The thumbhash library implements the
Thumbhash image placeholder generation
algorithm invented by Evan Wallace in Ruby.
A full explanation and interactive example of the algorithm can be found at https://evanw.github.io/thumbhash/
The ideal use case is to store the very compact binary hash representation of an image so that a placeholder image can be can be generated clientside while the original image loads asynchronously.
Using the MiniMagick library to process the image, this example shows how to generate a thumb hash that can be stored alongside an image as well as the method to convert the hash into a data string for the image placeholder.
require "../lib/thumbhash"
require "mini_magick"
image = MiniMagick::Image.open("flower.jpg")
rgba_pixels = image.get_pixels("RGBA").flatten
# Generate the binary hash
binary_thumb_hash = ThumbHash.rgba_to_thumb_hash(
image.width,
image.height,
rgba_pixels
)
# Generate the placeholder image data
ThumbHash.thumb_hash_to_data_url(binary_thumb_hash)