sharp/lib/channel.js

High performance Node.js image processing, the fastest module to resize JPEG, PNG, WebP and TIFF images

'use strict';

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

/**
 * Boolean operations for bandbool.
 * @private
 */
const bool = {
  and: 'and',
  or: 'or',
  eor: 'eor'
};

/**
 * Remove alpha channel, if any. This is a no-op if the image does not have an alpha channel.
 *
 * @example
 * sharp('rgba.png')
 *   .removeAlpha()
 *   .toFile('rgb.png', function(err, info) {
 *     // rgb.png is a 3 channel image without an alpha channel
 *   });
 *
 * @returns {Sharp}
 */
function removeAlpha () {
  this.options.removeAlpha = true;
  return this;
}

/**
 * Ensure alpha channel, if missing. The added alpha channel will be fully opaque. This is a no-op if the image already has an alpha channel.
 *
 * @example
 * sharp('rgb.jpg')
 *   .ensureAlpha()
 *   .toFile('rgba.png', function(err, info) {
 *     // rgba.png is a 4 channel image with a fully opaque alpha channel
 *   });
 *
 * @returns {Sharp}
 */
function ensureAlpha () {
  this.options.ensureAlpha = true;
  return this;
}

/**
 * Extract a single channel from a multi-channel image.
 *
 * @example
 * sharp(input)
 *   .extractChannel('green')
 *   .toFile('input_green.jpg', function(err, info) {
 *     // info.channels === 1
 *     // input_green.jpg contains the green channel of the input image
 *    });
 *
 * @param {Number|String} channel - zero-indexed band number to extract, or `red`, `green` or `blue` as alternative to `0`, `1` or `2` respectively.
 * @returns {Sharp}
 * @throws {Error} Invalid channel
 */
function extractChannel (channel) {
  if (channel === 'red') {
    channel = 0;
  } else if (channel === 'green') {
    channel = 1;
  } else if (channel === 'blue') {
    channel = 2;
  }
  if (is.integer(channel) && is.inRange(channel, 0, 4)) {
    this.options.extractChannel = channel;
  } else {
    throw is.invalidParameterError('channel', 'integer or one of: red, green, blue', channel);
  }
  return this;
}

/**
 * Join one or more channels to the image.
 * The meaning of the added channels depends on the output colourspace, set with `toColourspace()`.
 * By default the output image will be web-friendly sRGB, with additional channels interpreted as alpha channels.
 * Channel ordering follows vips convention:
 * - sRGB: 0: Red, 1: Green, 2: Blue, 3: Alpha.
 * - CMYK: 0: Magenta, 1: Cyan, 2: Yellow, 3: Black, 4: Alpha.
 *
 * Buffers may be any of the image formats supported by sharp: JPEG, PNG, WebP, GIF, SVG, TIFF or raw pixel image data.
 * For raw pixel input, the `options` object should contain a `raw` attribute, which follows the format of the attribute of the same name in the `sharp()` constructor.
 *
 * @param {Array<String|Buffer>|String|Buffer} images - one or more images (file paths, Buffers).
 * @param {Object} options - image options, see `sharp()` constructor.
 * @returns {Sharp}
 * @throws {Error} Invalid parameters
 */
function joinChannel (images, options) {
  if (Array.isArray(images)) {
    images.forEach(function (image) {
      this.options.joinChannelIn.push(this._createInputDescriptor(image, options));
    }, this);
  } else {
    this.options.joinChannelIn.push(this._createInputDescriptor(images, options));
  }
  return this;
}

/**
 * Perform a bitwise boolean operation on all input image channels (bands) to produce a single channel output image.
 *
 * @example
 * sharp('3-channel-rgb-input.png')
 *   .bandbool(sharp.bool.and)
 *   .toFile('1-channel-output.png', function (err, info) {
 *     // The output will be a single channel image where each pixel `P = R & G & B`.
 *     // If `I(1,1) = [247, 170, 14] = [0b11110111, 0b10101010, 0b00001111]`
 *     // then `O(1,1) = 0b11110111 & 0b10101010 & 0b00001111 = 0b00000010 = 2`.
 *   });
 *
 * @param {String} boolOp - one of `and`, `or` or `eor` to perform that bitwise operation, like the C logic operators `&`, `|` and `^` respectively.
 * @returns {Sharp}
 * @throws {Error} Invalid parameters
 */
function bandbool (boolOp) {
  if (is.string(boolOp) && is.inArray(boolOp, ['and', 'or', 'eor'])) {
    this.options.bandBoolOp = boolOp;
  } else {
    throw is.invalidParameterError('boolOp', 'one of: and, or, eor', boolOp);
  }
  return this;
}

/**
 * Decorate the Sharp prototype with channel-related functions.
 * @private
 */
module.exports = function (Sharp) {
  Object.assign(Sharp.prototype, {
    // Public instance functions
    removeAlpha,
    ensureAlpha,
    extractChannel,
    joinChannel,
    bandbool
  });
  // Class attributes
  Sharp.bool = bool;
};