sharp/lib/colour.js

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

'use strict';

const color = require('color');
const is = require('./is');

/**
 * Colourspaces.
 * @private
 */
const colourspace = {
  multiband: 'multiband',
  'b-w': 'b-w',
  bw: 'b-w',
  cmyk: 'cmyk',
  srgb: 'srgb'
};

/**
 * Tint the image using the provided chroma while preserving the image luminance.
 * An alpha channel may be present and will be unchanged by the operation.
 *
 * @example
 * const output = await sharp(input)
 *   .tint({ r: 255, g: 240, b: 16 })
 *   .toBuffer();
 *
 * @param {string|Object} rgb - parsed by the [color](https://www.npmjs.org/package/color) module to extract chroma values.
 * @returns {Sharp}
 * @throws {Error} Invalid parameter
 */
function tint (rgb) {
  const colour = color(rgb);
  this.options.tintA = colour.a();
  this.options.tintB = colour.b();
  return this;
}

/**
 * Convert to 8-bit greyscale; 256 shades of grey.
 * This is a linear operation. If the input image is in a non-linear colour space such as sRGB, use `gamma()` with `greyscale()` for the best results.
 * By default the output image will be web-friendly sRGB and contain three (identical) color channels.
 * This may be overridden by other sharp operations such as `toColourspace('b-w')`,
 * which will produce an output image containing one color channel.
 * An alpha channel may be present, and will be unchanged by the operation.
 *
 * @example
 * const output = await sharp(input).greyscale().toBuffer();
 *
 * @param {Boolean} [greyscale=true]
 * @returns {Sharp}
 */
function greyscale (greyscale) {
  this.options.greyscale = is.bool(greyscale) ? greyscale : true;
  return this;
}

/**
 * Alternative spelling of `greyscale`.
 * @param {Boolean} [grayscale=true]
 * @returns {Sharp}
 */
function grayscale (grayscale) {
  return this.greyscale(grayscale);
}

/**
 * Set the pipeline colourspace.
 *
 * The input image will be converted to the provided colourspace at the start of the pipeline.
 * All operations will use this colourspace before converting to the output colourspace,
 * as defined by {@link #tocolourspace|toColourspace}.
 *
 * This feature is experimental and has not yet been fully-tested with all operations.
 *
 * @since 0.29.0
 *
 * @example
 * // Run pipeline in 16 bits per channel RGB while converting final result to 8 bits per channel sRGB.
 * await sharp(input)
 *  .pipelineColourspace('rgb16')
 *  .toColourspace('srgb')
 *  .toFile('16bpc-pipeline-to-8bpc-output.png')
 *
 * @param {string} [colourspace] - pipeline colourspace e.g. `rgb16`, `scrgb`, `lab`, `grey16` [...](https://github.com/libvips/libvips/blob/41cff4e9d0838498487a00623462204eb10ee5b8/libvips/iofuncs/enumtypes.c#L774)
 * @returns {Sharp}
 * @throws {Error} Invalid parameters
 */
function pipelineColourspace (colourspace) {
  if (!is.string(colourspace)) {
    throw is.invalidParameterError('colourspace', 'string', colourspace);
  }
  this.options.colourspaceInput = colourspace;
  return this;
}

/**
 * Alternative spelling of `pipelineColourspace`.
 * @param {string} [colorspace] - pipeline colorspace.
 * @returns {Sharp}
 * @throws {Error} Invalid parameters
 */
function pipelineColorspace (colorspace) {
  return this.pipelineColourspace(colorspace);
}

/**
 * Set the output colourspace.
 * By default output image will be web-friendly sRGB, with additional channels interpreted as alpha channels.
 *
 * @example
 * // Output 16 bits per pixel RGB
 * await sharp(input)
 *  .toColourspace('rgb16')
 *  .toFile('16-bpp.png')
 *
 * @param {string} [colourspace] - output colourspace e.g. `srgb`, `rgb`, `cmyk`, `lab`, `b-w` [...](https://github.com/libvips/libvips/blob/3c0bfdf74ce1dc37a6429bed47fa76f16e2cd70a/libvips/iofuncs/enumtypes.c#L777-L794)
 * @returns {Sharp}
 * @throws {Error} Invalid parameters
 */
function toColourspace (colourspace) {
  if (!is.string(colourspace)) {
    throw is.invalidParameterError('colourspace', 'string', colourspace);
  }
  this.options.colourspace = colourspace;
  return this;
}

/**
 * Alternative spelling of `toColourspace`.
 * @param {string} [colorspace] - output colorspace.
 * @returns {Sharp}
 * @throws {Error} Invalid parameters
 */
function toColorspace (colorspace) {
  return this.toColourspace(colorspace);
}

/**
 * Update a colour attribute of the this.options Object.
 * @private
 * @param {string} key
 * @param {string|Object} value
 * @throws {Error} Invalid value
 */
function _setBackgroundColourOption (key, value) {
  if (is.defined(value)) {
    if (is.object(value) || is.string(value)) {
      const colour = color(value);
      this.options[key] = [
        colour.red(),
        colour.green(),
        colour.blue(),
        Math.round(colour.alpha() * 255)
      ];
    } else {
      throw is.invalidParameterError('background', 'object or string', value);
    }
  }
}

/**
 * Decorate the Sharp prototype with colour-related functions.
 * @private
 */
module.exports = function (Sharp) {
  Object.assign(Sharp.prototype, {
    // Public
    tint,
    greyscale,
    grayscale,
    pipelineColourspace,
    pipelineColorspace,
    toColourspace,
    toColorspace,
    // Private
    _setBackgroundColourOption
  });
  // Class attributes
  Sharp.colourspace = colourspace;
  Sharp.colorspace = colourspace;
};