利用Elixir / Vix / libvips去除色度键

Question

这只是从Vix示例中复制的一些处理程序代码。

defmodule VixExt do
  alias Vix.Vips.Image
  alias Vix.Vips.Operation

  @max_height 500

  def show(%Image{} = image) do
    height = Image.height(image)

    # scale down if image height is larger than 500px
    image =
      if height > @max_height do
        Operation.resize!(image, @max_height / height)
      else
        image
      end

    # write vips-image as png image to memory
    {:ok, image_bin} = Image.write_to_buffer(image, ".png")
    Kino.render(Kino.Image.new(image_bin, "image/png"))

    :ok
  end
end

做事情的代码：

import VixExt

{:ok, fore} = Image.open("/home/user/Downloads/greenscreen.jpg")

{:ok, back} = Image.open("/home/user/Downloads/background.jpg")

# Lower bound green
{:ok, l_green} = Image.Math.greater_than(fore, [0.0, 100.0, 0.0])
# Upper bound green
{:ok, u_green} = Image.Math.less_than(fore, [100.0, 255.0, 95.0])

{:ok, color_fore_mask} = Image.Math.boolean_and(l_green, u_green)

{:ok, fore_mask} = Vix.Vips.Operation.bandbool(color_fore_mask, :VIPS_OPERATION_BOOLEAN_AND)

{:ok, masked} = Image.Math.subtract(fore, fore_mask)

{:ok, inverted_fore_mask} = Vix.Vips.Operation.invert(fore_mask)

{:ok, masked_back} = Image.Math.subtract(back, inverted_fore_mask)

{:ok, masked_bin} = Vix.Vips.Image.write_to_buffer(masked, ".jpg")
{:ok, masked_clone} = Vix.Vips.Image.new_from_buffer(masked_bin)


{:ok, masked_back_bin} = Vix.Vips.Image.write_to_buffer(masked_back, ".jpg")
{:ok, masked_back_clone} = Image.from_binary(masked_back_bin)

{:ok, composite} = Vix.Vips.Operation.add(masked_back, masked_clone)

show(composite)

我一开始遇到的问题是，剪裁后的图像没有被正确地添加到一起。长生不老，所以我有点期待这种行为。然而，它们都指向相同的图像，所以当我试图将它们加在一起时，这是一种原始数据的混搭。

我可以通过加载预先剪裁的图像来强制它达到正确的行为，然后像我所期望的那样运行，但是我不想因为明显的原因而不得不保存到磁盘。所以现在我试图强制复制，以便我得到剪裁的版本，而不是原来的版本。

所显示的图像是我想要的结果。这个人从一个绿色的背景开始，这个背景被移除并合成到场景中。

我现在遇到的错误是

** (MatchError) no match of right hand side value: {:error, "Failed to write VipsImage to memory"}

每当我尝试写两次缓冲区时，都会发生这种情况。

我会认为绿色屏幕删除是一个相当例行的用例，这样做会更容易。我很高兴能采取更好的方法。

Answer 1

针对来自@GeneticJam的这一挑战，图像药剂库现在提供Image.chroma_key/2。像这样用基本上是：

Image.chroma_key!(foreground) 
|> then(&Image.compose!(background, &1))

默认的色度包括可能的色域绿色。

Answer 2

我设法用两种不同的方法解决了这个问题。

import VixExt
# Opening with this option makes it possible to have more than one pipeline so it avoids the above error.
{:ok, fore} = Image.open("/home/kevinedey/Downloads/greenscreen.jpg", access: :random)

{:ok, back} = Image.open("/home/kevinedey/Downloads/background.jpg", access: :random)

# Lower bound green
{:ok, l_green} = Image.Math.greater_than(fore, [0.0, 100.0, 0.0])
# Upper bound green
{:ok, u_green} = Image.Math.less_than(fore, [100.0, 255.0, 95.0])

{:ok, color_fore_mask} = Image.Math.boolean_and(l_green, u_green)

{:ok, fore_mask} = Vix.Vips.Operation.bandbool(color_fore_mask, :VIPS_OPERATION_BOOLEAN_AND)

{:ok, masked} = Image.Math.subtract(fore, fore_mask)

{:ok, inverted_fore_mask} = Vix.Vips.Operation.invert(fore_mask)

{:ok, masked_back} = Image.Math.subtract(back, inverted_fore_mask)

{:ok, masked_bin} = Vix.Vips.Image.write_to_buffer(masked, ".jpg")
{:ok, masked_clone} = Vix.Vips.Image.new_from_buffer(masked_bin)

{:ok, masked_back_bin} = Vix.Vips.Image.write_to_buffer(masked_back, ".jpg")
{:ok, masked_back_clone} = Image.from_binary(masked_back_bin)

{:ok, comp} = Vix.Vips.Operation.add(masked_back_clone, masked_clone)

show(comp)

可能更接近贵宾打算如何使用，因为额外的管道是不需要的。

import VixExt

{:ok, fore} = Image.open("/home/kevinedey/Downloads/greenscreen.jpg")

{:ok, back} = Image.open("/home/kevinedey/Downloads/background.jpg")

# Lower bound green
{:ok, l_green} = Image.Math.greater_than(fore, [0.0, 100.0, 0.0])
# Upper bound green
{:ok, u_green} = Image.Math.less_than(fore, [100.0, 255.0, 95.0])

{:ok, color_fore_mask} = Image.Math.boolean_and(l_green, u_green)

{:ok, fore_mask} = Vix.Vips.Operation.bandbool(color_fore_mask, :VIPS_OPERATION_BOOLEAN_AND)

{:ok, inverted_fore_mask} = Vix.Vips.Operation.invert(fore_mask)

{:ok, masked_person} = Vix.Vips.Operation.bandjoin([fore, inverted_fore_mask])

{:ok, comp} = Image.compose(back, masked_person)

show(comp)