Subtract compositing node

Subtracts the foreground image from the background image.

All

Parameters

Local variables

See also: Diff, Add, Composite, Layer

Subtracts the foreground image from the background image. The Subtract operation is defined as:

C = C2 - C1

Subtract may produce negative values, which may not be seen in data formats that do not represent negative values (8bit, 16bit integer). Diff can be used to produce the absolute difference (sign of the difference is ignored).

Tip

The Layer COP allows multiple inputs to be composited instead of just two, each with its own compositing operation. The Composite COP is the more general version of this COP, allowing you to choose any compositing operation, and an optionally different operation for alpha.

Scoping

This operation may be restricted to certain planes, or components of planes. In addition, the operation may be applied to a subset of frames within the sequence. An image must have both its frame and plane scoped to be modified.

Images that are not modified are passed through, which does not take any memory or processing time.

Masking

This operation may be masked, which restricts the operation to an area of the image. The mask may be inverted, brightened or dimmed.

The mask input is on the side of the node. The label on the connector indicates the plane being used as a mask.

The mask input can also be scaled to fit the output image’s resolution, if they differ. However, if this node changes more often than the mask input, it is faster to place a Scale COP in front of the mask input to do the resize, as the resize will not occur on every cook of this node.

Parameters

Composite

Image Units

Selects pixels or UV units for the transform.

Translate, Rotate, Scale, Pivot

Transforms the foreground in X,Y relative to the background.

Image Filter

Specifies the filter to use when transforming.

Image Wrap

Specifies the foreground image’s wrapping style.

Motion Blur

Toggles on motion blur, and specifies the time range around the current frame to blur.

Motion Frame Bias

Shifts the time range for the blur.

Motion Blur Segments

Number of samples to blur together in the specified time range.

Motion Blur Method

Velocity	Only uses the current frame and the transform to compute past and future positions.
Deformation	Cooks the images at all time samples.

Merge

Overview	These parameters specify how to build the output sequence when there are differences between the input sequences.
Plane Merge	If the planes in the inputs differ, this specifies what the output planes should be.
Raster Depth	If the raster depth for a given plane differs between inputs, this specifies when the output raster depth for the plane should be.
Frame Range	If the frame ranges of the inputs differ, this determines what the output range should be.
Frame Rate	If the frame rates of the inputs differ, this determines what the output frame rate should be.
Frame Match	If the frame rates of the inputs differ, this determines which input frame to pick when the cook time doesn’t reside on a frame boundary.

Mask

A mask can be chosen to limit the effect of the operator to areas defined by the mask. The mask can be taken from the mask input (side input) or from the first input itself.

Effect Amount

If no mask is present, this blends the output with the input by a constant amount (0 = all input, 1 = all output).

If a mask is present, this amount multiplies the mask.

Operation Mask

Selects the mask plane to use as a mask from the mask input. The mask can be selected from:

A mask can be a component of a plane or an entire plane. If a vector plane is supplied as a mask, its components are multiplied by the images' components.

Scalar Mask ('A', 'C.r')

C.r = I.r * M
C.g = I.g * M
C.b = I.b * M

Vector Mask ('C')

C.r = I.r * M.r
C.g = I.g * M.g
C.b = I.b * M.b

First Input	Useful for masking the operation to the image’s own alpha plane.
Mask Input	Selects the mask from the side mask input.
Off	Turns off masking, without requiring disconnection of the mask input (useful for temporarily disabling the mask).

Resize Mask to Fit Image

If the mask image is a different resolution than the output image, turning on this parameter will scale the mask to the output image’s resolution.

If this node is changing constantly, and the mask is not, it is somewhat faster to put a Scale COP down to do the resize for the mask image. Otherwise, the scale will occur every time this node cooks.

Invert Mask

Inverts the mask so that all fully 'masked' portions become unmasked. This saves you from inserting an Invert COP after the node with the mask.

Scope

Plane Scope

Specifies the scope for both the RGB components of Color, Alpha, and other planes. The (C)RGBA mask only affects Color components and Alpha. 'C' will toggle all the RGB components.

For planes other than Color and Alpha, the plane name (plus component, if applicable) should be specified in the string field. The pulldown menu can be used to select planes or components present in this node.

A plane is specified by its name. A component is specified by both its plane and component name. The '*' wildcard may be used to scope all extra planes. Any number of planes or components can be specified, separated by spaces.

Examples:

P
N.x N.y
P N Pz

Frame Scope

Allows scoping of specific frames in the frame range. This is in addition to the plane scope (so a plane at a certain frame must be both plane scoped and frame scoped to be modified).

All Frames	All frames are scoped.
Inside Range	All frames inside a subrange are scoped.
Outside Range	All frames outside a subrange are scoped.
Even Frames	Even numbered frames are scoped.
Odd Frames	Odd numbered frames are scoped.
Specific Frames	A user-defined list of frames are scoped.

Frame Range

For Inside/Outside range, this parameter specifies the subrange of the sequence to scope (or unscope). This can be edited in Timeline viewer mode ( Ctrl + 2 in viewer).

Frame Dropoff

For Inside/Outside Range, this parameter specifies certain number of frames before and after to slowly ramp up to scoped. The operation will be blended with its input to 'ease in' or 'ease out' the scoping effect over a number of frames. This can be edited in Timeline viewer mode ( Ctrl + 2 in viewer).

Non-scoped Effect

For unscoped frames, this sets the blend factor between the input and modified images. Normally this is zero (use the input image). By setting this to a non-zero value, you can make unscoped frames be 'slightly' unscoped. The value can vary between 0 (unscoped) and 1 (scoped).

Frame List

The frame list for 'Specific Frames'. Frame numbers should be separated by spaces.

Automatically Adjust for Length Changes

If the sequence range changes, enabling this parameter will adjust the subrange and frame dropoff lengths to fit the new range.

Local variables

L	Sequence length
S	Start of sequence
E	End of sequence
IL	Input sequence length
SR	Sequence frame rate
NP	Number of planes in sequence
W,H	Width and height of image
I	Image index (0 at start frame)
IT	Image time (0 at start frame)
AI	Current plane array index
PI	Current plane index
PC	Num of channels in current plane
CXRES	Composite Project X resolution
CYRES	Composite Project Y resolution
CPIXA	Composite Project pixel aspect ratio
CDEPTH	Composite Project raster depth
CBP	Composite Project black point
CWP	Composite Project white point

Usages in other examples

Example name	Example for
Types	Composite compositing node	Load \| Launch