如何在UIImage / CIImage中隔离单一颜色？

Question

我想在UIImage中隔离某种颜色的元素，以便我可以在另一个工具中处理该图像。

假设我有以下图片，我想隔离所有红色元素。

输入：

所需输出：所有红色元素

我可以采取哪些措施来实现这一目标？我认为它是CIFilter中的东西，但还没找到合适的过滤器。有没有直接的方法来实现这个目标？

Answer 1

好的，得到了​​一些帮助并整理好了！以下是如何执行此操作：

// First, turn our UIImage into a CIImage
let ciImage = CIImage(image: image)!

// Next, let's make a CIVector for the color we want.
let colorToIsolate = CIVector(x: 0.239, y: 0.951, z: 0.937) // normalized RGB

// OK, here's where it gets interesting. 
// We're going to write a CIColorKernel that maps every pixel in the image. 
// If it's the color we want, then we turn it white, otherwise, black.
// This is iOS-10 friendly; in iOS 11 there's a non-string-based way,
// which helps with compiler type-checking and non-runtime error detection.
// NOTE: The 0.5 value is a tolerance; adjust and adapt it to your needs for your task. 
// I was surprised that we needed it that large to get the desired effect; 
// had hoped that I could use a tighter value like 0.01

let kernelString = "kernel vec4 filterColorMatch(sampler image, vec3 match) {" +
        "vec2 dc = destCoord();" +
        "vec3 color = sample(image, samplerTransform(image, dc)).rgb; " +
        "return distance(color, match) < 0.5 ? vec4(1,1,1,1) : vec4(0,0,0,1); }"

let colorIsolate = CIColorKernel(string: kernelString)

// Now we can run our kernel, and extract the image!
let after = colorIsolate?.apply(
  withExtent: ciImage.extent, 
  arguments: [ciImage, colorToIsolate]
)

let result = UIImage(ciImage: after)