January 2015 - Digital Group - Visual Mechanisms

Meeting Notes March 2009 to 2018.
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spb
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January 2015 - Digital Group - Visual Mechanisms

Post by spb » Thu Jan 08, 2015 4:23 pm

APS member Clive Bartram, gave us the benefit of his professional experience with a talk entitled; Visual Mechanisms and the Art of Photography

Some fundamentals of vision were explored: the nature of light and colour harmony, how the retina works with its red, green and blue sensitive cones for colour vision and the rods for luminance. The concept of opponency in colour vision, with red opposed to green, and blue to yellow was discussed and how a complex arrangement starting in the retinal linkage of cones and rods to ganglia emphasises contrast in the visual process. Several illusions show how this process is not exact. Full dark adaptation takes 30mins but in normal daylight the rods still play a role in darker areas, and this increased eye sensitivity explains why gamma correction is required for otherwise linear response systems. The visual cortex is complex and problems with equiluminant colours and the contextual nature of colour appreciation were illustrated.

The 2 stage process (capture and software manipulation) of creating a photographic image requires translation from the perceived or imaged 3D world into an artificial 2D structure. The art lies in communicating an equivalent visual and emotional response in observers.

We look at an image with rapid short eye movements called saccades that fix upon salient features in the image. With continued attention we then look into an image in greater detail that brings into play a number of cortical areas of the brain. How we compensate for the lack of stereoscopic vision is interesting and again illusions showed that the brain is not always accurate in how objects are perceived. Blurred, white or black backgrounds are common in portraiture but may with white/black backgrounds lead to a loss of depth perception and ambiguity into how the image is read. Low luminance/definition backgrounds have been used by artists such as Rembrandt and also work in photography to give a true sense of space around the sitter. Blurring does not attract attention but reduces depth perception. However, it is a useful device in portraiture and landscapes to give some division of space without diverting attention, whereas perspective always draws attention and will draw the eye in along its path. Relative size, such as figures or familiar objects are important to provide scale in landscapes.

The lecture finished with recommendations for a successful image - a balanced composition that gets attention and an emotional response.


Many thanks to Clive for a stimulating and original approach to our hobby. It goes some way to explaining why an image worth a certain 20 (in my mind) only gets 15 from a judge! If you are intrigued (or confused) by this brief synopsis, Clive can often be found on a Weds morning at Cafe Africa at our weekly socials.

Cheers, Steve Brabner.

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