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# Compressed matte atom ('kmat')

An atom that specifies the image description structure and the matte data associated with a particular matte atom.

## Overview

The compressed matte atom specifies the image description structure and the matte data associated with a particular matte atom. Compressed matte atoms have an atom type value of `'kmat'`.

The layout of the compressed matte atom is as follows.

|Compressed matte atom                                                                                               |Bytes   |
|--------------------------------------------------------------------------------------------------------------------|--------|
|``doc://com.apple.qtff/documentation/quicktime-file-format/Compressed_matte_atom/Size``                             |4       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Compressed_matte_atom/Type``                             |4       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Compressed_matte_atom/Version``                          |1       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Compressed_matte_atom/Flags``                            |3       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Compressed_matte_atom/Matte_image_description_structure``|Variable|
|``doc://com.apple.qtff/documentation/quicktime-file-format/Compressed_matte_atom/Matte_data``                       |Variable|

## Topics

### Data fields

[`Size`](/documentation/quicktime-file-format/Compressed_matte_atom/Size)

A 32-bit integer that specifies the number of bytes in this compressed matte atom.

[`Type`](/documentation/quicktime-file-format/Compressed_matte_atom/Type)

A 32-bit integer that identifies the atom type.

[`Version`](/documentation/quicktime-file-format/Compressed_matte_atom/Version)

A 1-byte specification of the version of this compressed matte atom.

[`Flags`](/documentation/quicktime-file-format/Compressed_matte_atom/Flags)

Three bytes of space for flags.

[`Matte image description structure`](/documentation/quicktime-file-format/Compressed_matte_atom/Matte_image_description_structure)

An image description structure associated with this matte data.

[`Matte data`](/documentation/quicktime-file-format/Compressed_matte_atom/Matte_data)

The compressed matte data, which is of variable length.


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