更改UIImage中某些像素的颜色 [英] Change color of certain pixels in a UIImage

问题描述

对于给定的多色PNG UIImage （透明度），最佳/ Swift惯用法是什么：

For a given multi-color PNG UIImage (with transparency), what is the best/Swift-idiomatic way to:

1. 创建一个重复的 UIImage


2. 查找副本中的所有黑色像素并更改它们红色


3. （返回修改后的副本）

关于SO的一些相关问题但是我找不到有用的东西。

There are a few related questions on SO but I haven't been able to find something that works.

推荐答案

你必须提取图像的像素缓冲区，哪一点你可以循环，根据你的需要改变像素。最后，从缓冲区创建一个新图像。

You have to extract the pixel buffer of the image, at which point you can loop through, changing pixels as you see fit. At the end, create a new image from the buffer.

在Swift 3中，这看起来像：

In Swift 3, this looks like:

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
    }
}

对于Swift 2格式，请参阅此答案的上一版本。

For Swift 2 rendition, see previous revision of this answer.

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