The solution of https://stackoverflow.com/a/40237504/3286489, only works on sRGB colorspace type of image. However, for a different colorspace (extended sRGB??), it doesn't work.
So to make it work, need to convert it to a normal sRGB image type first, before getting the color from the cgImage. Note we need to add padding to the calculation to ensure the width is always a factor of 8
public extension UIImage {
func getPixelColor(pos: CGPoint) -> UIColor {
// convert to standard sRGB image
guard let cgImage = cgImage,
let colorSpace = CGColorSpace(name: CGColorSpace.sRGB),
let context = CGContext(data: nil,
width: Int(size.width), height: Int(size.height),
bitsPerComponent: 8, bytesPerRow: 0, space: colorSpace,
bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)
else { return .white }
context.draw(cgImage, in: CGRect(origin: .zero, size: size))
// Get the newly converted cgImage
guard let newCGImage = context.makeImage(),
let newDataProvider = newCGImage.dataProvider,
let data = newDataProvider.data
else { return .white }
let pixelData: UnsafePointer<UInt8> = CFDataGetBytePtr(data)
// Calculate the pixel position based on point given
let remaining = 8 - ((Int(size.width)) % 8)
let padding = (remaining < 8) ? remaining : 0
let pixelInfo: Int = (((Int(size.width) + padding) * Int(pos.y)) + Int(pos.x)) * 4
let r = CGFloat(pixelData[pixelInfo]) / CGFloat(255.0)
let g = CGFloat(pixelData[pixelInfo+1]) / CGFloat(255.0)
let b = CGFloat(pixelData[pixelInfo+2]) / CGFloat(255.0)
let a = CGFloat(pixelData[pixelInfo+3]) / CGFloat(255.0)
return UIColor(red: r, green: g, blue: b, alpha: a)
}
}
Optionally, if one doesn't want to convert to cgImage, just replace
// Get the newly converted cgImage
guard let newCGImage = context.makeImage(),
let newDataProvider = newCGImage.dataProvider,
let newData = newDataProvider.data
else { return .white }
let pixelData: UnsafePointer<UInt8> = CFDataGetBytePtr(newData)
With
// Get the data and bind it from UnsafeMutableRawPointer to UInt8
guard let data = context.data else { return .white }
let pixelData = data.bindMemory(
to: UInt8.self, capacity: Int(size.width * size.height * 4))
Updated
To get an even more concise code, we can improve the convert to sRGB using UIGraphicsImageRenderer directly. The calculation does changes a bit as due such redrawing refine the pixel to be 2x further.
func getPixelColor(pos: CGPoint) -> UIColor {
let newImage = UIGraphicsImageRenderer(size: size).image { _ in
draw(in: CGRect(origin: .zero, size: size))
}
guard let cgImage = newImage.cgImage,
let dataProvider = cgImage.dataProvider,
let data = dataProvider.data else { return .white }
let pixelData: UnsafePointer<UInt8> = CFDataGetBytePtr(data)
let remaining = 8 - ((Int(size.width) * 2) % 8)
let padding = (remaining < 8) ? remaining : 0
let pixelInfo: Int = (((Int(size.width * 2) + padding) * Int(pos.y * 2)) + Int(pos.x * 2)) * 4
let r = CGFloat(pixelData[pixelInfo]) / CGFloat(255.0)
let g = CGFloat(pixelData[pixelInfo+1]) / CGFloat(255.0)
let b = CGFloat(pixelData[pixelInfo+2]) / CGFloat(255.0)
let a = CGFloat(pixelData[pixelInfo+3]) / CGFloat(255.0)
return UIColor(red: r, green: g, blue: b, alpha: a)
}
This is as per solution of convert to sRGB in https://stackoverflow.com/a/64538344/3286489
