In order to use transparency in HP Reveal you need to store the alpha information in the alpha channel of the png - when applying the png as a diffuse colour Maya or 3DS Max will automatically connect the alpha channel of the png to the alpha in the shader.
It is worth noting that transparency can be a little bit temperamental in the HP Reveal 3D engine, so we recommend that you use it with caution; too much transparency applied to different objects in the same scene can cause rendering sorting issues, and end up rendering unwanted effects and artefacts.
Why would you use transparency?
We can use transparency for different reasons, however two of the main ones would be:
1. Define the amount of visibility, translucency and or thickness of an object
- Effect is used in glass and or thin materials
- We recommend trying to use opaque materials when possible
2. Define the silhouette of an object without the need for geometry
- Usually used for foliage, and other geometry that has many duplicates in the scene
- We recommend cutting the geometry when possible even if that would mean increasing the poly-count as long as it is not a massive increase
In order to understand more about transparency please read the following article at wiki.polycount.com where transparency is explained in depth.