for a png image, if its alpha is [0, 255], it looks fine, but if its alpha is 0 Or 255, it looks not correct
https://share.weiyun.com/c6a6e0492705cc ... 7809aa843a

first image alpha is [0, 255]
second is 0 Or 255
third is PreMultiplyAlpha version of second
and I use FreeImage for PreMultiplyAlpha convert

Hi UE4,

Unfortunately UE4 fills in the masked out parts of PNG images (alpha == 0) with colors from adjacent texels, which means PNG images cannot be used with the pre-multiplied alpha images required by NoesisGUI.

For the time being, please convert the image to another format, such as TGA, and import again.

There's more information, including a link to the Unreal forums where the problem is explained, in this forum thread: How to use transparent images In UE4