Pixiq

Sharpness…Yes, I've been thinking about it again for the seemingly simple things- those familiar words we bandy about - are often the hardest to address conceptually.

It's a bit like kids asking those fundamental questions that seem to cut right through the crap and leave you reeling. My two, Hannah and Rhodri, were practiced experts at doing this just before bedtime knowing full well their dad could never resist the chance to explain...they later studied psychology and philosophy respectively. Clearly, I didn't have a chance.

In photography, sharpness is often confused with resolution, especially now when ideas from film days are transferred to the digital era. Some wrong suppositions are made about spacing of sensor sites, for example, being analogous to line pairs per mm on film. People forget about that jiggery-pokery of interpolation that goes on in their camera's imaging engine and that complicates matters. It does not help that we are in the dark about such processes and manufacturers are cagey about enlightening us.

Moreover, when we talk about a 'sharp' lens it might not be the one to come top in the tests but it is a balance between resolution and acutance (the way it handles transitions at edges between light and dark). Leitz knew all about this.

You can set criteria for resolution and then quantify it. However, the thing about sharpness is that it is subjective and it is nigh on impossible to put numbers to such things although people do try with smells, tastes and so on…witness a scale of ‘heat’ for chillies! Anyone who has touched on philosophy in their studies comes quickly to the perennial 'perception' problem: how can you tell that your friend sees the colour blue exactly as you do. Answer you can't - move on, pour another beer.

I've been thinking of a slightly different approach (for me at least - schooled on the math of diffraction) to sharpness and that whole business of fooling the eye. It's nothing new so I thought I'd look at two things that really interest me: mosaics constructed by humans (part 1) and their counterpart in nature (part 2) that can tell us a lot about what makes things seem sharp to us.

I remember learning about the simple biology and optics of the human eye at school and thinking it incredible that this was such a great optical system. Later I found out that it isn’t and that a huge amount of image processing and correction goes on in the brain.

Our brains struggle to make sense of the world for us and, incredibly, work to impose order when we are at limits of perception (low light for example). Do you remember how as a kid, folds in a curtain could begin to look like faces - especially if you'd seen the video of the exorcist? Then, every year, people see faces in the sky in the clouds, cheese shapes on pizza (when sober)…unsurprisingly with a ‘religious’ significance. It is part of our 'hot wiring' - I am always on the lookout for shapes in rocks, gnarled bits of olive trees and so on that look like faces or creatures of some sort. Too much Stephen King or H.P. Lovecraft maybe...?

The French Impressionist painter Claude Monet used short strokes of his brush to capture the essence and cleverly deployed colour that our visual senses mix - close to, it looks a mess but stand far enough away and your eye integrates these into a picture. George Surat moved away from this to use small dots of paint to create images: again the brain mixes them to create other tones.

You see the same thing in reverse on a screen when you move in on an image that looks sharp on screen - enlarge 100%, 200% and more.  This deception is all around us for our TV screens build up detailed pictures from dots (RGB) and, anyone who works with video knows - if a picture is moving you can get away with much lower resolution in each of the frames. Same thing with pairs of frames for 3-D. Magazine pictures are assembled from coloured dots of Cyan, Magneta, Yellow and black (CMYK).

So the camera does not lie - but maybe it never tells the truth either (whatever that is).

Go back even further to classical times and we find that artists in Greece and Rome were great at creating images out of pieces of colored stone. I love mosaics and find the way the old masters of this art created detail, light and shade astonishing. If ever you get the chance to visit the National Archaeological Museum in Naples you will see some of the best things that were found at Pompeii – incredible mosaics of astonishing detail because the bits they used (tesserae) were small.

Images of Mosaics

Some of the best mosaics are found in Mediterranean countries that are hot and dusty in summer. These days many mosaics are under cover for protection for, having been revealed after being buried for centuries, they can deteriorate quickly. Northern Cyprus is a land forgotten by time for the moment following the Turkish invasion and the ejection of its Greek populace in 1974. However, progress in the form of developers will change that. Little money is available to protect ancient sites and so we were able to visit mosaics in the rain - a great time to see them for the colours return. Many years ago on an assignment in the southern part of Cyprus, where I had lived, archaeologists had been prepared to wet some newly found mosaics with a bucket of water…

An archaeologist friend once told me of a famous member of his profession who, rather than wait for a bucket to wash the dusty uncovered mosaic would instruct ladies to turn the other way..ahem.

Post-production soaking: metaphorical

In both Photoshop and Lightroom you can effectively "wet" mosaics to rejuvenate the colours if you want to: I  find clarity, vibrance and a touch of sharpening are all you need. If mosaics are under translucent cover that tends to defuse ambient light and reduce surface reflections.

When mosaics are wet you might find a polariser will be effective in cutting surface reflection. If mosaics are out in the open and you can choose time of day and season to visit then morning or evening light away from high summer when the sun is low in the sky creates those tiny shadows that produce relief and the sense of increased sharpness. 

It is not unlike the way we sharpen things in Photoshop - effectively by darkening pixels at edges...drawing a dark line to accentuate. Nature got there first.