From Portable Network Graphics (PNG) Specification (Second Edition) ( 2003-11-10) representing an image by a palette , an alpha table , and an array of indices pointing to entries in the palette and alpha table.
The systematic arrangement of entries designed for users to locate information in a document. There are many types of indexes, from cumulative indexes for journals to computer database indexes. An indexer reads the page proofs, lists headings and subheadings, and annotates the location of each pertinent reference. After completing a rough index, the indexer edits it for structure, clarity, and consistency, formats it to specifications, proofreads it, and submits it. Although software advances and effective multipurposing methods can automate indexes, multi-level indexes require human interaction to reference pages in which a concept is discussed without a specific keyword appearing.
the practice of creating a comprehensive yet concise set of "entry points" into the different concepts contained in a piece of information. This can mean the index in the back of a textbook (which should have an entry for every major concept in the book, as well as redundant references when there are different ways to describe those concepts). It can also mean the different concepts in a journal article (in which case a database like MEDLINE serves as the index, rather than there being an index in the article itself). Without indexing much of the world's intellectual output remains unusable because it is too hard to find literature relating to the concepts you are interested in, and too time consuming (nay, impossible) to read all of it yourself.