channel.js

'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.
 *
 * See also {@link /api-operation#flatten|flatten}.
 *
 * @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 the output image has an alpha transparency channel.
 * If missing, the added alpha channel will have the specified
 * transparency level, defaulting to fully-opaque (1).
 * This is a no-op if the image already has an alpha channel.
 *
 * @since 0.21.2
 *
 * @example
 * // rgba.png will be a 4 channel image with a fully-opaque alpha channel
 * await sharp('rgb.jpg')
 *   .ensureAlpha()
 *   .toFile('rgba.png')
 *
 * @example
 * // rgba is a 4 channel image with a fully-transparent alpha channel
 * const rgba = await sharp(rgb)
 *   .ensureAlpha(0)
 *   .toBuffer();
 *
 * @param {number} [alpha=1] - alpha transparency level (0=fully-transparent, 1=fully-opaque)
 * @returns {Sharp}
 * @throws {Error} Invalid alpha transparency level
 */
function ensureAlpha (alpha) {
  if (is.defined(alpha)) {
    if (is.number(alpha) && is.inRange(alpha, 0, 1)) {
      this.options.ensureAlpha = alpha;
    } else {
      throw is.invalidParameterError('alpha', 'number between 0 and 1', alpha);
    }
  } else {
    this.options.ensureAlpha = 1;
  }
  return this;
}

/**
 * Extract a single channel from a multi-channel image.
 *
 * @example
 * // green.jpg is a greyscale image containing the green channel of the input
 * await sharp(input)
 *   .extractChannel('green')
 *   .toFile('green.jpg');
 *
 * @example
 * // red1 is the red value of the first pixel, red2 the second pixel etc.
 * const [red1, red2, ...] = await sharp(input)
 *   .extractChannel(0)
 *   .raw()
 *   .toBuffer();
 *
 * @param {number|string} channel - zero-indexed channel/band number to extract, or `red`, `green`, `blue` or `alpha`.
 * @returns {Sharp}
 * @throws {Error} Invalid channel
 */
function extractChannel (channel) {
  const channelMap = { red: 0, green: 1, blue: 2, alpha: 3 };
  if (Object.keys(channelMap).includes(channel)) {
    channel = channelMap[channel];
  }
  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, alpha', 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.
 * 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;
};