Cinematography-Theory-And-Practice

Figure 10.21. (left) An 11-step grayscaleproperly exposed. On thewaveform monitor, the darkest areasare down at 0% (pure black) and thewhite bars are 100% (pure white).The rest of the tones are evenly distributed.The “X” is linear, meaningthat contrast is normal. These illustrationsshow the image on top andthe waveform monitor display forthat image underneath.Figure 10.22. (middle) A badlyunderexposed shot of the grayscale.On the waveform the tones are allcrushed together at the bottom.Figure 10.23. (right) In this veryoverexposed shot, all of the lighteststeps of the grayscale are blown outpure white, with no separation. Onthe waveform they are clipped: flatlinedat the top. Notice that the stepsare no longer linear. This clearlyshows how overexposure in HDvideo is much more than just being“too light” — everything about theimage is adversely affected.ship of the gamma (the angle of the straight-line portion of the film)to the toe and the shoulder is what determines a film’s latitude. Itcan be viewed as two characteristics: room for error and the emulsion’s(or video camera’s) ability to accept a certain brightness range— which is called its latitude.Higher Brightness Range in the SceneThe problem is exacerbated if we consider a scene that has more thanseven stops of brightness (seven stops is just an average; it all dependson the particular film stock or video camera). Here there is no aperturesetting that will place all of the values on the useful part of thecurve. If we expose for the shadows (open up the aperture), we getgood rendition of the dark gray areas, but the light values are hopelesslyoff the scale. If we “expose for highlights” (by closing downto a smaller f/stop), we record all the variations of the light tones,but the dark values are pushed completely off the bottom edge anddon’t record at all; there is no information on the negative, no detailto be pulled out.How do we deal with this situation? This is done by lighting orby modifying the existing lighting. This is one of the most essentialjobs of lighting and grip work: to render the scene in a scale ofbrightness values that can be accommodated by the optics and emulsionof a film camera or by the optics and electronics of video.DETERMINING EXPOSUREIn measuring and setting exposure on the lens, shutter, frame rate,with neutral density filters, or by altering the brightness levels of thescene, we have two basic tasks:properly reproduced on film or video.atepart of the curve.In practice these often turn out to be two sides of the same coin.The first task is essentially the work of lighting and lighting control,and the second task involves measuring the scene and making a judgmentabout the best setting for the lens.VIDEO EXPOSUREThe same principals of exposure apply to video; the same ideas ofthe curve, toe and shoulder, also apply, although in video the highlightsare called the knee and the darkest parts of the scene (calledtoe in film) are simply referred to as shadow areas. Exposure is evencinematography198