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111 lines
3.2 KiB
Markdown
111 lines
3.2 KiB
Markdown
<!-- Generated by documentation.js. Update this documentation by updating the source code. -->
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### Table of Contents
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- [extractChannel][1]
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- [Parameters][2]
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- [Examples][3]
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- [joinChannel][4]
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- [Parameters][5]
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- [bandbool][6]
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- [Parameters][7]
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- [Examples][8]
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## extractChannel
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Extract a single channel from a multi-channel image.
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### Parameters
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- `channel` **([Number][9] \| [String][10])** zero-indexed band number to extract, or `red`, `green` or `blue` as alternative to `0`, `1` or `2` respectively.
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### Examples
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```javascript
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sharp(input)
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.extractChannel('green')
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.toFile('input_green.jpg', function(err, info) {
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// info.channels === 1
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// input_green.jpg contains the green channel of the input image
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});
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```
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- Throws **[Error][11]** Invalid channel
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Returns **Sharp**
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## joinChannel
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Join one or more channels to the image.
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The meaning of the added channels depends on the output colourspace, set with `toColourspace()`.
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By default the output image will be web-friendly sRGB, with additional channels interpreted as alpha channels.
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Channel ordering follows vips convention:
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- sRGB: 0: Red, 1: Green, 2: Blue, 3: Alpha.
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- CMYK: 0: Magenta, 1: Cyan, 2: Yellow, 3: Black, 4: Alpha.
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Buffers may be any of the image formats supported by sharp: JPEG, PNG, WebP, GIF, SVG, TIFF or raw pixel image data.
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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.
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### Parameters
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- `images` **([Array][12]<([String][10] \| [Buffer][13])> | [String][10] \| [Buffer][13])** one or more images (file paths, Buffers).
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- `options` **[Object][14]** image options, see `sharp()` constructor.
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- Throws **[Error][11]** Invalid parameters
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Returns **Sharp**
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## bandbool
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Perform a bitwise boolean operation on all input image channels (bands) to produce a single channel output image.
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### Parameters
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- `boolOp` **[String][10]** one of `and`, `or` or `eor` to perform that bitwise operation, like the C logic operators `&`, `|` and `^` respectively.
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### Examples
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```javascript
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sharp('3-channel-rgb-input.png')
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.bandbool(sharp.bool.and)
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.toFile('1-channel-output.png', function (err, info) {
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// The output will be a single channel image where each pixel `P = R & G & B`.
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// If `I(1,1) = [247, 170, 14] = [0b11110111, 0b10101010, 0b00001111]`
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// then `O(1,1) = 0b11110111 & 0b10101010 & 0b00001111 = 0b00000010 = 2`.
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});
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```
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- Throws **[Error][11]** Invalid parameters
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Returns **Sharp**
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[1]: #extractchannel
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[2]: #parameters
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[3]: #examples
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[4]: #joinchannel
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[5]: #parameters-1
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[6]: #bandbool
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[7]: #parameters-2
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[8]: #examples-1
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[9]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number
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[10]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String
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[11]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Error
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[12]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Array
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[13]: https://nodejs.org/api/buffer.html
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[14]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object
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