Operations

A mandatory operation when requesting an image.

This provides a list of optional operations for transforming an image.

Affine

Perform an affine transform on an image. You must provide a matrix array of length 4 affine transformation matrix.

By default, new pixels are filled with a black background. You can provide a background color with the background option. A particular interpolator may also be specified via the interpolator option.

Options

Example

{ "operation": "affine", "matrix": [1, 0.3, 0.1, 0.7] }

Blur

Blur the image. When used without options, performs a fast, mild blur of the output image.

When a sigma is provided, performs a slower, more accurate Gaussian blur.

Options

Example

{ "operation": "blur", "sigma": 10 }

Clahe

Perform contrast limiting adaptive histogram equalization (CLAHE)

This will, in general, enhance the clarity of the image by bringing out darker details.

Options

Example

{ "operation": "clahe", "width": 3, "height": 3 }

Colorspace

Output colourspace e.g. srgb, rgb, cmyk, lab, b-w ...

Options

Composite

Composite an image over the base image. The image to composite must be the same size or smaller than the base image.

If both top and left options are provided, they take precedence over gravity.

Options

Convolve

Convolve the image with the specified kernel.

Options

Example

{
  "operation": "convolve",
  "width": 3,
  "height": 3,
  "kernel": [-1, 0, 1, -2, 0, 2, -1, 0, 1]
}

Extend

Extends/pads the edges of the image with the provided background colour.

This operation will always occur after resizing and extraction, if any.

Options

Example

{
  "operation": "extend",
  "top": 42,
  "bottom": 84,
  "left": 16,
  "right": 16,
  "background": "#FFA03F"
}

Extract

Zero-indexed offset in pixels from the top edge.

Options

Flatten

Merge alpha transparency channel, if any, with a background, then remove the alpha channel.

Options

Flip

Flip the image about the vertical Y axis.

Options

No options available

Example

{ "operation": "flip" }

Flop

Flop the image about the horizontal X axis.

Options

No options available

Example

{ "operation": "flop" }

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 optimization when applying a gamma correction.

Options

Example

{ "operation": "gamma", "gamma": 2.2, "gammaOut": 2.2 }

Grayscale

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 optimization when applying a gamma correction.

Options

Example

{ "operation": "grayscale" }

Linear

Apply the linear formula a * input + b to the image (levels adjustment).

Options

Example

{ "operation": "linear", "a": 4, "b": 8 }

Median

Square mask size: size x size.

Note larger sizes can significantly reduce the performance of processing image e.g. a size of 15 on a 500x500 image adds around 1.5s to processing time.

Options

Example

{ "operation": "median", "size": 3 }

Modulate

Transforms the image using brightness, saturation and hue rotation.

Options

Example

{
  "operation": "modulate",
  "brightness": 0.5,
  "saturation": 0.5,
  "hue": 90
}

Negate

Produce a "negative" of the image.

Options

No options available

Example

{ "operation": "negate" }

Recomb

Transforms the image using brightness, saturation and hue rotation.

The matrix option is an array of 3 arrays with 3 numbers values.

Options

Example

{
  "operation": "recomb",
  "matrix": [
    [0.3588, 0.7044, 0.1368],
    [0.299, 0.587, 0.114],
    [0.2392, 0.4696, 0.0912]
  ]
}

Resize

How the image should be resized to fit both provided dimensions.

Options

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.

Options

Example

{ "operation": "rotate", "angle": 20 }

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.

Options

Example

{ "operation": "sharpen", "sigma": 1000 }

Text

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.

Options

Threshhold

Any pixel value greater than or equal to the threshold value will be set to 255, otherwise it will be set to 0.

Options

Example

{ "operation": "threshold", "threshold": 128 }

Tint

Tint the image using the provided chroma while preserving the image luminance.

An alpha channel if present will be unchanged by the operation.

Options

Trim

Trim "boring" pixels from all edges that contain values similar to the top-left pixel. Images consisting entirely of a single colour will calculate "boring" using the alpha channel, if any.

Options