Thumbhash

This is a pure Elixir implementation of ThumbHash.

中文教程

Current status

Which only implements the encoding-related APIs, without decoding functionality. During the alpha release phase, the API may undergo incompatible changes.

Preview

File	Original	Placeholder	base64
flower.jpg			k0oGLQaSVsN0BVhn2oq2Z5SQUQcZ

Installation

Add Thumbhash to your mix.exs dependencies:

def deps do
  [
    {:thumbhash, "~> 0.1.0-alpha.0"},
  ]
end

Usage

Example (use Image to get image data):

image = Image.open!(Path.join("img", "flower.jpg"))

rgba =
  if Image.has_alpha?(image) do
    {:ok, data} = Vix.Vips.Image.write_to_binary(image)
    :binary.bin_to_list(data)
  else
    image = Image.add_alpha!(image, 255) # If there is no alpha channel, add a fixed value of 255.

    {:ok, data} = Vix.Vips.Image.write_to_binary(image)
    :binary.bin_to_list(data)
  end

bin = Thumbhash.rgba_to_thumb_hash(75, 100, :array.from_list(rgba))

# Encode the data as a string (base64).
Base.encode64(bin) # => "k0oGLQaSVsN0BVhn2oq2Z5SQUQcZ"

As shown in the code above, you have to get the RGBA data of the image manually, as this library only performs calculations and does not handle image files.

Additionally, you cannot lose the alpha channel data. Even for non-transparent images, the alpha value must be filled in for every pixel.

Benchmark

Name                           ips        average  deviation         median         99th %
rgba_to_thumb_hash/3         55.17       18.13 ms    ±16.46%       16.57 ms       28.34 ms