Vix

Vix is an Elixir extension for the libvips image processing library.

About libvips from its documentation:

libvips is a demand-driven, horizontally threaded image processing library. Compared to similar libraries, libvips runs quickly and uses little memory.

About Vix

Vix is a NIF-based bindings library for libvips.

Major Features:

• Vix can take full advantage of libvips optimizations, such as joining operations in the pipeline and caching, since Vix is a native binding.
• Experimental support for streaming. User can read or write images without keeping the complete image in memory. See Vix.Vips.Image.new_from_enum/1 and Vix.Vips.Image.write_to_stream/2
• Efficient interoperability (zero-copy) with other libraries, such as Nx and eVision. See Vix.Vips.Image.new_from_binary/5 and Vix.Vips.Image.write_to_tensor/1
• By default, Vix provides pre-built NIF and libvips binaries for major platforms, so don't worry about handling the libvips dependencies or compiling the NIF. Just add Vix and you are good to go! See below for more details.
• Ergonomic bindings with auto-generated documentation for operations using vips introspection, so they always match the installed libvips version. If a newer libvips version updates adds or modify operations, you don't have to wait for Vix to be updated — bindings for the operations (along with documentation) will be available automatically.

Check Vips operation documentation for the list of available operations and type specifications.

Pre-compiled NIF and libvips

Starting from v0.16.0, Vix can use either pre-built binaries or platform-provided binaries.

By default, Vix provides pre-built NIF and libvips and uses them for operations. This makes deployment and release of your application simple. No need to install any compiler toolchain or dependencies to use Vix. Pre-built libvips supports reading these formats: SVG, PNG, TIFF, JPEG, WEBP, RAW, HEIF, and GIF. If you find that the pre-built libvips is missing support for an image format, you can bring your own libvips by installing it manually and configuring Vix to use that instead. Vix makes sure to generate relevant functions and documentation based on the dependencies you bring. For example, if you install libvips with dzsave support, Vix will generate dzsave bindings for you.

You can choose this using the environmental variable, VIX_COMPILATION_MODE. This variable must be set during compilation and at runtime. Possible values are:

• PRECOMPILED_NIF_AND_LIBVIPS (Default): Uses the Vix-provided NIF and libvips. No need to install any additional dependencies. Big thanks to the sharp library maintainers, which pre-compiled libvips is based on: https://github.com/lovell/sharp-libvips/.

  Run the command below to generate the required checksum.exs file.

  MIX_ENV=dev mix elixir_make.checksum --all --ignore-unavailable

• PLATFORM_PROVIDED_LIBVIPS: Uses the platform-provided libvips. NIF will be compiled during compilation phase. Install the required build tools to compile the NIF. To build a NIF you need the following:

  • libvips with development headers
    • macOS: using brew brew install libvips
    • Linux: using deb apt install libvips-dev For more details see https://www.libvips.org/install.html
  • pkg-config
  • C compiler

Should I use Vix or Image?

Vix is focused on bridging the BEAM and libvips. It tries to stay close to the libvips interface in order to support a large set of use cases, so some basic operations might feel unintuitive. Image, an excellent library by @kipcole9, builds on top of Vix and provides more Elixir-friendly wrapper functions for common operations, along with many additional features: handling Exif, Math operators, and more. And all of this is accompanied by good documentation, so for most, using Vix via Image might be better choice.

Introduction

The easiest way to get started or explore the operations is to run the Introduction Livebook.

# print vips version
IO.puts("Version: " <> Vix.Vips.version())

# contains image read/write functions
alias Vix.Vips.Image

# Reading an image from a file. Note that the image is not actually loaded into memory at this point.
# `img` is an `%Image{}` struct.
{:ok, img} = Image.new_from_file("~/Downloads/kitty.png")

# You can also load an image from a binary, so you can work with images without touching the file system.
# It tries to guess the image format from the binary and uses the correct loader.

bin = File.read!("~/Downloads/kitty.png")
{:ok, %Image{} = img} = Image.new_from_buffer(bin)

# If you know image format beforehand, you can use the appropriate function from
# `Vix.Vips.Operation`. For example, use `Vix.Vips.Operation.pngload_buffer/2` to load a PNG.

bin = File.read!("~/Downloads/kitty.png")
{:ok, {img, _flags}} = Vix.Vips.Operation.pngload_buffer(bin)

# writing an `Image` to a file.
# Image type selected based on the image path extension. See documentation for more options
:ok = Image.write_to_file(img, "kitty.jpg[Q=90]")

# let's print the image dimensions
IO.puts("Width: #{Image.width(img)}")
IO.puts("Height: #{Image.height(img)}")


# Operations

# contains image processing operations
alias Vix.Vips.Operation

# getting a rectangular region from the image (crop)
{:ok, extract_img} = Operation.extract_area(img, 100, 50, 200, 200)

# create image thumbnail
#
# This operation is significantly faster than normal resize
# due to several optimizations such as shrink-on-load.
# You can read more about it in the libvips docs: https://github.com/libvips/libvips/wiki/HOWTO----Image-shrinking
#
# Check Vix docs for more details about several optional parameters
width = 100
{:ok, thumb} = Operation.thumbnail("~/Downloads/dog.jpg", width)


# resize the image to 400x600. `resize` function accepts scaling factor.
# Skip `vscale` if you want to preserve aspect ratio
hscale = 400 / Image.width(img)
vscale = 600 / Image.height(img)
{:ok, resized_img} = Operation.resize(img, hscale, vscale: vscale)

# flip the image
{:ok, flipped_img} = Operation.flip(img, :VIPS_DIRECTION_HORIZONTAL)

# Gaussian blur
{:ok, blurred_img} = Operation.gaussblur(img, 5)

# convert the image to grayscale
{:ok, bw_img} = Operation.colourspace(img, :VIPS_INTERPRETATION_B_W)

# adding gray border
{:ok, extended_img} =
  Operation.embed(img, 10, 10, Image.width(img) + 20, Image.height(img) + 20,
    extend: :VIPS_EXTEND_BACKGROUND,
    background: [128]
  )

# rotate the image 90 degrees clockwise
{:ok, rotated_img} = Operation.rot(img, :VIPS_ANGLE_D90)

# join two images horizontally
{:ok, main_img} = Image.new_from_file("~/Downloads/kitten.svg")
{:ok, joined_img} = Operation.join(img, main_img, :VIPS_DIRECTION_HORIZONTAL, expand: true)

# render text as image
# see https://libvips.github.io/libvips/API/current/libvips-create.html#vips-text for more details
{:ok, {text, _}} = Operation.text(~s(<b>Vix</b> is <span foreground="red">awesome!</span>), dpi: 300, rgba: true)
# add text to an image
{:ok, img_with_text} = Operation.composite2(img, text, :VIPS_BLEND_MODE_OVER, x: 50, y: 20)


## Creating GIF
black = Operation.black!(500, 500, bands: 3)

# create images with different grayscale values
frames = Enum.map(1..255//10, fn n ->
  Operation.linear!(black, [1], [n/255,n/255,n/255])
end)

{:ok, joined_img} = Operation.arrayjoin(frames, across: 1)

# set frame delay metadata. See `Image.mutate` documentation for more details
{:ok, joined_img} =
  Image.mutate(joined_img, fn mut_img ->
    frame_delay = List.duplicate(100, length(frames))
    :ok = Vix.Vips.MutableImage.set(mut_img, "delay", :VipsArrayInt, frame_delay)
  end)

:ok = Operation.gifsave(joined_img, Path.expand("~/Downloads/bw.gif"), "page-height": 500)

The libvips reference manual has more detailed documentation about the operations.

Livebooks

• Livebook implementing picture language defined in Structural and Interpretation of Computer Programs section 2.2.4.

• Creating Rainbow. Quick introduction to complex numbers and operations mapim and buildlut.

• Auto correct Document Rotation. Quick introduction to Fourier Transformation, Complex planes, and Arithmetic Operations.

NIF Error Logging

Vix NIF code writes logs to stderr on certain errors. This is disabled by default. To enable logging set VIX_LOG_ERROR environment variable to true.

Installation

def deps do
  [
    {:vix, "~> x.x.x"}
  ]
end