MERGING IMAGES
With Nuke, you can merge images in a wide variety of ways. In this chapter, we teach you how to use the Merge, ContactSheet, and CopyRectangle nodes. The Merge node is used for layering multiple images together. The ContactSheet node lets you create a contact sheet that shows your frame sequence(s) lined up next to each other in a matrix. The CopyRectangle node can be used for copying a rectangular region from one image to another. Layering Images Together with the Merge Node The Merge node with its compositing algorithms allows you to control just how your images are combined. Note When using most of the available merge algorithms, Nuke expects premultiplied input images. However, with the matte
Operation you should use unpremultiplied images. To layer images with the Merge node:
1. Select Merge > Merge (or press M on the node graph) to insert a Merge node after the images you want to layer together.
2. Connect your images to the Merge node’s A and B inputs.
3. If necessary, you can connect multiple A images to the Merge node. Once you have got the A and B inputs
Connected as instructed in step 2, drag more connectors from the left side of the Merge node to the images you
Want to use as additional A inputs. Layering Images Together with the Merge Node Each input is merged in the order connected, for example A1, A2, A3, B.
4. Connect a Viewer to the output of the Merge node so you can see the effect of your merge operation.
5. In the Merge node’s controls, select how you want to layer the images together from the operation pulldown
Menu. The default and the most common operation is over, which layers input A over input B according to the
Alpha of input A. For descriptions of all the available operations, see “Merge Operations” below.
6. Using the A channels and B channels menus, select which channels to use from the A and B inputs and which
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Channels to use as the A and B alpha. If you want to merge more channels than these and output them into
The same channels, select them from the also merge pulldown menus and checkboxes.
7. From the output menu, select the channels you want to write the merge of the A and B channels to. Channels
Named in the also merge list are written to the same output channels.
8. If necessary, you can also adjust the following controls:
– To select which input’s metadata to pass down the tree, use the metadata from menu. For more information on
File metadata
– To dissolve between the original input B image (at 0) and the full Merge effect (at 1), adjust the mix slider. A
Small light gray square appears on the node in the node graph to indicate that the full effect is not used.
– If you want to mask the effect of the Merge operation, select the mask channel from the mask pulldown
Menus. To invert the mask, check invert. To blur the edges of the mask, check fringe. Layering Images Together with the Merge Node
Note that you should not use the alpha of the inputs for the mask. It produces erroneous results (though the
Error is often hard to see); you can achieve better results by turning on alpha masking.
– From the Set BBox to pulldown menu, select how you want to output the bounding box. The default is union,
Which combines the two bounding boxes. You can also choose intersection to set the bounding box to the
Area where the two bounding boxes overlap, A to use the bounding box from input A, or B to use the bound-ing box from input B.
– By default, Nuke assumes that images are in linear color space.
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