sharp/docs/api-channel.md

removeAlpha

Remove alpha channel, if any. This is a no-op if the image does not have an alpha channel.

Examples

sharp('rgba.png')
  .removeAlpha()
  .toFile('rgb.png', function(err, info) {
    // rgb.png is a 3 channel image without an alpha channel
  });

Returns Sharp

ensureAlpha

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.

Examples

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

Meta

• since: 0.21.2

extractChannel

Extract a single channel from a multi-channel image.

Parameters

• channel (number | string) zero-indexed band number to extract, or red, green or blue as alternative to 0, 1 or 2 respectively.

Examples

sharp(input)
  .extractChannel('green')
  .toColourspace('b-w')
  .toFile('green.jpg', function(err, info) {
    // info.channels === 1
    // green.jpg is a greyscale image containing the green channel of the input
   });

• Throws Error Invalid channel

Returns Sharp

joinChannel

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.

Parameters

• images (Array<(string | Buffer)> | string | Buffer) one or more images (file paths, Buffers).

• options Object image options, see sharp() constructor.

• Throws Error Invalid parameters

Returns Sharp

bandbool

Perform a bitwise boolean operation on all input image channels (bands) to produce a single channel output image.

Parameters

• boolOp string one of and, or or eor to perform that bitwise operation, like the C logic operators &, | and ^ respectively.

Examples

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`.
  });

• Throws Error Invalid parameters

Returns Sharp