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## resize

Resize image to `width` x `height`.
By default, the resized image is centre cropped to the exact size specified.

Possible kernels are:

-   `nearest`: Use [nearest neighbour interpolation][1].
-   `cubic`: Use a [Catmull-Rom spline][2].
-   `lanczos2`: Use a [Lanczos kernel][3] with `a=2`.
-   `lanczos3`: Use a Lanczos kernel with `a=3` (the default).

### Parameters

-   `width` **[Number][4]?** pixels wide the resultant image should be. Use `null` or `undefined` to auto-scale the width to match the height.
-   `height` **[Number][4]?** pixels high the resultant image should be. Use `null` or `undefined` to auto-scale the height to match the width.
-   `options` **[Object][5]?** 
    -   `options.kernel` **[String][6]** the kernel to use for image reduction. (optional, default `'lanczos3'`)
    -   `options.fastShrinkOnLoad` **[Boolean][7]** take greater advantage of the JPEG and WebP shrink-on-load feature, which can lead to a slight moiré pattern on some images. (optional, default `true`)

### Examples

```javascript
sharp(inputBuffer)
  .resize(200, 300, {
    kernel: sharp.kernel.nearest
  })
  .background('white')
  .embed()
  .toFile('output.tiff')
  .then(function() {
    // output.tiff is a 200 pixels wide and 300 pixels high image
    // containing a nearest-neighbour scaled version, embedded on a white canvas,
    // of the image data in inputBuffer
  });
```

-   Throws **[Error][8]** Invalid parameters

Returns **Sharp** 

## crop

Crop the resized image to the exact size specified, the default behaviour.

Possible attributes of the optional `sharp.gravity` are `north`, `northeast`, `east`, `southeast`, `south`,
`southwest`, `west`, `northwest`, `center` and `centre`.

The experimental strategy-based approach resizes so one dimension is at its target length
then repeatedly ranks edge regions, discarding the edge with the lowest score based on the selected strategy.

-   `entropy`: focus on the region with the highest [Shannon entropy][9].
-   `attention`: focus on the region with the highest luminance frequency, colour saturation and presence of skin tones.

### Parameters

-   `crop` **[String][6]** A member of `sharp.gravity` to crop to an edge/corner or `sharp.strategy` to crop dynamically. (optional, default `'centre'`)

### Examples

```javascript
const transformer = sharp()
  .resize(200, 200)
  .crop(sharp.strategy.entropy)
  .on('error', function(err) {
    console.log(err);
  });
// Read image data from readableStream
// Write 200px square auto-cropped image data to writableStream
readableStream.pipe(transformer).pipe(writableStream);
```

-   Throws **[Error][8]** Invalid parameters

Returns **Sharp** 

## embed

Preserving aspect ratio, resize the image to the maximum `width` or `height` specified
then embed on a background of the exact `width` and `height` specified.

If the background contains an alpha value then WebP and PNG format output images will
contain an alpha channel, even when the input image does not.

### Parameters

-   `embed` **[String][6]** A member of `sharp.gravity` to embed to an edge/corner. (optional, default `'centre'`)

### Examples

```javascript
sharp('input.gif')
  .resize(200, 300)
  .background({r: 0, g: 0, b: 0, alpha: 0})
  .embed()
  .toFormat(sharp.format.webp)
  .toBuffer(function(err, outputBuffer) {
    if (err) {
      throw err;
    }
    // outputBuffer contains WebP image data of a 200 pixels wide and 300 pixels high
    // containing a scaled version, embedded on a transparent canvas, of input.gif
  });
```

-   Throws **[Error][8]** Invalid parameters

Returns **Sharp** 

## max

Preserving aspect ratio, resize the image to be as large as possible
while ensuring its dimensions are less than or equal to the `width` and `height` specified.

Both `width` and `height` must be provided via `resize` otherwise the behaviour will default to `crop`.

### Examples

```javascript
sharp(inputBuffer)
  .resize(200, 200)
  .max()
  .toFormat('jpeg')
  .toBuffer()
  .then(function(outputBuffer) {
    // outputBuffer contains JPEG image data no wider than 200 pixels and no higher
    // than 200 pixels regardless of the inputBuffer image dimensions
  });
```

Returns **Sharp** 

## min

Preserving aspect ratio, resize the image to be as small as possible
while ensuring its dimensions are greater than or equal to the `width` and `height` specified.

Both `width` and `height` must be provided via `resize` otherwise the behaviour will default to `crop`.

Returns **Sharp** 

## ignoreAspectRatio

Ignoring the aspect ratio of the input, stretch the image to
the exact `width` and/or `height` provided via `resize`.

Returns **Sharp** 

## withoutEnlargement

Do not enlarge the output image if the input image width _or_ height are already less than the required dimensions.
This is equivalent to GraphicsMagick's `>` geometry option:
"_change the dimensions of the image only if its width or height exceeds the geometry specification_".
Use with `max()` to preserve the image's aspect ratio.

The default behaviour _before_ function call is `false`, meaning the image will be enlarged.

### Parameters

-   `withoutEnlargement` **[Boolean][7]**  (optional, default `true`)

Returns **Sharp** 

## extend

Extends/pads the edges of the image with the colour provided to the `background` method.
This operation will always occur after resizing and extraction, if any.

### Parameters

-   `extend` **([Number][4] \| [Object][5])** single pixel count to add to all edges or an Object with per-edge counts
    -   `extend.top` **[Number][4]?** 
    -   `extend.left` **[Number][4]?** 
    -   `extend.bottom` **[Number][4]?** 
    -   `extend.right` **[Number][4]?** 

### Examples

```javascript
// Resize to 140 pixels wide, then add 10 transparent pixels
// to the top, left and right edges and 20 to the bottom edge
sharp(input)
  .resize(140)
  .background({r: 0, g: 0, b: 0, alpha: 0})
  .extend({top: 10, bottom: 20, left: 10, right: 10})
  ...
```

-   Throws **[Error][8]** Invalid parameters

Returns **Sharp** 

## extract

Extract a region of the image.

-   Use `extract` before `resize` for pre-resize extraction.
-   Use `extract` after `resize` for post-resize extraction.
-   Use `extract` before and after for both.

### Parameters

-   `options` **[Object][5]** 
    -   `options.left` **[Number][4]** zero-indexed offset from left edge
    -   `options.top` **[Number][4]** zero-indexed offset from top edge
    -   `options.width` **[Number][4]** dimension of extracted image
    -   `options.height` **[Number][4]** dimension of extracted image

### Examples

```javascript
sharp(input)
  .extract({ left: left, top: top, width: width, height: height })
  .toFile(output, function(err) {
    // Extract a region of the input image, saving in the same format.
  });
```

```javascript
sharp(input)
  .extract({ left: leftOffsetPre, top: topOffsetPre, width: widthPre, height: heightPre })
  .resize(width, height)
  .extract({ left: leftOffsetPost, top: topOffsetPost, width: widthPost, height: heightPost })
  .toFile(output, function(err) {
    // Extract a region, resize, then extract from the resized image
  });
```

-   Throws **[Error][8]** Invalid parameters

Returns **Sharp** 

## trim

Trim "boring" pixels from all edges that contain values within a percentage similarity of the top-left pixel.

### Parameters

-   `tolerance` **[Number][4]** value between 1 and 99 representing the percentage similarity. (optional, default `10`)


-   Throws **[Error][8]** Invalid parameters

Returns **Sharp** 

[1]: http://en.wikipedia.org/wiki/Nearest-neighbor_interpolation

[2]: https://en.wikipedia.org/wiki/Centripetal_Catmull%E2%80%93Rom_spline

[3]: https://en.wikipedia.org/wiki/Lanczos_resampling#Lanczos_kernel

[4]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number

[5]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object

[6]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String

[7]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Boolean

[8]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Error

[9]: https://en.wikipedia.org/wiki/Entropy_%28information_theory%29
