Dynamic
Range Optimization
Over
the past few years much effort has be put into trying to make
digital camera image quality as good as if not better than that of
film. Generally this has been concerned with resolution and noise levels, but
another particular area where some effort has
been spent, is in attempts to widen dynamic range. Fuji have been at
the forefront of this producing cameras with different sensor
designs to those normally used, and involving pixels of differing sizes.
The
dynamic range that a sensor can cover is a vital part in the
production of the best possible image quality because it sets the
limits of the tonal range that can be captured in any scene. How
much detail can be depicted in areas of shade and shadow, and
perhaps more importantly with regard to digital cameras and where
the biggest problem usually occurs, how much detail can be retained
in areas of brightness.
In
scenes where these problems arise, those of high contrast, bright
sunny days at any time of the year where areas of both brightness and deep shadow exist,
attempting to allow for these, by either increasing exposure to
reveal shadow detail, or reducing exposure to preserve detail in
bright areas (highlights), means loosing detail at one end of the
spectrum or the other. Shadow
detail is only produced at the expense of lost highlights, whilst
these are only preserved at the expense of lost shadow detail. The
narrower the DR range the worse this problem becomes, and conversely
the wider the DR the less of a problem it is.
A
recent new arrival increasingly being added to camera
specifications, most notably DSLR's but increasingly digicams as
well, is the option to 'extend' or
'increase' the DR range. This is often implemented at the cost of a
narrower ISO range, comes with various different names depending on
the camera maker, dynamic range optimization, highlight tone
priority, shadow adjustment technology, active D-lighting, etc, but which all works in
roughly the same way, and
is software based.
In
spite of the rather grand sounding names that have arrived to
describe it there isn't really a lot to it actually, for it has nothing to do with sensor design, but post
processing of the sensor information often coupled with exposure
adjustment. It's one reason it is being so
widely incorporated into cameras, for it can be used with virtually any
camera and sensor design, and as such doesn't cost much either in
terms of extra camera specification.
In fact it's just an automated in-camera
method of image adjustment that anybody can carry out separately with any
camera and a decent image editor, for basically it's really nothing more than
either under-exposure to preserve highlights coupled with
subsequent levels adjustment to lighten shadow details. A method of
preserving highlight detail whilst still producing details in areas
of shadow. Or in many cases just shadow adjustment alone. Our
pages on Image Exposure
& Using Levels
deal with both these
issues, and show you how to undertake it and the results obtained, whilst
the page on Histograms
will
probably also be of benefit.
Having
the camera decide automatically when scene highlights will be
over-exposed and allow for it in this way, applying subsequent
alterations to shadow areas to produce a balanced final image which
needs no further alteration sounds
good. The problem is in discovering how efficient each particular
camera is at actually implementing this. For deciding at what level
to carry out these alterations, by how much to
under-expose the image, and at what level to raise the tones of the
shadows to, is something that can be very subjective. Because a
major side effect of under-exposure is that noise levels can rise, and
become much more evident in darker tones if these are
subsequently lightened. It needs a very deft touch to find the right
balance between the two. But if it is proved to work satisfactorily
then it is an advantage to have and to use.
Anyway,
all we can say is that welcome as these extra image processing
specifications are, they shouldn't be viewed as something that you
can't do without and are worth changing your present camera for,
just a useful additional bonus to have if you happen for other
reasons to purchase a new camera.