Cinematography-Theory-And-Practice

of compression. RGB video is usually represented with an equalnumber of bits for each of the three color component channels, butRGB is not normally transmitted and bandwidth is not as big a factorwhen dealing with a connection between the computer and displaydevice.The four represents 13.5 MHz, the sampling frequency of the Ychannel, and the twos each 6.75 MHz for both the R-Y, B-Y channels.D-1, D-5, Digital Betacam, and most digital disk recorders use4:2:2 digitizing.4:1:1This is a set of frequencies in the ratio 4:1:1, that is used to digitizethe luminance and color difference components (Y, R-Y, B-Y) of avideo signal. The 4 represents 13.5 MHz, the sampling frequency ofthe Y (luminance) channel, and the 1s each represent 3.75 MHz forthe R-Y and B-Y chrominance channels.4:2:0This is a set of frequencies in the ratio 4:2:0, that is used to digitizethe luminance and color difference components (Y, R-Y, B-Y) of avideo signal. 4:2:0 is used in PAL DV and DVCam, DVDs and a fewother formats. The 4 represents 13.5 MHz, the sampling frequencyof the Y channel, while both the R-Y and B-Y are sampled at 6.75MHz. In 4:2:0, 3/4 of the chrominance values have been deleted.YUVYUV is another way of indicating chroma subsampling. Y is stillluminance; U and V are the chrominance channels. YUV = four Ysamples, four U samples, and four V samples per unit of time.IS IT BROADCAST QUALITY?Broadcast quality is a term that frequently gets misused. It does notmean, as many people think, a “good-quality” picture or merely acertain level of resolution. Broadcast quality is actually a complexset of technical standards for the timing, synchronization, and levelsof the video signal. It is something that can only be measured withsophisticated test equipment. It is largely the province of video engineers,but it is important to understand the concept, particulary as itis used to refer to cameras.DO IT IN THE CAMERA OR IN POST?One question that comes up frequently in digital shooting is, “shouldwe fix the look in the camera or shoot it ‘straight’ and fix it in post?”Some people take a traditional purist approach and insist on doingeverything in the camera. In HD, this is referred to as being “bakedin,” meaning that alterations to the video signal (such as color balance,gamma, knee compression, and so on) are recorded and maybe difficult to change later on. That is a fine approach, but it ignoresthe incredible tools that are available for image manipulation in postproduction. Sometimes cinematographers feel that the only way thatcan retain control of the image is to do everything in camera, butincreasingly, it is important to be involved in the post process as well.When shooting in the RAW format, however, nothing is actuallybaked in and all final decisions are always still possible in postproduction.What can be altered is the LUT (Look Up Table)used for viewing;this LUT can also be used to serve as a guide in postproduction.See the chapter Image Control for more on LUTs.cinematography166