EXT

EXt, in the context of PNG files, refers to the tEXt chunk type, which stores textual metadata alongside image data. A tEXt chunk consists of two parts: a keyword that labels the metadata and a text string containing the content. The keyword is an ASCII string between 1 and 79 bytes, followed by a null separator, and then the text string encoded in ISO-8859-1 (Latin-1). The chunk data is appended to the PNG file as part of its standard chunk structure.

Multiple tEXt chunks may appear in a single PNG file, allowing different pieces of text to be embedded independently. Common examples include keywords like Title, Author, Description, Software, and Copyright. The tEXt chunk is uncompressed, distinguishing it from related chunk types such as zTXt, which stores compressed text, and iTXt, which supports UTF-8 text with optional compression.

Limitations of tEXt stem from its encoding and scope. Because the text is restricted to Latin-1, it is not ideal for non-Latin scripts; for broader character support, the iTXt chunk is preferred, as it supports UTF-8. Decoders and image editors may expose tEXt metadata in image properties or metadata panels, but the presence of tEXt chunks does not affect the displayed image data.

In practice, tEXt remains a widely used, vendor-neutral mechanism for embedding descriptive information and captions within PNG files, complementary to other metadata chunks designed for different encoding and compression needs.