Broadcast Spec
Broadcast Spec filters images to create “broadcast safe” color and luminance values. It has presets for Component and Composite video, and does its work without adversely affecting the colors in your images. It is designed to be the very last effect you use before you render to a video-destined QuickTime file.
What exactly is “broadcast safe?” The short answer is that it’s a complex set of criteria with which no single plug-in could hope to ensure compliance. Luckily, when taking the linear color space of After Effects and outputting through SDI (Serial Digital Interface) to a format such as D1 or Digital Betacam, it is very difficult to generate a truly unacceptable (or unbroadcastable) image. In fact, it is actually impossible to generate illegal luminance values. So Broadcast Spec’s component preset (the default) concentrates almost entirely on the other half of the video equation: the chrominance (chroma) signal.
The chroma signal is similar to the saturation values in your RGB working environment. It is these values that Broadcast Spec adjusts. It would be possible to make an image “safe” by simply desaturating it overall, but this would be a tragic adjustment to make to an image that only has a few “hot spots” of illegal values. Broadcast Spec looks for saturation values that are over a certain threshold that you define and adjusts only those.
The Broadcast Spec tool in After Effects
To use Broadcast Spec, apply it as a final step to your color-corrected video project. In After Effects this is easily achieved by using an Adjustment Layer, but we recommend that you create a dedicated NTSC Video Output Composition and apply the plug-in to your finished project there.
The first thing you will see is the Saturation Histogram. This is similar to the histogram in the After Effects Levels control, except that instead of showing the distribution of RGB values, it displays the saturation values. Concentrations of values at the far right of the graph indicate an image of predominantly low saturation, whereas peaks at the left end of the graph indicate high saturation pixels within the image. It is here that illegal values can crop up, and you will notice that the rightmost 20% of the graph contains a cross-hatch pattern indicating the parts of the graph above the current Maximum Saturation value.
Unsafe Broadcast Colors Display
Maximum Saturation is the master slider for this plug-in. Here you define the maximum legal saturation value to allow through. Anything above this will be adjusted in saturation to match this value. With this slider at 100%, you would not affect the saturation levels of the image at all. At 0% you will have a very safe black and white image. The default NTSC setting of 80% is not as strict as it could be—to meet the most stringent specifications it should be set to 75%. But you can get away with values up to 80%, and isn't film making all about pushing the limits.
A frame showing Unsafe saturation colors
Since we don’t want to just linearly clip off the values of saturation at the maximum, we have another slider that works with Maximum Saturation. It is called Saturation Rolloff, and it defines a range of saturation values just below the maximum that will get subtly adjusted to provide a smooth transition into safety. The default value of 15 is a good compromise between adjusting as few values as possible and avoiding too harsh a transition to the clipped values. Saturation Rolloff is represented in the histogram view by a faded area of the cross-hatch pattern. All saturation values below this faded range are untouched. In the image above the values that have the greatest yellow are those most saturated.
The Broadcast Safe Show menu
The last control is the Show pop-up menu. The default is Corrected Video, which means that Broadcast Spec is displaying your affected image. The other option is Unsafe Values. In this mode the plug-in highlights the areas of the image that may be to high in chroma using a zebra pattern. Values that are over the Maximum Saturation value you’ve selected will be 100% zebra, whereas values within the rolloff range will be partially zebrafied--thus you will see less visible stripes in these areas of the frame. Show Unsafe Values is useful for setting up the plug-in and gauging how much work it is doing, but you probably won’t want to render your project this way!
The Unsafe Colors controls allow you to specify which colors are used for the zebra pattern. Please be tasteful.