A Clojure implementation of Blurhash.

Blurhash is an algorithm by Dag Ågren of Wolt that decodes an image to a very compact (~ 20-30 bytes) ASCII string representation, which can be then decoded into a blurred placeholder image. See the main repo for the rationale and details.

Both the encoder and decoder are implemented and work in both Clojure and ClojureScript.

The encode->hash->decode cycle looks something like this:

→ UIGuXeS@x[xX_MORbuoy?uNGM{nTNHMzIVnn →

The Clojure implementation is written in CLJC files, so that they can be used from Clojure and ClojureScript code alike.

You can encode an image to a blurhash using the function blurhash.encode/encode. It takes an image as an RGB matrix, currently represented as nested native vectors. The blurhash.core namespace contains (Clojure-specific) functions to convert an image file into a matrix, so you can do something like this:

(ns my-namespace
  (:require [blurhash.core :refer [file->pixels]
            [blurhash.encode :refer [encode]]]))
(def image
  (file->pixels "./resources/example.jpg"))

(encode image)
=> "UIGuXeS@x[xX_MORbuoy?uNGM{nTNHMzIVnn"

Here's an example of how to decode a blurhash into a placeholder image:

(ns my-namespace
  (:require [blurhash.core :refer [pixels->file]
            [blurhash.decode :refer [decode]]]))

(def blurred-image
  (decode "UIGuXeS@x[xX_MORbuoy?uNGM{nTNHMzIVnn" 300 236))

(pixels->file blurred-image "blurred-image.jpg")

In ClojureScript (Reagent), you can decode a hash and render the placeholder like this:

(ns blurhash-example.core
  (:require [reagent.core :as r]
            [blurhash.decode :refer [decode]
            [blurhash.util :as util]]))

(defn draw-canvas-contents [canvas]
  (let [pixels (decode "UIGuXeS@x[xX_MORbuoy?uNGM{nTNHMzIVnn" 100 100)
        ctx (.getContext canvas "2d")
        imageData (.createImageData ctx 100 100)]
    (do
      (.set (. imageData -data) pixels)
      (. ctx putImageData imageData 0 0))))

(defn div-with-canvas []
  (let [dom-node (r/atom nil)]
    (r/create-class
      {:component-did-update
       (fn [_]
         (draw-canvas-contents (.-firstChild @dom-node)))
       :component-did-mount
       (fn [this]
         (reset! dom-node (r/dom-node this)))
       :reagent-render
       (fn []
         [:div
          [:canvas (if-let [node @dom-node]
                     {:width (.-clientWidth node)
                      :height (.-clientHeight node)})]])})))

(defn home-page []
  [:div [:h2 "Look at this blur!"]
   [div-with-canvas]])

(defn mount-root []
  (r/render [home-page] (.getElementById js/document "app")))

(defn init! []
  (mount-root))

Copyright (c) 2019-2022 Tuomo Virolainen

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

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