How to check if UIImage has transparency

user_14716075 0
Viewed 849

I use this function to detect if UIImage has transparency:

extension UIImage {
  public func isTransparent() -> Bool {
    guard let alpha: CGImageAlphaInfo = self.cgImage?.alphaInfo else { return false }
    return alpha == .first || alpha == .last || alpha == .premultipliedFirst || alpha == .premultipliedLast
  }
}

But it doesn't work. I tried it with a png Image with no transparency but it still return true.

Loop for each pixel is not a good idea because it's too expensive i guess. Any idea how to check if UIImage has transparency, like this image: image

uiimage swift ios
2 Answers

You asked about Swift. Menaim gave a useful answer, but in Objective-C.

Here is a Swift version:

extension UIImage {
    var hasAlpha: Bool {
        guard let alphaInfo = self.cgImage?.alphaInfo else {return false}
        return alphaInfo != CGImageAlphaInfo.none &&
            alphaInfo != CGImageAlphaInfo.noneSkipFirst &&
            alphaInfo != CGImageAlphaInfo.noneSkipLast
    }
}

I just tested the above on a PNG image with no alpha channel and it worked.

Here is a PNG image with no alpha channel (Assuming SO's site preserves it...) PNG image with no alpha

user_2051850

Your solution seems to be good and working without issues but you can check out this one as well:

- (BOOL)hasAlpha : (UIImage*) img
{
    CGImageAlphaInfo alpha = CGImageGetAlphaInfo(img.CGImage);
    return (
            alpha == kCGImageAlphaFirst ||
            alpha == kCGImageAlphaLast ||
            alpha == kCGImageAlphaPremultipliedFirst ||
            alpha == kCGImageAlphaPremultipliedLast
            );

}
user_144374110
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