Since GeoDict 2023 we offer the option to have structures with up to 256 different material IDs. For the ExportGeo-Base to image stack export, each ID number simply is mapped to the same grey value number (for 8 bits they are in the range of 0-255).
It might lead to image stackes, where one grey value is 0 and the other is 1, which are very close to the same tone of grey. This means that the stack is not "completely" black, but hard to distinguish for the human eye. If you import those pictures into a program you can still continue working with discrete pixel information.
If you want to have a closer look at the picture with the bare eye, you can reassign the materials IDs before exporting. For example, if you have a structure with the material IDs 0, 1 and 2 you can use ProcessGeo:Reassign:
That way the IDs will corresponde to the grey values, 0, 127 and 255, which are very well distinguishable on a 2d image.