Rotospline Node

The Rotospline node enables you to create and manipulate matte shapes with precision and control. Most commonly this functionality is used to create garbage mattes.

Garbage mattes are used to remove unwanted elements from an image before compositing it with other imagery. For example, a garbage matte could be used to remove lights or other equipment from a bluescreen shot before the subject was composited over a background scene.

A Rotospline matte can also be used as a "stencil," or mask; that is, to isolate a portion of an image for further manipulation such as color correction. For example, a matte could be drawn to isolate an automobile that was filmed in black-and-white, thus enabling you to colorize only the car while leaving the background monochrome.

The Rotospline node can be used to create a control image, or mask, for another node, such as Vector Warp or Color Correct.

The Rotospline node features a work monitor that provides you with tools for drawing matte shapes around portions of an image. You can edit, scale, rotate, invert, duplicate, and animate these shapes.

The drawing tools enable you to draw both straight (linear) and curved (spline) line segments. You control the splines by dragging handles that extend from the spline's anchor points.

You can display the source image in the work monitor, to use as a reference when drawing a shape that will be used to isolate a specific object or area in the image, or you can display the matte channel only.

The Rotospline work monitor also enables you to access a key frame editor to set and delete key frames to control the interpolation of shape characteristics over time.

You can create as many matte shapes as you need for an image, and for each shape you can set different parameter values (such as frame range, opacity, and edge characteristics). You can also invert the pixel values of any shape, and use it as a cutout to punch a hole in another shape. And you can change the order in which the shapes are layered.

The Rotospline node accepts one input, which may or may not have an alpha channel:

  • If the alpha channel of the source image is unsuitable for any reason, you can clear the incoming alpha to black or white, or you can invert it.
  • If the source image does not have an alpha channel, the Rotospline node will generate one in which every pixel is black or white, as you choose.

The node output is either an RGBA or a one-channel (alpha) image, as you specify.

Using the Rotospline Work Monitor

In addition to the standard Monitor Toolbar, the Rotospline work monitor panel provides a shape panel with controls for creating and editing shapes. The shape outlines are displayed over the input imagery in the image area of the work monitor.

Rotospline Shape Panel

The Rotospline shape panel consists of three sections:

  • a Shape List section, for selecting, naming, reordering, and deleting shapes;
  • a Shape Tools section, for drawing and editing shapes; and
  • a Shape Characteristics section, for setting frame range, opacity, edge type, and other shape parameters.

Shape List

The Shape list displays a list of every shape you create. As soon as you create or replicate a shape, a new entry appears in the list.

Select Shape

Click the Select Shape button to make the corresponding shape the active shape. All of the other parameter settings in the panel apply to the currently selected shape.

Up Arrow

The top entry in the Shape list is the bottom layer of the matte image. Each time you create a new shape, that shape is layered over any previous shapes. The Up arrows are used to reorder the list, and consequently the order of the shapes themselves. The order in which shapes are layered affects how overlapping shapes interact.

Click the Up icon for a shape to move that shape one step closer to the top of the list, which is one layer back in the image.

Name

You can use the Name field to assign descriptive names to shapes. Simply select the current name, key in a new name, and press the Enter key.

Delete Shape

Click the Delete Shape button to delete the corresponding shape. Both the shape and the list entry are deleted.

Shape Characteristics

These parameters apply to the currently selected shape. You can select another shape and apply a different set of values to the same parameters.

Opacity, Edge, and Gamma values can all be animated over time by clicking the associated STED button to access the Chalice Space-Time Editor. For more information, see chapter 9, "Space-Time Editor (STED) ."

Range

This parameter enables you to specify a range of frames in which the currently selected shape will appear by keying a starting and ending frame number into the data entry fields.

Opacity

This parameter enables you to set the opacity (or relative transparency) of the currently selected shape. A setting of 1 shows pure white (completely opaque) inside the matte; a setting of 0 shows pure black (completely transparent) inside the matte; intermediate values show shades of gray.

You can set the Opacity parameter by keying in a numerical value between 0 and 1 or by using the mouse to set the tuner to the desired value. The default value is 1.

Edge Type

This parameter controls the softness, or blur, of the matte edge of the currently selected shape. Select one of three options from the Edge Type popup menu:

No Edges

Obviously, this option (the default) specifies that no blurring be applied to the edges.

Uniform Edges

This option blurs every edge evenly by the value you enter in the associated tuner, which only becomes active when this option is selected. A value of 0 generates no blurring and a value of 1 produces an extremely soft, blurred edge that is 10 percent of the total width of the image.

Nonuniform Edges

This option enables you to apply a different edge to each spline. This parameter is a special case, in that (unlike the Uniform edge option):

  • nonuniform edges must be used in Edge Mode (click the Edge Mode button in the Shape Tools menu to select Edge Mode), and
  • nonuniform edge values are adjusted by manipulating edge points in the work monitor, not by using the tuner.

With Edge Mode selected, the points of the selected shape change appearance (they look like hollow squares) to indicate that they can be manipulated to set the width and direction of the edge blur. Simply drag one of these "edge points" to a new position and examine the resulting blur.

When you select another mode, such as Point Mode, you will see that the actual anchor point of the spline has not moved from its original position.

Invert

Click the checkbox of this shape-specific parameter to invert the pixel values of the matte (e.g., white changes to black, and vice-versa).

Tip:
Invert is an easy way to create cutouts. For example, to quickly create a donut-shaped matte, you could first create a large circular shape, then create a small circular shape and invert it, and finally center the small inverted circle over the large one.

Shape Tools

The Shape Tools section features nine buttons that control the drawing and editing tools and open the Rotospline key frame editor.

Draw Mode (Alt D)

Draw Mode enables you to draw straight (linear) and curved-line (spline) segments. When you open the Rotospline work monitor for the first time, Draw mode is selected by default (once you have created a shape, the monitor defaults to Point Mode when opened).

Click the Draw Mode button to enter Draw Mode.

  • To draw a linear segment (straight line), click anywhere in the image area to create an anchor point, move the mouse, then click again to create a second anchor point. Chalice draws a linear segment connecting the two points. Continue moving and clicking the mouse to add additional segments.
  • To draw a spline (curved line), click and drag the left mouse button. The spline will terminate when you release the mouse button. You will be able to adjust the slope of the curve by dragging the rotating handles that extend from the anchor points of the spline.

Point Mode (Alt P)

Click the Point button to enter Point Mode. Point Mode enables you to reposition anchor points to adjust the paths of shape segments you create using the other drawing tools.

Click and drag any anchor point or slope handle to reposition it, or use the arrow keys on your keyboard to translate the selected point or handle in 1-pixel increments: the Up arrow key moves the point or point handle up a pixel, the Right arrow moves it a pixel to the right, and so forth.

You can zoom in to position the anchor points more precisely, if necessary, by clicking the Zoom button on the monitor toolbar.

Tip:
To select multiple points, hold down the Shift key while clicking on each point you wish to select, or click and drag in the monitor to draw a bounding box around the points you wish to select.
To translate all selected points simultaneously, either hold down the Shift key while dragging one of the points, or use the arrow keys to nudge the selected points in 1-pixel increments in the direction of the arrow.

Shape Mode (Alt S)

Click the Shape button to enter Shape Mode. Shape Mode enables you to work with shapes as a whole. You can translate, scale, and rotate the selected shape in this mode. When you click on an established path or shape, Chalice displays a control device that features a boundary box and a circle-with-crosshairs tool:

Hot Keys:
You can use the arrow keys on your keyboard to translate, scale, and rotate a shape in small increments. The default mode for the arrow keys is transform. To scale or rotate the shape, hold down a modifier key while pressing the arrow keys: to scale, hold down the "s" key; to rotate, hold down the "r" key.

Add Point Mode (Alt V)

Add Point Mode enables you to add new anchor points to the shape. Click the Add Point button to enter Add Point Mode. Then click on an established path to add a new point to the shape.

Note:
Whenever you add--or delete--a point from a shape, that point is added or deleted from the shape in every frame of the sequence in which the shape appears, not just the current frame.

Edge Mode (Alt E)

The Edge Mode button only becomes accessible when the Nonuniform Edges option is selected from the Edge Type menu, which is described in the previous section on "Shape Characteristics."

In Edge Mode the points of the selected shape become hollow squares. Any of these "edge points" can be moved by dragging the mouse to adjust the edge blur for the associated spline.

Note:
The position of an edge point affects only the level and direction of blur of the associated edge; moving an edge point does not change the position of the corresponding point when you switch back to another mode.

Delete Point / Shape (Del)

Delete Point/Shape button enables you to delete selected anchor points and shapes:

  • If you click the Delete Point/Shape button while an anchor point is selected, that point is deleted and a new line segment is drawn between the anchor points that bordered the deleted point.
  • If you click the Delete Point/Shape button while a shape is selected, the entire shape is deleted.

Replicate Shape (Alt R)

Replicate Shape mode enables you to create additional copies of a shape. When you click the Replicate Shape button, Chalice replicates the selected shape, and creates a new, untitled entry in the Shape List. The shape is copied whether the entire shape is selected, or just a single anchor point of the shape.

Expand Points (Alt O)

The Expand Points button enables you to transform linear segments into splines . While in Point Mode, click on a straight-line anchor point to select it. Then click the Expand Points button. Chalice transforms the point into a spline anchor point and any linear segment connected to the point becomes a spline.

Compress Points (Alt C)

The Compress Points button enables you to transform splines into linear segments . While in Point Mode, click on a spline anchor point to select it. Then click the Compress Points button. Chalice transforms the point into a straight-line anchor point and any spline connected to the point becomes a linear segment.

Keyframe Editor

You click the Keyframe Editor button to access the Rotospline Keyframe Editor.

A key frame for a shape is created automatically whenever you move to a new frame in a sequence and modify the shape in any way. The node performs a linear interpolation of the shape characteristics and associated parameter values for the frames between each key frame.

The Rotospline Keyframe Editor displays, in graph form, all key frames for a selected shape. The Keyframe Editor is the most convenient and precise way to create, move, and delete key frames in a sequence:

  • To create a key frame, click and hold the right mouse button at any point on the graph and select "Copy" from the popup menu that appears under the cursor.
  • To move a key frame, drag the key frame along the graph using the left mouse button.
  • To delete a key frame, click on the key frame to select it. Then click and hold the right mouse button and select "Delete" from the popup menu that appears under the cursor.

The editor displays key frame data for the currently selected shape only. To view and modify key frames for another shape, select that shape from the Shape list in the node panel. The editor graph will update to display the key frame data for the new shape.

Tip:
To obtain the smoothest effect when animating a matte shape, set as few key frames as possible. This will help to avoid the "rotoscope flicker" effect that can occur at the matte edges when the interpolation from key frame to key frame is too abrupt. The ability to move and delete key frames quickly and easily in the Rotospline Keyframe Editor should help you achieve this goal.

By default, when you open the Keyframe Editor, a graph displays the entire range of frames in the sequence. You can adjust the graph display range by keying new start and end frame values into the text entry fields. The scroll bar enables you to navigate back and forth through the graph display.

Rotospline 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. The functionality of the Rotospline monitor drawing and editing tools is described in the previous section, "Using the Rotospline Work Monitor ."

Display As

The Display As popup menu provides three options to control the display of matte shapes in the Alpha channel view of the work monitor. (In RGB view, matte shapes always display in wireframe mode to enable you to see the image behind them.)

The edge settings you specify for each shape in the work monitor are used for the final output. The Display As options affect only how the shapes are displayed in the work monitor:

  • Wireframe: This setting displays all matte shapes as outlines only and speeds redraws.
  • Matte: This setting enables you to display matte shapes with soft, or blurred, edges, providing that you have set the associated Edge parameter to a nonzero value.
  • Matte (No Edge): This setting displays all matte edges as crisp and hard, without any edge detail, even if the Edge parameter is not set at 0. To see edge detail, select the Matte option instead.

Channels Out

The Channel parameter enables you to specify whether the node should output an RGBA image, or the Alpha channel only.

Anti-Alias

The Anti-Alias popup menu enables you to specify the level of anti-aliasing to apply, if any, to the shapes you draw in the work monitor. The higher the setting, the smoother the splines will be displayed and rendered. Of course, higher settings also take correspondingly longer to process.

Incoming Alpha

The Incoming Alpha popup menu enables you to specify the characteristics of the alpha channel data used by the Rotospline node:

  • If the input image has no alpha, you can specify that the node create a black (all pixels have a value of 0) or white (all pixels have a value of 1) alpha.
  • If the input image does have an alpha channel, you can use it unchanged, invert it, or clear it to black or white.




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