Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: File Format
ID_PAINTTEXTURE_SAVEFORMATParameter: Filename
ID_PAINTTEXTURE_FILENAMEParameter: Color Profile
ID_PAINTTEXTURE_ICCPROFILEParameter: DPI
ID_PAINTTEXTURE_DPIParameter: Aspect Ratio
ID_PAINTTEXTURE_ASPECTRATIO