Monday, 22 September 2014

Birds and Light - Lighting and Composition

The 6th Image Quality Parameter

Birders might use the term "Viewing Conditions" to describe the quality of an observation of a bird in the field.  The nearest equivalent in photographic terms is "Lighting and Composition".  I have been wrestling with the thought of including lighting and composition as an additional image quality parameter from the very start.  Eventually, I decided that the Image Quality Tool was complicated enough without trying to factor in such a challenging aspect.

Through the eye of a photographer, lighting and composition is what puts an individual's stamp on an image and sets the tone or emotion of the scene.  When it comes to bird identification images however we are far less concerned with aesthetics and more interested in the accurate capture of colour and fine detail.  We are also looking for that perfect angle or composition that leaves us in no doubt about the veracity of the evidence.


The quality of light has a huge impact on focus, acutance, exposure, colour and artefacts.  In other words, it strongly influences virtually all aspects of image quality.  

The diagram above pretty much summarises the main lighting conditions encountered by birders in the field.  I have put a number of these situations under the microscope HERE, particularly with a view to understanding the influence of different lighting conditions on colour and white balance (HERE).  

But light also affects the image in various other ways.  Direct sunlight tends to produce higher contrast images and therefore improves acutance (the impression of edge sharpness).  On the other hand, cameras do not handle lighting contrast as well as the human eye and, as a result, bright sunshine challenges the dynamic range of the camera and makes it more difficult to obtain a good exposure (for more see HERE).

Diffuse light is far more comfortable to work in, both for the birder and for the photographer.  A bright, overcast day offers perhaps the ideal lighting.  Clouds scatter white light evenly and create low contrast images with soft, grey shadows and even, saturated colours.  The position of the sun in the sky determines how shadows fall and as the sun nears the horizon the colour temperature and brightness of light shifts dramatically.

The advice from every photographer and birder is the same - for the best results try and keep the sun to your back when viewing or photographing a bird.  With little practice it is possible to read the lighting in virtually any photograph.  From the length, position and contrast of the shadows to the sun's glint in the bird's eye, it pays to pay close attention to the lighting in an image during the identification process. 


Here, what we are interested in is the perspective, or angle of view.  The image below depicts some typical photographic perspectives.  If we exclude the influence of lighting for the moment, there are clearly some viewing perspectives that are more useful to us than others for identification purposes.  Side profile (or slightly offset) seems to be consistently the best viewing angle.

But remember, a bird has joints and can move it's head, it's wings, it's feet and legs, and even individual feather tracts in different directions.  So, the ideal composition tends to become an image where the body, head, legs and wings are all aligned in profile.

An unstable partnership

Now let us consider the combination of lighting and composition together.  It doesn't take much thought to conclude that ideal lighting and composition only exists fleetingly and requires a lot of luck and persistence on the part of the photographer.  Conversely, more often than not, when faced with an identification puzzle involving a difficult set of images, poor lighting and/or composition often plays a big part in the challenge.

Shadows are NOT image artefacts

I have occasionally noticed shadows being referred to as image artefacts in bird identification discussions.  I feel I must point out that this is an incorrect use of the term.  An artefact is anything which distorts an image, ie, it impacts the light after it has left the subject.  Light and shade are both intrinsic parts of the image itself and are not distortions.  Artifical shading (eg. vignetting) is an artefact as it alters the image as it passes through the lens.

I think a much more appropriate description of these image or identification anomalies would be simply what they are - i.e. "Lighting Effects" or "Shading Effects".

The left hand image might suggest that his bird has a dark head but it is purely a shading effect, as clarified by the right hand image.  Incidentally, at the time this bird was photographed it was perfectly identifiable as a Subalpine Warbler (Sylvia cantillans).  However, thanks to Lars Svennson's ground breaking paper and proposed 3-way split of the species, (British Birds 106:651 - 668), even with images like these it may no longer be assignable to form, shadows or no shadows!

Despite the subtle shadow effects that can happen during any photographic setting or session, the above images were taken in lovely soft, diffuse lighting, approaching sunset.  Contrast these images with that of an even rarer warbler which turned up around the same time on the same island (the famous Cape Clear Island in Co. Cork).

This Eastern Olivaceous Warbler (Iduna pallida) is a mega rarity in Ireland.  It's subtle plumage colour tones are a key part of it's complex identification.  This bird was very confiding, defending it's preferred Sycamore for well over a week.  It afforded superb opportunities for frame-filling, portrait compositions but unfortunately the lighting in almost every shot was pretty terrible.  Again, the dappled light and shade is not an image artefact but just a normal part of lighting.  As stark as the light was, it might be argued that the dynamic range of the light was beyond the range of the camera at times - the tail tip is a blown highlight for instance and there is a hint of blooming (artefact) on the left hind claw.  Therefore perhaps one might argue there is a distortion of the true image here.  I would still probably refer to it as extreme lighting rather than use the term artefact to describe the high contrast discrepancy.

This image is also useful because of it's challenging white balance.  There are in fact two competing ambient light sources here.  Firstly, we have the sunlit part of the bird, which is extremely bright and overexposed in this image and of a very pure white colour.  Then we have the shade, which is correctly exposed but which is effectively lit by the sky and therefore has a blue colour cast to it.  I have actually white balanced this image by eye but the technically correct thing to do would have been to introduce a grey card to the shade of the tree and capture an image of that for white balance purposes.  Given that the part of the bird in the shade is the correctly exposed part, the correct white balance in this instance is the part of the bird in shadow.  Then again, had I been following the ETTR model of image exposure I would have been under-exposing the image, trying to avoid blown highlights.  Well, I never claimed to be a great photographer!  For more on dual white balance see HERE and for more on ETTR and other thoughts on image exposure see HERE and HERE.

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