In photography, bokeh (Originally: "boh-kay,"
and also sometimes "boh-ka," Japanese: "boke")
is the blur, or the aesthetic quality of the blur, in
out-of-focus areas of an image, or "the way the lens
renders out-of-focus points of light." Differences
in lens aberrations and aperture shape cause some lens
designs to blur the image in a way that is pleasing to
the eye, while others produce blurring that is unpleasant
or distracting—"good" and "bad"
bokeh, respectively. Bokeh occurs for parts of the scene
that lie outside the depth of field. Photographers sometimes
deliberately use a shallow focus technique to create images
with prominent out-of-focus regions.
Bokeh is often most visible around small background highlights,
such as specular reflections and light sources, which
is why it is often associated with such areas. However,
bokeh is not limited to highlights; blur occurs in all
out-of-focus regions of the image.
The term comes from the Japanese word boke, which means
"blur" or "haze", or boke-aji, the
"blur quality". The Japanese term boke is also
used in the sense of a mental haze or senility. The term
bokashi is related, meaning intentional blurring or gradation.
The English spelling bokeh was popularized in 1997 in
Photo Techniques magazine, when Mike Johnston, the editor
at the time, commissioned three papers on the topic for
the March/April 1997 issue; he altered the spelling to
suggest the correct pronunciation to English speakers,
saying "it is properly pronounced with bo as in bone
and ke as in Kenneth, with equal stress on either syllable".
The spellings bokeh and boke have both been in use at
least since 1996, when Merklinger had suggested "or
Bokeh if you prefer." The term bokeh has appeared
in photography books at least since 1998. It is sometimes