ReShade

ReShade is a lightweight utility designed to help improve the look of older video games. To put it simply, since these games do not support the technologies of modern video cards, the program grants you the necessary tools to include new video tech and hence, get an improved new look.

According to the developer, the tool acts as a generic post-processing injector and can add features such as real depth, field effects, ambient occlusion, color correction, cross processing, dynamic film grain, chromatic aberration and numerous more features that are available with modern video cards. The developer stands for fair play and this is why the color depth information is automatically disabled for multiplayer games to avoid any exploit. Nevertheless, you can access frame color and depth information for single player games and make the desired modifications.

It is worth mentioning that the tool relies on its own shading trans-compiler dubbed Reshade FX, which is basically a HLSL syntax that can add various features used in post-processing effects. You can define, employ and render textures directly or add custom value timers or key states. If you are planning to write your own shaders, then take note that they can be used with any games with Direct3D or OpenGL.