ガンマ補正

Mix.install([
  {:req, "~> 0.5"},
  {:evision, "~> 0.2"},
  {:kino, "~> 0.14"},
  {:nx, "~> 0.9"},
  {:kino_vega_lite, "~> 0.1"}
])

準備

import Nx.Defn

画像のダウンロード

img =
  "https://upload.wikimedia.org/wikipedia/en/7/7d/Lenna_%28test_image%29.png"
  |> Req.get!()
  |> Map.get(:body)
  |> Evision.imdecode(Evision.Constant.cv_IMREAD_COLOR())

ガンマ補正

defmodule GammaCorrection do
  defn generate_gamma_tensor(gamma) do
    (Nx.iota({256, 1}) / 255) ** (1 / gamma) * 255
  end

  def correct(img, gamma) do
    gamma_tensor = generate_gamma_tensor(gamma)
    Evision.lut(img, gamma_tensor)
  end
end

[
  img,
  GammaCorrection.correct(img, 5.0)
]
|> Kino.Layout.grid(columns: 2)

1..8
|> Enum.to_list()
|> Enum.map(fn gamma_seed -> GammaCorrection.correct(img, gamma_seed / 4) end)
|> Kino.Layout.grid(columns: 4)

演算内容の確認

gamma_tensor = GammaCorrection.generate_gamma_tensor(0.1)

data =
  [0.1, 0.25, 0.5, 1.0, 2.0, 5.0, 10.0]
  |> Enum.reduce(%{gamma: [], src: [], dst: []}, fn gamma, acc ->
    %{
      gamma: acc.gamma ++ List.duplicate(gamma, 256),
      src: acc.src ++ Enum.to_list(0..255),
      dst: acc.dst ++ (gamma |> GammaCorrection.generate_gamma_tensor() |> Nx.to_flat_list())
    }
  end)

VegaLite.new()
|> VegaLite.data_from_values(data, only: ["src", "dst", "gamma"])
|> VegaLite.mark(:line)
|> VegaLite.encode_field(:x, "src", type: :quantitative)
|> VegaLite.encode_field(:y, "dst", type: :quantitative)
|> VegaLite.encode_field(:color, "gamma", type: :nominal)