites and using TexturePacker, which allows you to drag & drop individual sprites in and it'll create an optimized sprite sheet for you.
So my question is: What size should the individual sprites be? For instance, let's take Angry Birds, how large would the individual bird sprites be on the sprite sheet? Would it be 512x512 or higher for each bird and their bird movements? To have 'retina' quality images, what size should the sprites be? (e.g.: What size were the birds in Angry Birds to look that great on screen?) Sorry if this is a basic question, but I'm trying my best to understand it and have my artwork be represented properly on the screen.
Thanks so much for any help or advice! :)