Represents the "Matte" entry of the image dictionary object.

It is an optional entry defined as part of the PDF 1.4 specification.

It contains an array which contains doubles, representing PDF numeric objects.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 89, page 206.

Adobe Supplement to the ISO 32000, BaseVersion: 1.7, ExtensionLevel: 3; Table: 4.39, page 27.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 87, page 255.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 146, page 349.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 144, page 418.

The Matte array gives the color of the background against which the image was pre-composited. When present, the reader applies inverse pre-multiplication to recover the original alpha information before re-compositing against the actual backdrop.

Matte processing is needed when an image was pre-multiplied against a specific background color and that background differs from the actual PDF page background.