Atop
compositing node
Composites the first input (Foreground) over the second (background), but only where the background alpha exists.
See also: Over, Composite, Layer, Under
Atop is similar to an Over operation, but the over is restricted to the area of the background image’s alpha matte. The atop operation is defined as
C = C2 * A1 + C1 *(1-A2)
The foreground is considered to be premultiplied, so it will not be multiplied by its alpha channel. If your alpha plane has been replaced (by a ChannelCopy or SwitchAlpha COP, for instance), use a Premultiply COP to correct the color plane.
Planes containing geometric data are handled differently (like Zdepth, Normal, Velocity). Alpha blending does not occur on these planes; the operation either takes the foreground (A>0) or the background pixel data (A=0). This avoids edges artifacts when using geometric data after compositing.
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.
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
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Image Units |
Selects pixels or UV units for the transform. |
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Translate, Rotate, Scale, Pivot |
Transforms the foreground in X,Y relative to the background. |
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Image Filter |
Specifies the filter to use when transforming. |
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Image Wrap |
Specifies the foreground image’s wrapping style. |
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Motion Blur |
Toggles on motion blur, and specifies the time range around the current frame to blur. |
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Motion Frame Bias |
Shifts the time range for the blur. |
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Motion Blur Segments |
Number of samples to blur together in the specified time range. |
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Motion Blur Method |
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Merge
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Overview |
These parameters specify how to build the output sequence when there are differences between the input sequences. |
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Plane Merge |
If the planes in the inputs differ, this specifies what the output planes should be. |
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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. |
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Frame Range |
If the frame ranges of the inputs differ, this determines what the output range should be. |
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Frame Rate |
If the frame rates of the inputs differ, this determines what the output frame rate should be. |
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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.
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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. |
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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 * MVector Mask ('C') C.r = I.r * M.r C.g = I.g * M.g C.b = I.b * M.b
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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. |
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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. |
Local variables
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L |
Sequence length |
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S |
Start of sequence |
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E |
End of sequence |
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IL |
Input sequence length |
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SR |
Sequence frame rate |
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NP |
Number of planes in sequence |
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W,H |
Width and height of image |
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I |
Image index (0 at start frame) |
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IT |
Image time (0 at start frame) |
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AI |
Current plane array index |
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PI |
Current plane index |
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PC |
Num of channels in current plane |
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CXRES |
Composite Project X resolution |
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CYRES |
Composite Project Y resolution |
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CPIXA |
Composite Project pixel aspect ratio |
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CDEPTH |
Composite Project raster depth |
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CBP |
Composite Project black point |
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CWP |
Composite Project white point |