How to make even more powerful luma keys

- [Instructor] Building on what we…saw in the previous video, here we'll look…at more advanced techniques, such as building…a custom luma key, and how to…luma key a high-dynamic-range image.…But first we need to know how to cope…with a background gradient that is non-linear,…like most of the gradients in the real world.…So here we have a non-linear gradient.…Here we go, you can see that, in fact,…you can see it better in the sampler mode.…Let me adjust this here a little…bit so I can see my RGB channels.…

So you can see right here that it has this curvature…in the back, it's not a straight line like we saw before.…So let's see what happens when we try to level it…with a straight ramp, as we did before,…and we subtract that from the image.…Let me put my viewer back.…And it straightened it out pretty much,…so let's take a look at this now.…Well but we do have this little dip in the middle,…because it's a non-linear gradient,…and we tried to do a linear fix.…Let's see what happens.…

So we'll come here and we will pull our key,…