Monday 23 November 2015

Birding Image Quality Tool - Rev. 4.0 Field Marks

For the seasoned birder in the field many an initial identification may be based on hearing a call or knowing a bird's distinctive gestalt.  But if you stop and take a critical look at any bird, and certainly if you need to identify a bird from a photograph, field marks play a big part in the identification process.  For clarity I like to consider field marks as a bird's distinctive markings and colours alone.  Sometimes size and shape (broadly morphology) is also considered a part of what defines the term field marks.  But I like to keep a bird's markings and it's morphology separate for the purposes of this blog.  I cover morphology under the heading of gestalt.

In the blog I have a page devoted to the subject of field marks called A Spotlight - On Field Marks.  This year I have spent a good deal of time considering field marks for the purposes of identification from bird images.  I have concluded that there are two basic classes of field marks - The Bold and The Bland.  The crucial distinction between the two is that bold markings and colours can be appreciated in even the worst of images because they exhibit characteristics that make them stand out under pretty much all observational and photographic conditions.  Obviously bold field marks perform some vital signally function so it is not too surprising that even in the worst viewing or photographic conditions they hit the mark almost every time.  Take for instance the bright, contrasting fresh adult scapulars and coverts of this 1st calendar year European Turtle Dove.  Compared alongside the faded, diffuse brown gradient at the centre of the older juvenile feathers, these newer feathers create a bold impact.  The older feathers are clearly bland by comparison.  They probably form part of the bird's camouflage, and therefore not surprisingly they evade the camera just as effectively as they do the eye.  My analysis of the bold versus the bland has been consistent, whether the problem is image resolution, focus, exposure, colour accuracy, artefacts, or all of the above.

So, having recently expanded the Image Capture Quality Tool to include a tool that measures the quality of image lighting and another that measures the accuracy of colours, is it possible perhaps to generate a tool who's purpose is to gauge the overall quality of field marks captured in an image.  I believe it's possible and here is my first stab.

Essentially what I have done here is build upon the three other tools with a simple analysis of the effective capture of bold markings and bland markings.  Unlike the other tools however I have allowed the operator to deselect anything that one considers may not be relevant to the analysis.  

Bold Field Marks and Bland Field Marks
Your subject may be all bold (such as this stunning male Moussier's Redstart on the left), in which case the analysis of bland field marks is not applicable and can be deselected from the analysis.  Or visa-versa - this male Trumpeter Finch on the right, though no less stunning consists of subtle field marks (apart perhaps from the bill which could be considered bold).  So, one may decide to exclude bold field marks from the analysis if one so chooses.

Lighting and Colour
Lighting is critical to the accurate capture of field marks in bird images.  After all, light and shade can easily mirror the impression of a field mark to confuse the unwary (eg. HERE).  The Lighting Quality Tool captures all the key elements from lighting quality, direction and shadows to dynamic range issues and the effect of multiple lighting sources.   Colours can be of significance in some identifications but less so in others.  So once again I have given the option to exclude colour from our analysis if it is deemed more helpful to do so.  On the other hand, where colour analysis is critical to an identification the Colour Quality Tool provides a very good measure of accuracy.

Broadening the Image Capture Quality Tool out to include additional critical analysis tools has allowed me to draw a line under much of the work of the last two years in this blog.  The purpose of the blog has been to work on a manual to assist birders who are interested in identifying birds from photographs.  These tools aid that effort by getting the observer to focus on those factors that confound an identification, be it a problem with how an image was captured, or the lighting, or how accurately the colours and details have been expressed in the image.

Once again, all that remains now is to provide you with the tools so you can play around with them and have a go at scoring the quality of your own bird images.  Feedback is as always much welcome and appreciated.

(Note you will have to download the file and open it in MS Excel for the tool to work properly).

In the example below image capture was very good at a score of 98%.  Particularly good for an old digiscoping camera (the classic work horse Nikon Coolpix 4500).  Lighting wasn't bad but bright sunlight does create problems such as blooming artefacts, clipping and shadows.  So the score was lower at just 75%.  Though the colour quality looks quite good, as the image is a jpeg that has underwent a certain amount of manipulation including manual brightness, contrast and manual white balance adjustment, colour reliability is really quite poor overall.  This is reflected in a score of just 40%.  However all is not lost.  When assessing overall the quality of the field marks capture it could be argued that accurate colour isn't all that important for this particular species.  Booted, like a lot of Old World warblers is a fairly bland species.  So I have discounted both the bold field marks and colour quality elements of the field mark test.  Field marks are therefore scored on the basis of the bland field marks, the overall image capture quality and the overall lighting quality, yielding a pretty good score of 91% overall.

There is subjectivity in deciding whether a bird should be scored on the basis of all five field mark parameters.  At least by presenting all the data everyone can see how the score was arrived at.  I hope you find these tools of use not just for assessing your image quality, but also for drawing your attention to parameters that you might often overlook or take for granted when studying bird images.

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