Metal nanoparticles (NPs) fabricated by means of the solid state dewetting (SSD) approach are applicable in many optoelectronic, biomedical and catalytical applications. However, the fabrication of metallic NPs with the low diffusivity elements such as platinum (Pt) has been challenging for the well-defined configuration and uniformity due to the low diffusivity of Pt atoms and thus the optical properties suffer. In this paper, the evolution of well-defined configuration and improved uniformity of Pt NPs are demonstrated by the altered solid state dewetting (ASSD) approach using a sacrificial indium (In) layer. Upon annealing, the high diffusivity In atoms can lead to the formation of In-Pt alloy due to the inter-mixing at the interface and the dewetting process advances along with the enhanced diffusion of In-Pt alloy atoms. Eventually, well-defined Pt NPs are formed by means of complete desorption of In atoms by sublimation. By the control of In and Pt ratio in the bilayers with the fixed total thickness such as In4.5 nm/Pt1.5 nm, In3 nm/Pt3 nm, In1.5 nm/Pt4.5 nm, the isolated dome shaped Pt NPs of various size are demonstrated, which reflects the significant impact of In component in the dewetting process. The optical characterization of Pt NPs exhibits the formation of quadrupolar resonance and strong dipolar resonance bands in the UV and VIS regions respectively, which are tunable based on the morphology of Pt NPs. In specific, the dipolar resonance peaks demonstrate a red shifting behavior with the increment of size of Pt NPs and gradually become narrower along with the improvement of uniformity of Pt NPs.