Swift4) Pixel 단위 변환 코드

픽셀 Structure

32비트짜리에서 LSB부터 8비트씩 RGBA값을 갖기 때문에 아래와 같은 시프트 연산을 통해서 Structure을 구성했다.

public struct RGBAPixel {
    public var raw: UInt32
    public var red: UInt8 {
        get { return UInt8(raw & 0xFF) }
        set { raw = UInt32(newValue) | (raw & 0xFFFFFF00)}
    }
    public var green: UInt8 {
        get { return UInt8((raw & 0xFF00) >> 8) }
        set { raw = (UInt32(newValue) << 8) | (raw & 0xFFFF00FF)}
    }
    public var blue: UInt8 {
        get { return UInt8((raw & 0xFF0000) >> 16) }
        set { raw = (UInt32(newValue) << 16) | (raw & 0xFF00FFFF)}
    }
    public var alpha: UInt8 {
        get { return UInt8((raw & 0xFF000000) >> 24) }
        set { raw = (UInt32(newValue) << 24) | (raw & 0x00FFFFFF)}
    }
}

이미지 변환 코드

func changeWhiteToTransparent(image: UIImage) -> UIImage {

    let height = Int(image.size.height)
    let width = Int(image.size.width)

    let bitsPerComponents = 8
    let bytesPerRow = 4 * width
    let colorspace = CGColorSpaceCreateDeviceRGB()
    let rawdata = UnsafeMutablePointer<RGBAPixel>.allocate(capacity: width*height)
    let bitmapInfo: UInt32 = CGBitmapInfo.byteOrder32Big.rawValue | CGImageAlphaInfo.premultipliedLast.rawValue
    let imageContext = CGContext(data: rawdata, width: width, height: height, bitsPerComponent: bitsPerComponents, bytesPerRow: bytesPerRow, space: colorspace, bitmapInfo: bitmapInfo)

    imageContext?.draw(image.cgImage!, in: CGRect(origin: CGPoint.zero, size: image.size))

    let pixels = UnsafeMutableBufferPointer<RGBAPixel>(start: rawdata, count: width*height)

    for y in 0 ..< height {
        for x in 0 ..< width {
            var p = pixels[x+y*width]
            p.alpha = 0
            pixels[x+y*width] = p
        }
    }

    let outcontext = CGContext(data: pixels.baseAddress, width: width, height: height, bitsPerComponent: bitsPerComponents, bytesPerRow: bytesPerRow, space: colorspace, bitmapInfo: bitmapInfo, releaseCallback: nil, releaseInfo: nil)
    // let cgimg = outcontext?.makeImage()
    let outImage = UIImage(cgImage: (outcontext?.makeImage())!)

    return outImage

}

for y in 0 ..< height {
    for x in 0 ..< width {
        var p = pixels[x+y*width]
        p.alpha = 0
        pixels[x+y*width] = p
    }
}

위의 부분을 변경해서 픽셀 단위로 변환시키면 된다.

출처: https://www.youtube.com/watch?v=S9fbO9l4mVM