Blackmagic ATEM Television Studio HD User Manual Keying using ATEM Switchers

Keyers are a powerful production tool that allow the arrangement of visual elements from different sources on the same video image.

To do this, multiple layers of video or graphics are stacked on top of the background video. Altering the transparency of various parts of these layers allows the background layer to be visible. This process is called keying. Various techniques are used to create this selective transparency and these correspond to the different types of keyers available on your switcher.

The following section explains luma and linear keyers, which are available either upstream or downstream. It also explains chroma, pattern and DVE keys, which are upstream keyers.

Understanding Keying

A key requires two video sources; the fill signal and the key or cut signal. The fill signal contains a video image which is to be stacked on top of the background, while the key signal is used to select regions of the fill signal to be made transparent. The fill and key signals can be selected from any of the switcher’s external inputs or internal sources, allowing both still and moving images to be used as fill or key sources.

Fill and key signals are selected on the software control panel from drop down lists in the upstream and downstream key palettes. On the ATEM switcher, fill and key signals are selected using the select bus.

There are two types of keyers used in the switcher; upstream keyers and downstream keyers. Four upstream keyers, also known as effects keyers, are available in the switcher’s M/E block. Each upstream keyer can be set up as a luma, linear, pre-multiplied, chroma, pattern or DVE key. Two downstream keyers are available in the dedicated DSK block. Each downstream keyer can be set up as a luma or linear key.

Luma Key

A luma key or self key consists of one video source containing the video image that will be stacked on top of the background. All of the black areas defined by the luminance in the video signal will be made transparent so that the background can be revealed underneath. Since only one image is used to define the areas to be cut out, a luma key uses the same signal for fill and key. The following images are an example of what background, luma key signals and the resulting combined image might look like.

Combining a background and fill/key in a luma key

Background

A full screen image, often a camera source.

Fill

The graphic you plan to display on top of your background video. Notice that the final composition does not retain any black from the graphic because all of the black parts have been cut out of the image.

Linear Key

A linear key consists of two video sources; the fill signal and the key or cut signal. The fill signal contains a video image which is to be stacked on top of the background, while the key signal contains a grayscale mask that is used to define regions of the fill signal to be made transparent. Since both the fill and key signals are video inputs, both signals can be in motion while on screen. The following images are examples of what background, fill, key signals and the resulting combined image might look like.

Combining a background, fill and key in a linear key

Background

A full screen image, often a camera source.

Fill

The graphic you plan to display on top of your background video. Notice that the black parts of the graphic remain intact because the key signal is used to determine the transparency of the fill signal. The fill signal is often provided by a graphics system.

Key

A grayscale image that defines the region in the image that will be removed so that the fill signal can be correctly stacked on top of the background. The key signal is often provided by a graphics system.

Pre multiplied Key

A modern graphics system or character generator that offers fill and key outputs will most likely provide what is known as a pre-multiplied or shaped key. A pre-multiplied key is a special combination of the fill and key signal where the fill signal has been pre-multiplied with the key signal over a black background. Photoshop generated images that contain an alpha channel are pre-multiplied.

ATEM switchers have an auto key adjustment for pre-multiplied keys so that when the pre-multiplied key setting is enabled, the clip and gain parameters are automatically set by the system.

When using a Photoshop generated image, generate graphics over a black background layer and place all content on the upper layers. Add an alpha channel in your Photoshop document that the ATEM can use for blending the graphic over the live video. Then, when saved as a Targa image file, or downloaded direct to the media pool, you can select pre-multiplied in the keyer and you should have a great key!

Photoshop documents are pre-multiplied by nature, so you should always use the pre-multiplied settings on the ATEM switcher when keying them.

Performing an Upstream Luma/Linear Key

Since luma and linear keys use the same parameters, they are set up on the software control panel and the ATEM switcher using a common menu, called the luma key menu. What defines the key as being either luma or linear is in the selection of fill and key sources. In a luma key, fill and key sources are the same. For a linear key, fill and key sources are different.

The Upstream Key palette has a menu for resetting parameters at the top of each tab. Select the sections you wish to reset from the menu.

To set up a luma/linear key on upstream keyer 1 on ATEM Television Studio HD8:

1. Press the ‘key 1’ button to enable the keyer on the preview output. This automatically selects the keyers menu on the system control LCD, but you can also press the ‘keyers’ button to enter the menu directly.

2. Use the control knob underneath the ‘key type’ indicator to choose the ‘luma’ key.

3. Rotate the ‘fill source’ and ‘key source’ control knobs to choose a fill and key source.

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   TIP You can also press the corresponding buttons on the source select bus to select the fill and key source.

4. Once you have chosen a key type, fill and source, press the ‘right’ arrow button to scroll through to the next menu item and use the control knobs to adjust key parameters such as mask, gain, clip, enable or disable pre multiplied key, etc.

To set up a luma/linear key on upstream keyer 1 on the software control panel:

1. Expand the upstream key 1 palette and select luma tab.

2. Select the fill source and key source.

If performing a luma key, select the same source for both fill and key.

Adjust the key parameters to refine the key. For a description of luma key parameters, refer to the table below.

Upstream key luma/linear key parameters include:

Performing a Downstream Luma/Linear Key

To set up a luma/linear key on downstream keyer 1 on ATEM Television Studio HD8:

1. Press the ‘DSK 1 tie’ button to enable the downstream keyer on the preview output. This automatically selects the downstream key menu on the system control LCD, but you can also press the ‘keyers’ button and press the right arrow to enter the menu directly.

2. Press the ‘DSK 1’ or ‘DSK 2’ soft button to select which downstream keyer you wish to use.

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   TIP You don’t have to select the key type as the downstream keyer is always a luma key.

3. Use the control knobs under the LCD menu to select the fill source and key source. You can also use the corresponding source select buttons to select the fill and key source.

4. Once you have chosen the fill source and key source, use the ‘left’ and ‘right’ control buttons to scroll through additional menu screens containing key parameters such as mask, gain, clip, pre multiplied key settings and more.

To set up a luma/linear key on downstream keyer 1 on the software control panel:

1. Select the downstream key 1 palette.

2. Use the drop down controls labeled fill source and key source to specify the fill and key sources. If performing a luma key, select the same source for both fill and key.

3. Adjust the key parameters to refine the key.

Downstream Keyer Settings

Chroma Key

Chroma key is commonly used for weather broadcasts, where the meteorologist appears to be standing in front of a large map. In the studio the presenter is actually standing in front of a blue or green background. In a chroma key two images are combined using a special technique and a color from one image is removed, revealing another image behind it. This technique is also referred to as color keying, color-separation overlay, green screen, or blue screen.

A very common use for chroma keys for backgrounds is computer generated graphics. It’s simple to connect an external computer to your ATEM switcher using the HDMI output of the computer or a video card such as the Blackmagic Design DeckLink or Intensity range and then play back video clips to your ATEM switcher. If you render a green background on your animations, you can then key this green to create fast and clean animations of any length. Keying is easy as the green is computer generated so it’s a very flat color that’s easy to key.

Combining a background with a fill and chroma key/cut

Background

A full screen image; in the case of a chroma key it is often a weather map.

Fill

The image you plan to display on top of your background video. In the case of a chroma key, this is video of the meteorologist in front of the green screen.

Key/Cut

In the case of a chroma key the key/cut signal is generated from the fill signal.

Performing an Advanced Chroma Key

Your ATEM switcher features advanced chroma keying, with more detailed chroma sampling and adjustment options. These controls help you achieve the best key, improving the blend of foreground and background so you can create a more convincing visual effect.

To set up a chroma key on upstream keyer 1 on ATEM Television Studio HD8:

1. Press the ‘key 1’ button to enable keyer 1 on the preview output. This automatically selects the keyers menu on the system control LCD, but you can also press the ‘keyers’ button to enter the menu directly.

2. Select the ‘chroma’ key type using the corresponding ‘key type’ control knob.

3. Select your fill source by turning the corresponding LCD control knob. Typically, this source would be from a camera facing a presenter in front of a green screen, or a graphic loaded in a media player. You can also select a fill source by pressing the corresponding button in the source select bus.

4. Use the ‘right’ arrow buttons to access the chroma adjustments screen.

5. Click the ‘sample chroma’ button.

To set up a chroma key on upstream key 1 on the software control panel:

1. Expand the upstream key 1 palette and select ‘chroma’ from the key types bar.

2. Select the fill source. Typically, this source would be from a camera facing a presenter in front of a green screen, or a graphic loaded in a media player.

3. Click the ‘chroma sample’ button. With the chroma sample selected, you’ll see a new panel appear with a box cursor. This cursor is also visible on the preview output. The chroma sample setting lets you position a cursor over the screen area you want to sample

4. Click and drag on the box cursor to move it to the position you want to sample.

Choose a representative area of your green screen that covers as much of the luminance range of the screen as possible. The default size of the box cursor is well suited to most green screens that are relatively evenly lit, however if there is a lot of variance in your green screen, you can adjust the size of the box by clicking on the slider to the right of the sample window and dragging it up or down. On the switcher, use the corresponding knobs to move the position of the box and the z axis to increase or decrease the size.

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TIP When sampling uneven green screens, we recommend sampling the darkest area first before increasing the size of the sample box. This can give you a more accurate key.

You can preview your key at any time by clicking the ‘preview’ button above the chroma sample panel or by pressing the ‘preview chroma’ button above the LCD screen on the system control.

Use the preview button to check what your key will look like in the preview output

Fine Tuning your Key using Key Adjustments

Once you have achieved a good chroma sample that removes most of your green screen while generally retaining foreground elements, it is time to fine tune your key with the ‘key adjustments’ controls. On ATEM Television Studio HD8, press the right arrow to navigate to the ‘chroma adjustments’ menu.

Foreground /

Use the ‘foreground’ slider or control knob to adjust how opaque the foreground mask is. This determines the strength of the foreground against the background. By increasing the slider, you can fill in any small areas of transparency inside your foreground image. We recommend moving this slider and stopping as soon as the foreground becomes solid.

Background

The ‘background’ slider and control knob adjusts the opacity of the keyed area. Use this slider to fill in any small foreground artifacts left over in the area of the image you want to remove. We recommend moving the slider until your keyed area is consistently opaque.

Key Edge

The ‘key edge’ slider and control knob moves the edge of your keyed area in or out, helping to remove background elements from the very edge of your foreground or extending the foreground out a little if your key is too aggressive. This can be especially useful with fine details like hair. We recommend moving this slider until the edge of your key is generally clean, without any background artifacts visible.

Using the key or chroma adjustment controls, your foreground elements should be cleanly separated from the background.

Chroma Correction using Color Spill and Flare Suppression

Light bouncing off a green screen can create a green edge to foreground elements as well as a general tint to the foreground, or fill image. This is called color spill and flare. The ‘chroma correction’ settings let you improve the areas of the foreground that are affected by color spill and flare. You can correct these areas in the key using the ‘chroma correction’ settings.

Spill

Adjust the spill slider to remove colored tint from the edges of foreground elements. For example, green reflections bouncing off a green screen.

Flare Suppression

Flare suppression removes overall green tint evenly across all foreground elements.

Matching your foreground and background

Once your foreground is properly separated from your green screen and you have adjusted spill and flare suppression, use the ‘color adjustments’ controls to match your foreground with the background.

Adjusting the brightness, contrast, saturation and color balance of your foreground image will help blend it with the background so the effect is more convincing.

Use the color adjustments controls to match your foreground with the background

Pattern Key

A pattern key is used to display a geometric cut out of one image on top of another image. In a pattern key the key or cut signal is generated using the switcher’s internal pattern generator. The internal pattern generator can create 18 shapes that can be sized and positioned to produce the desired key signal.

Combining a background with a fill and pattern key

Background

A full screen image.

Fill

Another full screen image you wish to overlay on top of the background.

Key/Cut

In the case of a pattern key the key/cut signal is generated by the switcher’s internal pattern generator.

Performing an Upstream Pattern Key

To set up a pattern key on upstream keyer 1 on ATEM Television Studio HD8:

1. Press the KEY 1 next transition button to enable the key on the preview output. This automatically selects the keyers menu on the system control LCD. Pressing the KEY 1 next transition button ties the key to the next transition so it will transition to air when the next transition is performed.

2. In the keyers LCD menu, select the ‘pattern’ key type using the corresponding ‘key type’ control knob.

3. Select the fill source using the corresponding soft control knob or by pressing a source button on the source select bus.

4. Turn the corresponding soft control knobs to choose the ‘pattern’ you want for the pattern key and set the ‘size’ of the pattern.

5. Press the system control left and right arrow buttons to navigate through the pattern key parameters and adjust settings using the control knobs. Watch the preview output as you refine the key.

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TIP Some patterns can have their center point repositioned. Use the corresponding control knobs to move the position of the pattern. If you need to reset the position, navigate to the ‘pattern type’ setting, change it to another pattern and then return to your chosen pattern to reset the position to its default.

Pattern Key Settings

To set up a pattern key on upstream keyer 1 on the software control panel:

1. Expand the upstream key 1 palette and select pattern from the key types bar.

2. Select the fill source.

3. Select the key pattern.

4. Adjust the key parameters to refine the key. For a description of pattern key parameters, refer to the table below.

Adjusting the X/Y Position of a Pattern

Some of the patterns may have their center point repositioned. To position a pattern, navigate to the pattern selection page of the keyer you are setting up. Use the control knobs to move the pattern vertically and horizontally. To re-center the pattern, press the pattern select button of the current pattern in the menu. This will reset the position and symmetry of the pattern.

DVE Key

DVEs (digital video effects) are used to create picture-in-picture boxes with borders. Most models have 1 channel of 2D DVE that allows scaling, rotation, 3D borders and offers a drop shadow.

Combining a background, DVE fill and DVE key/cut

Background

A full screen image.

Fill

Another full screen that has been scaled, rotated or has added borders and will be overlaid on top of the background.

Key/Cut

In the case of a DVE key, the key/cut signal is generated by the switcher’s internal DVE processor.

Performing an Upstream DVE Key

To set up a DVE key on upstream keyer 1 on ATEM Television Studio HD8:

1. Press the KEY 1 next transition button to enable the keyer on the preview output.

2. In the keyers LCD menu, select the DVE key type using the corresponding soft control knob.

3. Select the fill source using the corresponding control knob or via the a source button on the source select bus.

4. Press the system control left and right arrow buttons to navigate through the DVE parameters and use the soft control knobs to adjust settings, such as rotation, position, size, mask settings, light source, border and key frames for movement.

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TIP When using the number pad to enter numeric values for settings, hold the ‘reset’ button down for several seconds to enable negative values. Hold down again to return to standard values.

To set up a DVE key on upstream keyer 1 on the software control panel:

1. Expand the upstream key 1 palette and select DVE from the key types bar.

2. Select the fill source.

3. Adjust the key parameters to refine the key. For a description of DVE key parameters, refer to the table below.

DVE Key Settings

DVE parameters

Adding DVE Borders

DVE border parameters

The knobs and soft buttons in the system control are used to adjust the border parameters. There are multiple parameters, each requiring an adjustment, therefore the soft/color button and SHIFT button is used to toggle the parameters that each knob adjusts.

Key Masking

Both upstream and downstream keyers have an adjustable rectangular mask that can be used to crop out harsh edges and other artifacts in the video signal. The mask consists of left, right, top and bottom crop controls. Masking can also be used as a creative tool to build rectangular cut outs on screen.

On the hardware panel the mask is set up for each upstream and downstream key from the system control mask menu which is available from the EFFECTS KEYS or DSK KEYS menus.

On the software control panel the mask is set up for each upstream or downstream key from the palettes in the settings tab.

Flying Key

Luma, chroma and pattern upstream key types include a flying key setting. If a DVE channel is available the Flying Key setting allows DVE effects to be applied to the key.

Performing Upstream Keyer Transitions

The upstream keyers are accessible from the transition control block or the system control. The upstream keyers are taken on and off the program output using the next transition buttons or ON buttons.

ON buttons

Take the upstream keyers on or off the program output using the ON (on air) buttons as follows:

1. Press the ON button above the corresponding next transition KEY button to immediately turn on or turn off the upstream key on the program output.

2. The ON button also indicates if the upstream keyer is currently on or off the program output.

Next transition buttons

Take the upstream keyers on or off the program output using the next transition buttons as follows:

1. Select the elements you wish to transition using the BKGD, KEY 1, KEY 2, KEY 3 and KEY 4 next transition buttons.

2. Verify the preview output, which will show you exactly what your program output will look like after you perform the transition.

3. Press CUT, AUTO, or use the fader bar to perform the transition.

In order to help you understand the various ways in which multiple keys can be taken on and off the program output, we have provided a few examples. In the examples below KEY 1 contains a live bug on the top left of the screen while KEY 2 contains a bug at the bottom right hand side of the screen.

Example 1:

In this example none of the upstream keyers are currently on-air. The next transition has key 1 selected, therefore the next transition will change the state of key 1 and turn it ON so that it is visible on the program output.

Example 2:

In this example, key 1 is currently on air, indicated by the illuminated ON button. The next transition has Key 1 selected, therefore the next transition will change the state of key 1 and turn it OFF so that it is not visible on the program output.

Example 3:

In this example, key 1 and key 2 are on-air, indicated by the illuminated ON buttons. The next transition has the background selected, indicated by the illuminated BKGD button, therefore the next transition will only transition the background leaving both key 1 and key 2 on-air.

Example 4:

In this example, key 1 and key 2 are on-air. The next transition has the background and key 2 selected, therefore the next transition will transition the background and change the state of key 2 turning it OFF so that it is not visible on the program output.

There are multiple ways to transition a key to the program output. The key can be cut on or off, it can be mixed on or off, or it can be mixed along with a background transition. Upstream keys are transitioned to the program output using the next transition block. Downstream keyers can be transitioned using their own transition buttons or by using the DSK TIE button to link the transition with the main transition control block.

Performing Downstream Keyer Transitions

The downstream keyers have their own transition buttons and transition rate windows. Once a downstream keyer is configured it can be easily taken on and off the program output using one of the following three methods:

1. Press the DSK CUT button to immediately turn on or turn off the downstream key on the program output.

2. Use the DSK AUTO button to gradually transition the downstream key on or off the program output at the rate displayed in the DSK rate window.

3. Use the DSK TIE button to link the downstream key with the main transition control block. Once linked the DSK will be mixed on or off along with any transition type selected in the main transition control block at the rate specified by the transition control block. Pressing the DSK TIE button shows the downstream keyer on the preview output. It is not possible to preview a downstream keyer transition when linked with the main transition block. If the DSK TIE button is on when you switch to preview transition mode the tie functionality will be ignored until the preview transition mode is turned off.

DSK parameters