Swift 3中绘制CGImage的直方图

我有一个问题vImageHistogramCalculation_ARGB8888方法，同时尝试将库从 Swift 2 转换为 Swift 3 版本。问题是该方法仅接受“直方图”参数

UnsafeMutablePointer<UnsafeMutablePointer<T>?> 

但 Swift 3 构建

let histogram = UnsafeMutablePointer<UnsafeMutablePointer<vImagePixelCount>>(mutating: rgba)  

返回未包装的值，因此我无法将其转换为正确的类型。

编译器错误是：

：无法调用类型的初始值设定项 'UnsafeMutablePointer?>' 与 类型为 '(mutating: [不安全可变指针])'

你有什么想法吗？我尝试添加“？”直方图常数，但随后我收到错误：

'init' 不可用：使用 'withMemoryRebound(to:capacity:_)' 来 暂时将内存视为另一种布局兼容的类型。

有一些编译器建议，但我不知道如何使用它。

Cast to UnsafeMutablePointer<vImagePixelCount>?:

let alphaPtr = UnsafeMutablePointer<vImagePixelCount>(mutating: alpha) as UnsafeMutablePointer<vImagePixelCount>?

完整的编译示例：

var inBuffer = vImage_Buffer() // set your buffer here

let alpha = [UInt](repeating: 0, count: 256)
let red = [UInt](repeating: 0, count: 256)
let green = [UInt](repeating: 0, count: 256)
let blue = [UInt](repeating: 0, count: 256)

let alphaPtr = UnsafeMutablePointer<vImagePixelCount>(mutating: alpha) as UnsafeMutablePointer<vImagePixelCount>?
let redPtr = UnsafeMutablePointer<vImagePixelCount>(mutating: red) as UnsafeMutablePointer<vImagePixelCount>?
let greenPtr = UnsafeMutablePointer<vImagePixelCount>(mutating: green) as UnsafeMutablePointer<vImagePixelCount>?
let bluePtr = UnsafeMutablePointer<vImagePixelCount>(mutating: blue) as UnsafeMutablePointer<vImagePixelCount>?

let rgba = [redPtr, greenPtr, bluePtr, alphaPtr]

let histogram = UnsafeMutablePointer<UnsafeMutablePointer<vImagePixelCount>?>(mutating: rgba)
let error = vImageHistogramCalculation_ARGB8888(&inBuffer, histogram, UInt32(kvImageNoFlags))

// alpha, red, green, blue are set now