This week, we learn how to roto and track from a vedio.
How we can remove the alpha?
Shuffle
- rearrange up to 8 channels from a single image (B input). For example, you can use it to swap rgba.red for rgba.green, and vice versa,
- rearrange channels between two separate nodes (A and B input), like a foreground and background branch,
- replace a channel with black (removing the alpha channel, for example) or with white (making the alpha solid, for example),
- create new channels.
Premult
By default, Premult multiplies the input’s rgb channels by its alpha (in other words, premultiplies the input image). You may need this node when:
- Merging unpremultiplied images. Because Merge nodes in Nuke expect premultiplied images, you should use this node before any Merge operations if your input images are unpremultiplied. This avoids unwanted artifacts, such as fringing around masked objects.
- Color correcting premultiplied images. When you color correct a premultiplied image, you should first connect an Unpremult node to the image to turn the image into an unpremultiplied one. Then, perform the color correction. Finally, add a Premult node to return the image to its original premultiplied state for Merge operations.
Typically, most 3D rendered images are premultiplied. As a rule of thumb, if the background is black or even just very dark, the image may be premultiplied.
Roto (pressing O on Node Graph)
The Roto node is an optimal choice if you’re doing rotoscoping only – it allows you to create and edit Bezier and B-spline shapes.
The toolbar on the left side of the Viewer includes point selection and manipulation, and shape creation tools. Click and hold or right-click on a toolbar button to open a sub-menu to select any of its available tool types. Options related to the current tool appear in a toolbar along the top of the Viewer. Click on a toolbar item to cycle through the available options for that class of tools.
As a general workflow guide:
- Select your tool from the left-hand Viewer tool bar.
- Use the Roto tool settings above the Viewer to adjust the tool’s properties.
- Draw your shape or shapes:
- Click in the Viewer to place points. You can drag while clicking to pull out Bezier handles or adjust B-Spline tension.
- Ctrl/Cmd+drag to sketch the shape freely.
- To close the shape, click the first point or press Return. To leave the shape open, press Esc.
- Ctrl/Cmd+Alt+click to add points to an existing shape.
- To increase the smoothness of a point, select the point and press Z.
- To cusp a point, select the point and press Shift+Z.
- To delete a point, select the point and press Delete.
- Beziers: Shift+drag on a tangent handle to snap the opposite handle to the same length. Ctrl/Cmd+drag on a tangent handle to move it independently of its opposite handle.
- B-Splines: Ctrl/Cmd+Alt+drag on a point to adjust its tension.
- Select a shape using the Select tools or the shape list in the control panel.
- Use the control panel to adjust or fine-tune your shape(s).
Copy (pressing K on Node Graph)
Replaces channels in the B input with channels from the A input. You can use a mask channel to indicate which input is used for each pixel or whether both inputs should be mixed for some pixels.