在swift中从UIImage / CGImage获取像素数据作为数组

Posted 2021-04-04

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（如草图板）。

我想将原始RGB像素数据（作为0到255整数值）作为多维数组获取，因此我可以将其输入到机器学习算法中。或者是否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中有一个简单的方法吗？

答案

Converting a CGImage to an array of intensity values

我的函数接受一个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。我写了这段代码用于灰度图像。将其扩展为颜色应该是将Gray更改为RGB并将每像素的字节数更改为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
}

另一答案

在Swift 3和Swift 4中，使用Core Graphics，很容易做到你想要的：

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
    }
 }