For a given multi-color PNG UIImage
(with transparency), what is the best/Swift-idiomatic way to:
UIImage
There are a few related questions on SO but I haven't been able to find something that works.
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.
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
}
}
For Swift 2 rendition, see previous revision of this answer.