This post-process filter acts as a post-render image viewer, and also allows you to tweak the overall image, seeing the changes in the view panel as you edit the parameters.  When you close the window, the render itself is updated.

You may resize the window by dragging your mouse at the lower right side of the panel.  If the panel is smaller than the image, you can drag the image around with the mouse to expose different areas.

fog

overlay