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sharp/docs/api-operation.md
Lovell Fuller f00928dedb Doc refresh for #1438 #1439
2018-11-11 17:40:19 +00:00

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<!-- Generated by documentation.js. Update this documentation by updating the source code. -->
## rotate
Rotate the output image by either an explicit angle
or auto-orient based on the EXIF `Orientation` tag.
If an angle is provided, it is converted to a valid positive degree rotation.
For example, `-450` will produce a 270deg rotation.
When rotating by an angle other than a multiple of 90,
the background colour can be provided with the `background` option.
If no angle is provided, it is determined from the EXIF data.
Mirroring is supported and may infer the use of a flip operation.
The use of `rotate` implies the removal of the EXIF `Orientation` tag, if any.
Method order is important when both rotating and extracting regions,
for example `rotate(x).extract(y)` will produce a different result to `extract(y).rotate(x)`.
### Parameters
- `angle` **[Number][1]** angle of rotation. (optional, default `auto`)
- `options` **[Object][2]?** if present, is an Object with optional attributes.
- `options.background` **([String][3] \| [Object][2])** parsed by the [color][4] module to extract values for red, green, blue and alpha. (optional, default `"#000000"`)
### Examples
```javascript
const pipeline = sharp()
.rotate()
.resize(null, 200)
.toBuffer(function (err, outputBuffer, info) {
// outputBuffer contains 200px high JPEG image data,
// auto-rotated using EXIF Orientation tag
// info.width and info.height contain the dimensions of the resized image
});
readableStream.pipe(pipeline);
```
- Throws **[Error][5]** Invalid parameters
Returns **Sharp**
## flip
Flip the image about the vertical Y axis. This always occurs after rotation, if any.
The use of `flip` implies the removal of the EXIF `Orientation` tag, if any.
### Parameters
- `flip` **[Boolean][6]** (optional, default `true`)
Returns **Sharp**
## flop
Flop the image about the horizontal X axis. This always occurs after rotation, if any.
The use of `flop` implies the removal of the EXIF `Orientation` tag, if any.
### Parameters
- `flop` **[Boolean][6]** (optional, default `true`)
Returns **Sharp**
## sharpen
Sharpen the image.
When used without parameters, performs a fast, mild sharpen of the output image.
When a `sigma` is provided, performs a slower, more accurate sharpen of the L channel in the LAB colour space.
Separate control over the level of sharpening in "flat" and "jagged" areas is available.
### Parameters
- `sigma` **[Number][1]?** the sigma of the Gaussian mask, where `sigma = 1 + radius / 2`.
- `flat` **[Number][1]** the level of sharpening to apply to "flat" areas. (optional, default `1.0`)
- `jagged` **[Number][1]** the level of sharpening to apply to "jagged" areas. (optional, default `2.0`)
- Throws **[Error][5]** Invalid parameters
Returns **Sharp**
## median
Apply median filter.
When used without parameters the default window is 3x3.
### Parameters
- `size` **[Number][1]** square mask size: size x size (optional, default `3`)
- Throws **[Error][5]** Invalid parameters
Returns **Sharp**
## blur
Blur the image.
When used without parameters, performs a fast, mild blur of the output image.
When a `sigma` is provided, performs a slower, more accurate Gaussian blur.
### Parameters
- `sigma` **[Number][1]?** a value between 0.3 and 1000 representing the sigma of the Gaussian mask, where `sigma = 1 + radius / 2`.
- Throws **[Error][5]** Invalid parameters
Returns **Sharp**
## flatten
Merge alpha transparency channel, if any, with a background.
### Parameters
- `options` **[Object][2]?**
- `options.background` **([String][3] \| [Object][2])** background colour, parsed by the [color][4] module, defaults to black. (optional, default `{r:0,g:0,b:0}`)
Returns **Sharp**
## gamma
Apply a gamma correction by reducing the encoding (darken) pre-resize at a factor of `1/gamma`
then increasing the encoding (brighten) post-resize at a factor of `gamma`.
This can improve the perceived brightness of a resized image in non-linear colour spaces.
JPEG and WebP input images will not take advantage of the shrink-on-load performance optimisation
when applying a gamma correction.
Supply a second argument to use a different output gamma value, otherwise the first value is used in both cases.
### Parameters
- `gamma` **[Number][1]** value between 1.0 and 3.0. (optional, default `2.2`)
- `gammaOut` **[Number][1]?** value between 1.0 and 3.0. (optional, defaults to same as `gamma`)
- Throws **[Error][5]** Invalid parameters
Returns **Sharp**
## negate
Produce the "negative" of the image.
### Parameters
- `negate` **[Boolean][6]** (optional, default `true`)
Returns **Sharp**
## normalise
Enhance output image contrast by stretching its luminance to cover the full dynamic range.
### Parameters
- `normalise` **[Boolean][6]** (optional, default `true`)
Returns **Sharp**
## normalize
Alternative spelling of normalise.
### Parameters
- `normalize` **[Boolean][6]** (optional, default `true`)
Returns **Sharp**
## convolve
Convolve the image with the specified kernel.
### Parameters
- `kernel` **[Object][2]**
- `kernel.width` **[Number][1]** width of the kernel in pixels.
- `kernel.height` **[Number][1]** width of the kernel in pixels.
- `kernel.kernel` **[Array][7]&lt;[Number][1]>** Array of length `width*height` containing the kernel values.
- `kernel.scale` **[Number][1]** the scale of the kernel in pixels. (optional, default `sum`)
- `kernel.offset` **[Number][1]** the offset of the kernel in pixels. (optional, default `0`)
### Examples
```javascript
sharp(input)
.convolve({
width: 3,
height: 3,
kernel: [-1, 0, 1, -2, 0, 2, -1, 0, 1]
})
.raw()
.toBuffer(function(err, data, info) {
// data contains the raw pixel data representing the convolution
// of the input image with the horizontal Sobel operator
});
```
- Throws **[Error][5]** Invalid parameters
Returns **Sharp**
## threshold
Any pixel value greather than or equal to the threshold value will be set to 255, otherwise it will be set to 0.
### Parameters
- `threshold` **[Number][1]** a value in the range 0-255 representing the level at which the threshold will be applied. (optional, default `128`)
- `options` **[Object][2]?**
- `options.greyscale` **[Boolean][6]** convert to single channel greyscale. (optional, default `true`)
- `options.grayscale` **[Boolean][6]** alternative spelling for greyscale. (optional, default `true`)
- Throws **[Error][5]** Invalid parameters
Returns **Sharp**
## boolean
Perform a bitwise boolean operation with operand image.
This operation creates an output image where each pixel is the result of
the selected bitwise boolean `operation` between the corresponding pixels of the input images.
### Parameters
- `operand` **([Buffer][8] \| [String][3])** Buffer containing image data or String containing the path to an image file.
- `operator` **[String][3]** one of `and`, `or` or `eor` to perform that bitwise operation, like the C logic operators `&`, `|` and `^` respectively.
- `options` **[Object][2]?**
- `options.raw` **[Object][2]?** describes operand when using raw pixel data.
- `options.raw.width` **[Number][1]?**
- `options.raw.height` **[Number][1]?**
- `options.raw.channels` **[Number][1]?**
- Throws **[Error][5]** Invalid parameters
Returns **Sharp**
## linear
Apply the linear formula a \* input + b to the image (levels adjustment)
### Parameters
- `a` **[Number][1]** multiplier (optional, default `1.0`)
- `b` **[Number][1]** offset (optional, default `0.0`)
- Throws **[Error][5]** Invalid parameters
Returns **Sharp**
[1]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number
[2]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object
[3]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String
[4]: https://www.npmjs.org/package/color
[5]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Error
[6]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Boolean
[7]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Array
[8]: https://nodejs.org/api/buffer.html
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