Softening Edges with Alpha

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‌Softening Edges with Alpha

ViewShift produces an alpha channel to indicate which pixels it has shifted (ie are present) to the output image. For transparent effects, especially removals, you typically want to have a soft edge around the shifted area, as a sharp edge will often stand out as artificial, potentially with staircased jaggies. You can soften the actual edge pixels using the Edge Antialiasing control, which defaults to Low. It can be increased to Mid or High at the cost of a slight runtime increase.

For removals, it's often desirable to go even further, to blend the transition over a larger number of poixels.To accommodate that, you typically want the area being removed to be a bit larger than necessary, so that the alpha channel can be softened inwards.

For hard edges, such as the edge of a building, you can't soften the edge inwards, or you'll leave a very visible halo around the affected area. To minimize that, you want to soften the alpha channel outwards, which requires "making up" some new pixels that don't exist in the source image by replicating pixels that are inside the edge to its outside.

You can accomplish these manipulations using ViewShift's Pull in and Push out spinners. (You can do both at once.) They permit adjustments in fractions of a pixel, although that is more statistical, changing the generated alpha values, than literal. If you're more familiar with your downstream compositing application, you can output raw

alpha and soften in there. Doing the softening in SynthEyes is very convenient for quick previews in either case.

Tip: When using Pull in or Push out, you should turn up the Edge antialiasing to at least Mid, to generate more accurate results.

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