‘Hard Comp — Soft Comp’ And Efficient Delta Keyer Workflows

Fusion Chroma Keying Part 4: Learning to simplify chroma keying by tackling different problems independently

When different areas within the frame exhibit different challenges, you should combine different keying techniques. Learning how to combine two different keys – or adjust one key in different ways – to address all issues in the best way possible is an important skill to master. One great example of this is a technique known as ‘Hard Comp—Soft Comp’.

What is ‘Hard Comp—Soft Comp’?

In chroma keying, the best key to extract a hard edge usually differs from the ideal key that retains soft hair detail. A key that removes tracking markers in the background is often different from a solution that ensures a reflective foreground stays fully opaque.

This is why, within a single shot, we frequently combine different keying techniques to get the best possible result.

Sometimes, the solution is to post-process the same matte/alpha channel in two different ways. For example, a soft mask that gives us great hair detail might also exhibit holes in the actor’s clothes. On the flip side, we can shrink the same matte/alpha channel into a harder mask that stays clear of the edges. We then combine the hard mask to fill in the holes of the soft mask with the soft mask that retains the edge detail.