Match Move and Stabilize Nodes

The Match Move and Stabilize nodes enable you to apply track data to the control of translation, rotation, and scaling operations. As their names imply, the Match Move node is used to match the movement of a foreground element to a background and the Stabilize node is used for image stabilization.

Both nodes provide popup menus to select the Track node to reference--it is not necessary to enter mathematical expressions to use them.

Note:
Match Move and Stabilize do not create tracking data. Refer to the Track Node description in chapter 13, "Tool Nodes ," for detailed instructions on generating track data.

Both nodes feature the same set of parameter tabs for specifying the operations to perform and any filtering or motion blurring to use; therefore both nodes are described together here.

Match Move and Stabilize each accept one or two inputs. The second, optional input is used to resize the primary input and as a visual reference in the work monitor.

Using the Match Move Node

A match move is performed to position a foreground element at each frame to match the movement of an object in a background image. The Match Move node uses data previously created in a Track node by tracking an appropriate area of the background (one that doesn't move off camera, e.g.).

For match moves, follow these steps:

  1. In the Apply Track tab, specify a Track node from which the Match Move node should access x,y position data.

  2. You can enter the name of the track node into the Track Node parameter field, or you can use the associated popup menu to select any existing Track node in the file.

    Once a Track node is selected, other relevant parameters on the Apply Track tab become active
  3. Be sure that Match Move is selected in the Translation menu.

  4. The Translation menu enables you to choose Match Move (the default) or No Translation. (The No Translation option is provided for doing Scaling or Rotation only.)
  5. Specify the Translation Point to use.

  6. The Track node being accessed may include data for multiple track points. Therefore, you should specify which track point to use by selecting it from the Translation Point popup menu, which automatically lists all track points in the node specified in the Track Node parameter.
  7. Connect the background image to the second input of the Match Move node.

  8. This changes the output resolution of the foreground image to match the size of the background input.
  9. Open the work monitor.

  10. This will enable you to view the foreground over the background image as a reference while setting parameters.
  11. Optionally, you can create an Offset for the position data.

  12. You can either key x,y coordinate values directly into the Offset parameter fields or drag the image in the work monitor to reposition it by eye.
  13. Optionally, you can modify scaling and rotation.

  14. Refer to "Matching or Undoing Scaling and Rotation " for details.

Note:
The Match Move operation is the equivalent of entering the following expressions in the Translation fields of the Transform node, in which values are accessed for x (XV) and y (YV) positions, respectively, at the current frame ($F) of track point 1 (1) in a node named "track1":

track("track1",XV,1,$F)
track("track1",YV,1,$F)

Using the Stabilize Node

To stabilize imagery, for instance to remove camera jitter, the Track node that is accessed must contain a track point that was placed to follow a background element that is meant to remain stationary throughout the scene.

For image stabilization, follow these steps:

  1. In the Apply Track tab, specify a Track node from which the Stabilize node should access x,y position data.

  2. You can enter the name of the track node into the Track Node parameter field, or you can use the associated popup menu to select any existing Track node in the file.

    Once a Track node is selected, other relevant parameters on the Apply Track tab become active.
  3. Be sure that Stabilize is selected in the Translation menu.

  4. The Translation menu enables you to choose Stabilize (the default) or No Translation. (The No Translation option is provided for doing Scaling or Rotation only.)
  5. Specify the Translation Point to use.

  6. The Track node being accessed may include data for multiple track points. Therefore, you should specify which track point to use by selecting it from the Translation Point popup menu, which automatically lists all track points in the node specified in the Track Node parameter.
  7. Open the work monitor.

  8. This will enable you to view the image while setting parameters.
  9. Optionally, you can create an Offset for the position data.

  10. You can either key x,y coordinate values directly into the Offset parameter fields or drag the image in the work monitor to reposition it by eye.
  11. Optionally, you can modify scaling and rotation.

  12. Refer to "Matching or Undoing Scaling and Rotation " for details.

Note:
The Stabilize Image operation is the equivalent of entering the following expressions in the Translation fields of the Transform node, in which the position coordinates of a track point at the current frame are subtracted from the values of the same coordinates at the first frame:

track("track1",XV,1,1)-track("track1",XV,1,$F)
track("track1",YV,1,1)-track("track1",YV,1,$F)

Matching or Undoing Scaling and Rotation

You can match or undo scaling and rotation in both the match move and stabilize operations. Additionally, both nodes provide a "No Translation" option to use tracking data to match or undo scaling and rotation alone.

Note:
The scale and rotate operations in the Match Move and Stabilize nodes are specifically designed to use track data to adjust scaling and rotation over time.
If the image needs preprocessing on another basis--for example, if the image needs to be resized to fit the scale of other objects in the background scene--use the appropriate node (Scale or Transform, e.g.) between the source image and these nodes.

  1. Select an option from the Rotation and/or Scale parameters for how the track data should be applied to the operation.

  2. For example, you can choose to match or undo the rotation in the original track. You can match or undo both size and distance scaling. Refer to the "Rotation and Scale Parameters " description for more detailed information.
  3. S elect a pair of tracking points to use from the Rotate Point and/or Scale Point menus, which list all track points in the Track node being accessed.

  4. The Rotation and Scale operations each require the specified Track node to have at least two points tracked because the scale and rotation values are controlled by changes in the length or relative position of the vector between the two track points selected.

Track and Image Data Filtering

The Advanced parameter tab of the Match Move and Stabilize nodes features parameters you can use to filter both

  • the track data, if you need to smooth the motion curve over time, and
  • the image data, to reduce aliasing and other image artifacts that can be caused by scaling and rotation operations.

You can also specify motion blur for an operation.

Whether to use these options, and which options to use, is specific to the imagery and track data being accessed and the decision requires an examination of the initial result. For more information, refer to the descriptions of the Advanced and Motion Blur parameter tabs.

Apply Track Parameter Tab

Work Monitor / At Resolution

First, select a display resolution for the work monitor from the At Resolution popup menu. Then click the plus icon to display the work monitor for this node, which is used to specify an offset interactively by dragging the image in the monitor. It also enables you to view the placement of the image over a reference image in a temporary composite.

Transparency

If you connect a reference image to the second input of the node, you can view the primary image superimposed over this reference image. The Transparency tuner enables you to change the overall opacity of the foreground image in the work monitor by specifying a multiplier for the alpha channel data. By default, the Transparency parameter is set to 1, to use the full opacity of the input alpha channel.

Use Image Alpha with Transparency

When this option is checked, the alpha channel value of each pixel of the primary input is multiplied by the Transparency parameter value to govern the overall transparency of the temporary composite image in the work monitor. Otherwise, Chalice will assume an alpha value of 1 for each pixel.

Track Node

Use this parameter to specify the Track node from which to access tracking data. You can use the popup menu, which lists all existing Track nodes in the grail file, or you can key in the name of the Track node to use.

Translation

This parameter offers a popup menu from which you choose the type of translation operation to be performed:

  • In the Match Move node, the choices are Match Move or No Translation.
  • In the Stabilize node, the choices are Stabilize or No Translation.

No Translation

The No Translation option should be selected only if you are using the Match Move or Stabilize node strictly to match or undo rotation or scaling, without any other translation.

Translate Point

This parameter enables you to specify which track point to use for the translation. The Translate Point popup menu will display all track points available from the specified Track node.

Offset

The Offset parameter enables you to offset the position data used for translation, rotation, and scaling. You can key specific x,y values into the Offset data fields, or you can use the work monitor to drag the image to the offset position you desire. The Offset parameter values will update accordingly.

Rotation and Scale Parameters

The Rotation and Scale parameters enable you to select from several options for the type of operation. Unlike the Translation operation, the Scale and Rotation operations each require two sets of track data, as the changes in length or position of the vector between two track points is used to calculate the values.

Rotation

The Rotation popup menu enables you to select No Rotation (the default), Undo Rotation, or Match Rotation.

The associated Rotate Pivot and Rotate Reference parameters become active whenever Undo or Match Rotation is selected. Use the popup menus to select the track point data to use for each parameter.

For Rotate Pivot , use the track point that represents the pivot of the rotation; for Rotate Ref , use the point that represents the position of the moving end of the rotation vector.

Scale

The Scale popup menu enables you to select No Scale (the default), Undo Size Scale, Undo Distance Scale, Match Size Scale, or Match Distance Scale:

  • The Size Scale options enable you to match or undo a scale up or down in size, such as a zoom.
  • The Distance Scale options enable you to match or undo relative changes in distance between objects.

The associated Scale Reference parameters become active whenever any option other than No Scale is selected. Use the Scale Ref A and Scale Ref B popup menus to select the track point to use to represent each end of the vector defining the scale value.

Advanced Parameter Tab

The Advanced parameter tab enables you to choose from several types of data smoothing and image filtering operations. The Smoothing parameters modify the track data, while the Filtering parameters modify the imagery.

Smoothing

This parameter menu enables you to apply a smoothing filter to the track data, to effectively smooth out excessive jerkiness in the motion curve from frame to frame. Instead of using the raw track point data, smoothing will average the values using the function you specify in the popup menu: No Data Smoothing (the default), Weighted Smooth (using a triangle filter), or Average Smooth (a box filter).

Amount

This parameter is activated whenever Weighted or Average Smooth is selected from the Smoothing menu. It enables you to specify the sample size, in frames, to use for the Smoothing filter: Small (3 samples), Medium (5 samples), or Large (7 samples).

Filtering

This menu enables you to select an option for filtering. The default is "Best (Dynamically Chosen)," which means that Chalice will choose between Mitchell and Lanczos filtering. However, you can also select "Good (Bilinear Interpolation)" to speed processing, or the fastest option, "Fast (No Filtering)," when image quality is not a top concern, as when reviewing your initial settings.

The "Advanced - User Set" option activates the Filter Type parameter, which enables you to select a specific type of filter operation.

Filter Type

The Filter Type menu includes Box, Triangle, Quadratic, Cubic, and Gaussian; as well as Catmull-Rom/Overhauser Spline, Mitchell, Sinc (Windowed), Bessel (Windowed), Lanczos 2-lobe Sinc, and Lanczos 3-lobe Sinc.

Box, Triangle, Quadratic, Cubic and Gaussian refer to the shape of the function curve that defines the filter. Box equals constant, triangle is linear; and so on in increasing precision and processing time.

The other filter options are named for the individuals who developed them, and the best choice will depend on the individual characteristics of the image as well as on the type of operations the node is performing.

The Mitchell and Lanczos filters are among the most popular filter options. Mitchell filtering is often preferred for Jpegs or images with a lot of fine lines. Lanczos filtering provides a good compromise between sharpness, ringing and aliasing reduction. It is best used on images which are reduced or scaled down.

Mitchell B and C

The Mitchell B and C parameters are activated when Mitchell filtering is selected in the Filter Type menu to enable you to make adjustments to the Mitchell filtering process.

The default values, 0.333 for both parameters, fall within a recommended range of roughly 0.25 to 0.5. Since the quality of the result must be judged based on your imagery and intentions, the best course may be to experiment with these settings.

As a guideline, note that values above 0.5 for the Mitchell B parameter may produce unnecessary blurring. Values above 0.5 for the Mitchell C parameter may result in excessive ringing (rippling patterns). When both parameters are set at values above 0.6 or below 0.2, anisotropic artifacts may appear.

Window Type

The Window Type parameter is activated only when the Sinc or Bessel filter type is selected from the Filter Type menu. Choices are Hanning, Hamming, Blackman, or Kaiser.

Kaiser A

When Kaiser is chosen in the Window Type parameter, this additional control parameter is activated.

Blur

The Blur parameter can be used with any filter option when heavy blurring is needed. The default value of 1 adds no blurring to the image; values greater than 1 represent increased blurring, up to the maximum of 4.

Motion Blur Parameter Tab

These parameters are activated when Motion Blur is enabled on the Apply Track tab.

Shutter Phase

The Shutter Phase parameter enables you to specify where in a frame to "open the shutter," in a range of -1 to 1. The default is 0, which represents the beginning of the frame.

Shutter Speed

The Shutter Speed parameter enables you to specify the duration of the effect for each frame in a range of 0 to 2, where 2 represents the duration of one complete frame.

Automatic Sampling

Automatic Sampling is enabled by default, to let Chalice set this value for the operation. However, you can turn off Automatic Sampling to set a specific sample value in the Samples parameter.

Samples

The Samples parameter enables you to specify the number of subframes to examine when computing the motion, when you have disabled Automatic Sampling. The faster the motion in the sequence being blurred, the greater the number of samples needed. Larger sample values mean longer processing times .




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