Join Steve Wright for an in-depth discussion in this video Premultiply and unpremultiply, part of VFX Keying: Master Course.
- [Narrator] And now for everybody's favorite topic,…premultiplied and unpremultiplied images.…Here's the rule.…Color correction and color space conversion…must be done on the unpremultiplied image.…In this video, we'll see why this is true…and what happens if you get it wrong.…So here in my setup I've got this Roto here,…which represents a four-channel premultiplied image.…Now this is either a CG image or a keyed image…that you've already done the premult operation.…
So the Roto goes to this Grade node,…which at the moment has no settings, so no change there,…and then we comp over the background…and everything looks lovely.…However, let's apply a color correction operation.…I'm going to take the gamma for the blue channel up to two…and ooh, now I've got these ugly blue edges.…So let's track this down and see what's going on.…Let's go back up to our Roto node…and take a look at the Unpremult node.…Here's the story.…
When this Roto was initially created inside the node,…it was actually built like this,…the RGB channels were the same value…
Note: This course was created by Steve Wright, author of the seminal book, Digital Compositing for Film and Video. We are proud to host this course in our library.
- Creating an uber key
- Keying green-screen vs. blue-screen footage
- Preprocessing footage
- Building a clean plate
- Making luma keys
- Keying on hue and saturation
- Pasting keys together
- Grain management
- Saving time with garbage mattes
- Using spill suppression
- Improving edges
- Color correcting keys
- Sweetening the comp
- Alternative compositing workflows
- Fixing edge problems
- Using KEYLIGHT, Primatte, Ultimatte, and other tools
Skill Level Intermediate
Photorealistic Lighting with Maya and Nuke (2012)with Mark Lefitz2h 24m Intermediate
Compositing a Sci-Fi Force Field in NUKEwith Steve Wright2h 12m Intermediate
Compositing an Alien Portal in NUKEwith Steve Wright2h 20m Intermediate
1. Keying Workflows
2. Pre-Processing the Green Screen
3. Other Types of Keys
4. Building the Uber Key
5. Spill Suppression
6. Compositing Techniques
7. Color Correcting
How to match grade two clips4m 15s
8. Workflow Examples
9. Sweetening the Comp
10. Fixing Edge Problems
11. Special Keying Solutions
12. Appendix: Keyer Tutorials
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