Chroma key


This effect provides professional quality removal of any color from a source with precision control over edge detail, edge color correction and advanced spill replacement.

Item

Description

View

Source - shows the original unkeyed layer.

Status - shows a black and white matte. This makes it easy to see at a glance which areas are not fully opaque. This mode does not show gradients of transparency.

Matte - shows a greyscale matte. This provides an accurate view of opaque and transparent areas.

Despill mask - displays the despill mask, if one is being used.

Despill map - shows the area being spill suppressed.

Result - shows the final composited result.

Note that the View menu will affect final output.

Adaptive Color

This method is particularly effective when working with uneven green screens. Even slight changes in tone or brightness across your green screen can cause keying complications. Adaptive color aims to improve results in such cases and can be particularly effective with fine detail areas such as lace and hair.

Note that when adaptive color is activated the Gain setting will have a minimal effect. Key adjustments should be made primarily using the Clip Foreground and Clip Background settings.

Color

Defines the color to be keyed.

Gain

Gain is the base sensitivity of the chroma key.

This is best used for the initial background removal. It should be adjusted until the subject is isolated, though you don't want to push the gain too far as you will start to lose edge detail.

Balance & Hue Balance

These two settings adjust the emphasis of the chroma key, affecting the range of colors that are affected.

In practical use, it is usually best to try them at the minimum and maximum values to see which best suits your image.

Pre-Blur

Applies a blur to the footage prior to keying. This can help with lower resolution footage.

Clip Background

Crushes the black point of the matte, so that more parts of the image are removed. If parts of your green screen are still visible this should be used to remove them.

Clip Foreground

Clips the white point of the matte, returning detail to the foreground. If parts of your subject are semi-transparent, you should reduce the clip foreground to make it fully opaque.

Clip Rollback

After adjusting the clip foreground you may want to return some of the semi-transparency to the outer edges of your foreground. This helps to create a softer edge, although increasing this setting too much will cause an undesirable band of semi-transparency around the edge.

Gamma

Adjusts the strength of the key. This can be useful for adjusting the fine detail at the edges of the key, particularly around hair and semi-transparent areas.

Erode/Expand

This works in a similar way to the standalone Erode White filter and can be used to expand or erode the alpha matte. If you need to add or remove pixels from the edge of the key this can be very useful.

Despot Foreground/Background

Aims to remove holes in the background or foreground. Used subtly this can improve overall keying quality without affecting edge detail.

Softness

Blurs the alpha, creating a softer edge to the key.

Bias

Performs a white balance using the selected color, prior to applying the key.

Subtract Background Color

Increasing the subtract setting removes the background color (for example, green if you're using a green screen) from the semi-transparent areas of the image. This can be very effective for reclaiming the correct color in semi-transparent areas, such as glass.

Recover Edge Color

A thin dark line can sometimes be seen on the keyed edges of white clothing or pale skin.

The recover setting can counter this problem by adjusting the colors of the outer pixels. Rather than using their actual color, instead they will take on the color of the pixels further inside the foreground. Best used subtly.

Expansion Region Color: Method

If the Expand setting is used, this determines the content of the expansion region. The default despilled source usually provides best results.

Retain/Remove Mask

Separate layers can be specified as additional masks to aid with the overall keying. Retain masks identify areas the key should ignore, while remove masks identify areas that should definitely be removed.

The chroma key effect also includes built-in spill suppression.

Even a perfectly shot clip can still suffer from color spill. This is when the green or blue of the screen is reflected on the subject. While this is often difficult to see in the original image, once it has been composited it becomes extremely obvious, resulting in unwanted color fringing around edges.

Item

Description

Amount

Varies the strength of the spill suppression.

Hue Range/Balance/Hue Balance

Expands or contracts the spill suppression area. Best adjusted while in the despill map view mode.

Spill Replacement

Spill replacement aims to replace the unwanted spill with a new spill color.

Luminance Change

Varies the luminance adjustment based on the replacement color.

Source Layer

A specific layer can be selected for spill replacement. This then updates the replacement color as the selected layer changes.

Color

A color can be selected manually for spill replacement.

Blur

When using a source layer for spill replacement, the layer can be blurred for a subtler effect.

Despill Mask

A specific layer can be used to manually define areas to be spill suppressed.

From

Selects the despill mask layer.

Color Dist Max

Adjusts the range of color to be suppressed.

Softness

Blurs the despill mask.

Color correction is integrated into the chroma key effect, enabling you to color correct the foreground, background and edge of your key.

Item

Description

Enable

Turns the color correction features on and off.

Edge Resize

The edge area can be blurred and enlarged.

Foreground/Edge/Background

Each area's strength, hue, saturation and lightness can be individually adjusted.