(Enum.OutOfBoundsError) out of bounds error

[alexgleason]

I'm trying to decode an image, but it always throws this error:

iex(1)> file = "/home/alex/Pictures/me-avatar.png"
"/home/alex/Pictures/me-avatar.png"
iex(2)> image = Mogrify.open(file) |> Mogrify.verbose() |> Mogrify.format("rgb") |> Mogrify.save()
%Mogrify.Image{
  animated: false,
  buffer: nil,
  dirty: %{},
  ext: ".rgb",
  format: "rgb",
  frame_count: 1,
  height: 600,
  operations: [],
  path: "/tmp/529046-me-avatar.rgb",
  width: 600
}
iex(3)> pixels = File.read!(image.path) |> :binary.bin_to_list()
[112, 208, 0, 112, 208, 0, 112, 208, 0, 112, 208, 0, 112, 208, 0, 112, 208, 0,
 112, 208, 0, 112, 208, 0, 112, 208, 0, 112, 208, 0, 112, 208, 0, 112, 208, 0,
 112, 208, 0, 112, 208, 0, 112, 208, 0, 112, 208, 0, 112, 208, ...]
iex(4)> BlurHash.encode(pixels, 600, 600, 4, 4)
[error] Task #PID<0.1052.0> started from #PID<0.1040.0> terminating
** (Enum.OutOfBoundsError) out of bounds error
    (elixir 1.11.2) lib/enum.ex:884: Enum.fetch!/2
    (blurhash 1.0.0) lib/blur_hash.ex:107: anonymous fn/10 in BlurHash.get_factors/5
    (elixir 1.11.2) lib/enum.ex:3449: Enum.reduce_range_inc/4
    (blurhash 1.0.0) lib/blur_hash.ex:92: anonymous fn/8 in BlurHash.get_factors/5
    (elixir 1.11.2) lib/task/supervised.ex:90: Task.Supervised.invoke_mfa/2
    (elixir 1.11.2) lib/task/supervised.ex:35: Task.Supervised.reply/5
    (stdlib 3.14.1) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Function: #Function<5.74243370/0 in BlurHash.get_factors/5>
    Args: []
** (EXIT from #PID<0.1040.0>) shell process exited with reason: an exception was raised:
    ** (Enum.OutOfBoundsError) out of bounds error
        (elixir 1.11.2) lib/enum.ex:884: Enum.fetch!/2
        (blurhash 1.0.0) lib/blur_hash.ex:107: anonymous fn/10 in BlurHash.get_factors/5
        (elixir 1.11.2) lib/enum.ex:3449: Enum.reduce_range_inc/4
        (blurhash 1.0.0) lib/blur_hash.ex:92: anonymous fn/8 in BlurHash.get_factors/5
        (elixir 1.11.2) lib/task/supervised.ex:90: Task.Supervised.invoke_mfa/2
        (elixir 1.11.2) lib/task/supervised.ex:35: Task.Supervised.reply/5
        (stdlib 3.14.1) proc_lib.erl:226: :proc_lib.init_p_do_apply/3

I've had better luck hardcoding the value to 30, no matter the real image size:

iex(4)> BlurHash.encode(pixels, 30, 30, 4, 4)
"UKMQ*Jx]t7x]nlt7RkRj~qs=WBR%^+V[ozoM"

This at least returns a blurhash, but it doesn't look quite right.

So I tried resizing the image to 30x30 first:

file =
  image
  |> Mogrify.format("rgb")
  |> Mogrify.resize("30x30")
  |> Mogrify.save()

pixels =
  File.read!(file.path)
  |> :binary.bin_to_list()

BlurHash.encode(pixels, 30, 30, 4, 4)

But this just gives me the OutOfBoundsError as before. 😕