How can I improve my PNG sprites?

Hello all.

Today I started placing some PNG in to a new project and it seems that Unity is not liking them. I have tried adjusting the camera scale, the pixels per unit, generate Mip Maps, different filter modes and the various override settings but I cannot get the PNG in Unity to look anywhere like the original. The files are 256x256 PNG24 files. I have sized them at 256x256 and am sizing them to be pixel perfect as per...

Camera Size = y / (2 * s) ---- {Where y = Screen Height (px) and s = Desired Height of Photoshop Square (px)}

I have searched the forums and looked at the tutorials but cannot find anything that cleans up my PNG. I have included two examples. The first is how the PNG looks when I open it on my desktop. The second is how it looks in Unity. As you can see, there is serious degradation.

I would really appreciate any help. Thank you!!