sharp/test/unit/alpha.js

// Copyright 2013 Lovell Fuller and others.
// SPDX-License-Identifier: Apache-2.0

const assert = require('node:assert');
const fixtures = require('../fixtures');
const sharp = require('../../');

describe('Alpha transparency', function () {
  it('Flatten to black', function (done) {
    sharp(fixtures.inputPngWithTransparency)
      .flatten()
      .resize(400, 300)
      .toBuffer(function (err, data, info) {
        if (err) throw err;
        assert.strictEqual(400, info.width);
        assert.strictEqual(300, info.height);
        fixtures.assertSimilar(fixtures.expected('flatten-black.jpg'), data, done);
      });
  });

  it('Flatten to RGB orange', function (done) {
    sharp(fixtures.inputPngWithTransparency)
      .resize(400, 300)
      .flatten({
        background: { r: 255, g: 102, b: 0 }
      })
      .jpeg({ chromaSubsampling: '4:4:4' })
      .toBuffer(function (err, data, info) {
        if (err) throw err;
        assert.strictEqual(400, info.width);
        assert.strictEqual(300, info.height);
        fixtures.assertSimilar(fixtures.expected('flatten-orange.jpg'), data, done);
      });
  });

  it('Flatten to CSS/hex orange', function (done) {
    sharp(fixtures.inputPngWithTransparency)
      .resize(400, 300)
      .flatten({ background: '#ff6600' })
      .jpeg({ chromaSubsampling: '4:4:4' })
      .toBuffer(function (err, data, info) {
        if (err) throw err;
        assert.strictEqual(400, info.width);
        assert.strictEqual(300, info.height);
        fixtures.assertSimilar(fixtures.expected('flatten-orange.jpg'), data, done);
      });
  });

  it('Flatten 16-bit PNG with transparency to orange', function (done) {
    const output = fixtures.path('output.flatten-rgb16-orange.jpg');
    sharp(fixtures.inputPngWithTransparency16bit)
      .flatten({
        background: { r: 255, g: 102, b: 0 }
      })
      .toFile(output, function (err, info) {
        if (err) throw err;
        assert.strictEqual(true, info.size > 0);
        assert.strictEqual(32, info.width);
        assert.strictEqual(32, info.height);
        fixtures.assertMaxColourDistance(output, fixtures.expected('flatten-rgb16-orange.jpg'), 10);
        done();
      });
  });

  it('Do not flatten', function (done) {
    sharp(fixtures.inputPngWithTransparency)
      .flatten(false)
      .toBuffer(function (err, _data, info) {
        if (err) throw err;
        assert.strictEqual('png', info.format);
        assert.strictEqual(4, info.channels);
        done();
      });
  });

  it('Ignored for JPEG', function (done) {
    sharp(fixtures.inputJpg)
      .flatten({ background: '#ff0000' })
      .toBuffer(function (err, _data, info) {
        if (err) throw err;
        assert.strictEqual('jpeg', info.format);
        assert.strictEqual(3, info.channels);
        done();
      });
  });

  it('Flatten with options but without colour does not throw', () => {
    assert.doesNotThrow(() => {
      sharp().flatten({});
    });
  });

  it('Flatten to invalid colour throws', () => {
    assert.throws(() => {
      sharp().flatten({ background: 1 });
    });
  });

  it('Enlargement with non-nearest neighbor interpolation shouldn’t cause dark edges', function () {
    const base = 'alpha-premultiply-enlargement-2048x1536-paper.png';
    const actual = fixtures.path(`output.${base}`);
    const expected = fixtures.expected(base);
    return sharp(fixtures.inputPngAlphaPremultiplicationSmall)
      .resize(2048, 1536)
      .toFile(actual)
      .then(function () {
        fixtures.assertMaxColourDistance(actual, expected, 102);
      });
  });

  it('Reduction with non-nearest neighbor interpolation shouldn’t cause dark edges', function () {
    const base = 'alpha-premultiply-reduction-1024x768-paper.png';
    const actual = fixtures.path(`output.${base}`);
    const expected = fixtures.expected(base);
    return sharp(fixtures.inputPngAlphaPremultiplicationLarge)
      .resize(1024, 768)
      .toFile(actual)
      .then(function () {
        fixtures.assertMaxColourDistance(actual, expected, 102);
      });
  });

  it('Removes alpha from fixtures with transparency, ignores those without', function () {
    return Promise.all([
      fixtures.inputPngWithTransparency,
      fixtures.inputPngWithTransparency16bit,
      fixtures.inputWebPWithTransparency,
      fixtures.inputJpg,
      fixtures.inputPng,
      fixtures.inputWebP
    ].map(function (input) {
      return sharp(input)
        .resize(10)
        .removeAlpha()
        .toBuffer({ resolveWithObject: true })
        .then(function (result) {
          assert.strictEqual(3, result.info.channels);
        });
    }));
  });

  it('Ensures alpha from fixtures without transparency, ignores those with', function () {
    return Promise.all([
      fixtures.inputPngWithTransparency,
      fixtures.inputPngWithTransparency16bit,
      fixtures.inputWebPWithTransparency,
      fixtures.inputJpg,
      fixtures.inputPng,
      fixtures.inputWebP
    ].map(function (input) {
      return sharp(input)
        .resize(10)
        .ensureAlpha()
        .png()
        .toBuffer({ resolveWithObject: true })
        .then(function (result) {
          assert.strictEqual(4, result.info.channels);
        });
    }));
  });

  it('Valid ensureAlpha value used for alpha channel', async () => {
    const background = { r: 255, g: 0, b: 0 };
    const [r, g, b, alpha] = await sharp({
      create: {
        width: 8,
        height: 8,
        channels: 3,
        background
      }
    })
      .ensureAlpha(0.5)
      .raw()
      .toBuffer();

    assert.deepStrictEqual({ r, g, b, alpha }, { ...background, alpha: 127 });
  });

  it('Invalid ensureAlpha value throws', async () => {
    assert.throws(() => {
      sharp().ensureAlpha('fail');
    });
  });
});