PROJECT: DYNAMIC RANGE

Previously in this module, our studies have covered linear capture, highlight clipping and digital noise.  The latter artefacts being bi-products of digital camera exposure, and each found at opposite ends of the tonal scale (or histogram).

These topics lead us nicely to the issue of achieving a high dynamic range within our images, which ROCKWELL (2008) defines it as ‘the difference between the lightest light and the darkest dark which can be seen in a photo’.  He also goes on to say that ‘once your subject exceeds the camera’s dynamic range, the highlights wash out to white, and the darks become black blobs’.

There are several ways of measuring a cameras dynamic range, but most commonly we can identify the dynamic range of a camera by the number of f-stops it takes to capture one perfectly exposed photograph.  Alternatively, within a scene, the dynamic range is the number of f-stops counted between the brightest highlights and the darkest shadows, (we will be looking at this shortly).

As dictated by its histogram, this image appears to have been exposed within the dynamic range of the camera.

A Photo that is exposed within the Dynamic Range of the Camera

A Photo that is exposed within the Dynamic Range of the Camera

 

 

Histogram showing exposure within the Dynamic Range of the Camera

Histogram showing exposure within the Dynamic Range of the Camera

If the dynamic range of our camera is greater than that of the scene we plan to shoot, then there should be no issue with capturing a well exposed image (as shown above), but if the scene has a larger dynamic range than that of our camera, we will experience visible issues when capturing the information and something within the scene will have to be lost.

… the ideal exposure for images is when the values fill the range from dark to light – in other words, a fully expanded histogram …

Freeman (2011, p.50)

In order to understand the dynamic range of our camera, we need to identify both the darkest and brightest points that can be captured within an image.

As we saw in previous exercises, the easiest digital artefact to identify are the brightest highlights; these appear at the top end of the tonal scale (to the right of our histogram) and can be found by using the camera’s highlight clipping facility.  In reverse, the hardest digital artefact to identify is digital noise, which is found in the darkest shadows of our images and at the bottom end of the tonal scale (to the left of our histogram).

We will be conducting dynamic range tests for our next exercise, but as an alternate to this, we are able to check the dynamic range of our camera by photographing either a grey card, or neutral blank surface using a consistent light source and then changing the cameras exposure by one f-stop to capture a range of readings, which in turn (when using in conjunction with digital software editing packages) will confirm the dynamic range of a camera.

Another source for managing a satisfactory tonal range within our images is the use of the Zone System, devised by Ansel Adams; it is an attempt to provide the perfect exposure of an image using a zone ruler, or tonal scale.  Although this system was originally used for the exposure of black and white images, this system is also relevant to not only colour photography, but also to digital photography too, and has been adapted by some academics for use in today’s digital era.  But, because the Zone System is based on how we feel a scene should look or feel, it is not the same as the actual tonal or dynamic range produced by our cameras internal workings, so should not be used to determine the dynamic range of our camera.

Source:

Reference:

Freeman, M.  (2011) The Digital SLR Handbook.  Revised 3rd Edition.  East Sussex: The Ilex Press Limited.

Rockwell, K.  (2008) Dynamic Range [Online Article].  Available at: <http://www.kenrockwell.com/tech/dynamic-range.htm&gt; [Accessed 3 June 2013].

Bibliography:

Cambridge in Colour.  (n.d.) Dynamic Range in Digital Photography [Online Article].  Available at: <http://www.cambridgeincolour.com/tutorials/dynamic-range.htm&gt; [Accessed 3 June 2013].

Cambridge in Colour.  (2011/2012) Zone System – Ansel Adams [Online Forum Thread].  Available at: <http://www.cambridgeincolour.com/forums/thread15529.htm&gt; [Accessed 3 June 2013].

Freeman, M.  (2011) The Digital SLR Handbook.  Revised 3rd Edition.  East Sussex: The Ilex Press Limited.

Koren, N.  (n.d.) Making fine prints in your digital darkroom – Tonal quality and dynamic range in digital cameras [Online Article].  Available at: <http://www.normankoren.com/digital_tonality.html&gt; [Accessed 3 June 2013].

Koren, N.  (2005) A Simplified Zone System [Online Article].  Available at: <http://www.luminous-landscape.com/tutorials/zone_system.shtml&gt; [Accessed 3 June 2013].

Rockwell, K.  (2008) Dynamic Range [Online Article].  Available at: <http://www.kenrockwell.com/tech/dynamic-range.htm&gt; [Accessed 3 June 2013].

Rockwell, K.  (2006) The Zone System [Online Article].  Available at: <http://www.kenrockwell.com/tech/zone.htm&gt; [Accessed 3 June 2013].

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