Easy-to-follow video tutorials help you learn software, creative, and business skills.Become a member

Understanding luma keys

From: Compositing with Premiere Pro CS5.5

Video: Understanding luma keys

When I use the word key or keying, what I mean in this context is using some kind of reference to define the transparency, or the opacity, or effectively the alpha level for pixels in my image. A classic key is, of course, the Chroma Key. The traditional weather reporter in front of a blue screen and anything bright blue is made transparent and you see another layer of video behind it. There is also another system of keying called Luma key, which works instead on the brightness, the luminence of individual pixels.

Understanding luma keys

When I use the word key or keying, what I mean in this context is using some kind of reference to define the transparency, or the opacity, or effectively the alpha level for pixels in my image. A classic key is, of course, the Chroma Key. The traditional weather reporter in front of a blue screen and anything bright blue is made transparent and you see another layer of video behind it. There is also another system of keying called Luma key, which works instead on the brightness, the luminence of individual pixels.

It's very easy to apply a Luma key inside of Premiere Pro, and the results, sometimes they're great, sometimes they're not so great. It's one of those effects where you get the most magnificent results by planning for it and shooting, knowing that your shadows, dark part of your pictures are going to become transparent. If you plan for it, and you get nice hard lighting and strong shadows, you can get some really powerful effects where content or subjects, performers seem to emerge from another layer. Putting a Luma key on is just a question of dragging and dropping.

And straight away, you can see here in the example, in my background, I've got some color bars and in the foreground, I've got this black and white gradient. Putting the Luma key on immediately puts some transparency into the gradient. You don't get that many controls. You've got a threshold which will define at the point to which the foreground becomes visible and the point at which the background becomes visible, that's pretty self-explanatory. And there's also a cutoff so you can say, beyond a certain point it's just going to be visible or invisible. You can see I can even invert that by crossing my own threshold and that's pretty much all you get.

You can get some interesting results by combining it obviously with more interesting media. if I switch off my background here, for example, in my foreground now, I've got my balloon shot. If I turn off the Luma key, you can see here's the original. If I put on my background, so you can see, I've got my color bars, and turn on my balloons. There you go. You can see, I can layer these together, and I'm getting a partial key here. I'm getting bits of the clouds, the balloons, which are more solid shapes, and I'm using the fact that there's a reasonable variation in the luminence between the clouds and the sky to create the key.

Now, if you color correct, you can enhance the difference. You could always bring down the midtones to get a stronger key, and you'd get a much better result with this. But even with a partial key like this, if I put a regular sky pattern behind it instead of those nasty color bars, you can see right away, I get a much more interesting composition. Now, of course, these are still frames so they are not quite as alive and convincing as they would be if they were moving. But again, you can see there's my original foreground and here is the background.

But the two together create a much more interesting, compelling image. Since we're working with luminance here rather than chrominance, I can probably just get away with throwing on a Luma curve. And then, if I just take away my background for a moment so I can see what's going on here, just by turning off the eyeball for the layer, I can switch my Luma curve output to Luma, which is just going to give me a clear indication of what's going on without being distracted by the chrominence.

And then, maybe I can pull in the shadows on this a little bit while keeping everything else nice and bright. And what I'm looking to do here is deepen that blue sky while keeping everything else looking fairly natural. And if I set this back to composite, that's probably going to give me a, a much better key. If I turn on my background, you see I'm going to get more of the sky behind this way, because I've deepened the darker parts of my foreground image, but the foreground, the brighter parts, are nice and clear. So, combining the Luma key effect with something like a Luma curve gives you a little bit more control, simply because the Luma key effect itself doesn't give you any of that preempt color correction adjustment that you might need. Still, using the Luma key is well worth the investment of your time. Some of the looks that you'll get by using the Luma rather than a Chroma to define your key are a little bit more subtle, a little bit more nuanced than perhaps you'll get with Chroma keys.

Show transcript

This video is part of

Image for Compositing with Premiere Pro CS5.5
Compositing with Premiere Pro CS5.5

23 video lessons · 1172 viewers

Maxim Jago
Author

 

Start learning today

Get unlimited access to all courses for just $25/month.

Become a member
Sometimes @lynda teaches me how to use a program and sometimes Lynda.com changes my life forever. @JosefShutter
@lynda lynda.com is an absolute life saver when it comes to learning todays software. Definitely recommend it! #higherlearning @Michael_Caraway
@lynda The best thing online! Your database of courses is great! To the mark and very helpful. Thanks! @ru22more
Got to create something yesterday I never thought I could do. #thanks @lynda @Ngventurella
I really do love @lynda as a learning platform. Never stop learning and developing, it’s probably our greatest gift as a species! @soundslikedavid
@lynda just subscribed to lynda.com all I can say its brilliant join now trust me @ButchSamurai
@lynda is an awesome resource. The membership is priceless if you take advantage of it. @diabetic_techie
One of the best decision I made this year. Buy a 1yr subscription to @lynda @cybercaptive
guys lynda.com (@lynda) is the best. So far I’ve learned Java, principles of OO programming, and now learning about MS project @lucasmitchell
Signed back up to @lynda dot com. I’ve missed it!! Proper geeking out right now! #timetolearn #geek @JayGodbold
Share a link to this course

What are exercise files?

Exercise files are the same files the author uses in the course. Save time by downloading the author's files instead of setting up your own files, and learn by following along with the instructor.

Can I take this course without the exercise files?

Yes! If you decide you would like the exercise files later, you can upgrade to a premium account any time.

Become a member Download sample files See plans and pricing

Please wait... please wait ...
Upgrade to get access to exercise files.

Exercise files video

How to use exercise files.

Learn by watching, listening, and doing, Exercise files are the same files the author uses in the course, so you can download them and follow along Premium memberships include access to all exercise files in the library.


Exercise files

Exercise files video

How to use exercise files.

For additional information on downloading and using exercise files, watch our instructional video or read the instructions in the FAQ.

This course includes free exercise files, so you can practice while you watch the course. To access all the exercise files in our library, become a Premium Member.

Join now "Already a member? Log in

Are you sure you want to mark all the videos in this course as unwatched?

This will not affect your course history, your reports, or your certificates of completion for this course.


Mark all as unwatched Cancel

Congratulations

You have completed Compositing with Premiere Pro CS5.5.

Return to your organization's learning portal to continue training, or close this page.


OK
Become a member to add this course to a playlist

Join today and get unlimited access to the entire library of video courses—and create as many playlists as you like.

Get started

Already a member?

Become a member to like this course.

Join today and get unlimited access to the entire library of video courses.

Get started

Already a member?

Exercise files

Learn by watching, listening, and doing! Exercise files are the same files the author uses in the course, so you can download them and follow along. Exercise files are available with all Premium memberships. Learn more

Get started

Already a Premium member?

Exercise files video

How to use exercise files.

Ask a question

Thanks for contacting us.
You’ll hear from our Customer Service team within 24 hours.

Please enter the text shown below:

The classic layout automatically defaults to the latest Flash Player.

To choose a different player, hold the cursor over your name at the top right of any lynda.com page and choose Site preferencesfrom the dropdown menu.

Continue to classic layout Stay on new layout
Exercise files

Access exercise files from a button right under the course name.

Mark videos as unwatched

Remove icons showing you already watched videos if you want to start over.

Control your viewing experience

Make the video wide, narrow, full-screen, or pop the player out of the page into its own window.

Interactive transcripts

Click on text in the transcript to jump to that spot in the video. As the video plays, the relevant spot in the transcript will be highlighted.

Are you sure you want to delete this note?

No

Your file was successfully uploaded.

Thanks for signing up.

We’ll send you a confirmation email shortly.


Sign up and receive emails about lynda.com and our online training library:

Here’s our privacy policy with more details about how we handle your information.

Keep up with news, tips, and latest courses with emails from lynda.com.

Sign up and receive emails about lynda.com and our online training library:

Here’s our privacy policy with more details about how we handle your information.

   
submit Lightbox submit clicked
Terms and conditions of use

We've updated our terms and conditions (now called terms of service).Go
Review and accept our updated terms of service.