PNG chunk
Definition
The basic structural unit of a PNG file. Each chunk has a four-character type code, a length field, a data payload, and a CRC-32 checksum. Critical chunks (IHDR, IDAT, IEND) must be present and in a defined order; ancillary chunks are optional. Unexpected or malformed chunks indicate post-processing.
Related terms
- EXIF (Exchangeable Image File Format)
- A metadata standard embedded in JPEG and TIFF files by capture devices. EXIF fields record camera make and model, lens data, exposure...
- File signature (magic bytes)
- The fixed byte sequence at the start of a file that identifies its format. JPEG files begin with FF D8 FF; PNG...
- JPEG quantisation table
- A matrix of 64 values embedded in a JPEG file that controls the precision with which each frequency component of the image...
- Thumbnail inconsistency
- Many cameras embed a reduced-resolution preview image inside the EXIF header of a JPEG. If the main image has been cropped or...
- XMP (Extensible Metadata Platform)
- An Adobe-defined metadata format stored as an XML packet embedded in image files. XMP carries a software history field (xmpMM:History) that editing...
Explained in
- Image File Format and Integrity ChecksThe basic structural unit of a PNG file. Each chunk has a four-character type code, a length field, a data payload, and a CRC-32 checksum. Critical chunks (IHD...