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[OM] Apical dynamic range interview: Digital Photography Review

Subject: [OM] Apical dynamic range interview: Digital Photography Review
From: "tOM Trottier" <tom@xxxxxxxxxxxxx>
Date: Thu, 19 Mar 2009 18:47:27 -0400
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.

...

===================================================


-- Absum! --    
tOM Trottier,  +1 613 860-6633 
469 Ancaster Ave,  Ottawa, ON K2B 5B6  Canada
http://Information.Architecture.Abacurial.com
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