How many megapixels is my eye?

Roger - Well, the first thing to say here is that the human eye and the camera see things very differently. The eyes got about 160 million rods and cones, which are the light sensitive elements in the retina but they're not spread evenly and the central part of the retina, which is known as the 'macula,' which is the bit we look with when we're looking at something and we want to see something as clearly as possible. Here the cones are packed in very tightly and they give the eye it's best resolving power, and they also provide it with colour vision. This area of very accurate sight only accounts for about two degrees of our whole visual field.

Andrew - It's kind of interesting, if I understand what you're saying correctly, that at the resolution of our eyes is tailing off into our peripheral vision and yet the experience of looking at things, I don't really feel like everything's sort of fuzzy on the edges of my vision, I feel like I can just see things. So how do those things fit together?

Roger - Well that's because you've always seen like that.

Chris - We don't know any better.

Roger - But the digital camera doesn't have any of that sophistication. It sees equally sharply at every point on the sensor or the film, whichever it may be, the periphery and the centre. If it were to see as well as we see with our macular vision, our central vision, we wouldn't be talking about millions of pixels, we'd be talking about billions of pixels.

Chris - Giles.

Giles - You know our eyes are always scanning so when we're actually looking we're only looking at a very, very, tiny portion of it. So what we're actually seeing is really a result of our eyes scanning the entire time.

Roger - You're absolutely right. We're scanning all the time and the brain is filtering out the scanning so everything appears to be still. And more than that, we can actually see in three dimensions because we happen to have a pair of eyes at the front of our heads, looking forward and getting two slightly different images which the brain, once again, can compare, put together, and allow us to appreciate distance and depth. In other words, see in 3D.

Chris - I suppose the main consideration here is that when you take a digital picture, that is literally a snapshot in time. Whereas our eyes, there's about a million nerve fibres in each optic nerve feeding a train of information in through a series of relay stations and onto the back of the brain where we decode what we see.

And, actually, there's an enormous amount of processing going on in what's being fed to our consciousness that we are totally unaware of, and so the visual world we live in is a complete creation, complete artifice made up for us by the way our brain works. And what I call for instance blue, may not be what Kirsten calls blue or red at all, it's just someone's told me that this neurological experience that I call blue happens to look blue to me, but that might be seen by Kirsten's brain as a completely different experience. But we can't compare, we can never find out.