So, do you know what chroma key is?
Chroma key is a visual effects technique that superimposes one image over another by nullifying a specific hue, like blue, red, or green. It’s frequently used in videos when there’s a need to replace the background with a different image, whether it’s moving or still.
Chroma key is a powerful ally in audiovisual productions for a multitude of purposes. It’s a simple tool that can rescue many productions, particularly when the budget is tight and there isn’t a lot of set variety – but there’s plenty of desire to innovate, to do something unique and creative.
Scene from the movie “The Avengers” with green chroma key Chroma key is a commonly used strategy in Hollywood studios, particularly in famous superhero movies filled with fantastic scenes and packed with special effects.
In addition to significantly reducing the filming budget, chroma key is also frequently used because it’s a practical tool that can be implemented in controlled environments like film studios. In a major production in the heart of New York or Tokyo, for instance, shutting down a plaza, a park, or any other large space can be quite labor-intensive – both in securing authorization and in making that place “pause” for a moment until the takes are filmed. This is where the convenience of chroma key comes in.
However, this might give the false impression that chroma key is a strategy used only by large production companies. With technical knowledge, creativity, and of course, the right tools, this technique can also be leveraged for more homemade projects.
With that in mind, I’ve put together these 17 professional tips for filming with chroma key. They are the result of over 20 years of experience in the industry, after much trial and error, as well as the creation of countless materials for clients across a broad range of industries and market sizes. In other words, this is advice from someone who knows their stuff.
These are the best professional tips you will ever find on the web:
- Plan Your Chroma Key Scenes
- Use The Right Color for your Chroma Key
- Apply the ideal distance from the background
- Double your attention regarding other colors
- Adjust the camera angle according to the background
- Use lighting at the correct temperature
- Light the background evenly
- Use a backlight or “cleaning light”
- Use Minus Green gel to remove spill
- Use green lighting for the background
- Record at the highest possible resolution
- Choose the Best File Format
- Use Cameras that Record in 4:2:2 and 10 Bit
- Avoid Recording in Log
- Record with the Camera’s Native ISO
- Use the Correct Aperture Setting
- Use the Correct Frame Rate
Please take your time to thoroughly absorb all the information.
1. Plan Your Chroma Key Scenes
It’s crucial to choose the background you’ll use in your chroma key video edit before you start recording. Only with proper planning can we calculate the positioning of lights, frame the shot, and most importantly, place people and objects within the scene. Additionally, you should decide ahead of time whether or not there will be camera movements and the size of the studio you will need.
Did you know you can use a device to monitor your recording? Thanks to advancements in technology, there are now affordable options on the market that allow us to operate a real-time chroma key system. The Atem Mini from Blackmagic Design, for example, lets you replace the green background with an image of your choice while you record or broadcast the final result live, just like a weather reporter.
2. Use the right color for your chroma key
People often ask me:
Why does chroma key have to be green? Does any green work?
Actually, chroma key can be any color, but the most commonly used are blue and green. Some also use red, but it’s not recommended for filming people, as it’s present in human skin.
The word “Chroma” means “color”, while “key” signifies “key” in English. So, “chroma key” does not refer to an object, a color, or a software. Chroma key is a technique, a process.
Firstly, to prepare the background with the appropriate color, you must decide what material will be used for the background – paint, screen, or fabric. Next, we’ll talk about preparation for each of these.
Paint: Chroma key with wall paint
If the idea is to create a painted background, you need to pay attention to the choice of paint brand and its quality. The official brands most used in the film industry currently are: Rosco, Pro Cyc, and Cineshop.
Gold Tip to save on chroma key without losing quality:
You can buy green paint at a more affordable price than the brands mentioned above. You can request a custom mix at any Suvinil store or representative by providing the following code: PANTONE 354 C. If you prefer the Sherwin-Williams brand, use code SW 6925 Envy. This type of preparation typically offers a better cost-benefit ratio and still ensures excellent wall coverage.
Like any other paint job, you need to prepare the chosen space to be the chroma-key background surface so that it’s perfectly even and smooth.
How many coats of paint are necessary?
You can feel the needs of each surface – however, a minimum of 4 coats of paint is recommended so that the hue is strong and the surface is uniform. Remember that when we paint an interior wall, we seldom put a lot of light on it or stare at it constantly looking for defects. But when the objective is to use that wall for professional recording, we need to pay attention to every detail.
Fabric: Chroma key with fabric
The second material you can use to make your chroma key background is fabric.
In this case, it’s essential for the fabric to be 100% stretched, uniformly. The chosen shade should be the same green mentioned earlier for the paint. Unsure about the choice?
You can verify the ideal green shade for your chroma key setup using Pantone 354 C code. Remember it!
Golden Tip to avoid mistakes when buying chroma key fabric:
Be very careful with fabrics sold online for this purpose. Many have a yellowish shade, which can result in a wasted investment. The yellow tone in the fabric can significantly impair the outcome, especially when filming people. In general, human skin has yellow tones, which are even more apparent in brown-skinned people.
The fabric also shouldn’t be used in front of a surface that hasn’t been pre-smoothed. This is because it’s natural for some fabrics to be slightly transparent, thus revealing imperfections behind them.
Electronic Screens: Chroma key using a screen
Finally, the third way to apply chroma key technique is through screens. It’s possible to replace the background of a TV, a cellphone, and even a laptop in a scene, using this tool.
To apply chroma key to screens, you need to project an image with a solid color, preferably in the .PNG extension, with the following highlighted codes:
Green Chroma Key
- RGB: 0, 177, 64
- Hexadecimal: #00b140
- Websafe: #009933
- CMYK: 81, 0, 92, 0
Blue Chroma Key
- RGB: 0, 71, 187
- Hexadecimal: #0047bb
- Websafe: #0033cc
- CMYK: 90, 68, 0, 0
Golden Tip: Moving scenes with chroma key:
If there’s movement with the screens during the take, it’s recommended to also use apps with markers to generate reference points, which in post-production are called tracking.
Here is a list of some of the most commonly used Chroma Key apps for this purpose:
- EZ Greenscreen (Free)
- ChromaGeek (Free with paid option)
- VFX Tracking Markers (Free with paid option)
- VFX screens Pro (Paid)
3. Apply the ideal distance from the background
There is little discussion about the distance that a person or object should maintain from the solid background to achieve the most professional and flawless results possible. In this sense, the recommended is for the person or the object in focus, that is, in the foreground, to be positioned at least 4 meters away from the background (which we’ll refer to here as the second plane). However, in larger spaces, the recommendation is that this distance be 6 meters. If possible, opt for this.
Why such a large distance?
In general, the green color in the appropriate tone for the chroma key technique has a high reflective capacity, which makes it physically impossible to be close to the green without being “contaminated” by it.
Thus, by placing the person or object too close to the background, there’s a high chance of the solid color from the background reflecting on the person, generating recording flaws that will only be noticed during the compositing process (post-production).
What to do when the recording location is very small?
In smaller recording spaces, the recommendation is for the person or object in the foreground to be positioned as far away from the background as possible – considering, of course, the specifics of the environment, and compensate for the lack of space with a lighting technique that I’ll present later on.
4. Double your attention regarding other colors
Wearing white clothes, or any other very light tone, should be avoided as much as possible to prevent the background color from invading the foreground.
Therefore, remember: whenever you are instructing a guest, presenter or interviewee, advise them to come to the recording studio wearing darker clothes;
Clothes with prints or images that have tones equal to or very similar to the chroma key background color should be discarded. In this case, the information from the print may end up conflicting with the background, creating a flaw in the final composition.
Another common mistake is not creating the ideal contrast between the colors of the foreground and background. To do this, it is necessary to know more about the color wheel.
How can a Color Wheel help with video compositions?
You must have seen a color wheel, especially in elementary school art classes. It is made up of primary, secondary and tertiary colors – a very useful tool for creating compositions in various areas related to art.
As our goal here is to improve the Chroma Key technique, we will focus on the concept of complementary colors. To identify a complementary color, just find the colors that are on opposite sides of the wheel.
You will see that the circle is divided into a region of warm colors and another of cool colors. Complementary colors are always on opposite sides, creating a highly contrasting harmony. Notice that the colors red and purple are complementary to green and yellow. This information is quite relevant to our technique.
To avoid the “spill” effect – when the green of the background reflects on the person or object in the foreground, in addition to remembering the distancing that is essential, it is also interesting to choose objects and costumes that have shades of red and purple to create a strong contrast and favor the background cut in post-production.
Of course, it will not always be possible to work with red and purple in the foreground, and when this is the case, remember to at least totally avoid the use of analogous colors in the composition. Analogous colors are located very close to each other within the color wheel. Therefore, know that if you use shades of bluish-green or yellowish-green, you will have big problems.
If you use the chroma key technique to record only one person in the foreground, my suggestion is that you opt for a blue background, instead of green. This is because blue is directly opposite the shades of yellow on the color wheel, providing an ideal contrast with skin tones. In this case, you need to pay attention to the costume: no jeans or shades of blue in the clothes. Remember: contrast is everything!
5. Adjust the camera angle according to the background
Often the error in using chroma key can be in what we consider one of the foundations of good audiovisual work: the choice of camera angle.
The correct use of the camera is straight, at the height of the top of the object or person (in this case, the camera can be positioned facing the torso and/or head of the individual).
Inclined angles, in general, are not recommended – especially when from above or below the individual’s body. These angles bring a false sense of depth, making objects (and especially the human body) look strange.
Always know that, in chroma key, you will replace the green background with an image of another scenario. This image, in turn, is usually taken at a zero angle, that is, without any inclination. If at the time of capturing the images you opt for an inclined angle, whether upwards or downwards, it will not “match” with the new background image.
Therefore, in terms of inclination, it is important to consider the perspective of the background that will be applied in post-production. If the perspectives of the foreground and background differ, the result will be uncomfortable and unprofessional.
6. Use lighting at the correct temperature
White balancing is really fundamental and is part of the basic adjustments when we talk about the audiovisual capture process. However, the choice of lighting temperature used in chroma key significantly influences this process.
Never use cheap lighting when recording with chroma key!
Generally, I do not recommend the use of any lighting that is above 5600 on the Kelvin scale, as the light used for recording ends up being extremely artificial – resulting in lower quality for the recorded material.
High CRI (95% or +) is very important!
LED bulbs allow for more accessible lighting fixtures, but many of them work with temperatures above 6000K and that is very bad, not to mention that the CRI is on average below 60%. So make sure your lighting fixture works below 5600K and offers a CRI of 95% or more.
The Kelvin Color temperature scale is divided into 10 tones that go exactly from 1,000 to 10,000. Therefore, it is recommended to use only up to the 5th scale, which is 5,000.
And what about warm light? Is it a good alternative?
Yes! Warm light, at 3200K, usually becomes a good choice for use with a green background. However, it is a fact that the environment itself is not always suitable for working with this type of brightness, especially when talking about warm light in a location without air conditioning.
The solution then may be to use 5000K LED panels, which will bring quality to the images without making them look artificial.
The white control on the equipment, in turn, can be done with the help of an official White Balance chart. This accessory can be easily found in photography stores and/or audiovisual production equipment stores. I highly recommend it!
7. Light the background evenly
Once you have set up your chroma key background structure, it’s time to learn how to light it correctly and uniformly.
How to evenly light a chroma key background?
To light the area, it is recommended to use four or more light points. This is because two of them are focused on the background; and the other light points are used for lighting the person and/or object positioned in the foreground.
Diffuse light illuminators
To achieve an even better and more uniform result in lighting, it is highly recommended to use illuminators that emit diffuse light. Some examples in this regard are cold light panels with PL bulbs and LED panels.
It’s important to know that the larger the space, the more illuminators will be necessary to maintain the uniformity of the brightness present in the solid color background. The secret is not in the power of the light, but in its correct positioning.
Is Fresnel recommended for this type of work?
No. Generally, Fresnel is not a very suitable illuminator for this type of structure, as its light is funneled and narrow like a flashlight. However, it can be a good supporting actor if combined with a suitable diffuser.
Use diffusers as allies
Diffusers can also help make the background more uniform. The most recommended in this case is to use the diffusers inside the illuminators.
What is the best material for the diffuser?
The most recommended are paper or “Butterfly” fabric diffusers.
8. Use a backlight or “cleaning light”
The term “cleaning light” or “backlight” is often used in photography and is very important when setting up your green screen. Basically, it is a counter light used to “wash off” the green reflections, and can be used anywhere there is a green reflection (such as in the hair, clothes, or neck, for example).
Here, it is indeed worth using a Fresnel light with a diffuser. And if you are working with cool light, remember to use corrective gel to match the temperature of the light sources. This kind of light can help to diminish the ‘spill’ effect where the green color reflects on the subject and interferes with the keying process in post-production.
9. Use Minus Green gel to remove spill
Did you know that colors are not in objects but in light? If you’re looking at a red apple, it is merely reflecting the color red, which comes from light. That’s why I recommend using Rosco brand Minus Green gel (code 279) to remove the green output from your light source. You should do this only on the front lights that are pointed towards the foreground. This gel is especially recommended for lights with PL bulbs and LED lights with a Color Rendering Index (CRI) below 85%, as they emit a larger amount of green. In addition, this gel is an excellent ally for the cleaning light mentioned in the previous tip.
The “Minus Green” gel filter can help to reduce green color spill from the lighting onto your subject or object in the foreground, allowing a cleaner key in post-production. This can be particularly useful when working with green screens, as it can help to minimize the ‘green spill’ effect that can occur when green light is reflected onto the subject from the green screen.
10. Use green lighting for the background
This tip might sound a bit excessive, I know.
But the truth is that, in the film industry, green lights for the background are widely used and are great allies in professional filming. These special lights make the chroma-key background even more uniform, bringing a perfect result for the recording. So, go for it!
Golden Tip: Green light to uniformize the chroma-key without spending a lot:
As it is a bit more difficult to find these background-colored lights in Brazil, you can add gel to change the light color and achieve a very similar result.
Here are the codes of the gels that I use:
Rosco Roscolux Chroma Green, 20×24″ Color Effects Lighting Filter
Lee #738 JAS Green Gel Filter
These gels can be placed over your lighting sources to emit a green light that can help to make your green screen background more uniformly lit. This can make it easier to key out the background in post-production and can contribute to a more professional end result. Remember, consistency in lighting is key when it comes to green screen work.
11. Record at the highest possible resolution
Did you know that the resolution of your image can also influence the quality of your production? Yes, it can.
In the eagerness to save space with lighter files that reduce editing time, many professionals end up recording at a resolution lower than the maximum allowed by their equipment – which can be considered a big mistake.
In this sense, we recommend that every recording be made at the highest possible resolution of the equipment. So, if your camera has a maximum resolution of 8K, you already know what we expect, right? That’s right, record in 8K!
Why should the standard resolution be the maximum?
The more pixels available in the image, the higher the chance that the computer or other device used for editing can more precisely determine which is the section with the solid color background – and which is the section of the foreground.
Blackmagic Design, aware of this, created a camera capable of recording in 12K, greatly facilitating the lives of audiovisual producers.
This will not only increase the quality of your footage but also allow for better keying out of the background. Higher resolution will provide more detail and allow for cleaner edges when removing the green screen in post-production. It’s always best to capture as much detail as possible when recording, as you can always scale down your footage in post-production if necessary.
12. Choose the Best File Format
The moment you hit the “record” button on your camera, a complex process of information compression begins. It is during this process where our green screen can easily become a significant issue during post-production.
The choice of the file format for recording, however, largely depends on the specific model of your equipment. It’s recommended to consult the manual of your camera to determine which format it uses for recording with the least compression.
That said, always opt for the more robust formats – such as the RAW or ProRes video formats. For instance, I particularly enjoy using the latter when working with chroma-key. No matter what, avoid more compressed file formats, like AVC, h.264, or similar types.
13. Use Cameras that Record in 4:2:2 and 10 Bit
The difference between an 8 bit or 10 bit camera – as well as a 4:0:0 or 4:2:2 camera, is significant, as both parameters are related to color depth.
A 10 bit camera, when compared to an 8 bit camera, has a distinct advantage in image quality – while also tending to have smaller file sizes.
A 4:2:2 camera, in turn, has a higher concentration of pixels, resulting in superior brightness and color values compared to other models.
Therefore, for better color depth, opt for cameras that operate in 4:2:2 and 10 bit.
14. Avoid Recording in Log
Do you know what log is?
Log is a type of camera recording system or profile. In this type of recording, the result appears “washed out”, which can significantly increase the editing time.
There are only two camera models where using log for a green screen can prove beneficial: RED and Arri cameras. Otherwise, using log (or its variations, such as s-log, v-log, c-log, and others) is not recommended.
Why should you avoid it?
Essentially, log and green screen are not a good match – when working with chroma key, it’s necessary to apply measures capable of generating the highest possible contrast between the foreground and background, as we’ve already discussed in this article, right?
However, log does the exact opposite; it prevents this contrast: and that’s why it can create a lot of work during post-production.
15. Record with the Camera’s Native ISO
First and foremost: do you know what your camera’s native ISO is – and more importantly, how it can affect the recording of your green screen images? Let’s dive in.
As we already know, ISO is the camera feature that measures the sensor’s sensitivity to light. Therefore, the higher the ISO, the greater its sensitivity to light.
This means the camera understands that the space to be photographed requires more light, thus increasing light capture. Conversely, the lower the ISO, the lesser this value.
So, a camera’s native ISO is essentially the base sensitivity obtained without the need to amplify the signal previously received from the sensor.
When we set the camera to its native ISO, we extract the best possible performance from the sensor. This means we will capture with the maximum dynamic range that the sensor can offer, and with the minimum possible image noise.
In chroma key, the amount of light can make all the difference in image capture, as we’ve already discussed in this material. Therefore, try recording with the native ISO and watch the magic happen.
16. Use the Correct Aperture Setting
In chroma key recording, the central goal is to ensure that both the background (green, blue, or red screen) and the foreground (object or person) are in focus. Only in this way will the editing software recognize both planes more easily and accurately.
The ultimate aim here is to have all planes in focus. Therefore, I recommend setting the aperture to f/8. In some cases, this aperture can be reduced a bit more, to f/10 or f/12. Everything will depend on the lens, the camera, and even the space available for recording.
When adjusting the aperture, it’s very important to also pay attention to the ISO setting. If it’s set too high, it can make the image grainy, reducing the quality of the film and consequently making the editing process much longer. This is one of the reasons why cameras with a full-frame sensor are more coveted by filmmakers, as they allow for easier ISO adjustment without generating much noise in the image, but that’s a topic for another day.
17. Use the Correct Frame Rate
When recording with a green, blue, or red background, it is not advised to record at 24 frames per second – and even less so at a low shutter speed, such as 1/48.
With a low speed, the frames can end up blending, making it difficult to differentiate between what is the foreground and background (i.e., the person and the solid color background).
Camera setup for chroma key:
I like to set my camera to 30 frames per second and a shutter speed of 1/60 when recording video lessons, i.e., when the movement tends to be less abrupt and more deliberate.
However, when the scene involves more movement (even if it’s just hand gestures), it’s recommended to double the frames and speed: recording at 60 frames per second and a shutter speed of 1/120. This way, movements are captured without the frames blending together.
Chroma key isn’t a seven-headed beast, but it can create many problems if you try to do it without the help of a professional.
I myself have made many mistakes during the process of capturing images for composition, and what has helped me improve in this technique was seeking help from the best professionals in Brazil and, most importantly, conducting a lot of tests.
What did you think of these professional tips on using chroma key? If you have any questions about using a green screen, don’t hesitate to get in touch with us.
What is chroma key?
Chroma key is a visual effects technique that overlays one image or video over another by eliminating a specified color, commonly green or blue. It is used to replace the background with another image or video.
What color is typically used for chroma keying?
The most commonly used colors for chroma key are green and blue. These colors are used because they differ most distinctly from human skin tones.
What kind of materials are used for the chroma key background?
Typically, a fabric or painted wall that is uniformly colored in either green or blue is used as the background for chroma key.
Can chroma key be used with any kind of camera?
In general, any camera that can capture video in good quality can be used for chroma key effects. However, higher-quality cameras will yield better results.
How important is lighting in chroma key?
Lighting is crucial in chroma keying. The background must be lit evenly to ensure the key color is consistent. Good lighting on the subject is also important to avoid shadows.
Why do I see a green or blue outline around the subject?
This is called "spill". It happens when the background color reflects onto the subject. To prevent this, make sure your subject is not too close to the background and use good lighting.
Can I wear clothes the same color as the background when using chroma key?
If you wear clothes the same color as the background, that part of you will become transparent along with the background. It's best to avoid wearing the same color as your chroma key screen.
How can I make the replacement background look natural?
Ensuring that the lighting and perspective of your replacement background match with those of the main subject can greatly enhance the realism.
What software can I use to apply chroma key effects?
There are many software options for chroma keying, including Adobe Premiere Pro, Final Cut Pro, and free options like OBS Studio.
Can I use chroma key for live streaming?
Yes, chroma key is commonly used in live streaming. Most streaming software allows you to apply chroma key effects in real-time.
Can I use the color red for chroma key?
Yes, you can technically use any color for chroma keying, including red. However, it's important to consider what colors are in the scene you're filming. The color you choose for your backdrop should ideally be distinct from the colors present in the subjects of your scene. This is why bright green and blue are most commonly used, as these colors are least likely to occur naturally in human skin tones or clothing.
Using red as a chroma key color can be challenging, especially when filming people, as red tones are often present in skin color, hair, or clothing. If your subjects contain red, parts of them may become transparent when you remove the red background in post-production, which is not typically the desired effect.
It's also worth noting that different cameras handle color differently, which could affect how successfully you can key out certain colors. For example, many digital cameras are more sensitive to green, making green screens a popular choice.
Overall, while you can use red for chroma keying, it's essential to consider your specific circumstances and the potential challenges it might bring.
Does the colors: red, blue and green used on chroma key process have any relation to RGB technology inside digital video cameras?
RGB, which stands for Red, Green, and Blue, is the color model used in digital video cameras and displays. The RGB model is additive, which means that different colors are created by combining these three primary colors at various intensities.
When it comes to chroma keying, or "green screening," the choice of green, blue, or occasionally red isn't directly related to the RGB color model. Instead, it's based more on practical considerations. Here's why:
1. Green is used most frequently because digital cameras are most sensitive to green, due to the Bayer filter mosaic pattern used in most digital camera sensors. This filter pattern has twice as many green sensors as red or blue to mimic the human eye's own sensitivity to green. As a result, green screens can produce the cleanest key with the least noise.
2. Blue is the second most common choice. It was more popular in the past, especially in film, because film emulsion was more sensitive to blue light. Blue screens are also used in scenes where the subject is predominantly green (like plants).
3. Red is rarely used because it's a color often present in skin tones, and using it could result in parts of a person being keyed (made transparent) along with the background.
So while the colors used in chroma keying are indeed the primary colors of the RGB model used in digital cameras, the reason those specific colors are used has more to do with how cameras (and film) respond to different colors and less to do with the RGB model per se.