Saturday, 27 September 2014

An Artefact or Not an Artefact

HERE I listed the most common image artefacts.  An artefact is anything that distorts an image, so artefacts are introduced from the moment the light leaves the subject until the final edited image is created and saved.

In the table above I have broken down the formation of a digital image into five stages and identified the artefacts that are introduced at each of those stages.  I have also listed imaging aspects that are not normally considered digital artefacts.  People may disagree with the distinctions I have made here and if so I would like to hear some alternative arguments.  The guiding principal I am using is that if the original image is not distorted (or can be retrieved) there is no artefact.  

There are various limitations with all imaging systems, including the human visual system.  Most of the time these limitations amount to a deletion or loss of image detail, clarity and/or colour.  The distinction between this loss of information and an artefact as I see it is that an artefact tends to introduce false information, data or colour.  Therein lies the problem.  Artefacts can confuse an identification or worse.  It may even lead us to make incorrect assumptions and identifications.  That is not to say of course that the omission of details or colours due to data loss couldn't also result in an incorrect identification.  But, we can only work with what we can see.  We just need to be aware of the potential for image data loss and be mindful of it. 

Lighting and Dynamic Range

HERE I explored the importance of lighting and composition in digital images.  Where there is light there is shade.  Occasionally shading is referred to as an artefact and this is clearly not an appropriate use of the term.  Dynamic range is another interesting one.  Harsh light with high dynamic range challenges the camera's ability to properly expose images and glare or reflection can also obscure detail.  Again I don't see these issues as digital artefacts.  There is a loss of image detail but nothing new or false is introduced.

Image reconstruction

HERE I explored the similarities between how images are captured by the camera and by the human visual system.  Clearly both imaging systems drastically transform an image - the original light from the subject is absorbed by photo-receptors and turned into an electrical signal that is later reconstructed as the image we see.  Ultimately, when it comes to studying a digital photograph, the original image has gone through both of these transformations - first by the camera and computer, then our own visual system.  

We would not consider the process of transforming and reconstructing the image as an artefact in itself.  We look for telltale glitches in the process and theses glitches are the artefacts.  Mostly artefacts are found around the edges, or at the borderline between contrasting colours and tones in the image.

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