hughsk / png-chunk-text

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

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.

png-chunk-text's Issues

Remove previous

Would it be possible to remove earlier chunks without rewriting the entire file?

png-chunk-text usable from chrome extension?

Hi!

png-chunk-text seems an interesting project - i didn't know that there are node modules that dive into the depths of the png format :-)

one question: is png-chunk-text also usable from a google chrome extension? I like to integrate it into a extension that captures a screenshot of the current chrome tab. I like to use png-chunk-text to annotate the screenshot png (e.g. store the exact version of the webapp being captured in the screenshot in an iText chunk), much like EXIF is used to annotate the shooting settings of a digital photo.

Best,

Franz