在swift中从UIImage/CGImage中获取像素数据作为数组

Question

到目前为止，我有一个应用程序，允许用户在UIImageView元素上自由绘制（就像素描板一样）。

我想将原始RGB像素数据（作为0到255整数值）作为多维数组，以便将其输入到机器学习算法中。或者有没有其他方法可以将原始图像数据发送到单独的C++函数？

在Swift中有一种简单的方法可以做到这一点吗？

Answer 1

将CGImage转换为强度值数组

我的函数取一个CGImage，并返回一个无符号8位整数数组以及图像的宽度和高度。我写了这个代码用于灰度图像。将其扩展到颜色应该是将Gray更改为RGB，并将每个像素的字节更改为3（假设没有alpha通道）。

func pixelValues(fromCGImage imageRef: CGImage?) -> (pixelValues: [UInt8]?, width: Int, height: Int)
{
    var width = 0
    var height = 0
    var pixelValues: [UInt8]?
    if let imageRef = imageRef {
        width = imageRef.width
        height = imageRef.height
        let bitsPerComponent = imageRef.bitsPerComponent
        let bytesPerRow = imageRef.bytesPerRow
        let totalBytes = height * bytesPerRow
        let colorSpace = CGColorSpaceCreateDeviceGray()
        var intensities = [UInt8](repeating: 0, count: totalBytes)
        let contextRef = CGContext(data: &intensities, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: 0)
        contextRef?.draw(imageRef, in: CGRect(x: 0.0, y: 0.0, width: CGFloat(width), height: CGFloat(height)))
        pixelValues = intensities
    }
    return (pixelValues, width, height)
}
func image(fromPixelValues pixelValues: [UInt8]?, width: Int, height: Int) -> CGImage?
{
    var imageRef: CGImage?
    if var pixelValues = pixelValues {
        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
        })
    }
    return imageRef
}

Answer 2

在Swift 3和Swift 4中，使用Core Graphics，可以很容易地执行您想要的操作：

extension UIImage {
    func pixelData() -> [UInt8]? {
        let size = self.size
        let dataSize = size.width * size.height * 4
        var pixelData = [UInt8](repeating: 0, count: Int(dataSize))
        let colorSpace = CGColorSpaceCreateDeviceRGB()
        let context = CGContext(data: &pixelData,
                                width: Int(size.width),
                                height: Int(size.height),
                                bitsPerComponent: 8,
                                bytesPerRow: 4 * Int(size.width),
                                space: colorSpace,
                                bitmapInfo: CGImageAlphaInfo.noneSkipLast.rawValue)
        guard let cgImage = self.cgImage else { return nil }
        context?.draw(cgImage, in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
        return pixelData
    }
 }

Answer 3

请尝试一下。这对我很有效。

func pixelValues(fromCGImage imageRef: CGImage?) -> [UInt8]?
    {
        var width = 0
        var height = 0
        var pixelValues: [UInt8]?
        if let imageRef = imageRef {
            width = imageRef.width
            height = imageRef.height
            let bitsPerComponent = imageRef.bitsPerComponent
            let bytesPerRow = imageRef.bytesPerRow
            let totalBytes = height * bytesPerRow
            let bitmapInfo = imageRef.bitmapInfo
            let colorSpace = CGColorSpaceCreateDeviceRGB()
            var intensities = [UInt8](repeating: 0, count: totalBytes)
            let contextRef = CGContext(data: &intensities,
                                      width: width,
                                     height: height,
                           bitsPerComponent: bitsPerComponent,
                                bytesPerRow: bytesPerRow,
                                      space: colorSpace,
                                 bitmapInfo: bitmapInfo.rawValue)
            contextRef?.draw(imageRef, in: CGRect(x: 0.0, y: 0.0, width: CGFloat(width), height: CGFloat(height)))
            pixelValues = intensities
        }
        return pixelValues
}