Question

我尝试使用加速vImageHistogramCalculation_ARGBFFFF函数计算图像的直方图，但我得到的vImage_Error类型为kvImageNullPointerArgument（错误代码为{ {1}}）。

这是完全相同的问题，但我在Swift工作：Compute the histogram of an image using vImageHistogramCalculation

-21772

问题在于直方图变量，我需要重新创建这样的东西：

    // Get CGImage from UIImage
    var image:UIImage = UIImage(named: "happiness1")!
    var img:CGImageRef = image.CGImage

    // Create vImage_Buffer with data from CGImageRef
    var inProvider:CGDataProviderRef = CGImageGetDataProvider(img)
    var inBitmapData:CFDataRef = CGDataProviderCopyData(inProvider)

    // The next three lines set up the inBuffer object
    var height:vImagePixelCount = CGImageGetHeight(img)
    var width:vImagePixelCount = CGImageGetWidth(img)
    var rowBytes:UInt = CGImageGetBytesPerRow(img)
    var data:UnsafePointer<Void> = UnsafePointer<Void>(CFDataGetBytePtr(inBitmapData))

    // Setup inBuffer
    var inBuffer = vImage_Buffer(data: &data, height: height, width: width, rowBytes: rowBytes)

    var histogram_entries:UInt32 = 4
    var minVal:Pixel_F = 0
    var maxVal:Pixel_F = 255
    //let flags:vImage_Flags = kvImageNoFlags = 0

    var histogram = UnsafeMutablePointer<UnsafeMutablePointer<vImagePixelCount>>()

    var error:vImage_Error = vImageHistogramCalculation_ARGBFFFF(&inBuffer, histogram, histogram_entries, minVal, maxVal, 0)

    println(error)

建议？

Answer 1

我已将vImageHistogramCalculation_ARGB8888实现为Swift中UIImage的扩展，具体如下：

 func SIHistogramCalculation() -> (alpha: [UInt], red: [UInt], green: [UInt], blue: [UInt]) {
   let imageRef = self.CGImage
   let inProvider = CGImageGetDataProvider(imageRef)
   let inBitmapData = CGDataProviderCopyData(inProvider)

   var inBuffer = vImage_Buffer(data: UnsafeMutablePointer(CFDataGetBytePtr(inBitmapData)), height: UInt(CGImageGetHeight(imageRef)), width: UInt(CGImageGetWidth(imageRef)), rowBytes: CGImageGetBytesPerRow(imageRef))

   var alpha = [UInt](count: 256, repeatedValue: 0)
   var red = [UInt](count: 256, repeatedValue: 0)
   var green = [UInt](count: 256, repeatedValue: 0)
   var blue = [UInt](count: 256, repeatedValue: 0)

   var alphaPtr = UnsafeMutablePointer<vImagePixelCount>(alpha)
   var redPtr = UnsafeMutablePointer<vImagePixelCount>(red)
   var greenPtr = UnsafeMutablePointer<vImagePixelCount>(green)
   var bluePtr = UnsafeMutablePointer<vImagePixelCount> (blue)

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

   var histogram = UnsafeMutablePointer<UnsafeMutablePointer<vImagePixelCount>>(rgba)
   var error = vImageHistogramCalculation_ARGB8888(&inBuffer, histogram, UInt32(kvImageNoFlags))
   return (alpha, red, green, blue)
 }

（取自https://github.com/FlexMonkey/ShinpuruImage）

Answer 2

对于Swift 5，您需要明确让编译器知道您的指针是可选的。将您的UnsafeMutablePointer声明更改为以下内容：

Swift 5版本：

let redPtr = red.withUnsafeMutableBufferPointer { $0.baseAddress }
let greenPtr = green.withUnsafeMutableBufferPointer { $0.baseAddress }
let bluePtr = blue.withUnsafeMutableBufferPointer { $0.baseAddress }
let alphaPtr = alphaChannel.withUnsafeMutableBufferPointer { $0.baseAddress }
let histogram = UnsafeMutablePointer<UnsafeMutablePointer<vImagePixelCount>?>.allocate(capacity: 4)

histogram[0] = redPtr
histogram[1] = greenPtr
histogram[2] = bluePtr
histogram[3] = alphaPtr
let error:vImage_Error = vImageHistogramCalculation_ARGB8888(&inBuffer, histogram, UInt32(kvImageNoFlags))

Swift 4版本：

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

Answer 3

今天，我编写代码来分析照片的 RGB 直方图。它现在正在工作。

func getHistogram(_ image: UIImage) ->  (alpha: [UInt], red: [UInt], green: [UInt], blue: [UInt]) {
    
        guard
            let cgImage = image.cgImage,
            var imageBuffer = try? vImage_Buffer(cgImage: cgImage)
        else {
            return nil
        }
        defer {
            imageBuffer.free()
        }

        var redArray: [vImagePixelCount] = Array(repeating: 0, count: 256)
        var greenArray: [vImagePixelCount] = Array(repeating: 0, count: 256)
        var blueArray: [vImagePixelCount] = Array(repeating: 0, count: 256)
        var alphaArray: [vImagePixelCount] = Array(repeating: 0, count: 256)
        var error: vImage_Error = kvImageNoError

        redArray.withUnsafeMutableBufferPointer { rPointer in
            greenArray.withUnsafeMutableBufferPointer { gPointer in
                blueArray.withUnsafeMutableBufferPointer { bPointer in
                    alphaArray.withUnsafeMutableBufferPointer { aPointer in

            var histogram = [ rPointer.baseAddress, gPointer.baseAddress, bPointer.baseAddress, aPointer.baseAddress ]
            histogram.withUnsafeMutableBufferPointer { hPointer in
              
              if let hBaseAddress = hPointer.baseAddress {
                
                error = vImageHistogramCalculation_ARGB8888(&imageBuffer, hBaseAddress, vNoFlags)
                            }
                        }
                    }
                }
            }
        }

        guard error == kvImageNoError else {
            printVImageError(error: error)
            return nil
        }
        
  
        return (alphaArray, redArray, greenArray, blueArrat)
    }

使用swift中的vImageHistogramCalculation计算图像的直方图

3 个答案: