welcome to Aladeseun's blog: INTRODUCTION;HUMAN VISION,THE CAMERA AND EXPOSURE

welcome to Aladeseun's blog: INTRODUCTION;HUMAN VISION,THE CAMERA AND EXPOSURE: What You See The human eye is a truly astounding piece of biological engineering. It is able to pick up images both in near-darkness...

INTRODUCTION;HUMAN VISION,THE CAMERA AND EXPOSURE

What You See

The human eye is a truly astounding piece of biological engineering. It is able

to pick up images both in near-darkness and in blazing sunlight. Overall, the

human eye can perceive light in a range light to darkness of almost a billion to

one. Unfortunately, when shooting video or film, the critical visual receptor is

not your eye but the camera. And the camera perceives light differently from

your eye and in a much more restricted range. The differences in this perception

are critical to your understanding of how to light and expose video or film,

because the camera simply can’t see the extended range of light the way the

human eye can.

Bear with me for a moment while we take a look at the whole system of human

vision and how it differs from the camera. Light in certain wavelengths is

reflected off of objects; some of this reflected light finds its way into the eye.

There, the light beams are focused on a multilayered receptor called the retina,

where 125 million rods and 6 million cones translate the photons into neural

impulses. The rods, spread all around the retina, are responsible for dim light

and peripheral perception and really do not perceive color. The cones, which

are concentrated in a central area called the macula, are responsible for color

perception and see in the most detail. They require a higher light level to perceive

color and detail.

But the eye is not the most amazing instrument of vision; that really is the

human brain—the place where the neural impulses from rods and cones in

the back of the eye are assembled and interpreted. What we glibly call “vision”

is an incredibly complex event that involves the entire brain and is much

more than sight. There are at least 32 centers for visual processing distributed

throughout the brain. And the visual experience we normally have every

waking

minute is a multilayered integration of two different sets of peripheral

vision and the detailed vision of the macula, the concentration of cones near

the center of the retina. The neural impulses from these two sets of rods and

cones are transmitted to the brain, where they are integrated and interpreted

to assemble an understanding of the objects around us. When you think this

process through, this is the part that is truly amazing. The brain keeps track of

position, motion, and orientation, and integrates the signals from two separate

receptors to perceive

depth. With the merest glance and without conscious

thought, you know that the variation in reflected light is a pencil on the table,

and that it is about two feet away from you. Again without conscious thought,

you could reach over and pick it up—without even looking at it directly. It’s

really pretty amazing.

The brain uses a huge variety of very subtle details and cues to interpret and

understand what the eyes are registering. And because of this, the brain is quite

forgiving. It can utilize existing knowledge to fill in blanks that are poorly

perceived; through depth perception and slight motion, the brain can piece

together what an object is even when it is just on the edge of visibility. Slight

motions of the head and eyes apparently play a huge role in supplying the

brain with enough data to accurately interpret the world “out there,” outside

of ourselves.

This is actually quite important for our topic of study because when we

translate that complex, 3D world of trees and rocks and dust bunnies under

beds into a two-dimensional representation, the brain

suddenly loses several of the subtle cues that it

uses to interpret the world. In particular, we

find that it does not fill in blanks or vague

areas in the same way. So whether the twodimensional

representation is a television

screen or a photographic print or a line drawing,

the creator of the representation must compensate for

what is missing. In short, the representation needs to be better drawn and

more carefully created than the reality would have to be. The important elements

must be clear and well defined. Sometimes it is effective even to blur

out nonessential elements to help focus the eye (and the mind) on what is

essential.

Let me give an example of what I’m talking about here. Suppose you’re sitting

in a dimly lit room you are unfamiliar with. Something in the corner

catches your eye; you can’t quite tell what it is. So you’ll move your head a

little bit, giving the brain extra data about the dimly perceived object; you

may squint or shield your eyes from the light source to allow you a little better

dim light perception. The little bit of extra information gained from this

movement may allow you to figure out what the object is. If it’s not enough,

you always have the option of getting up and walking over there, or of turning

on another light. And if that fails, you can still

touch the object to findout more about it!