swift – 为什么过滤裁剪的图像比过滤尺寸调整的图像慢4倍(两者

它工作得很好.它将图像裁剪为200×200并使用SepiaTone进行过滤.现在这是我面临的问题 – 我的MacBook Air整个过程需要600毫秒.现在,当我将输入图像调整(而不是裁剪)到相同尺寸(200×200)时,需要150ms.

这是为什么？在这两种情况下,我都会过滤尺寸为200×200的图像.我正在使用this particular image进行测试(5966×3978).

更新：

在处理裁剪图像时,这段特殊代码需要4倍的时间：

var ciImage:CIImage = CIImage(cgImage: cgImage)

更新结束

裁剪代码(200×200)：

// parse args and get image path
let args:Array = CommandLine.arguments
let inputFile:String = args[CommandLine.argc - 1]
let inputURL:URL = URL(fileURLWithPath: inputFile)

// load the image from path into NSImage
// and convert NSImage into CGImage
guard
    let nsImage = NSImage(contentsOf: inputURL),var cgImage = nsImage.cgImage(forProposedRect: nil,context: nil,hints: nil)
else {
    exit(EXIT_FAILURE)
}

// CROP THE IMAGE TO 200x200
// THIS IS THE ONLY BLOCK OF CODE THAT IS DIFFERENT
// IN THOSE TWO EXAMPLES
let rect = CGRect(x: 0,y: 0,width: 200,height: 200)

if let croppedImage = cgImage.cropping(to: rect) {
    cgImage = croppedImage
} else {
    exit(EXIT_FAILURE)
}

// END CROPPING



// convert CGImage to CIImage
var ciImage:CIImage = CIImage(cgImage: cgImage)

// initiate SepiaTone
guard
    let sepiaFilter = CIFilter(name: "CISepiaTone")
else {
    exit(EXIT_FAILURE)
}

sepiaFilter.setValue(ciImage,forKey: kCIInputImageKey)
sepiaFilter.setValue(0.5,forKey: kCIInputIntensityKey)

guard
    let result = sepiaFilter.outputImage
else {
    exit(EXIT_FAILURE)
}

let context:CIContext = CIContext()

// perform filtering in a GPU context
guard
    let output = context.createCGImage(sepiaFilter.outputImage!,from: ciImage.extent)
else {
    exit(EXIT_FAILURE)
}

调整大小的代码(200×200)：

// parse args and get image path
let args:Array = CommandLine.arguments
let inputFile:String = args[CommandLine.argc - 1]
let inputURL:URL = URL(fileURLWithPath: inputFile)

// load the image from path into NSImage
// and convert NSImage into CGImage
guard
    let nsImage = NSImage(contentsOf: inputURL),hints: nil)
else {
    exit(EXIT_FAILURE)
}

// RESIZE THE IMAGE TO 200x200
// THIS IS THE ONLY BLOCK OF CODE THAT IS DIFFERENT
// IN THOSE TWO EXAMPLES
guard let CGcontext = CGContext(data: nil,height: 200,bitsPerComponent: cgImage.bitsPerComponent,bytesPerRow: cgImage.bytesPerRow,space: cgImage.colorSpace ?? CGColorSpaceCreateDeviceRGB(),bitmapInfo: cgImage.bitmapInfo.rawValue)
else {
    exit(EXIT_FAILURE)
}

CGcontext.draw(cgImage,in: CGRect(x: 0,height: 200))

if let resizeOutput = CGcontext.makeImage() {
    cgImage = resizeOutput
}

// END RESIZING



// convert CGImage to CIImage
var ciImage:CIImage = CIImage(cgImage: cgImage)

// initiate SepiaTone
guard
    let sepiaFilter = CIFilter(name: "CISepiaTone")
else {
    exit(EXIT_FAILURE)
}

sepiaFilter.setValue(ciImage,from: ciImage.extent)
else {
    exit(EXIT_FAILURE)
}