Masking and Rotoscoping > Refining the Mask >

# Animating a Tracer Mask

When using the Tracer, you can animate the basic vertex parameters, as well as the following additional parameters.

Parameter | Channel Folder and Name(s) | Channel Values
--- | --- | ---
The position of the two softness vertices relative to the mask vertex. | border: upper = outer vertex* bottom = inner vertex* |
Whether pickers are linked to tangents or not. Linked—Pickers move with tangents. Unlinked—Pickers remain in their current position when tangents are moved. | pickers: fixed | 0 = unlinked 1 = linked
The on/off status of pickers. | pickers: active | 0 = off, 1 = on
The position of the pickers relative to the mask vertex. | pickers: upper = outer picker* bottom = inner picker* |
The picker size. | pickers: u-size = outer picker size* b-size = inner picker size* |
The Sample on/off status of pickers. See Animating Picker Values. | sample: active | 0 = Sample off 1 = Sample on
The interpolation mode for picker values when Sample is off. See Animating Picker Values. | sample: interp. | 0 = Constant 1 = Linear

*Channel Editor designations for “upper” and “bottom” assume the mask was drawn clockwise.

## Animating Picker Values

Two options are available to control how picker values (that is, the sampled colour values) are animated: Sample On and Interpolation mode.

(a) Sample box(b) Interpolation button

Sample box
  Active resamples picker values at every frame (the default). Passive disables resampling for one or more frames. When Passive at a particular frame, the picker values previously sampled at another frame are used. It is useful to adjust the size and position of pickers at one particular frame until the result is optimal, and then apply these values to other frames. In this way, if movement in the clip in other frames causes the area being sampled to move away from the pickers, you do not need to readjust the pickers to get a good reading.

You can select Active or Passive for one or more selected pickers.

Selecting Passive works best when colour values remain fairly consistent throughout the clip. In this case, one picker sampling will often be enough for the entire clip.

Typical technique for using Sample On: one sample is used for the entire clip

(a) Sample Off(b) Sample On(c) Sample Off

When there is more colour variation in the clip, you may need to take samples at several frames.

To use one picker sampling throughout a clip:

1. Choose a frame in which the colour values are representative of the average colour values found in the clip.
2. Select the pickers you want to sample. See Selecting Pickers and Softness Vertices.
3. At that frame, make sure Active is selected from the Sample box (the default).
4. Set the picker values by setting their position and size until you get the optimal result.
5. Go to the next frame and select Passive from the Sample box.

   The sample values read at the frame you chose will be used to compute the softness for all other frames in the clip.

To take samples at several frames:

1. Follow the steps in the previous procedure to set a picker sampling for the clip.
2. Starting at the first frame sampled, examine your results frame by frame (either forward or backward through the clip).
3. When you come to an unsatisfactory result, select the pickers you want to re-sample and select Active.
4. Adjust the picker position and size until you get a good result.
5. Go to the next frame and select Passive from the Sample box.
6. Continue verifying frames until you come to one that needs to be adjusted.
7. Repeat steps 3-5.
8. Repeat for the remainder of the clip.

Interpolation button
  Displays the interpolation between keyframes that have Active selected as the Sampling option.

- Linear (enabled): Picker values are interpolated between keyframes with active sampling. The picker values for each frame are computed based on the values of the previous and next active sampling keyframes and the proximity of the frame to those keyframes.

- Constant (disabled): Picker values are fixed between keyframes with active sampling. This means that the picker values at the first active sampling keyframe will be used for all subsequent frames up until the sampling is active again.