A full screen effect is a way in which a variety of computer graphics applications can have different special effects added to a scene. Rather than actually rendering a scene with these effects applied to the objects and geometry within it, they are essentially applied after the render. This means that the graphics program creates an image that the user sees, and then applies an effect over this in a way that is seamless. A full screen effect can be used to accomplish a number of different tasks, including the addition of motion blur, bloom lighting, and color filtering.
In order for someone to understand the way in which computer graphics applications can use a full screen effect, it is often easiest to first realize how a scene appears. Programs that use Computer Generated Imagery (CGI), such as video games, often render scenes to a display in real time. This means that as a player navigates through a virtual environment, the various objects in a scene that have been created by the developers of that game appear in relation to the player’s position. When the player walks into a room with a box, the game software renders the walls, floor and ceiling, and the box in the room as a series of frames or images about 30 times every second.
A full screen effect can then be added to these individual rendered images to create various results. Motion blur, for example, is a phenomenon that can be seen in the real world or on film; objects often appear distorted and blurry as someone moves quickly past them. While this effect can be applied to objects in a virtual scene, it is often easier and less resource-intensive for it to be done as a full screen effect. Multiple partial renders of the objects in a game are created and overlapped so that a blurred image appears that conveys a greater sense of speed and movement for a player.
Bloom lighting can also be created as a full screen effect. This is often done to make lights in a game appear heavier, to make them stand out, or for a stylized aesthetic. After the different light sources are rendered, the game engine then creates additional renders of increased intensity for the lights and overlaps them. A player in a game can then see these lights as brighter, with a stronger glow.
Color filtering can be applied to a scene in much the same way. If a game developer wants someone to see a room in black and white part of the time, without creating multiple textures for objects within it, then this can be achieved through a full screen effect. While the actual textures in a scene are rendered properly, a filtered layer is placed over each frame to change the colors of objects for a player.