png-chunk-text

Create or parse a PNG tEXt chunk for storing uncompressed text data in PNG images.

Can be used in combination with png-chunks-extract and png-chunks-encode for adding and reading custom metadata in PNG images.

Works in Node, or in the browser using browserify.

Usage

chunk = text.encode(key, value)

Returns a chunk object containing the metadata for a given key and value:

{
  name: 'tEXt',
  data: Uint8Array([...])
}

const extract = require('png-chunks-extract')
const encode = require('png-chunks-encode')
const text = require('png-chunk-text')
const path = require('path')
const fs = require('fs')
 
const buffer = fs.readFileSync(path.join(__dirname, 'test.png'))
const chunks = extract(buffer)
 
// Add new chunks before the IEND chunk
chunks.splice(-1, 0, text.encode('hello', 'world'))
chunks.splice(-1, 0, text.encode('lorem', 'ipsum'))
 
fs.writeFileSync(
  path.join(__dirname, 'test-out.png'),
  new Buffer(encode(chunks))
)

data = text.decode(chunk)

Reads a Uint8Array or Node.js Buffer instance containing a tEXt PNG chunk's data and returns its keyword/text:

{
  keyword: 'hello',
  text: 'world'
}

const extract = require('png-chunks-extract')
const text = require('png-chunk-text')
const path = require('path')
const fs = require('fs')
 
const buffer = fs.readFileSync(path.join(__dirname, 'test-out.png'))
const chunks = extract(buffer)
 
const textChunks = chunks.filter(function (chunk) {
  return chunk.name === 'tEXt'
}).map(function (chunk) {
  return text.decode(chunk.data)
})
 
console.log(textChunks[0].keyword) // 'hello'
console.log(textChunks[0].text)    // 'world'
console.log(textChunks[1].keyword) // 'lorem'
console.log(textChunks[1].text)    // 'ipsum'

See Also

• png-chunks-extract
• png-chunks-encode

License

MIT, see LICENSE.md for details.