How could you remove the background and make it transparent?

[treeder]

Say it's a white background, how would you remove that and make it transparent?

[agammann]

For a solid white background, you can make matching pixels transparent by changing their alpha channel, then write a PNG:

import { Jimp } from 'jimp';

function removeWhite(image, threshold = 255) {
  const data = image.bitmap.data;
  image.scan((x, y, index) => {
    if (data[index] >= threshold &&
        data[index + 1] >= threshold &&
        data[index + 2] >= threshold) {
      data[index + 3] = 0;
    }
  });
  return image;
}

const image = await Jimp.read('input.png');
removeWhite(image);
await image.write('transparent.png');

The default removes exactly white pixels; a value such as 250 also removes near-white pixels. It affects every matching pixel, including white areas in the foreground. This is color-keying for a known background, not object/background segmentation, and does not remove color fringes from antialiased edges automatically.

Use PNG for the result because JPEG does not retain alpha transparency. Tested with Jimp 1.6.1: exact-white alpha became zero, colored pixels stayed unchanged, the threshold option handled near-white pixels, and transparency survived PNG write/read. Jimp bitmap/pixel API.