Post-processing effects are the effects that are created by re-rendering the image of the scene with a shader that alters the final image somehow. Think of it as if you took a screenshot of your scene, opened it up in your favorite image editor, and applied some filters. The difference is that we can do it in real time!
Examples of some simple post-processing effects are:
The basic technique for creating these effects is relatively simple: A framebuffer is created that is of the same dimensions as the canvas. At the beginning of the draw cycle, the framebuffer is set as the render target, and the entire scene is rendered normally to it. Next, a full-screen quad is rendered to the default framebuffer using the texture that makes up the framebuffer's color attachment. The shader used during the rendering of the quad is what contains the post-process effect. It can transform the color values of the rendered scene...