sharp/docs/api.md

API

var sharp = require('sharp');

Input

sharp([input])

Constructor to which further methods are chained. input, if present, can be one of:

• Buffer containing JPEG, PNG, WebP, GIF* or TIFF image data, or
• String containing the path to an image file, with most major formats supported.

The object returned implements the stream.Duplex class.

JPEG, PNG, WebP, GIF* or TIFF format image data can be streamed into the object when input is not provided.

JPEG, PNG or WebP format image data can be streamed out from this object.

* libvips 8.0.0+ is required for Buffer/Stream input of GIF and other magick formats.

sharp('input.jpg')
  .resize(300, 200)
  .toFile('output.jpg', function(err) {
    // output.jpg is a 300 pixels wide and 200 pixels high image
    // containing a scaled and cropped version of input.jpg
  });

metadata([callback])

Fast access to image metadata without decoding any compressed image data.

callback, if present, gets the arguments (err, metadata) where metadata has the attributes:

• format: Name of decoder to be used to decompress image data e.g. jpeg, png, webp (for file-based input additionally tiff, magick and openslide)
• width: Number of pixels wide
• height: Number of pixels high
• space: Name of colour space interpretation e.g. srgb, rgb, scrgb, cmyk, lab, xyz, b-w ...
• channels: Number of bands e.g. 3 for sRGB, 4 for CMYK
• hasProfile: Boolean indicating the presence of an embedded ICC profile
• hasAlpha: Boolean indicating the presence of an alpha transparency channel
• orientation: Number value of the EXIF Orientation header, if present
• exif: Buffer containing raw EXIF data, if present
• icc: Buffer containing raw ICC profile data, if present

A Promises/A+ promise is returned when callback is not provided.

var image = sharp(inputJpg);
image
  .metadata()
  .then(function(metadata) {
    return image
      .resize(Math.round(metadata.width / 2))
      .webp()
      .toBuffer();
  })
  .then(function(data) {
    // data contains a WebP image half the width and height of the original JPEG
  });

clone()

Takes a "snapshot" of the instance, returning a new instance. Cloned instances inherit the input of their parent instance.

This allows multiple output Streams and therefore multiple processing pipelines to share a single input Stream.

var pipeline = sharp().rotate();
pipeline.clone().resize(800, 600).pipe(firstWritableStream);
pipeline.clone().extract(20, 20, 100, 100).pipe(secondWritableStream);
readableStream.pipe(pipeline);
// firstWritableStream receives auto-rotated, resized readableStream
// secondWritableStream receives auto-rotated, extracted region of readableStream

sequentialRead()

An advanced setting that switches the libvips access method to VIPS_ACCESS_SEQUENTIAL. This will reduce memory usage and can improve performance on some systems.

limitInputPixels(pixels)

Do not process input images where the number of pixels (width * height) exceeds this limit.

pixels is the integral Number of pixels, with a value between 1 and the default 268402689 (0x3FFF * 0x3FFF).

Resizing

resize([width], [height])

Scale output to width x height. By default, the resized image is cropped to the exact size specified.

width is the integral Number of pixels wide the resultant image should be, between 1 and 16383 (0x3FFF). Use null or undefined to auto-scale the width to match the height.

height is the integral Number of pixels high the resultant image should be, between 1 and 16383. Use null or undefined to auto-scale the height to match the width.

crop([gravity])

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

gravity, if present, is a String or an attribute of the sharp.gravity Object e.g. sharp.gravity.north.

Possible values are north, northeast, east, southeast, south, southwest, west, northwest, center and centre. The default gravity is center/centre.

var transformer = sharp()
  .resize(300, 200)
  .crop(sharp.gravity.north)
  .on('error', function(err) {
    console.log(err);
  });
// Read image data from readableStream, resize and write image data to writableStream
readableStream.pipe(transformer).pipe(writableStream);

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.

sharp('input.gif')
  .resize(200, 300)
  .background({r: 0, g: 0, b: 0, a: 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
  });

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.

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
  });

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.

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".

ignoreAspectRatio()

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

interpolateWith(interpolator)

Use the given interpolator for image resizing, where interpolator is an attribute of the sharp.interpolator Object e.g. sharp.interpolator.bicubic.

The default interpolator is bicubic, providing a general-purpose interpolator that is both fast and of good quality.

Possible interpolators, in order of performance, are:

• nearest: Use nearest neighbour interpolation, suitable for image enlargement only.
• bilinear: Use bilinear interpolation, faster than bicubic but with less smooth results.
• vertexSplitQuadraticBasisSpline: Use the smoother VSQBS interpolation to prevent "staircasing" when enlarging.
• bicubic: Use bicubic interpolation (the default).
• locallyBoundedBicubic: Use LBB interpolation, which prevents some "acutance" but typically reduces performance by a factor of 2.
• nohalo: Use Nohalo interpolation, which prevents acutance but typically reduces performance by a factor of 3.

Compare the output of these interpolators

sharp(inputBuffer)
  .resize(200, 300)
  .interpolateWith(sharp.interpolator.nohalo)
  .background('white')
  .embed()
  .toFile('output.tiff')
  .then(function() {
    // output.tiff is a 200 pixels wide and 300 pixels high image
    // containing a nohalo scaled version, embedded on a white canvas,
    // of the image data in inputBuffer
  });

Operations

extract(top, left, width, height)

Extract a region of the image. Can be used with or without a resize operation.

top and left are the offset, in pixels, from the top-left corner.

width and height are the dimensions of the extracted image.

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

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

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

background(rgba)

Set the background for the embed and flatten operations.

rgba is parsed by the color module to extract values for red, green, blue and alpha.

The alpha value is a float between 0 (transparent) and 1 (opaque).

The default background is {r: 0, g: 0, b: 0, a: 1}, black without transparency.

flatten()

Merge alpha transparency channel, if any, with background.

rotate([angle])

Rotate the output image by either an explicit angle or auto-orient based on the EXIF Orientation tag.

angle, if present, is a Number with a value of 0, 90, 180 or 270.

Use this method without angle to determine the angle from EXIF data. Mirroring is supported and may infer the use of a flip operation.

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).

The use of rotate implies the removal of the EXIF Orientation tag, if any.

var pipeline = sharp()
  .rotate()
  .resize(null, 200)
  .progressive()
  .toBuffer(function(err, outputBuffer, info) {
    if (err) {
      throw err;
    }
    // outputBuffer contains 200px high progressive JPEG image data,
    // auto-rotated using EXIF Orientation tag
    // info.width and info.height contain the dimensions of the resized image
  });
readableStream.pipe(pipeline);

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.

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.

blur([sigma])

When used without parameters, performs a fast, mild blur of the output image. This typically reduces performance by 10%.

When a sigma is provided, performs a slower, more accurate Gaussian blur. This typically reduces performance by 25%.

• sigma, if present, is a Number between 0.3 and 1000 representing the approximate blur radius in pixels.

sharpen([radius], [flat], [jagged])

When used without parameters, performs a fast, mild sharpen of the output image. This typically reduces performance by 10%.

When a radius 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. This typically reduces performance by 50%.

• radius, if present, is an integral Number representing the sharpen mask radius in pixels.
• flat, if present, is a Number representing the level of sharpening to apply to "flat" areas, defaulting to a value of 1.0.
• jagged, if present, is a Number representing the level of sharpening to apply to "jagged" areas, defaulting to a value of 2.0.

threshold([threshold])

Converts all pixels in the image to greyscale white or black. Any pixel greather-than-or-equal-to the threshold (0..255) will be white. All others will be black.

• threshold, if present, is a Number, representing the level above which pixels will be forced to white.

gamma([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.

gamma, if present, is a Number between 1 and 3. The default value is 2.2, a suitable approximation for sRGB images.

This can improve the perceived brightness of a resized image in non-linear colour spaces.

JPEG input images will not take advantage of the shrink-on-load performance optimisation when applying a gamma correction.

grayscale() / greyscale()

Convert to 8-bit greyscale; 256 shades of grey.

This is a linear operation. If the input image is in a non-linear colour space such as sRGB, use gamma() with greyscale() for the best results.

The output image will still be web-friendly sRGB and contain three (identical) channels.

normalize() / normalise()

Enhance output image contrast by stretching its luminance to cover the full dynamic range. This typically reduces performance by 30%.

overlayWith(path)

Experimental

Alpha composite image at path over the processed (resized, extracted) image. The dimensions of the two images must match.

• path is a String containing the path to an image file with an alpha channel.

sharp('input.png')
  .rotate(180)
  .resize(300)
  .flatten()
  .background('#ff6600')
  .overlayWith('overlay.png')
  .sharpen()
  .withMetadata()
  .quality(90)
  .webp()
  .toBuffer()
  .then(function(outputBuffer) {
    // outputBuffer contains upside down, 300px wide, alpha channel flattened
    // onto orange background, composited with overlay.png, sharpened,
    // with metadata, 90% quality WebP image data. Phew!
  });

Output

toFile(path, [callback])

path is a String containing the path to write the image data to. The format is inferred from the extension, with JPEG, PNG, WebP, TIFF and DZI supported.

callback, if present, is called with two arguments (err, info) where:

• err contains an error message, if any.
• info contains the output image format, size (bytes), width and height.

A Promises/A+ promise is returned when callback is not provided.

toBuffer([callback])

Write image data to a Buffer, the format of which will match the input image by default. JPEG, PNG and WebP are supported.

callback, if present, gets three arguments (err, buffer, info) where:

• err is an error message, if any.
• buffer is the output image data.
• info contains the output image format, size (bytes), width and height.

A Promises/A+ promise is returned when callback is not provided.

jpeg()

Use JPEG format for the output image.

png()

Use PNG format for the output image.

webp()

Use WebP format for the output image.

raw()

Requires libvips 7.42.0+

Provide raw, uncompressed uint8 (unsigned char) image data for Buffer and Stream based output.

The number of channels depends on the input image and selected options.

• 1 channel for images converted to greyscale(), with each byte representing one pixel.
• 3 channels for colour images without alpha transparency, with bytes ordered [red, green, blue, red, green, blue, etc.]).
• 4 channels for colour images with alpha transparency, with bytes ordered [red, green, blue, alpha, red, green, blue, alpha, etc.].

toFormat(format)

Convenience method for the above output format methods, where format is either:

• an attribute of the sharp.format Object e.g. sharp.format.jpeg, or
• a String containing jpeg, png, webp or raw.

quality(quality)

The output quality to use for lossy JPEG, WebP and TIFF output formats. The default quality is 80.

quality is a Number between 1 and 100.

progressive()

Use progressive (interlace) scan for JPEG and PNG output. This typically reduces compression performance by 30% but results in an image that can be rendered sooner when decompressed.

withMetadata([metadata])

Include all metadata (EXIF, XMP, IPTC) from the input image in the output image. This will also convert to and add the latest web-friendly v2 sRGB ICC profile.

The optional metadata parameter, if present, is an Object with the attributes to update. New attributes cannot be inserted, only existing attributes updated.

• orientation is an integral Number between 0 and 7, used to update the value of the EXIF Orientation tag. This has no effect if the input image does not have an EXIF Orientation tag.

The default behaviour, when withMetadata is not used, is to strip all metadata and convert to the device-independent sRGB colour space.

tile([size], [overlap])

The size and overlap, in pixels, of square Deep Zoom image pyramid tiles.

• size is an integral Number between 1 and 8192. The default value is 256 pixels.
• overlap is an integral Number between 0 and 8192. The default value is 0 pixels.

sharp('input.tiff').tile(256).toFile('output.dzi', function(err, info) {
  // The output.dzi file is the XML format Deep Zoom definition
  // The output_files directory contains 256x256 pixel tiles grouped by zoom level
});

withoutChromaSubsampling()

Disable the use of chroma subsampling with JPEG output (4:4:4).

This can improve colour representation at higher quality settings (90+), but usually increases output file size and typically reduces performance by 25%.

The default behaviour is to use chroma subsampling (4:2:0).

compressionLevel(compressionLevel)

An advanced setting for the zlib compression level of the lossless PNG output format. The default level is 6.

compressionLevel is a Number between 0 and 9.

withoutAdaptiveFiltering()

Requires libvips 7.42.0+

An advanced setting to disable adaptive row filtering for the lossless PNG output format.

trellisQuantisation() / trellisQuantization()

Requires libvips 8.0.0+ compiled against mozjpeg 3.0+

An advanced setting to apply the use of trellis quantisation with JPEG output. Reduces file size and slightly increases relative quality at the cost of increased compression time.

overshootDeringing()

Requires libvips 8.0.0+ compiled against mozjpeg 3.0+

An advanced setting to reduce the effects of ringing in JPEG output, in particular where black text appears on a white background (or vice versa).

optimiseScans() / optimizeScans()

Requires libvips 8.0.0+ compiled against mozjpeg 3.0+

An advanced setting for progressive (interlace) JPEG output. Calculates which spectrum of DCT coefficients uses the fewest bits. Usually reduces file size at the cost of increased compression time.

Attributes

format

An Object containing nested boolean values representing the available input and output formats/methods, for example:

> console.dir(sharp.format);

{ jpeg: { id: 'jpeg',
    input: { file: true, buffer: true, stream: true },
    output: { file: true, buffer: true, stream: true } },
  png: { id: 'png',
    input: { file: true, buffer: true, stream: true },
    output: { file: true, buffer: true, stream: true } },
  webp: { id: 'webp',
    input: { file: true, buffer: true, stream: true },
    output: { file: true, buffer: true, stream: true } },
  tiff: { id: 'tiff',
    input: { file: true, buffer: true, stream: true },
    output: { file: true, buffer: false, stream: false } },
  magick: { id: 'magick',
    input: { file: true, buffer: true, stream: true },
    output: { file: false, buffer: false, stream: false } },
  raw: { id: 'raw',
    input: { file: false, buffer: false, stream: false },
    output: { file: false, buffer: true, stream: true } } }

queue

An EventEmitter that emits a change event when a task is either:

• queued, waiting for libuv to provide a worker thread
• complete

sharp.queue.on('change', function(queueLength) {
  console.log('Queue contains ' + queueLength + ' task(s)');
});

Utilities

sharp.cache([memory], [items])

If memory or items are provided, set the limits of libvips' operation cache.

• memory is the maximum memory in MB to use for this cache, with a default value of 100
• items is the maximum number of operations to cache, with a default value of 500

This method always returns cache statistics, useful for determining how much working memory is required for a particular task.

var stats = sharp.cache(); // { current: 75, high: 99, memory: 100, items: 500 }
sharp.cache(200); // { current: 75, high: 99, memory: 200, items: 500 }
sharp.cache(50, 200); // { current: 49, high: 99, memory: 50, items: 200}

sharp.concurrency([threads])

threads, if provided, is the Number of threads libvips' should create for processing each image. The default value is the number of CPU cores. A value of 0 will reset to this default.

This method always returns the current concurrency.

var threads = sharp.concurrency(); // 4
sharp.concurrency(2); // 2
sharp.concurrency(0); // 4

The maximum number of images that can be processed in parallel is limited by libuv's UV_THREADPOOL_SIZE environment variable.

sharp.counters()

Provides access to internal task counters.

• queue is the number of tasks this module has queued waiting for libuv to provide a worker thread from its pool.
• process is the number of resize tasks currently being processed.

var counters = sharp.counters(); // { queue: 2, process: 4 }