#21 Checking Brightness and Color with the YC Waveform Scope
Premiere Pro's YC Waveform scope (Figure 21a) displays the intensities of the luminance signal, essentially brightness (called luma, or Y) and color signal (called chroma, or C). In the onscreen chart, luma is presented as green and chroma blue, and both are measured as IRE values, which stands for Institute of Radio Engineers (go figure). The brighter the pixel value, the higher the IRE rating, which is shown on the vertical axis. Figure 21a. Here's Premiere Pro's YC Waveform scope. Note how all the pixels are grouped in the middle, indicating poor contrast.You can display the scope by clicking the Output button in the Program Monitor or Source Monitor, just above the timeline, as shown in Figure 21b. Figure 21b. Here's how you choose scopes in both the Program Monitor and Source Monitor.
For broadcast television, producers keep their signals between 100 IRE (pure white) and 7.5 IRE (pure black), a range referred to as broadcast legal. Computer monitors and television sets can display pixels that exceed these limits, but you shouldn't necessarily consider the full spectrum available on your computer as appropriate to your project, for several reasons.
First, if too much of the signal exceeds the broadcast-legal limits, the image will be over- or underexposed and lose detail at either end. Conversely, if the signal is bunched in the middle, the image will lack contrast and appear faded. This is the problem with Figure 21a, where most pixels are clustered between 20 and 90. You'll learn how to deal with insufficient contrast in #23. Finally, when correcting the brightness and contrast of your videos, you should check the YC Waveform to assess the levels and spread of both your starting point and subsequent adjustments. |