# Premultiply compositing node

Allows colour to be converted to or from a premultiplied form.

This operation allows color to be converted to or from a premultiplied form. Premultiplied color is color than has already been multiplied by alpha.

If multi-channel alpha is given (opacity), the appropriate components are multiplied (Cr x Ar, Cg x Ag, Cb x Ab).

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. 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.

## Premultiply

Operation

The color plane can either be multiplied or divided by the alpha plane.

Alpha Plane

The name of the alpha plane (or the plane to multiply or divide by).

Scope

The planes to affect (normally just Color).

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.

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

```

```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.

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.

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.

## Locals

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

## Examples

The following examples include this node.

Lighting3d Example for Lighting compositing node

This example demonstrates three different ways that the Lighting COP can simulate 3D lighting, using images with Point and Normal deep raster information. Point lighting, directional atmospheric lighting, and lighting without Normals are explored.

MakeShadow Example for Corner Pin compositing node

How to make an angled shadow on a flat surface with the Corner Pin COP.

# Compositing nodes

• Adds two images together.

• Creates an anaglyph from a pair of input images.

• Composites the first input (Foreground) over the second (background), but only where the background alpha exists.

• Averages the foreground image and the background image.

• Blends frames from two sequences together using a simple linear blend.

• Blurs an image.

• Adds a border to the image.

• Applies a brightness factor and bright shift to the first input.

• Builds a bump map from a plane.

• Copy channels from any of inputs into the output image.

• Mask or "key" an image based on its color.

• Creates a constant color image.

• Applies a variety of color corrections to the image

• Adjusts the R,G,B and/or A channels based on a user-defined curve.

• Maps a range of color to a new range.

• Replace a color region in an image with another region.

• Generates a simple HSV color wheel.

• Does a composite (over, under, inside, add, etc) between two images.

• Increases or decreases the contrast of an image.

• Changes the data format of a plane.

• Performs a generic convolve on the source image.

• Fits an image into an arbitrary quadrilateral.

• Generates a four corner ramp.

• Crops an image and changes its resolution.

• Extracts matte from Cryptomatte image.

• Flattens a Deep Shadow/Camera Map into a flat 2D raster.

• Defocuses an image similar to a real camera defocus.

• Deforms an image by moving the underlying UV coordinates.

• Removes film grain from an image.

• De-interlaces a frame of video by either averaging scanlines or copying a scanline.

• Removes planes or components from an input sequence.

• Removes white noise from an image.

• Darkens depth boundaries in an image.

• Creates a depth-of-field mask, which describes how out of focus parts of the image are.

• Computes the difference between the foreground image and the background image.

• Expands and shrinks mattes.

• Creates a blurred shadow offset of an image.

• Blurs the edges of an image.

• Detects edges in the input image.

• Adds a lighting effect to the image by using a bump map.

• Applies an environment map to an image.

• Equalizes colors by stretching or shifting the image histogram.

• Creates an image containing precomputed error function terms for hair albedo computation

• Expands and shrinks mattes.

• Extends the length of a sequence so that it can be animated beyond its frame range.

• Fetches a sequence of images from another COP, even in another network.

• Merges two fields into one Interlaced Frame.

• Splits an interlaced frame into two fields per frame (odd and even fields).

• Swaps the two fields containing the even and odd scanlines of the frame.

• Loads image files into Houdini.

• Flips the image horizontally and/or vertically.

• Adds a variety of atmospheric effects to an image, including fog, haze and heat waves.

• Renders anti-aliased text.

• Cleans up flipped normals by making them face the camera.

• Performs a variety of mathematical functions on the input image.

• Applies gamma correction to the image.

• Keys out parts of the image based on pixel position or normal direction.

• Renders geometry from a SOP as a single color image.

• Computes the gradient of an image.

• Adds grain to an image.

• Converts between RGB and HSV color spaces, or applies hue and saturation modifications.

• Adjusts the saturation or luminance of the image based on hue.

• Detects illegal pixels, like NAN and INF, in images.

• Restricts the foreground color to the area of the background’s alpha matte.

• Interleaves image sequences.

• Applies a photographic pixel inversion to the image.

• Layers a series of inputs together by compositing them one by one on the background image (input 1).

• Adjusts black point, white point, and midrange to increase, balance, or decrease contrast.

• Adds a light to the image.

• Limits the pixel range at the high end, low end or both.

• Applies a lookup table to the input.

• Cooks the subnet COPs multiple times in a loop, accumulating the results.

• Sets the alpha to the luminance of the color.

• Keys the image based on luminance (or similar function).

• Masks out an area of an image.

• Outputs the maximum value of the foreground and background images for each pixel, which tends to lighten the image.

• Applies a 3 x 3 or 5 x 5 median filter to the input image.

• Merges the planes of several inputs together.

• Applies metadata to an image sequence.

• Outputs the minimum value of the foreground and background images for each pixel, which tends to darken the image.

• Converts a color or vector into a scalar quantity, like luminance or length.

• Takes a sequence of images and combines them into 1 image by tiling them.

• Multiplies the foreground image with the background image.

• Generates continuous noise patterns.

• Does nothing.

• Restricts the foreground color to the area outside of the background’s alpha matte.

• Composites the first input (Foreground) over the second (background).

• Modifies an image’s pixels using expressions.

• Allows colour to be converted to or from a premultiplied form.

• Performs a pulldown (cine-expand) on the input sequence.

• Performs a pushup (cine-expand) on the input sequence.

• Quantizes input data into discrete steps.

• Renders frames out to disk.

• Does a radial or angular blur.

• Generates a variety of linear and radial ramps, which are fully keyframable.

• Copies the sequence information from its input.

• Change the name a plane.

• Renders a mantra output driver directly into a composite network.

• Simply reverses the frames in the sequence.

• Draws one or more curves or shapes.

• Imports a 2d Volume from SOPs as planes into a composite network.

• Changes the resolution of the image.

• Adds two images together, saturating at white like photographic addition.

• Sequences two or more inputs end to end.

• Generates simple shapes, such as circles, stars and regular N-sided polygons.

• Sharpens an image by enhancing the contrast of edges.

• Shifts an image sequence in time.

• Shuffle frames around to do out-of-order editing.

• Creates sky and ground images for use as environment maps.

• Either removes frames from a sequence or allows you to order them in a user-defined order.

• Streaks an image, adding a motion blur effect.

• Contains networks of other COPs.

• Subtracts the foreground image from the background image.

• Passes the input of one of its connected inputs through, acting like an exclusive switch.

• Replaces input 1's alpha with input 2's alpha.

• Generate noise suitable for terrain height maps.

• Tiles the image sequence with multiple copies of the input image.

• Blurs a pixel through several frames.

• Uses a second input to time warp the first input on a per pixel basis.

• Stretches or compresses a sequence in time.

• Warps time by slowing or speeding it up throughout the sequence.

• Translates, rotates and/or scales the input image without changing the image resolution.

• Trims an input sequence in time by adjusting the beginning or the end of the sequence.

• Creates a UV map.

• Composites the first input (Foreground) under the second (background).

• Extracts an arbitrary quadrilateral area out of the input image.

• Runs a VEX script on its input planes.

• Runs a VEX script on the planes it generates.

• Contains a VOP network that filters input image data.

• Contains a VOP network that generates image data.

• Performs vector operations on the input.

• Blurs an image by using pixel velocity to produce a motion blur effect.

• Cuts a small window out of a larger image.

• Does a wipe between two input sequences.

• Makes two elements mutually exclusive; if their alpha mattes overlap, the overlap is removed.

• Does a Z composite of two images.