Time passes by

by clabacchio

submit your photo


Hall of Fame
View past winners from this year

Please participate in Meta
and help us grow.

Take the 2-minute tour ×
Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. It's 100% free, no registration required.

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?

share|improve this question
3  
Two are completely different; Bokeh explained and Gaussian Blur is Photoshop filter, sometimes used to create fake tilt-shift effect, and or fake bokeh. –  Alen Mar 18 '12 at 22:03
    
Bokeh takes the shape of the aperture and you can create heart-shaped bokeh : diyphotography.net/diy_create_your_own_bokeh –  Gapton Nov 7 '12 at 7:44
    
See this diagram on how bokeh relates to blur overall. –  mattdm Mar 7 at 16:09

1 Answer 1

up vote 36 down vote accepted

Bokeh is specifically 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;
  • in bokeh, the smearing characteristics depend on configuration and aperture shape of the lens, whereas gaussian blur is always smooth;
  • a small light source will be rendered as an aperture-shaped figure with quite well-defined edges in bokeh; but gaussian blur renders it as a spot with fading edges;
  • in bokeh, noise is present at the same level as in in-focus parts of image with same luminance; gaussian blur kills noise, so there'll be less noise than in non-blurred parts of image;
  • in bokeh, light areas will dominate over dark ones, while gaussian blur gives preserves the ratio of dark-light areas.

To illustrate:

f/10

A sign in a train station, taken with f/10 (giving deep depth of field).

f/10 + Gaussian blur

Gaussian blur performed on background parts of the previous image.

f/2.8

A sign in a train station, taken with f/2.8 (giving shallow depth of field and natural bokeh).

So, all in all, you can use one to fake another, but the result will be similar only for low-noise bokeh containing items on roughly a plane parallel to focal plane, not including any significantly lighter areas or light sources, and taken with a lens that has a smooth bokeh.

share|improve this answer
    
great answer..thanks. –  Raj Nov 8 '12 at 19:19
    
Very well explained. Excellent answer. –  Parampreet Dhatt Nov 8 '12 at 19:31
    
Not well explained enough yet :). How would a progressive left to right Gaussian Blur be different from that nice Bokeh, in This picture ? –  Skippy Fastol Jul 5 at 8:48

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.