Chroma Key、Luma Key、Pattern Key and Linear Key
What They Are and When to Use Each
A practical live-production guide to choosing the right key for green screens, graphics, titles, and transitions.
You have probably seen all kinds of layered visuals in video production: a presenter in front of a green screen, a white logo over a black background, a broadcast graphic with separate fill and key signals, or a guest's video inside a circular frame.
These may seem like very different tasks, but they all rely on the same basic idea: using a key to determine which parts of one source are visible and which parts reveal another layer underneath. The difference is in what the key uses to make that decision. It could be color, brightness, a dedicated key signal, or a predefined shape.
That is why there is no single keying method for every situation. Chroma Key, Luma Key, Linear Key, and Pattern Key each use a different type of information to control the composite, making them useful for different production needs.
Once you understand what sets these four types apart, it becomes much easier to know which one fits a particular task. This guide walks through each type, how it works, and where you are most likely to use it.
Start With One Question: What Is a Key?
In live video production, a key is the information that tells a switcher which parts of an image should remain visible and which parts should become transparent.
That transparency allows one source to be layered over another: a presenter over a virtual background, a lower third over a camera feed, or a logo over the final program output.
The easiest way to think about keying is this:
A keyer cuts a controlled hole in one image so another image can appear through it.
The visible image placed on top is called the fill or foreground. The image behind it is the background. The keyer uses a key signal—also called a matte—to determine how transparent each part of the foreground should be.
A simple keying workflow looks like this:
Keyer
Real-Time Multi-Bus
Compositor
Output
BUS PATH FLOW DIAGRAM (VERBATIM LOGIC)
Console TTY
Not every workflow supplies a separate matte signal. Sometimes the keyer derives transparency from the foreground image itself; other times it uses a dedicated key source or a generated shape. The important idea is the same in every case: the key controls where the foreground appears, while the fill controls what the audience sees.
Once that distinction is clear, the four keying modes become much easier to understand: they simply use different kinds of information to create that “hole” in the foreground image.
The Fast Decision Table
The quickest way to choose a key type is to start with the kind of transparency information your source already provides. Use this table as a first-pass guide; the following sections explain the practical setup and trade-offs behind each option.
| Key Type | Uses | Best For | You Need | Avoid When |
|---|---|---|---|---|
| Chroma Key | Removes a selected color from an image | Green-screen or blue-screen presenters, virtual sets, and weather-style presentations | A clean, evenly lit green or blue background; foreground subjects separated from the key color | Clothing, props, or lighting contain the key color; the background is uneven, reflective, or heavily shadowed |
| Luma Key | Uses brightness values to create transparency | Simple logos, titles, and high-contrast monochrome graphics | One source with clear light-versus-dark contrast, such as white graphics on a black background | The graphic contains soft gradients, shadows, complex transparency, or compressed/noisy dark areas |
| Linear Key | Uses separate fill and key signals | Broadcast lower thirds, animated titles, scoreboards, and graphics with clean alpha edges | A matched color fill signal plus a grayscale key/matte signal | You have only one standard video or graphic source, or the fill and key signals are not aligned |
| Pattern Key | Uses a generated geometric shape as the matte | Shaped picture-in-picture windows, graphic reveals, wipes, and stylized transitions | A built-in pattern plus the desired foreground and background sources | You need to remove a real background around a person or isolate an irregular object |
Chroma keying is built around color, luma keying around brightness, and linear keying around separate fill and grayscale matte signals. Luma keying is often called a self key because one source provides both the visible graphic and the brightness information used to key it.
The keyer can only work with the information in the source. A clean green background, a high-contrast logo, a properly matched fill-and-key pair, or a deliberate geometric pattern will produce predictable results. A poorly prepared source will not become a clean key simply because a more advanced keying mode is selected.
Chroma Key: Best for People and Virtual Sets
Chroma key reads color. The keyer selects a hue—usually green or blue—and makes pixels close to that color transparent. That is why it is the right tool for a presenter, trainer, or host who needs to appear in front of a virtual set, slide, or product image.
It also explains why chroma key only works when the source cooperates: the keyer needs a clean, consistent background color to remove.
Most chroma-key problems begin before the signal reaches the switcher.
Light the Screen and Subject Separately
Light the screen evenly, then light the subject as a separate zone. Shadows, hot spots, wrinkles, and uneven exposure change the color the keyer sees, making the matte patchy or unstable.
Keep background light off the subject, and subject light off the screen wherever possible. Soft, controlled fixtures make it easier to create an even screen without creating unwanted spill or shadows. Clean chroma-key setups generally use separate lighting for the backdrop and the subject.tothecut+1
Keep the Subject Away From the Screen
A green or blue screen reflects colored light onto nearby skin, hair, clothing, and reflective objects. This is called spill. The keyer may interpret that reflected color as background, especially around hair and shoulders.
Keep the subject roughly 1.5–3 metres (5–10 feet) from the screen where space allows. The exact distance depends on the room, lighting, lens, and framing, but more separation generally means fewer shadows on the screen and less color bounce on the subject. Glasses, polished products, and shiny surfaces deserve extra attention because they can reflect the screen directly.
Physical Displacement Vector
Inverse-Square Isolation
1.5–3 Metres
(5–10 feet recommended)
Watch Wardrobe and Props
Anything close to the selected key color may disappear with the background. A green tie, green-tinted prop, or reflective surface picking up green spill can create exactly the “chest-shaped hole” described at the beginning of this guide.
Choose the key color after looking at wardrobe, props, and set design—not before.
Lock White Balance and Exposure
Lock white balance and exposure before going live. If either changes automatically during a show, the apparent color and brightness of the backdrop can shift, changing the key result with it.
Manual camera settings make the key more consistent and make troubleshooting much easier. Green-screen guidance consistently recommends locking exposure and white balance rather than relying on automatic camera adjustments.
Green or Blue?
Green is common because camera sensors generally capture green efficiently, so it can often be lit with less light. But it is not automatically the right choice.
If wardrobe, props, or the set contain green, blue can be safer. Choose the color that is easiest to keep out of the foreground and easiest to light evenly.
Luma Key:
Best for Simple Graphics From One Source
Luma key reads brightness, not a specific color—and not “black” by itself. The keyer uses a brightness threshold to determine transparency: areas on one side of the threshold remain visible, while areas on the other become transparent. That relationship can be reversed with an invert setting.
It is often called a self key because one source provides both the visible image and the brightness information used to create the key. Unlike a linear-key workflow, there is no separately supplied key signal or matte.
That makes luma key a good fit for simple, high-contrast graphics: a white logo on a black background, a basic title card, or a clean black-and-white animation. It is a poor fit for graphics with gradients, soft shadows, or complex semi-transparent edges, because those elements occupy the middle of the brightness range and give the keyer less clear separation to work with.
A quick example makes the logic concrete:
Step 1
White logo on black background
Step 2
Luma key makes the black area transparent
Step 3
The logo appears over the live camera feed
In this example, black becomes transparent and white remains visible. But that result depends on the threshold, range, and inversion settings—not on a fixed rule that “black always disappears.” Reverse the key, and the white area can become transparent instead. Luma-key tools commonly provide controls for threshold/range, edge rolloff or softness, and inversion to define which brightness values are removed.
The result is only as clean as the contrast in the source. A graphic with a solid black background and bright, clean elements gives the keyer a clear boundary. A graphic with soft drop shadows, gradients, or compressed dark areas contains many intermediate brightness values, so its edges and transparency can be harder to preserve consistently.
For that reason, use luma key for deliberately simple graphics. If the design depends on smooth alpha transparency, soft shadows, or finely anti-aliased edges, a linear key workflow with a dedicated fill and key/matte signal is usually the better choice.
Linear Key:
Best for Professional Fill-and-Key Graphics
Linear key uses two separate, matched signals rather than one.
The fill signal carries the visible image: the graphic, title, animation, or scoreboard that will sit over the background. The key, also called a matte, is a separate grayscale signal that defines transparency pixel by pixel:
White
Fully opaque
Gray
Partially transparent
Black
Fully transparent
That is the core difference from luma key. A luma key derives both the visible image and transparency information from one source. A linear key keeps them separate from the beginning: one signal supplies the color, and the other supplies the alpha information.
Why Linear Key Is Used for Professional Graphics
This separation makes linear key the standard workflow for broadcast-style lower thirds, scoreboards, animated titles, and graphics with soft edges, glows, or drop shadows.
Because transparency comes from a dedicated grayscale matte—not from the brightness or color of the visible graphic—the switcher can preserve partial transparency more accurately. A soft shadow can remain soft; a semi-transparent glow can remain semi-transparent; and a clean graphic edge does not need to be reduced to a simple brightness threshold.
Fill and Key Must Match
The trade-off is that both signals must exist and must remain correctly paired.
The fill and key should be:
√
Generated from the same graphics source
√
Matched in resolution and frame rate
√
Time-aligned and frame-synchronous at the switcher
√
Pixel-aligned in size and position
If the signals are offset, delayed by a frame, or incorrectly paired, the result can include edge misalignment, flashing, incorrect transparency, or a visible outline around the graphic.
A linear key cannot create a clean alpha channel from an ordinary video file with a baked-in background. If a graphics vendor supplies only a single standard video source, there is no separate matte for the switcher to use. Key-and-fill workflows are specifically designed to send the color image and transparency information as separate outputs.
Pattern Key:
Best for Designed Reveals, Not Natural Cutouts
Pattern key does not analyze a source for color, brightness, or object outlines. Instead, it uses a geometric matte generated by the switcher: a circle, diamond, rectangle, stripe, or similar shape.
The pattern determines where the foreground is visible. The source still determines what appears inside that shape.
Input
Foreground video
Input
Geometric pattern matte
Result
Foreground appears only inside the selected shape
Because the matte comes from a generated pattern rather than the source image, pattern key is designed for controlled graphic effects—not natural background removal.
Best Uses
▪ A circular or rectangular guest-video window
▪ A shaped reveal for a new segment or source
▪ A branded graphic composition
▪ A deliberate picture-in-picture treatment
▪ Live events, sports, corporate presentations, and educational content where a clear visual rhythm matters more than natural realism
Pattern key is especially useful when the shape itself is part of the design. A soft-edged circle around a remote guest, for example, can look intentional and polished because the viewer understands that the image is meant to appear inside a graphic window.
What Pattern Key Is Not For
Pattern key is not a replacement for chroma key. It cannot follow the natural outline of a person, object, hair, clothing, or shadow.
If you use a pattern key on a presenter, the switcher will not remove the presenter’s background. It will simply reveal the presenter inside the selected shape. If an arm or shoulder extends beyond the circle or rectangle, it will be cut off at the pattern edge.
A useful rule is:
Use a pattern key to reveal a guest video through a soft-edged circle—not to remove the background around the guest.
Set Up the Pattern Intentionally
In practice, a pattern-key workflow is simple:
01
Choose a shape that supports the visual design.
02
Adjust its size and position to frame the source deliberately.
03
Add edge softness only where it improves the composition.
04
Check that the pattern does not cut through important faces, text, hands, or on-screen graphics.
A hard-edged pattern can work for bold, graphic layouts. A small amount of softness can make a circular or shaped window feel less abrupt. The goal is not to hide the shape—it is to make the shape look intentional.
Keying Problems That Are Not
Always Keyer Problems
Have you ever set up a key, only to find a green outline around your presenter, a logo with rough edges, or parts of a graphic disappearing? It is tempting to assume that the keyer is the problem. But in many cases, the issue starts with the source material, the lighting, or the way the key is set up.
Before changing equipment, it helps to identify what is causing the problem. Here are some common keying issues, why they happen, and what you can try first.
| What You See | What Might Be Causing It | What to Try First |
|---|---|---|
| Green or blue edges around a presenter | Light from the green or blue screen reflects onto the subject, or the screen is unevenly lit | Move the subject farther from the screen, light the screen more evenly, and reduce reflections |
| Rough, dark, bright, or gray edges around graphics | The key signal may be low quality, the fill and key signals may not line up, or the graphic's transparency settings may be incorrect | Check the graphic's format, confirm that the fill and key signals match, and verify the alpha or premultiplication settings |
| Parts of a logo disappear | The luma key may be removing details that are too close to the selected brightness threshold | Adjust the threshold and edge softness. If the logo contains gradients or transparency, consider using a linear-key workflow |
| A pattern-key window looks too sharp or unnatural | The edge is too hard, or the shape does not fit the composition | Soften the edge and adjust the shape's size and position to better frame the source |
The important thing to remember is that not every keying problem needs a new keyer. Sometimes, a small change to the lighting, graphic, or key settings can make a noticeable difference.
For example, if a presenter has a green outline around their hair or shoulders, the green screen may be reflecting light onto them. Moving the presenter farther away from the screen can reduce this spill, while more even screen lighting can help create a cleaner key.
Graphic problems often need a different approach. If parts of a logo disappear, the luma threshold may be removing details along with the background. Adjusting the threshold and the transition between visible and transparent areas may help. If the graphic relies on gradients or varying levels of transparency, a linear-key workflow may be more suitable.
For graphics with separate fill and key signals, also check that the two signals are correctly matched and aligned. Incorrect alpha or premultiplication settings can cause unwanted dark or bright edges, even when the keyer itself is working as expected.
The goal is to find out where the problem begins before changing settings at random. Once you know whether the issue comes from lighting, the graphic, the signal, or the key itself, you can make a more targeted adjustment and get a cleaner result.
FAQ
Can I use a PNG with transparency directly in a live switcher?
Sometimes—but it depends on how the graphic reaches the switcher.
A PNG file can contain alpha transparency, but HDMI and SDI video outputs do not normally deliver that alpha as a separate key signal. If the PNG is played from a computer, media server, or graphics system, that system must either create the composite internally or output a matched fill-and-key pair for the switcher to use.
Should my logo use luma key or linear key?
Use luma key for a simple, high-contrast logo; use linear key when the logo includes transparency, gradients, shadows, or soft edges.
A flat white logo on black can work well as a luma key. A logo with translucent smoke, a glow, anti-aliased edge treatment, or a soft drop shadow is more likely to benefit from a proper alpha-based linear key workflow.
What is the difference between an upstream keyer and a downstream keyer?
An upstream keyer affects a source before it is included in the main mix; a downstream keyer adds graphics over the finished Program output.
In practical terms, use an upstream keyer for effects that need to be part of the scene composition—such as chroma-keying a presenter into a virtual background. Use a downstream keyer for persistent elements that should remain above everything else, such as a logo bug, clock, sponsor tag, or lower third.
Can I keep a logo on screen while using chroma key for a presenter?
Usually yes, if the switcher has enough independent keying layers and the workflow is configured correctly.
The presenter’s chroma key and the logo overlay are different compositing tasks. Whether they can run at the same time depends on the switcher’s number of keyers, their routing, and whether graphics are applied upstream or downstream.
Can I key over an NDI, SRT, or remote source?
Yes, but compression, latency, and color sampling can affect edge quality.
Chroma and luma keying work best with clean, stable sources. Highly compressed remote video can introduce noise, color artifacts, or softened edges that make a key less precise. For critical graphics or green-screen work, test the complete transport path—not only the local source.
Can I use the same graphic for a livestream and an in-room LED screen?
Yes, but design for the lowest common denominator: readable at distance, safe within screen margins, and appropriate for both aspect ratio and brightness.
A lower third that looks elegant on a laptop stream may be too small or bright on an LED wall. Test titles, logos, and key edges on the actual audience-facing display as well as the streaming output.
Conclusion: Choose the Information You Have
Keying becomes much easier to understand once you stop thinking of the four types as different versions of the same effect. They are simply different ways of working with different kinds of source information.
The practical takeaway is straightforward: start with the source, then choose the key. If the separation comes from color, use a chroma key. If brightness provides the separation, a luma key may be the better fit. If the graphic already comes with dedicated fill and key information, use a linear key workflow. And when you simply need to reveal an image through a defined shape, pattern keying provides a different approach.
This way of thinking also makes keying easier to troubleshoot. When the result does not look right, the first question is not always “Which setting should I change?” It is often “Am I using the right kind of key for this source?” Once that is clear, the rest of the setup becomes much more straightforward.For productions that work with different types of sources, having these keying methods available in the same system can make the workflow more flexible. Telycam Mix One supports Chroma, Luma, Linear, and Pattern Key, allowing different sources to be handled within the same production system rather than requiring a separate tool for each type of compositing task.
In the end, keying is less about creating a particular visual effect and more about making different visual elements work together cleanly. When you understand what information a source provides, choosing the right key becomes a much simpler part of the production process.
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