chenglou / png-diff

Small PNG diff utility, written in pure JS for Node.

PNG Diff

Small PNG diff utility, written in pure JS for Node.

npm install png-diff

Usage

(Check out the example folder.)

Both methods take two image paths/streams/buffers as input.

var fs = require('fs');
var PNGDiff = require('png-diff');

var image2Stream = fs.createReadStream('2.png');
PNGDiff.outputDiff('1.png', image2Stream, 'diffOutput.png', function(err, diffMetric) {
  if (err) throw err;
  // returns 0 if every pixel's the same; return 1 otherwise. Currently, these
  // are the only two possible metric values; possibility to tweak them in the
  // future
  console.log(diffMetric === 1 ? 'Difference detected.' : 'No difference');
  // highlights the difference in red
  console.log('Diff saved!');
});

var image1Buffer = fs.createReadStream('1.png');
PNGDiff.outputDiffStream(image1Buffer, '2.png', function(err, outputStream, diffMetric) {
  if (err) throw err;

  if (diffMetric === 0) {
    console.log('No difference, no need to output diff result.');
    return;
  }
  outputStream.pipe(fs.createWriteStream('diffOutput2.png'));
});

Second format:

var image2Stream = fs.createReadStream('2.png');
// output identical pixels as transparent instead of highlighting the diff
// (default: false)
PNGDiff.outputDiff('1.png', image2Stream, 'diffOutput.png', true , function(err, diffMetric) {
  if (err) throw err;
  console.log(diffMetric === 1 ? 'Difference detected.' : 'No difference');
  // does not highlight the difference, but replaces common pixels with
  // transparent ones
  console.log('Diff saved!');
});

License

MIT.

png-diff's Issues

Images not the same dimension. First: 929x1008. Second: 1920x1055

Why is not possible to compare images with a different resolutions? Useful then doing full height screenshot of web page.

Output actual diff metrics

Function to determine if two pngs differ

I would find it useful to be able to determine wether two pngs differ or not. Something like this:

PNGDiff.differ(streamA, streamB, function (err, differ) {
  if (err) throw err

  console.log(differ ? 'They are not a like' : 'They look exactly the same')
})

return error i there's any

test error

there is no method measureDiff

Use pngjs2 in order to support multiple bit depths and interlace

pngjs2 is a bugfixed pngjs with exactly the same interface, so upgrading should be easy.