Color me confused about this bug report! I have been having a devil of a time working out a relatively simple problem. I believe that Resolve 14B4 is partially to blame.
The basic objective is this: create an inverted vignette around a talking head that was recorded in front of a green screen.
I have a node tree as follows:
- Screen Shot 2017-06-22 at 3.41.17 PM.png (101.03 KiB) Viewed 18474 times
What has caused me no end of trouble is that there seem to be several factors that all, with heisenberg-like (un)certainty, either are a part of the problem or a part of the solution. I think Resolve should more rigorously initialize its variables so that if the node tree is wrong, it's always wrong, and if it's right, it's always right.
To wit:
1. When I have what I want in the color window and switch to the deliver window, the preview changes from the composition I expect to just the talking head in front of a black background. When I return to the color window, I see that where the Unmix icon used to be (now a series of stacked rhombuses), the icon is deselected. I get it back to the selected state, switch to the deliver window, and that fixes the preview. But when I render, it might still render the talking head against a black background rather than the one I expected.
2. The Key in Node 1 uses a Qualifier to select the Green Screen and inverts the key to make the green screen transparent and the subject opaque. The key in Node 07 behaves mysteriously. Initially I could not seem to get rid of the green edges (spill) of the key in 01. But I discovered that adding the 07 corrector, with all default settings except an inverted key output magically changed the bright green spill to a much less intense blue spill that passes for a shadow light. I'll take it! But that's not the end of the story.
When I double-click on the Key Mixer, I get a layering of the subject with only about a 50% alpha value on top of the overall opaque background. A second double-click gives me the expected white-on-white matte (where the opaque subject will overlay the opaque background). I would expect the correct matte computation first, last, and always.
3. But then, strangely, I have to invert the input to the key mixer's Channel 2. Since all 07 does is invert the key, and since the key mixer inverts the 2nd input, you'd think I could leave 07 non-inverted (purely default) and not invert the 2nd input. After two double-clicks, the key mixer's matte agrees with my intuition. But the rendered image comes up completely wrong: it shows the green screen in blue and the subject in a black silhouette. So instead I leave well-enough alone and pass an inverted output to an inverted input.
And at the end, I sometimes get the rendering I expect, and I sometimes get just the subject against a black background. I suspect what's happening is there's some very delicate condition whereby my alphas are not adding up perfectly (or, rather, as I expect) and the result is that sometimes the compositor decides to bring in the background and sometimes it decides to bring in black. And sometimes the first frame renders as expected by none of the following do (only black background), and sometimes the first frame renders with a black background and the rest are OK.
Help?!
Mon Jun 19, 2017 5:33 pm
