A Multifocus Method for Controlling Depth of Field
Paul Haeberli
Oct 1994
Introduction
When a photograph is taken with a camera, the lens is focused
at a particular distance. Objects nearer or farther than this
focal distance will appear blurred.
By changing the focus of the lens, near objects or
distant objects can be made to
appear in sharp focus. If you want to create an image where distant
objects as well as close objects are in focus, two or
more images can
be merged together to make an image with increased depth of field.
This is done using a simplification of a
pyramid-based technique described in [Ogden 85].
The Technique
Here are two images of the same scene, one focused close and the
other focused at a distance.
We can combine the in-focus parts of both photographs using the
following procedure. First each input image is blurred.
Next, we subtract the blurred image from the original above it, and
create an image
that shows the magnitude of the difference. This image will be dark where
the original image is smooth, and will be bright where the original image
has edges. The strength of the edge information maps directly into the
brightness of these edge images.
Now we compare the two edge images, and make an image that is black
where the left image has more edge information, and is white where
the right image has more edge information.
Finally, this is used to create an image with the best parts
of each original image. Where the image above is black, pixels from the left
image are used. Where the image above is white, pixels from the right image
are used.
A simple extension of this technique can be used to combine
the in-focus parts of any number of photographs.
References
[Ogden 85] J.M. Ogden, E.H. Adelson, J.R. Bergen, P.J. Burt,
Pyramid-based Computer Graphics, RCA Engineer, Sept/Oct, 1985.
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