About the Domain of Definition (DOD) |
The DOD is a rectangular zone that Shake uses to optimize rendering speed by bounding the significant pixels in the image. Everything outside of the DOD is considered to be the background, meaning black by default, and can therefore be ignored in most computations. Proper handling of the DOD is an extremely powerful way of speeding up your render times.
All images from disk will automatically get a DOD assigned to it equal to the resolution of the image. Here are five ways that you can alter the DOD:
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By a good understanding of the role of the DOD, you can optimize the tree both before and after the node in question. The above tree example will not only optimize any nodes you attach to Inside1, but it also will only execute the Primatte and read in the part of the image that is inside of the DOD, cutting down on both processing and IO activity. |
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This section talks about the area outside of the DOD, which we term the Background Color, or BGColor for short.
The two main keyers in Shake, Keylight and Primatte, both recognize the background color, and have a toggle to either key it in or out. By default, the background area is left black in the alpha by the keyer. However, by toggling BGColor on, it will turn it completely white.
When color correcting the BGColor, Shake will process it very quickly, as it recognizes there is a pure correction applied to previously black pixels. If the color correction doesn't change black, like Gamma or Mult, it will be ignored. If it does affect the black areas, like Add or Compress, it will process these areas, but understand that they are still the results of a lookup process. Therefore, the DOD does not get reasserted to the resolution frame. This is the same process that is used when the Infinite Workspace kicks in. So, the result is, even though the pixels outside of the DOD are visibly no different from the pixels inside, the DOD remains in place.
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There may be cases, however, where you do want to take advantage of the DOD for masking purposes. In this tree, we scale an image down, raise up the brightness with an Add command. This, however, turns the area outside of the image a medium grey. Since this area is recognized to be outside of the DOD, we can return it to black with the Color - SetBGColor node, which sets the color for the area outside of the DOD.
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Another node to help limit a process is the Layer - Constraint node. You can place any two images in the Constraint node, and then mix the two according to a combination of modes. The modes are Area of Interest (AOI), tolerance, channel, or field. The one that interests us the AOI. Toggle it on, and then set the area box. Only the area inside of the box of the second image will be calculated. |
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