Tailoring of thermal emittance has applications in smart radiators, camouflage, infrared (IR) scene generation, stealth, and thermal management. Various studies have explored avenues to achieve both passive and active emittance tuning using methods such as meta-surfaces, phase change materials, composites, nanostructure arrays and multi-layer stacks. Most of these methods often involve complex fabrication processes like multilayer depositions and micro/nano patterning, limiting their scalability for large-scale applications. This study presents a straightforward and scalable approach for passive and active emittance tuning using Indium Tin Oxide (ITO) films deposited on a high emissivity flexible polyethylene terephthalate (PET) substrate. By changing the deposition time, the thickness of the ITO film is controlled which changes the observed emissivity of the ITO/PET composite structure over a wide range (0.2-0.94) while maintaining optical transparency. Using this approach for passive emittance tuning, we demonstrate an IR scene generation application. As the ITO film is conducting, by applying voltage to the ITO/PET sheet, its temperature is changed using which active emittance tuning is also achieved. Compared to existing methods of emittance tuning, the presented approach is simpler, gives flexible films with optical transparency, and has the potential for large-scale integration, enabling cost-effective and scalable manufacturing of emittance-tuned surfaces.