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

It is an optional entry defined as part of the PDF 1.3 specification.

It contains an array which contains AlternateImageElements.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 89, page 207.

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 256.

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 Alternates array holds alternate image dictionaries. Each dictionary references a substitute image XObject and optionally flags it as the default for printing and associates it with an optional content group.

A conforming reader may choose an alternate based on the rendering context, such as selecting a low-resolution version for fast screen display or a high-resolution version for print output.