What's the difference between Bokeh and Gaussian Blur?

Question

I have heard multiple times in photography, the words Bokeh, and Gaussian Blur. To me, it seems that the words are used almost interchangeably, but in some instances, I have heard them contrasted. What's the difference, and what are the definitions of each of them?

Asked by J. Walker

Answer

Bokeh is the out-of-focus areas of an image. Gaussian blur is an algorithm to fog selected image areas, to hide details or make them look out of focus.

The main differences:

• bokeh is created optically, gaussian blur in post-production;
• in bokeh, the amount of how wide an out-of-focus point will be smeared is determined by its relative distance from focal plane, whereas gaussian blur is applied to a two-dimensional image where no distance information is present, thus all points are smeared equally;
• gaussian blur is always smooth, whereas in bokeh, the smearing characteristics depend on configuration and aperture shape of the lens;
• you can use one to fake another, but the result will be similar only for bokeh containing items on roughly a plane parallel to focal plane, provided the lens has a smooth bokeh.

Answered by Imre

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