So when you have an image with a transparent background and the edges are antialiased, downscaling makes it look bad.
Source image:
Source resolution and downscaled in ROBLOX:
Yeah the scaling is pretty ancient. Thanks for bringing this up.
What I did in the meantime is I made the edges along transparency dark on purpose…
Edit: for clarification, the tan background is just a frame color underneath
IIRC from my years of browsing gamedev.net, this is because the transparent areas also have color, and when the image is scaled down in the mipmapping process, those normally nonvisible colors are used for the interpolation which causes the downscaled image to have some extra darkness in those regions.
Fix by “flooding” the color from the opaque area into the adjacent transparent area. Eg in your case, the transparent area should be yellow (you probably can just use paint bucket to color it as yellow at 100% transparency)
Of course its possible that the paint software or roblox changes the transparent areas to be black at some point which would prevent you from fixing it.
Roblox COULD add a special case to color the 100% transparent areas to match the color of the adjacent opaque areas, but that can be a lot of processing and you can do it yourself so…