Optimized Blurhash

[renchap]

I am looking at using Blurhash to get very small but nice blurred image previews : https://blurha.sh

The algorithm is quite simple and defined here: https://github.com/woltapp/blurhash/blob/master/Algorithm.md

There is a Ruby native Blurhash implementation, and it works fine using something like this:

image = Vips::Image.new_from_file(path)
Blurhash.encode(image.width, image.height, image.to_a.flatten)

Unfortunately this involves creating a huge array with all pixels and this is quite slow.

Do you think there is a way to have a more efficient implementation using Vips directly? I would be happy to have pointers, I am not really familiar with the low-level VIPS functions and if they can be used for this to avoid doing the computation using Ruby.

Thanks :)

[Nakilon]

While it's still not the "using Vips directly", try resizing the image to 100x100 and see if it works enough well for you:

  size = 100
  image = Vips::Image.new_from_file(filename, access: :sequential)
  image = image.resize(size.fdiv(image.width), vscale: size.fdiv(image.height))
  Blurhash.encode(image.width, image.height, image.to_a.flatten)

[jcupitt]

I think the DCT would probably need to be implemented in C or C++. Let's tag this as an enhacement.

[jcupitt]

... an enhancement on libvips, I mean

[renchap]

@Nakilon Thanks for the suggestion, I am already doing a resize before calculating the blurhash to reduce the number of ruby allocations, but I think it can be even faster and memory-efficient :)

@jcupitt Ok, I was not sure it could be done, if vips gets primitives to do this it would be awesome!