What was the resolution of PNG?
Which import option have you used?
And what is the resolution of Harmony scene and also scale factor?
When you see the pixelated bitmap of Harmony, there are two main reasons
-Either the resolution of the bitmap is low related to the scene and scale factor in Harmony
-If the original bitmap has sufficient resolution and you have imported it ‘keep as original bitmap’ and the pixelation only be seen in the OpenGL view (not final view), try change the bitmap image display quality.
Harmony by default creates a thumbnail for the bitmap to optimize the performance by reading a small image for animating (OpenGL view).
Also you can try importing bitmap as texture or use .SWF or .AI to convert vector to vector to avoid pixelation issue due to bitmap.