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Isolating Image Channels to Work with Chroma and Luma in Premiere

Mastering color correction means understanding the color channels that make a good image. Here’s how to isolate the chroma and luma channels in Premiere.

I’ve covered noise reduction somewhat extensively over the past few months. In my article on manual noise reduction in Resolve, we took a look at the powerful results you can get from isolating the chroma and luma channels to apply noise reduction to each.

Today, we’re going to learn how to isolate and work with image channels in Premiere — or any other similarly functional NLE. As with Resolve, there isn’t a plugin or button to quickly split your channels for you, so we’re going to do it manually.

Before we start, what is the point of splitting the component channels?

Each video clip is actually a blend of three distinct image channels. To put it simply, these component channels contain Luminance (or brightness and contrast) information, red color information, and blue color information. Baking these three channels into a single video stream enables much faster playback and simplicity of use.

It is always good to know how to break down anything into its component parts, so without further ado, it’s time to split . . .


Splitting Image Channels

Isolating Image Channels to Work with Chroma and Luma in Premiere — Splitting Image Channels

Underexposed Donuts! The first step after you load your clip into a timeline is to duplicate the clip. In Premiere, the default quick keys for duplicating clips are alt+left click for windows and option+left click on mac.

Separating Luminance

Isolating Image Channels to Work with Chroma and Luma in Premiere — Separating Luminance

To pull the chroma information out of our luma channel, all we need to do is navigate to the Basic Correction tab in the Lumetri color panel and slide the saturation to 0%.

Isolating Image Channels to Work with Chroma and Luma in Premiere — Separation

Separating Chroma Channels

Separating the chroma channels involves a few more steps. To start, duplicate your original (full-color) clip and place it above your luminance clip on the timeline. From here, navigate to the Curves tab in Lumetri and drag the top right point on all the curves (except for red) all the way to the bottom. Essentially, we’re cutting everything except for the red color in the shot.

Isolating Image Channels to Work with Chroma and Luma in Premiere — Separating Chroma Channels

Duplicate the original clip once more, and place it on top of your red and luma clips. Now repeat the curves adjustments, but this time, isolate the blue channel.

Isolating Image Channels to Work with Chroma and Luma in Premiere — Isolate Blue Channel

Now repeat the whole process once more for the green channel, placing it on top of everything.

Isolating Image Channels to Work with Chroma and Luma in Premiere — Isolate Green Channel

Technically, there isn’t a green color channel in the original clip, but I usually find the best results by including it. Test using or excluding it for your own clips.

Now, go through each color layer and set its Opacity Blend mode to Lighten, but leave the opacity at 100%. (There are multiple blend modes and methods that will yield similar results, so experiment.)

Your footage channels are now separated out by luminance and color, and you should finally have a normal-looking image again.


Working with Split Channels

Now, let’s look at a couple of things we can do to improve our donuts a little more.

First, I’ll clean the timeline up a bit by nesting the three color channels. This is entirely optional, but I prefer previewing as few video layers as possible.

Isolating Image Channels to Work with Chroma and Luma in Premiere — Nest Color Channels

One of the most useful reasons to separate luma from chroma is for sharpening your clip. Because the luma channel determines how we perceive sharpness, we can sharpen it individually from the color info, resulting in a clearer image without a lot of the nastiness that comes from sharpening footage in the color channels.

Isolating Image Channels to Work with Chroma and Luma in Premiere — Sharpen Footage

But be careful not to go overboard — I’ve sharpened this clip by less than 20%.

Cleaning up Blockiness

Isolating Image Channels to Work with Chroma and Luma in Premiere — Fix Artifacting

On the window to the left of the donut, we can see some severe artifacting caused by bringing the levels up on this shot. Let’s fix that.

Select the chroma layer, and then head to the HSL/Secondary tab in Lumetri. Enable grey selection preview, and then find where the problematic blocking is by qualifying each channel.

I’m fairly happy with my selection, so I’m just doing some basic tweaks to reduce its visibility.

Isolating Image Channels to Work with Chroma and Luma in Premiere — Reduce Visibility

While we haven’t eliminated the blockiness entirely, we’ve pretty effectively covered it up. So let’s pull it out just a touch more.


Chroma Channel Noise Reduction

Now, we’ll apply Neat Video to the chroma layer and launch the plugin. I’ll do my best here to select this specific region of noise, despite Neat Video’s attempts to tell me that the region is too small. I usually shoot for 60% or greater selection quality, but here I was only able to get to about 45%, which should still work.

Isolating Image Channels to Work with Chroma and Luma in Premiere — Noise Reduction

Now move into the Noise Filter Settings to preview and tweak the results. With a bit of (uncharacteristic) luck, I think I’m good with the default filter settings. So, I’ll commit the changes and return to Premiere to ensure everything looks good there.

Isolating Image Channels to Work with Chroma and Luma in Premiere — Noise Filter Settings

I’ve tweaked the color on the results just a hair, and I think we’re looking great!

Isolating Image Channels to Work with Chroma and Luma in Premiere — Before
Before.

Isolating Image Channels to Work with Chroma and Luma in Premiere — After
After.

And that’s it! We have successfully split out our original footage into its component channels and brought the exposure to a much more appealing level while making the clip look even better than before.

So try this method out if you’re having trouble salvaging your underexposed clips. There is so much more that you can do with your image channels separated — load up some clips, and see for yourself.


Cover image via Simon Mayer.

Looking for more articles on post-production? Check these out.

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