You might also consider:

• Image.from_kino/2 which allows you to consume an image from Kino directly or
• Image.open/2 which can open an image from the file system, or a stream.

I implemented my requirement with this Image library.

Mix.install([
  {:image, "~> 0.37"},
  {:kino, "~> 0.10.0"},
  {:vix, "~> 0.5"}
])

Section

file = Kino.Input.file("File")

file_reading = Kino.Input.read(file)
file_path = Kino.Input.file_path(file_reading.file_ref)
{:ok, img} = Vix.Vips.Image.new_from_file(file_path)
color = Image.dominant_color(img, [{:bins, x}])
Image.Color.rgb_to_hex(color)