# Thumbhash
This is a pure Elixir implementation of [ThumbHash](https://github.com/evanw/thumbhash).
## 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:
```elixir
def deps do
[
{:thumbhash, "~> 0.1.0-alpha.0"},
]
end
```
## Usage
Example (use [`Image`](https://github.com/elixir-image/image) to get image data):
```elixir
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
```plaintext
Name ips average deviation median 99th %
rgba_to_thumb_hash/3 55.17 18.13 ms ±16.46% 16.57 ms 28.34 ms
```
