4

我正在尝试使用 AcceleratevImageHistogramCalculation_ARGBFFFF函数计算图像的直方图，但我得到了一个vImage_Error类型kvImageNullPointerArgument（错误代码是-21772）。

这是完全相同的问题，但我正在使用 Swift：Compute the histogram of an image using vImageHistogramCalculation

    // 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)

问题出在直方图变量中，我需要重新创建如下内容：

// create an array of four histograms with eight entries each.
vImagePixelCount histogram[4][8] = {{0}};  
// vImageHistogramCalculation requires an array of pointers to the histograms.
vImagePixelCount *histogramPointers[4] = { &histogram[0][0], &histogram[1][0], &histogram[2][0], &histogram[3][0] };
vImage_Error error = vImageHistogramCalculation_ARGBFFFF(&inBuffer, histogramPointers, 8, 0, 255, kvImageNoFlags);
// You can now access bin j of the histogram for channel i as histogram[i][j].
// The storage for the histogram will be cleaned up when execution leaves the
// current lexical block.

建议？

4

3 回答 3

6

我已经将 vImageHistogramCalculation_ARGB8888 实现为 Swift 中 UIImage 的扩展，其中包含以下内容：

 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）

于 2015-05-26T10:25:48.647 回答
3

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：

斯威夫特 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))

斯威夫特 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)
于 2020-03-04T22:55:46.850 回答
0

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)
    }
于 2021-05-15T16:29:23.610 回答