Sunday, 23 February 2014

Forensics - CSI RAW


With this blog I will be opening up a few different lines of enquiry.  I won't confine it to a pursuit solely for the ideal Birding Image Quality Tool.  I also hope to explore interesting and relevant areas like:-

  • Human Bias
  • The Human Eye and Brain V's the Camera Lens and Processor
  • Forensic Analysis of Photos
  • etc.
Here is a touch of forensics.

Though a lot of birders are big into photography and many shoot in RAW or RAW + JPEG people don't tend to make RAW files available for close scrutiny.  I must admit I have only recently bothered to process some of my own photos with RAW and it has been a real eye-opening exercise.  

A JPEG is a compressed image file.  It is compressed to save space, allowing more images to be stored on a camera's storage card, it's convenient for emailing, websites, adding to documents etc.
One of the downsides with JPEG is it is a LOSSY FORMAT which means data is permanently discarded when a JPEG is made from an original RAW file and this data cannot be retrieved unless the original RAW file has been saved alongside.  If the image was only created in JPEG and there was no RAW file available or saved (many compact cameras, camera phones don't provide RAW files) this data is lost forever.

JPEGs also lose additional data every time they are re-edited and re-saved.  The greater the level of compression, the greater the loss of fidelity.  Another problem with JPEGS is that they often contain small image distortions called COMPRESSION ARTEFACTS which, like any other artefact can obscure valuable details.

For a birder trying to identify a difficult bird from a relatively poor image, one of the greatest frustrations is the not knowing what the true potential of the image could have been.  RAW images contain so much more potential locked within their data than JPEG images.   Below I have rather simplistically shown what happens when a JPEG is made automatically by a camera processor.  

Let us imagine that a particular original RAW file has captured 7 fine details which would all greatly help with the ID of the subject bird.  When the JPEG is made by the processor the processor of course has no idea what may be relevant from a bird ID perspective.  It applies a compression logic plus some user-defined settings and spits out a JPEG which may or may not preserve the details we are looking for.  In the example below the JPEG produced automatically by the camera has preserved 4 of the 7 details captured by the RAW image.  

If we have access to the RAW file we can create our own JPEG image from it having adjusted various settings to display all of the critical details we are after.

Having access to the RAW image files is a big advantage and well worth pursuing if you are faced with a very difficult ID from one or more images.  Of course, with the best will in the world, it may not be possible to improve much on the camera's original attempt.  Here I compare on the left a jpeg produced by the camera versus on the right a JPEG which I produced from RAW.  I was trying to bring out the throat-strap feature, a key marking that would help confirm an ID of Pacific Diver.  

Unfortunately the image quality is simply not good enough to confirm this ID feature, even with the RAW file as backup.  Note: Black-throated Divers can occasionally show a false throat-strap (Mullarney & Millington, 2008, Birding World 21 (2)).

Here I have an image of a 1st winter Kumlien's Gull which I photographed in Dingle, Co. Kerry in January, 2014.  The day was bright and I didn't get a chance to correct exposure before the bird took flight.  It was somewhat over-exposed in the original JPEG and much of the detail was burnt out as a result.  Luckily I was shooting in RAW + JPEG and I was able to retrieve the detail I was looking for in Camera Raw (Adobe, Version 8.3).

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