A lot is written these days about design, marketing & creativity etc. However it is quite amazing (to me anyway) that no one ever seems to comment about the limitations of the equipment that we all have. I'm not talking about your computer here, but your eyes, your brain and your vision.
The eye is a wonderful thing, but without our brilliant brain and the interpretive process, it would be little more than a camera, albeit a very sophisticated one. The eye though has limitations and these are often forgotten about (or not even known) by designers.
The cells of the eye are divided in 2 types. One cell type, the rods, deals with grey scale, the other cells called cones (about 5%of the number of rods) deal with colour. The rods are also more sensitive, and so for easy to read information we need contrast. Hence black & white is so powerful. I don't want to go into the actual biology of the eye here too much, but really this should be taught in Graphic Design courses before a computer is even turned on, but it isn't. Some of the limitations of our visual system are in the way that the colour cells are "wired". They can either send a blue signal or a yellow signal on one connection and a red or green signal on the other. They cannot however send a yellowish-blue signal nor a greenish-red signal. You will see examples of this here:
You will see straight away that your brain cannot discern the colour in the center. Being clever and knowing that something is there the brain then uses the grey scale cells to fill in the space, hence we see grey through the middle. I have seen these fades used in business card and sign design it will always have the same effect.
Another limitation to our eyes that also impacts on our pick-up of information is the way that they cells are grouped and the way that images fall across the back of the eye (retina). This has to do with edges and tone of colours.
Microscopic cross section of photoreceptors in the human retina.
(Picture courtesy of Dr Peter Munro, UCL Institute of Ophthalmology, London EC1V 9EL)
Photoreceptors generate electrical signals in response to light. The small circular cells seen here are rod photoreceptors, which are used for night vision and the larger cells are cones, which are used for daytime and colour vision. Each human eye contains about 125 million rods and 6 million cones.
Casting and image with straight lines across the retina results in it missing a lot of the colour cells (cones), the brain then has to struggle to find the edges if those colours fall into a similar tonal range.
Stay tuned for the next post, where I will show you what happens when we don't try to make it easy for the eye and the brain and ignore the above.