更改UIImage中某些像素的颜色

Question

对于给定的多色PNG UIImage (具有透明度)，最佳/Swift-惯用方式是：

1. 创建一个重复的UIImage
2. 查找副本中的所有黑色像素，并将其更改为红色。
3. (交回经修改的副本)

有几个相关的问题，所以，但我一直未能找到一些有用的东西。

Answer 1

你必须提取图像的像素缓冲区，在这一点上你可以循环通过，改变你认为合适的像素。最后，从缓冲区创建一个新图像。

在Swift 3中，如下所示：

func processPixels(in image: UIImage) -> UIImage? {
    guard let inputCGImage = image.cgImage else {
        print("unable to get cgImage")
        return nil
    }
    let colorSpace       = CGColorSpaceCreateDeviceRGB()
    let width            = inputCGImage.width
    let height           = inputCGImage.height
    let bytesPerPixel    = 4
    let bitsPerComponent = 8
    let bytesPerRow      = bytesPerPixel * width
    let bitmapInfo       = RGBA32.bitmapInfo

    guard let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo) else {
        print("unable to create context")
        return nil
    }
    context.draw(inputCGImage, in: CGRect(x: 0, y: 0, width: width, height: height))

    guard let buffer = context.data else {
        print("unable to get context data")
        return nil
    }

    let pixelBuffer = buffer.bindMemory(to: RGBA32.self, capacity: width * height)

    for row in 0 ..< Int(height) {
        for column in 0 ..< Int(width) {
            let offset = row * width + column
            if pixelBuffer[offset] == .black {
                pixelBuffer[offset] = .red
            }
        }
    }

    let outputCGImage = context.makeImage()!
    let outputImage = UIImage(cgImage: outputCGImage, scale: image.scale, orientation: image.imageOrientation)

    return outputImage
}

struct RGBA32: Equatable {
    private var color: UInt32

    var redComponent: UInt8 {
        return UInt8((color >> 24) & 255)
    }

    var greenComponent: UInt8 {
        return UInt8((color >> 16) & 255)
    }

    var blueComponent: UInt8 {
        return UInt8((color >> 8) & 255)
    }

    var alphaComponent: UInt8 {
        return UInt8((color >> 0) & 255)
    }        

    init(red: UInt8, green: UInt8, blue: UInt8, alpha: UInt8) {
        let red   = UInt32(red)
        let green = UInt32(green)
        let blue  = UInt32(blue)
        let alpha = UInt32(alpha)
        color = (red << 24) | (green << 16) | (blue << 8) | (alpha << 0)
    }

    static let red     = RGBA32(red: 255, green: 0,   blue: 0,   alpha: 255)
    static let green   = RGBA32(red: 0,   green: 255, blue: 0,   alpha: 255)
    static let blue    = RGBA32(red: 0,   green: 0,   blue: 255, alpha: 255)
    static let white   = RGBA32(red: 255, green: 255, blue: 255, alpha: 255)
    static let black   = RGBA32(red: 0,   green: 0,   blue: 0,   alpha: 255)
    static let magenta = RGBA32(red: 255, green: 0,   blue: 255, alpha: 255)
    static let yellow  = RGBA32(red: 255, green: 255, blue: 0,   alpha: 255)
    static let cyan    = RGBA32(red: 0,   green: 255, blue: 255, alpha: 255)

    static let bitmapInfo = CGImageAlphaInfo.premultipliedLast.rawValue | CGBitmapInfo.byteOrder32Little.rawValue

    static func ==(lhs: RGBA32, rhs: RGBA32) -> Bool {
        return lhs.color == rhs.color
    }
}

有关Swift 2版本，请参见previous revision of this answer。

Answer 2

为了获得更好的结果，我们可以搜索图像像素的颜色范围，参考我更新的@Rob答案，现在结果更好了。

func processByPixel(in image: UIImage) -> UIImage? {

    guard let inputCGImage = image.cgImage else { print("unable to get cgImage"); return nil }
    let colorSpace       = CGColorSpaceCreateDeviceRGB()
    let width            = inputCGImage.width
    let height           = inputCGImage.height
    let bytesPerPixel    = 4
    let bitsPerComponent = 8
    let bytesPerRow      = bytesPerPixel * width
    let bitmapInfo       = RGBA32.bitmapInfo

    guard let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo) else {
        print("Cannot create context!"); return nil
    }
    context.draw(inputCGImage, in: CGRect(x: 0, y: 0, width: width, height: height))

    guard let buffer = context.data else { print("Cannot get context data!"); return nil }

    let pixelBuffer = buffer.bindMemory(to: RGBA32.self, capacity: width * height)

    for row in 0 ..< Int(height) {
        for column in 0 ..< Int(width) {
            let offset = row * width + column

           /*
             * Here I'm looking for color : RGBA32(red: 231, green: 239, blue: 247, alpha: 255)
             * and I will convert pixels color that in range of above color to transparent
             * so comparetion can done like this (pixelColorRedComp >= ourColorRedComp - 1 && pixelColorRedComp <= ourColorRedComp + 1 && green && blue)
             */

            if pixelBuffer[offset].redComponent >=  230 && pixelBuffer[offset].redComponent <=  232 &&
                pixelBuffer[offset].greenComponent >=  238 && pixelBuffer[offset].greenComponent <=  240 &&
                pixelBuffer[offset].blueComponent >= 246 && pixelBuffer[offset].blueComponent <= 248 &&
                pixelBuffer[offset].alphaComponent == 255 {
                pixelBuffer[offset] = .transparent
            }
        }
    }

    let outputCGImage = context.makeImage()!
    let outputImage = UIImage(cgImage: outputCGImage, scale: image.scale, orientation: image.imageOrientation)

    return outputImage
}

我希望这能帮到别人