Cinematography-Theory-And-Practice

Figure 9.42. (top) Correct color balanceis achieved by either balancingto a white card or gray card.Figure 9.43. (bottom) Incorrectcolor balance happens when youeither don’t white balance or use thewrong filter (some HD cameras havebuilt-in filters for tungsten or daylightbalance; some do it electronically).In this case, the tungsten balancefilter on the camera was used indaylight, resulting in a blue cast onthe entire image.Gain/ISOOn some HD cameras, the control of sensitivity to light is called gain.Gain is measure in decibels (dB). Increasing the gain is electronic amplification.The trade-off is electronic noise. On some HD cameras,sensitivity is rated in ISO. Figure 9.40 shows frames from an HDcamera rated at ISO 200 and Figure 9.41 is ISO 2000. The resultsare quite good, but there is always a price to pay for increased ISOor gain — more noise. Many cinematographers set cameras at minus3dB to reduce noise, but others disagree with this practice.GammaGamma is contrast or, more precisely, the slope of the curve (specificallythe middle part of the curve). Overall contrast is one of themost basic components of a visual image, and many DPs make thisthe first adjustment they make. A typical normal gamma is .45; raisingthis number makes the image more contrasty and lowering itmakes the image less contrasty ( Figures 9.33 and 9.34).Black Gamma/Black StretchBlack gamma is the contrast of the shadow regions. It is an extremelyuseful tool in shaping the image. On most cameras, you can choosehow much of the shadow region you want to affect, either only thevery darkest shadows or all the way up to from middle gray down topure black. Black stretch is reducing the contrast of the shadows, thusreducing the overall contrast of the image and allowing the camerato see into the shadows a bit more (Figures 9.30 through 9.32).KneeThe knee is brightest parts of the scene — the highlights. Even withslight overexposure of the highlights, video will usually clip. Filmhas a much better ability to roll off the highlights more gradually. Forthis reason control of the knee is critical. Knee controls are generallyin two parts: point and slope. Point is a measure of where on the curvethis parameter starts to take effect. Slope is the relative gamma of theknee regions. See Figures 9.33 and 9.34 for a more visual example ofthe knee. Many cameras also have automatic knee control.Color SaturationChroma (color) saturation is simply how much color you have — howmuch saturation there is. Zero saturation is a black-and-white image.Oversaturation means that the image is recorded with more chromathan was present in the actual scene.MatrixNo, you don’t have to decide between the red pill or the blue pill.The matrix allows fine-tuning control of color. The matrix includescolor space; there are several HD color spaces defined by SMPTE(Society of Motion Picture and Television Engineers). See the chapter onColor for an explaination of color space. See Figures 9.22 and 9.23for examples.Color BalanceSome people think of color balance (often called white balance) as simplyadjusting the camera to daylight or tungsten balance. In fact, alteringthe color balance is one of the easiest and most accessible image controls.In Figures 9.42 and 9.43, the image manipulation is as simpleas it can get: this camera has built-in color balance filters for daylightand tungsten; here the camera is set on the “wrong” color filter.Using warm cards and gels to adjust the color balance was discussedearlier in this chapter.cinematography180