Measurement Tools

Measurement tools give you an objective handle on the technical parameters of your picture and sound and help ensure that you're getting consistent, high-quality results.

Waveform Monitors

The Waveform monitor (WFM) shows you a graph of the video signal, plotting the amplitude (voltage) of the signal vertically and time horizontally. The WFM lets you see exactly what the black level of your picture is; whether the whites in your images exceed 100 percent and whether the combined luma and chroma exceed broadcast-safe levels. The WFM come in handy when trying to color-correct two scenes: it unambiguously shows you any difference in levels.

An external WFM shows you what's happening with the video signal outside the active picture area, something that FCP's built-in WFM cannot do. You can use the WFM to view the sync pulses, blanking intervals, and colorburst of your equipment, letting you diagnose problems with equipment or with tapes of uncertain quality.

Most importantly, the external WFM serves as a quality-control element, ensuring that what you see inside FCP is actually making it onto the tape without level changes or other impairments. An external WFM lets you monitor signals at any point in your equipment chain; the FCP WFM only shows you what the digital video inside FCP looks like.

In its most common usage, the width of the display shows the duration of a single scanline, so the "picture" on the WFM is literally a voltage graph of the video image. The WFM thus shows you information on the brightness of your picture, just as a picture monitor does, but the WFM does it in a calibrated and measurable way.

With a composite video signal, the WFM literally plots the voltage of the signal against time. Filters let you see the entire signal complete with the color subcarrier signal, show just the luma signal, or show just the color subcarrier by itself. (FCP's built-in WFM shows just luma by default; you can superimpose the color information by choosing Saturation from the WFM's pop-up menu.)

Component and digital WFMs have modes to show you their raw signals, but they also synthesize the same view you'd get with a composite WFM, because that view is so useful in monitoring the overall status of the signal.

Vectorscopes

A vectorscope is a specialized display showing you only the color information in your signal. The vectorscope's main value comes in color correction: just as the WFM instantly shows you mismatches in levels, the vectorscope shows you an unbiased view of the colors in a scene. As you switch between two shots, or wipe between them, the vectorscope reveals color differences that may be too subtle to see by eyeand it certainly gives you a good idea of how to adjust the controls in the 3-way color corrector to get the scenes to match.

The vectorscope also aids in system setup: SMPTE or EBU color bars, displayed on the vectorscope, should display dots in the calibrated target regions; if they do not, you can adjust the saturation and color controls in the offending piece of equipment until they do line up. (Vectorscopes are also useful in calibrating color signals inside cameras, TBCs, and the like, but those details will have to wait for the Peachpit book Optimizing the Insides of Your Cameras and Studio Equipment.)

The center of the vectorscope is where grays reside: any signal in the center indicates an area of the picture with no color, whether white, black, or any shade of gray in-between. As you move away from the center, color saturation increases; as you move around the face of the display, you vary the hue. In essence, the face of the vectorscope is a color wheel against which the colors in your video are plotted.

Rasterizers

Rasterizers, or signal monitors, are computerized tools performing the same functions as stand-alone WFMs and vectorscopes, but displaying their results on video or computer monitors. Simple ones, like the Magni MM-400 shown, do little more than replicate the functions of the stand-alone scopes. More complex ones include audio metering, signal quality logging, gamut warnings when a signal exceeds defined limits, and picture-in-picture displays so you can see picture, audio levels, and measurements on the same screen.

FCP's Video Scopes

FCP has its own measurement tools built in in the Video Scopes window. In addition to a WFM and vectorscope, FCP includes a histogram and an RGB parade display. The histogram shows the distribution of brightness values through the image; the parade is essentially a WFM for each of the red, green, and blue channels of information, showing you when you're in danger of clipping a color component even when the WFM is well within limits.

These are valuable and useful tools, but they have three limitations:

• The internal scopes show you only what's happening inside FCP. They can't tell you anything about the video signals elsewhere in your studio.

• FCP's scopes don't show you every line of video; they sample every sixteenth line for performance purposes. That means they can miss fine details less than 16 scanlines tall. Small specular highlights, for example, are easily missed, so you might think you have a picture that's broadcast legal when in fact some parts of it exceed 100 percent brightness.

• FCP's scopes update only when you pause playback. They don't give a running commentary on video as it's playing.

It's worth having access to at least an external WFM if you're planning on finishing programs in FCP, just to catch things the internal scopes miss.

Picture Monitors

A good picture monitor is an invaluable final check for image quality. Computer screens don't render colors and brightness quite the way a picture monitor does, nor do they show the image cropping that a monitor's overscan does. (Televisions overscan the image, cropping about 10 percent off the edges of the picture, to ensure that innocent civilians are never exposed to the horror of an image smaller than the bezel of their TV screen.)

The standard reference for video monitoring and color correction is a CRT monitor using a SMPTE Type C phosphor. Most good professional and broadcast monitor lines have Type C phosphors; the spec sheet for the monitor should mention it if it's used. The Type C phosphor has a calibrated color gamut and response, soassuming the monitor itself is properly calibrated and white-balancedthe monitor will reproduce a picture the same way as any other Type C phosphor-equipped monitor will. Consumer televisions don't have standardized phosphors; most make a picture stronger in blue than they should. (Because blue phosphors are bright, and consumers tend to buy the brighter of two sets they see, manufacturers "cheat" towards blue for a competitive advantage.)

A good monitor has high resolution (600 TVl/ph or more for an SDTV monitor), an underscan button so you can see all the edges of the picture, and a blue-only switch so you can easily calibrate the monitor to color bars.

LCD monitors are usually disparaged for precise work; in the past their color gamuts and white points have been too inaccurate for critical monitoring. LCDs have improved markedly in recent years, but they still tend to have difficulties displaying the entire tonal scale without some brightness or color distortions.

Monitor Speakers

As with picture monitoring, accurate sound monitoring is essential for doing good work. Good monitor speakers have a flat and neutral response; the inexpensive speakers sold for computer use typically have peaks and valleys in their frequency response that distort or "color" the sound, possibly hiding sonic defects or masking problems with intelligibility.

You can press good headphones into service, especially where the venue doesn't lend itself to critical listening (hotel rooms, trade show floors, and so on), but most sound mixers prefer a good set of near-field monitor speakers in a controlled listening environment to headphones when the location allows for it.

It doesn't hurt to have "bad speakers" available, too. You need to ensure that your final mix works even when the thunderous bass and soaring treble accents get lost during playback on cheap speakers. Some editors keep an old, beat-up TV monitor with a tinny, 3-inch oval speaker handy, just to ensure that their pristine programs are watchable and intelligible even under less-than-ideal circumstances. Others use the cheapest computer speakers available. Both approaches work well.