Then it's definitely an odd one. I personally never had trouble using an image at it's native size with the export settings quality set to 100% in KM. Yours is mainly using a primary color (black #000000) so it's even stranger IMO but it may be nobody can see what is going on or help without your KM source and matching image source.

Then again, it could be those darn rctriangles (they never cooperate)