Thursday, August 15, 2013

Amount of Light


Composition is a vast subject to study, in any visual art. 

It is very similar in function to the choice and use of words in literature, their contextual, semantic and semiotic relationships and the grammar of a language.

 That way, in visual media, everything can ultimately be reduced to Composition. However, for a better understanding of the potential of the medium, the study is structured in a different way.

While composition talks about what to show and why to show, there are steps to reach the composition in mind – how to show.

 That way, a big issue in Cinematographic composition is Exposure. Probably the most important factor in Cinematography, exposure dictates if the image can be seen at all.

The most important property of any image is contrast. Just imagine drawing a beautiful portrait with a black marker pen on a blackboard. 

Theoretically, the image is there. It should be. But, the image is useless if it is so embedded in the background canvas (in this case, the blackboard) that it cannot be seen.

To understand the concept of contrast in a better way, it is first required to understand the concept of the negative and the positive spaces.

Consider the following image, for example.


If one considers the solid black portion as the image, one would see a vase, on a white background

However, the same person would see two white faces looking at each other on a black background, if he chooses to see like that.

It is important to notice that none can see both the images at the same time. There is always a switch from the one image to the other, with an interval in between.

The image one sees is known as Positive Space, while the background and any other supporting space in the frame as Negative Space.


Normally, none looks at the background with interest. Viewer's attention is limited to the foreground mostly. When the attention switches from foreground to background, the negative and positive spaces swap their positions.

There are many different ways of making an area in the frame positive (as opposed to the supporting area, or negative space.) Exposure is foremost among them.

Exposure means the level of brightness. To define it more correctly, Exposure is the amount of light used to create a particular gray tone in an image.


It is easy to understand if the whole image inside a frame has the same tone throughout it can never be seen, as it has no contrast. The frame will look as a flat gray tone like the image below.


For the image to be seen, and to look interesting, there should be different tones in different areas in the frame.

For example, the painting below.



It is the famous Guernica, the study of War, which Picasso painted as a reaction to the bombardment of the Basque town Guernica, in 1937, during the Spanish Civil War.

It is interesting to note that the mural painting was created in grayscale, and not in color. 

Whatever the reason for that choice would have been, it was necessary to play with different gray tones to produce a play in contrast that can capture the equivalent play in emotions when a city is destroyed, a culture marred, humanity strangled.

Had Picasso used fewer graytones, the painting would have lost much of its appeal. In more lay words, it would have been flat.

Tonal Contrast is necessary to show an image.  More subtly, proper contrast is necessary to extract the right kind of emotion from an image.

White less bright is gray, white least bright is black.  In photographic world, brightness at some area in the image means the amount light trapped to create that area.

 So, tonal contrast is guided by a choice of variable brightness across the frame – different amount of light trapped in different parts in the image.

Amount of light is known as Exposure, in photographic term.

To have different exposure in different areas in the image, it is necessary to measure the exposure.

Exposure is measured just like any other physical quantity like weight, distance or temperature.

There are a lot of units to measure exposure in different ways. However, in photography, two major units are used around the world. 

When photographers measure amount of light coming from a light source (such as, sun, moon, the household bulb, torchlight or candle flame), they use either of these two units.

British and the Americans use a unit called Lux, while most of the remaining world uses a related unit known as Foot-Candle. 1 foot-candle is approximately 10.76 lux.

However, for most practical purposes, exposure is measured as a relation among the three photographic controls any camera has.

Camera is basically a light tight box. That is how it got its unique name – camera. It comes from the Arabic word Kamraah, meaning a room. 

The origin of the derivation goes back to ancient civilizations in Greece, India, Egypt and china.

 However, in more comparatively modern world, it started with the Renaissance painters who used Camera obscura to paint models and landscapes with a 'photographic' realism.


Basically such a camera obscura was a similar light tight boxe – but such a big box that we can call it a room. It was totally light-tight except for a small pin-hole on one side, through which a light beam can enter the room.


Everyone knows images are made of light. Human vision, the images forming on the retina of the eye, is completely guided by light. Keep no light, and no image would form.


However, light can come from an object in two different ways – either the object emits light, or it can reflect light originally coming from some other radiating source.


Whatever maybe the case, man sees the world as light from the world strikes his eyes.


If the light is focused, and not too much scattered in different directions, man can create a facsimile image of the world on a surface too.

Precisely, the renaissance painters were doing that in the 15th and the 16th Centuries.



All modern cameras are built on the same concept. Basically, all of them are just light tight boxes, fitted with a few extra things to control exposure and sharpness in the image.



In modern cameras, a lens is fitted before the pin-hole (in fact, the pin-hole is incorporated in the lens) for selective focus and an overall sharper image.

There are three main mechanisms to control exposure in a modern camera. One is the size of the pin-hole. It is called aperture, in modern photographic parlance. Aperture is the Latin word for hole.


The other important control is the shutter. While the size of the aperture determines how much light is passing through at a single moment, the shutter speed determines for how long the light would pass.

Where the film stays in the camera, it is called the gate (as light passes through the gate to fall on the film, and make an image.)



The shutter shuts light off from entering gate. Only when the shutter is out, light can fall on the film, and the image can be recorded for that duration, on the film.

Most shutters for handy SLR and non-SLR cameras (and DSLRs too) look like Venetian blinds. In film cameras, the shutters are like opaque rotating discs.


The duration of light and the amount of light at a single moment, together determine the total amount of light falling on the film.

So, how bright a certain white wall looks depend on this total amount, controlled both by the size of the aperture and the duration of shutter out.

Shutter speed is calculated in fractions of a second, like 1/48", for the duration the shutter is out (and film is getting exposed to light.)

However, as previously seen, everything in the frame can not be of similar brightness. For the image to be visible it needs tonal contrast in different areas in the frame.

For the image to look interesting, the tonal contrast has to proper in its distribution.


For example, look at the image below.


This is an image of maximum contrast – pure black and pure white. There is no other tone in between. 

The image looks like a Chinese ink line-art, or a solarized image, as it is known in the Photoshop®.


However, for the image to look more natural, a number of gray tones is needed in between pure black and pure white.



It is the creative choice of the Cinematographer, keeping the mood of the particular scene in mind, how many different tones of gray (or in other words, how many different exposures) he wants to use.


The third major control mechanism for exposure, in a camera, is the film's sensitivity to light.

Normal exposure is the amount of light that extracts maximum details from an object surface to show in the image.

 Obviously, only few areas in the image will be normally exposed – usually areas in the positive space.

Under and over exposed areas surrounding the subject (these areas are normally in the foreground and the background only, maintaining a clear separation from the subject space) create the negative space, supporting the subject.





     
In the famous photograph by Ansel Adams above, the area in b, the mountain tops and most of the river are seen in normal exposure. 

However, the sky in area a lacks much visual details as it is too bright (Over-exposed). While the area c on the left of the river is so dark that again details is lost (underexposed.)

Any amount of light can fall on the film (or sensor, in case of a digital camera.) But, the film can be highly receptive to the light or less receptive.

In case of a low-sensitive film (it is called slow film), it needs more light to fall on its surface to show normal exposure.

Film's sensitivity is measured in ISO units – like ISO 100, ISO 250 or ISO 320. The higher the value, the more sensitive it would be to light.

The subject of exposure is highly interesting, and at the same time truly important in determining the aesthetic quality of the image.


The cinematographer takes a considerable time in controlling the tones in his images through exposure checking. More than anything else, a proper knowledge of exposure handling sets the class of the cinematographer as an artist.





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