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120 lines
3.5 KiB
Markdown
120 lines
3.5 KiB
Markdown
<!-- Generated by documentation.js. Update this documentation by updating the source code. -->
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## removeAlpha
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Remove alpha channel, if any. This is a no-op if the image does not have an alpha channel.
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### Examples
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```javascript
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sharp('rgba.png')
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.removeAlpha()
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.toFile('rgb.png', function(err, info) {
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// rgb.png is a 3 channel image without an alpha channel
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});
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```
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Returns **Sharp**
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## ensureAlpha
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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.
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### Examples
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```javascript
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sharp('rgb.jpg')
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.ensureAlpha()
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.toFile('rgba.png', function(err, info) {
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// rgba.png is a 4 channel image with a fully opaque alpha channel
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});
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```
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Returns **Sharp**
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**Meta**
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- **since**: 0.21.2
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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][1] \| [String][2])** 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][3]** 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][4]<([String][2] \| [Buffer][5])> | [String][2] \| [Buffer][5])** one or more images (file paths, Buffers).
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- `options` **[Object][6]** image options, see `sharp()` constructor.
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- Throws **[Error][3]** 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][2]** 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][3]** Invalid parameters
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Returns **Sharp**
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[1]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number
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[2]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String
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[3]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Error
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[4]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Array
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[5]: https://nodejs.org/api/buffer.html
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[6]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object
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