dpi-tools provides 2 utility functions that can change the dpi of canvas-generated image, of either dataUrl or blob formats. The functions separate the header from the image data, convert and manipulate just the header, then sticks the header back on the file. In this way, very large images can be converted quickly without having to convert the entire contents of an image file. This process is non-destructive—image data does not get modified in the process.

This package is forked from shutterstock/changeDPI in an attempt to modernize the build process using rollup and hopefully implement some new features!

npm install --save dpi-tools

/* ES6 */
import dpiTools from 'dpi-tools';
import { changeDpiDataUrl, changeDpiBlob } from 'dpi-tools';

/* ES5 */
var dpiTools = require('dpi-tools');

From a canvas element dataUrl:

// create the dataUrl at standard 72dpi
var dataUrl = canvas.toDataURL('image/jpeg', 0.92);
var daurl150dpi = changeDpiDataUrl(dataUrl, 150);

From a canvas element blob:

// create the blob at standard 72dpi
canvas.toBlob(
  function (blob) {
    changeDpiBlob(blob, 300).then(function (blob) {
      // use your changed blob
    });
  },
  'image/jpeg',
  0.92
);

  TODO add example with file reader.

This module uses ES6. To see a compiled ES5 version, run npm run build and look in dist/.

npm install
npm run test

Please do contribute! Open an issue or submit a pull request.

The project falls under @Shutterstock's Code of Conduct.

MIT.