Using the Broadcast Safe Filter

The Broadcast Safe filter provides a quick way to reduce luma and chroma levels that exceed the broadcast limits for NTSC, PAL, and HD video.

The easiest way to use the Broadcast Safe filter is by choosing one of the presets in the filter’s Luma/Chroma Mode pop-up menu. The presets provide varying degrees of luma and chroma limiting depending on the tolerance of your broadcast facility. For more precise control, you can use the Custom preset to manually adjust the luma and chroma saturation limits. You can also use the RGB Limiting controls to ensure that your video levels are acceptable when converted to RGB color (for example, when your video is displayed on a CRT monitor).

Clamping and Clipping

The Broadcast Safe filter and the RGB Limit filter (see Using the RGB Limit Filter) use clamping to adjust all values above or below a certain threshold to the threshold level. Clamping creates a waveform whose top or bottom appears flat, or clipped.

Clipping usually refers to signals that have been negatively affected by in-camera underexposure or overexposure, color space conversion, or improper use of color correction tools. When you shoot video, you should control your exposure to avoid clipping. It’s best to start with a signal that doesn’t have clipping and then clamp extreme levels as needed using a color correction filter.

Broadcast Safe Filter Controls

The following section describes controls in the Broadcast Safe filter.

Figure. Filters tab showing the Broadcast Safe filter controls.
Luma/Chroma Mode Pop-Up Menu
  • Luma/Chroma Mode Pop-Up Menu: Choose one of the presets in this pop-up menu to decide the maximum allowable chroma saturation. The normal setting of 120 should work in most situations; however, more conservative settings are available.

    Note: The number in the preset refers to the value of the combined luma and chroma signals, mostly weighted toward the luma signal.

    Figure. Luma/Chroma Mode pop-up menu.

    If you choose Custom from the Luma/Chroma Mode pop-up menu, you can use the sliders in the Custom Luminance Limiting and Custom Saturation Limiting areas to manually fine-tune clamping of luma and chroma levels. If any mode other than Custom is chosen, the Custom Luminance Limiting and Custom Saturation Limiting sliders have no effect.

Custom Luminance Limiting Controls
  • Enable: Select or deselect the checkbox to turn on or turn off the Custom Luminance Limiting controls.

    Note: The sliders below have an effect only when this checkbox is selected.

  • Clamp Above: All luma values above this parameter value are clamped to the parameter value. The lower you set this value, the more clipping occurs at the top of the waveform.
  • Max. Output: Compresses the range of values between the Start (Threshold) and Clamp Above values so the maximum output value is the value set here. Setting this value higher than the Clamp Above value has no effect. Values below the Start (Threshold) value clip the signal.
  • Start (Threshold): Defines the lowest value affected by the Custom Luminance Limiting controls.
Custom Saturation Limiting Controls
  • Enable: Select or deselect the checkbox to turn on or turn off the Custom Saturation Limiting controls.

    Note: You can still adjust the sliders below, but they have an effect only when this checkbox is selected.

  • Clamp Above: All chroma values above this parameter value are clamped to the parameter value. The lower you set this value, the more clipping occurs.
  • Max. Output: Compresses the range of values between the Start (Threshold) and Clamp Above values so the maximum output value is the value set here. Setting this value higher than the Clamp Above value has no effect. Values below the Start (Threshold) value clip the signal.
  • Start (Threshold): Defines the lowest value affected by the Custom Saturation Limiting controls.
  • Reduce Chroma/Luma: When the combination of the luma and chroma signals is too high and the Broadcast Safe filter can reduce either luma or chroma to make the combined signal legal, this parameter determines how much luma and chroma are reduced. When the slider is set to 100 (centered), the filter reduces luma and chroma equally.

    Note: The Custom Luminance Limiting and Custom Saturation Limiting controls are effective only when you choose Custom from the Luma/Chroma Mode pop-up menu.

RGB Limiting Controls
  • Enable: Select or deselect the checkbox to turn on or turn off the Max. RGB Output Level parameter. When this parameter is enabled, any equivalent RGB values that exceed the Max. RGB Output Level parameter value are clamped to that value. Negative RGB values are automatically clamped to zero.

    Note: Unlike the Custom Luminance Limiting and Custom Saturation Limiting controls, this option can always be enabled, regardless of the option currently selected in the Luma/Chroma Mode pop-up menu.

  • Max. RGB Output Level: This parameter value is the maximum RGB-equivalent value that the filter outputs.

    The Max. RGB Output Level slider goes between 75 and 125; 100 is the default setting. If you want to reduce RGB levels, set the slider to a value below 100. If you want the filter to tolerate higher RGB levels, set the slider to a value above 100.

    For more detailed control, you can use the RGB Limit filter instead (see Using the RGB Limit Filter).

About Custom Luminance Limiting and Custom Saturation Limiting

The following section gives some examples to show how the Custom Luminance Limiting and Custom Saturation Limiting controls in the Broadcast Safe filter work.

In the following example, Max. Output parameter values between 95 and 105 are compressed down to the range between 95 and 100. The shape of the waveform is preserved.

Figure. Diagram showing the waveforms of the Start parameter, Clamp Above parameter, and Max. Output parameter, with the Clamp Above parameter set at 105.

In the next diagram, values above 100 are clamped, removing details above a value of 100. In this case, the Max. Output parameter has no effect because its value is identical to that of the Clamp Above parameter.

Figure. Diagram showing that the details above 100 for the Clamp Above parameter have been removed.

In the following diagram, the Clamp Above parameter removes details above a value of 100. Then, the Max. Output parameter compresses the clamped values between 90 and 100 to the range between 90 and 95.

Figure. Diagram showing that the values between 90 and 100 have been compressed.

In the following example, the Clamp Above parameter removes details above a value of 100. Then, the Max. Output parameter compresses the clamped values between 90 and 100 down to 90, resulting in a signal that is clamped at a value of 90.

Figure. Diagram showing the final result of the last clamping.

Applying the Broadcast Safe Filter to Nested Sequences

The Broadcast Safe filter should always be the last filter applied to a clip to make sure other filters that can cause illegal values are corrected. However, in some cases, illegal values may be generated because of the order in which video is processed in Final Cut Pro.

Here are the video processing steps, in order:

  • Filters (filters that appear at the top of the Filters tab in the Viewer are processed first, followed by filters that appear later)

  • Motion parameters such as Scale and Rotation and attributes such as Crop and Distort

  • Transitions between two clips in a track

  • Compositing modes that blend one or more video clip items together

  • Filters applied to the entire sequence (achieved by nesting a sequence and then applying a filter to it)

Motion parameters, transitions, and compositing modes can alter the results of the Broadcast Safe filter applied to individual clips. In these cases, it’s best to create a nested sequence and then apply the Broadcast Safe filter to the nested sequence. For more information about nested sequences, see Methods for Editing Clips from One Sequence to Another. This is also more efficient than applying the Broadcast Safe filter to every clip in your sequence.