Feature: Apical dynamic range interview: Digital Photography Review
ACCESSED: Thu Mar 19 2009 17:46:10 GMT-0500 (EST)
PAGE URL: http://www.dpreview.com/news/0903/09031801apical.asp
...
Apical attempts to get 'round this problem by assessing the local environment
of each
pixel and considering its relationship to its immediate neighbors as well as
their context
within the image as a whole. 'To give it its technical name, our product,
Iridix, is a space-
variant dynamic range compression algorithm. What the eye does, in camera
language,
is apply a different gain, based on the local environment of a pixel - for
example, a pixel
with a specific R,G,B value in a bright region would be interpreted very
differently to a
pixel with the same R,G,B value in the shadows.' Iridix aims to mimic this
response: it
assesses how each pixel relates to the ones around it, in order to work out the
local
contrast, while also working out how that region fits in with the rest of the
image.
...
Using a single, homogenous, curves adjustment to try to correct the entire
image results
in a slightly flat, washed-out looking image. Iridix calculates a different
tone curve
adjustment for each part of the image (varying slightly between each pixel), in
an
attempt to preserve local contrast all the way across the image, lifting the
detail in the
shadow regions without the whole image looking washed-out.
'To achieve this, and ensure the image looks natural, there are four
non-trivial factors
that need to be considered,' explains Tusch:
1) The preservation of the black and white points of the image (to prevent
color
clipping and avoid true blacks becoming gray)
2) The preservation of true color
3) The exact preservation of local contrast.
4) The complete elimination of any spatial artifacts, such as halos
'Getting any of these four wrong results in a unnatural looking image. For
example, if you
look at tone mapping algorithms for high dynamic range imagery, they often
produce
rather un-natural, "painterly" images, this is simply the result of an
inappropriate
algorithm - the results should look completely natural.'
...to the hands of the professionals
The technology is no longer confined to compact cameras, however. 'We had faith
that it
would be a very useful tool for professional photographers,' says Tusch, ' if
well
implemented and well explained.' And to illustrate his point, he points out
that the
company's technology has become wide-spread in the DSLR sector, appearing in
products from Sony and Olympus, amongst others. 'We've built an image engine
that
produces image quality suitable for professional photographers. However, we
wouldn't
advocate this always being enabled because you may not always want the
photograph to
represent the scene the way it appeared - you may wish to present a more
creative
interpretation.
...
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http://Information.Architecture.Abacurial.com
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