Question

我写了以下函数：

    class func convertImageToBlackAndWhite(#data:UnsafeMutablePointer<UInt32>, inputWidth:UInt32, inputHeight:UInt32) -> UnsafeMutablePointer<UInt32> {
    var currentPixel = UnsafeMutablePointer<UInt32>()
    currentPixel = data

    for (var i = 0; i < Int(inputHeight); i++) {
        for (var j = 0; j < Int(inputWidth); j++) {
            var color:UInt32 = currentPixel.memory

            // Average of RGB = greyscale
            var averageColor:UInt32 = (R(color) + G(color) + B(color)) / 3
            var updatedColor:UInt32 = RGBAMake(averageColor, g: averageColor, b: averageColor, a: A(color))
            currentPixel.memory = updatedColor
            currentPixel++
        }
    }

    var outputData = UnsafeMutablePointer<UInt32>((calloc(UInt(inputHeight*inputWidth), UInt(sizeof(UInt32)))))
    outputData = currentPixel
    return outputData
}

我想返回outputData以在屏幕上显示它。因此我在另一个函数中创建了这段代码：

    class func processUsingPixels(#inputImage:UIImage) -> UIImage {

    var inputCGImage:CGImageRef = inputImage.CGImage
    var colorSpace:CGColorSpaceRef = CGColorSpaceCreateDeviceRGB()
    var inputWidth:UInt = CGImageGetWidth(inputCGImage)
    var inputHeight:UInt = CGImageGetHeight(inputCGImage)
    var bytesPerPixel:UInt = 4
    var bitsPerComponent:UInt = 8
    var inputBytesPerRow = bytesPerPixel * inputWidth

    let bitmapInfo = CGBitmapInfo(CGBitmapInfo.ByteOrder32Big.rawValue | CGImageAlphaInfo.PremultipliedLast.rawValue)

    let inputPixels = UnsafeMutablePointer<UInt32>(calloc(UInt(inputHeight*inputWidth), UInt(sizeof(UInt32))))

    var outputData = UnsafeMutablePointer<UInt32>()
    outputData = self.convertImageToBlackAndWhite(data: inputPixels, inputWidth: UInt32(inputWidth), inputHeight: UInt32(inputHeight))


    let context:CGContextRef = CGBitmapContextCreate(outputData, inputWidth, inputHeight, bitsPerComponent, inputBytesPerRow, colorSpace, bitmapInfo)
    CGContextDrawImage(context, CGRectMake(0, 0, CGFloat(inputWidth), CGFloat(inputHeight)), inputCGImage)


    return inputImage
}

outputData是我现在想要显示的数据。我期望通过for-loop在＆＃34; ConvertImageToBlackAndWhite＆＃34;中进行更改。会被反映出来，但根本没有变化。

感谢Rob我以前得到了一些有价值的见解。但这张照片仍然没有改变。

我的问题是：

1）将此输出数据var创建为返回值是否正确？它有意义吗？

2）我使用这个返回的outputData变量来创建Context并绘制上下文。但这没有效果。我需要先创建一个新的图像吗？ processusingPixels的返回值是UIImage。但我认为CGContextDrawImage就足够了。这是错的吗？

Answer 1

您正在currentPixel循环内初始化for。在开始循环之前执行此操作，例如：

var currentPixel = inputPixels

for row in 0 ..< inputHeight {
    for column in 0 ..< inputWidth {
        var color: UInt32 = currentPixel.memory
        print(String(format:"%X", color))
        currentPixel++
    }
}

完成后，您可以使用CGBitmapContextCreateImage创建新图片：

func processUsingPixels(inputImage inputImage: UIImage) -> UIImage {
    let inputCGImage = inputImage.CGImage
    let colorSpace = CGColorSpaceCreateDeviceRGB()
    let width = CGImageGetWidth(inputCGImage)
    let height = CGImageGetHeight(inputCGImage)
    let bytesPerPixel: UInt = 4
    let bitsPerComponent: UInt = 8
    let bytesPerRow = bytesPerPixel * width
    let bitmapInfo = CGBitmapInfo.ByteOrder32Big.rawValue | CGImageAlphaInfo.PremultipliedLast.rawValue

    let context:CGContextRef = CGBitmapContextCreate(nil, width, height, bitsPerComponent, bytesPerRow, colorSpace, bitmapInfo)
    CGContextDrawImage(context, CGRectMake(0, 0, CGFloat(width), CGFloat(height)), inputCGImage)

    let pixelBuffer = UnsafeMutablePointer<UInt32>(CGBitmapContextGetData(context))

    var currentPixel = pixelBuffer

    for row in 0 ..< inputHeight {
        for column in 0 ..< inputWidth {
            currentPixel.memory = grayScaleFromColor(currentPixel.memory)
            currentPixel++
        }
    }

    let outputCGImage = CGBitmapContextCreateImage(context)
    return UIImage(CGImage: outputCGImage)!
}

func grayScaleFromColor(color: UInt32) -> UInt32 {
    let r = Double(red(color))
    let g = Double(green(color))
    let b = Double(blue(color))
    let a = alpha(color)

    let gray = UInt8(0.2126 * r + 0.7152 * g + 0.0722 * b)

    return rgba(red: gray, green: gray, blue: gray, alpha: a)
}

注意，我从上面删除了calloc。如果您将其保留在日常工作中，请务必free。

原始问题隐含的功能是从UInt32颜色中提取RGBA值，还可以从RGBA值中创建颜色。为了完整起见，我将包括一些示例再现：

func red(color: UInt32) -> UInt8 {
    return UInt8(color & 255)
}

func green(color: UInt32) -> UInt8 {
    return UInt8((color >> 8) & 255)
}

func blue(color: UInt32) -> UInt8 {
    return UInt8((color >> 16) & 255)
}

func alpha(color: UInt32) -> UInt8 {
    return UInt8((color >> 24) & 255)
}

func rgba(#red: UInt8, green: UInt8, blue: UInt8, alpha: UInt8) -> UInt32 {
    return UInt32(red) | (UInt32(green) << 8) | (UInt32(blue) << 16) | (UInt32(alpha) << 24)
}

就个人而言，我真的不喜欢玩这种位移，所以我自然倾向于使用struct（就像我做in this answer;使用PremultipliedFirst而不是这里问题中使用的PremultipliedLast，但概念是相同的）。但是以任何你想要的方式访问/操作缓冲区。

循环显示图片中的像素

1 个答案: