ios - 更新 UIImageView 的 UIImage 时出现 EXC_BAD_ACCESS (code=1)

Question

我是 iOS 和 CoreML 的新手。我有一个非常简单的 UI，有两个 UIImageView(一个应该是输入，第二个应该是输出)。点击第一个时，图像应由神经网络处理，输出应显示在第二个中。

但是，当我尝试从 MLMultiArray 输出对象下载图像并从中创建一个 UIImage，然后我可以将其上传到第二个 UIImageView 时，我得到一个 EXC_BAD_ACCESS (code=1)。

我已将问题简化为根本不调用神经网络处理，只是尝试从 MLMultiArray 创建新图像。结果是一样的。

之后，我尝试从一个空缓冲区生成一个 UIImage。图像创建正确，但如果我尝试更新 UIImageView 以使用它，我会得到同样的错误。

如果我尝试将第二个 UIImageView 更新为不同的图像(例如:输入图像)，一切正常。

我认为这是关于我正在创建的 UIImage 对象的内存管理问题，但我无法弄清楚我做错了什么

class ViewController: UIViewController {

    @IBOutlet weak var out: UIImageView!

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    @IBAction func imageTapped(_ sender: UITapGestureRecognizer) {
        let imageView = sender.view as? UIImageView

        if let imageToAnalyse = imageView?.image {
            if let outImg = process(forImage: imageToAnalyse) {
                out.image = outImg
            }
        }
    }

    func process (forImage inImage:UIImage) -> UIImage? {

        let size = CGSize(width: 512, height: 512)
        let mlOut = try? MLMultiArray(shape: [1, size.height, size.width] as [NSNumber], dataType: .float32)
        let newImage = getSinglePlaneImage(inBuffer: mlOut!, width: Int(size.width), height: Int(size.height))

        return newImage
    }

    func getSinglePlaneImage(inBuffer: MLMultiArray, width: Int, height: Int) -> UIImage
    {
        var newImage: UIImage

//        let floatPtr =  inBuffer.dataPointer.bindMemory(to: Float32.self, capacity: inBuffer.count)
//        let floatBuffer = UnsafeBufferPointer(start: floatPtr, count: inBuffer.count)
//        let pixelValues : [UInt8]? = Array(floatBuffer).map({UInt8( ImageProcessor.clamp( (($0) + 1.0) * 128.0, minValue: 0.0, maxValue: 255.0) ) })

        //simulating pixels from MLMultiArray 
        let pixels : [UInt8]? = Array(repeating: 0, count: 512*512)

        var imageRef: CGImage?

        if var pixelValues = pixels {
            let bitsPerComponent = 8
            let bytesPerPixel = 1
            let bitsPerPixel = bytesPerPixel * bitsPerComponent
            let bytesPerRow = bytesPerPixel * width
            let totalBytes = height * bytesPerRow

            imageRef = withUnsafePointer(to: &pixelValues, {
                ptr -> CGImage? in
                var imageRef: CGImage?
                let colorSpaceRef = CGColorSpaceCreateDeviceGray()
                let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue).union(CGBitmapInfo())
                let data = UnsafeRawPointer(ptr.pointee).assumingMemoryBound(to: UInt8.self)
                let releaseData: CGDataProviderReleaseDataCallback = {
                    (info: UnsafeMutableRawPointer?, data: UnsafeRawPointer, size: Int) -> () in
                }

                if let providerRef = CGDataProvider(dataInfo: nil, data: data, size: totalBytes, releaseData: releaseData) {
                    imageRef = CGImage(width: width,
                                       height: height,
                                       bitsPerComponent: bitsPerComponent,
                                       bitsPerPixel: bitsPerPixel,
                                       bytesPerRow: bytesPerRow,
                                       space: colorSpaceRef,
                                       bitmapInfo: bitmapInfo,
                                       provider: providerRef,
                                       decode: nil,
                                       shouldInterpolate: false,
                                       intent: CGColorRenderingIntent.defaultIntent)
                }


                return imageRef
            })
        }

        newImage = UIImage(cgImage: imageRef!)

        return newImage
    }
}

Answer 1

似乎您的代码可以将 512x512-float32 数组成功转换为 512x512-UInt8 数组，因此我根据您代码的未注释版本编写了此答案。 (虽然，转换效率不够高，还有一定的改进空间。)

更新

以下描述不是 OP 问题的正确解决方案。只是留作记录。请跳至此答案底部的更新代码。

旧代码(不是正确的解决方案)

首先，代码中最严重的缺陷是以下两行:

imageRef = withUnsafePointer(to: &pixelValues, {

    let data = UnsafeRawPointer(ptr.pointee).assumingMemoryBound(to: UInt8.self)

上面的第一行传递了一个指向[UInt8]?的指针。 ，在 swift 中，[UInt8]? (又名 Optional<Array<UInt8>> )是一个 8 字节的结构，而不是像 C 数组那样的连续区域。

第二种更危险。 ptr.pointee是[UInt8]? ，但不能保证通过指针访问 Swift 数组。并将数组传递给 UnsafeRawPointer.init(_:)可能会创建一个时间区域，该区域将在调用初始化程序后立即释放。

如您所知，访问悬空指针偶尔在某些有限条件下不会造成伤害，但随时可能产生意想不到的结果。

---

我会这样写:

func getSinglePlaneImage(inBuffer: MLMultiArray, width: Int, height: Int) -> UIImage {

    //simulating pixels from MLMultiArray
    //...
    let pixelValues: [UInt8] = Array(repeating: 0, count: 1*512*512)

    let bitsPerComponent = 8
    let bytesPerPixel = 1
    let bitsPerPixel = bytesPerPixel * 8
    let bytesPerRow = bytesPerPixel * width
    let totalBytes = height * bytesPerRow

    let imageRef = pixelValues.withUnsafeBytes({bytes -> CGImage? in
        var imageRef: CGImage?
        let colorSpaceRef = CGColorSpaceCreateDeviceGray()
        let bitmapInfo: CGBitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue)

        let data = bytes.baseAddress!.assumingMemoryBound(to: UInt8.self)
        let releaseData: CGDataProviderReleaseDataCallback = {_,_,_ in }

        if let providerRef = CGDataProvider(dataInfo: nil, data: data, size: totalBytes, releaseData: releaseData) {
            imageRef = CGImage(width: width,
                               height: height,
                               bitsPerComponent: bitsPerComponent,
                               bitsPerPixel: bitsPerPixel,
                               bytesPerRow: bytesPerRow,
                               space: colorSpaceRef,
                               bitmapInfo: bitmapInfo,
                               provider: providerRef,
                               decode: nil,
                               shouldInterpolate: false,
                               intent: .defaultIntent)
        }


        return imageRef
    })

    let newImage = UIImage(cgImage: imageRef!)

    return newImage
}

当你想要一个指向数组起始元素的指针时，使用withUnsafeBytes并在闭包参数中使用指针(事实上，它是一个 UnsafeRawBufferPointer )。

还有一个，你的pixels或 pixelValues不需要成为可选的。

---

否则，您可以使用 Float32 创建灰度图像对于每个像素。

func getSinglePlaneImage(inBuffer: MLMultiArray, width: Int, height: Int) -> UIImage {

    //simulating pixels from MLMultiArray
    //...
    let pixelValues: [Float32] = Array(repeating: 0, count: 1*512*512)

    let bitsPerComponent = 32 //<-
    let bytesPerPixel = 4 //<-
    let bitsPerPixel = bytesPerPixel * 8
    let bytesPerRow = bytesPerPixel * width
    let totalBytes = height * bytesPerRow

    let imageRef = pixelValues.withUnsafeBytes({bytes -> CGImage? in
        var imageRef: CGImage?
        let colorSpaceRef = CGColorSpaceCreateDeviceGray()
        let bitmapInfo: CGBitmapInfo = [CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue),
                          .byteOrder32Little, .floatComponents] //<-
        let data = bytes.baseAddress!.assumingMemoryBound(to: Float32.self)
        let releaseData: CGDataProviderReleaseDataCallback = {_,_,_ in }

        if let providerRef = CGDataProvider(dataInfo: nil, data: data, size: totalBytes, releaseData: releaseData) {
            imageRef = CGImage(width: width,
                               height: height,
                               bitsPerComponent: bitsPerComponent,
                               bitsPerPixel: bitsPerPixel,
                               bytesPerRow: bytesPerRow,
                               space: colorSpaceRef,
                               bitmapInfo: bitmapInfo,
                               provider: providerRef,
                               decode: nil,
                               shouldInterpolate: false,
                               intent: CGColorRenderingIntent.defaultIntent)
        }


        return imageRef
    })

    let newImage = UIImage(cgImage: imageRef!)

    return newImage
}

在我的测试项目中两者都按预期工作，但如果您发现问题，请通知我。

---

更新代码(希望这是正确的解决方案)

我错过了一个事实 CGDataProvider使用 init(dataInfo:data:size:releaseData:) 创建时保留指针即使在 CGImage 之后被 build 。所以，关闭后可能会引用到withUnsafeBytes结束，当它无效时。

你最好使用CGDataProvider.init(data:)在这种情况下。

func getSinglePlaneImage(inBuffer: MLMultiArray, width: Int, height: Int) -> UIImage {
    var newImage: UIImage

    //let floatPtr =  inBuffer.dataPointer.bindMemory(to: Float32.self, capacity: inBuffer.count)
    //let floatBuffer = UnsafeBufferPointer(start: floatPtr, count: inBuffer.count)
    //let pixelValues: Data = Data((floatBuffer.lazy.map{
    //    UInt8(ImageProcessor.clamp((($0) + 1.0) * 128.0, minValue: 0.0, maxValue: 255.0))
    //})

    //simulating pixels from MLMultiArray
    //...
    let pixelValues = Data(count: 1*512*512) // <- ###

    var imageRef: CGImage?

    let bitsPerComponent = 8
    let bytesPerPixel = 1
    let bitsPerPixel = bytesPerPixel * bitsPerComponent
    let bytesPerRow = bytesPerPixel * width

    let colorSpaceRef = CGColorSpaceCreateDeviceGray()
    let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue)

    if let providerRef = CGDataProvider(data: pixelValues as CFData) { // <-###
        imageRef = CGImage(width: width,
                           height: height,
                           bitsPerComponent: bitsPerComponent,
                           bitsPerPixel: bitsPerPixel,
                           bytesPerRow: bytesPerRow,
                           space: colorSpaceRef,
                           bitmapInfo: bitmapInfo,
                           provider: providerRef,
                           decode: nil,
                           shouldInterpolate: false,
                           intent: CGColorRenderingIntent.defaultIntent)
    }

    newImage = UIImage(cgImage: imageRef!)

    return newImage
}

据我尝试，即使在具有重复触摸次数的实际设备中，这也不会崩溃。请尝试。感谢您的耐心等待。