Hi There,
I got some questions about data passes and why they are not anti-aliased. Since Cineware is out, perhaps more people are happy to explore data passes now, so I put some thoughts about it in this post.
The idea to oversample a pass to smooth its edges is, in most cases, a limitation of the final quality.
These passes are data-bases, not image material. Anti-aliasing or oversampling is like blurring the data of a spreadsheet.
If you would like to see more of this concept in a tutorial, please let me know whether such a series is wanted in the “Tutorial Suggestion” section, thanks!
All the best
Sassi
Some details
Let’s take the UV pass for example. UV is the translation between 2D images and 3D objects. It places the “Object Polygons” (via “UV Polygons”) on the image, to define where the parts of the image are used on the object. In this way the edges, which are connected on the 3D object, are not always connected in the UV Polygons.
The UV space is normalized and is measured in units from 0-1, in both directions.
This normalization leads to the option to represent this “Image Space” with two gradients for U and V direction. This creates the colors of the UV Pass. The pass should be at least 16/bits per channel to work properly. For example, with the Re:Vision plug-in for Ae RE:Map. (http://revisionfx.com/products/remap/features/)
As a result, each color is a representation of the specific position in the U 0-1 and V 0-1 space. The plug-in calculates the position based on the colors (which is the data, by the way!) based on the neighboring pixels, as well as the direction of how the image needs to be mapped, e.g., in AfterEffects.
In the moment one uses anti-aliasing or oversampling on the data passes directly, the two different edge (border) pixels become mixed into a new color value! THIS is, in fact, a position on the UV map which was never before designated for this edge. Using such a map results then in errors, as the content of the provided images is now strangely mixed on that edge.
The idea to oversample data passes is not a good one, as it leads to artifacts. The right way to do this is to double or triple the final resolution. And that should be done for anything in the comp (but perhaps with less AA needed then).
AFTER this work is done, it can be down-sampled, which excludes the UV pass. The down-sampling is (again) only applied, e.g., to the beauty pass.
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In a depth-path, an AA or “oversampling” leads to positions between the object and the background, which results in a smeary seam.
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The normal pass stands for the surface direction of the polygons. To AA or Oversample this pass before it is used, creates new surface directions (although this might be interesting in some cases).
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Bottom line, all these data passes, need to be set to Preserve RGB in After Effects—because the colors represent numbers here! Any profile or gamma treatment would distort the values of such. This (Preserve RGB) is an indicator that we use these passes here as a database, not as an image. This, in return, leads to a use that is free of Anti-Aliasing or Oversampling. AA and Oversampling need to be done on the beauty-pass.