Cinematography-Theory-And-Practice

The total brightness range of the sceneTotal brightnessrange the finalprint or videois capable ofreproducing.Figure 10.18. Compression of thereal-world brightness values so thatthey fit onto the film. This is whatmakes it possible to make usableimages even from scenes with highcontrastranges. The same principleapplies to video, whether analog ordigital. A great deal of the progressof video as a more acceptable imagingmedium has been improvementsin its ability to compress the imagebrightness in a way that gets closerto what film can usefully manage.tionof the photosensitive elements in the emulsion (the inertiapoint). Thus, the density rises gradually at first in this areacalled the toe, finally accelerating into the straight line portionof the curve. verted,until it has no more sensitive material to activate. Atthat point, increasing the exposure does not increase theultimate density of the developed negative. This “saturation”occurs gr adually a nd pr oduces what is k nown a s a s houlder.The toe of the film is a result of the fact that film reacts slowly tosmall amounts of light. It is only when greater amounts of light reachthe emulsion that the change becomes linear. This is the straightlineportion of the film. The film base itself always has some density,however slight. On top of this there is always a slight amount of fogdue to light scattering in the camera, the lens, the emulsion, and alsochemical fog in the processing. The cumulative effect of all of theseis called base plus fog. Density measurements are usually describedas x density above base plus fog.This toe and shoulder behavior actually results in a compression ofthe actual scene. If the contrast gradient of the film is correct andexposure is correct, this compression behavior will allow more ofthe brightness range of the scene to be represented on the final print.In effect, it is the failure of film emulsion and video receptors toaccurately represent the real world that allows us to produce photographsand video that are usable. Each film emulsion reacts to lightin a special way. Some react more quickly to low light than others,creating a rather abrupt initial rise in density or short toe. Others reactmore gradually to increases in light and have what is called a long toe.Another important factor is the range of subject luminance thatcan be usefully recorded (Figure 10.16). Low-contrast films can continueto build density over a long luminance range, whereas contrastyfilms saturate rather quickly and tend to “block” at either end.This is how we can match the type of film used to the type of scenebeing photographed. Cinematographer David Watkin used a lowcontrastfilm stock on Out of Africa, where he dealt with many verycontrasty situations in the harsh African sun. Both Fuji and Kodaknow make emulsions that are more moderate in contrast.exposure195