Compressing a PNG by using color indexing, for example. Or do only dimensions matter?
this is a trade off between two bottlenecks:
The answer depends on your hardware and compression method. I would recommend to use standard compression to reduce the file size. After reading the textures they are sent to the GPU via the Open GL interface. For CityEngine's procedural runtime 'GL Texture Compression' is enabled by default, what should give best GPU performance. Texture compression is provided by the driver and is independent of the original image format.
Retrieving data ...