ios - UIImage 裁剪出透明像素

Question

在使用 swift 4 从 UIImage 裁剪透明像素后，我需要帮助来创建完美清晰的图像。

I want to create image with remove transparent color, So for that ihave used below code. But it blur image with small small squarerectangles appears.

使用下面的代码

let imageCroppedBg = imgWithClearBackgroung!.cropAlpha()


//UIImage extension
extension UIImage {
    func cropAlpha() -> UIImage {
        
        let cgImage = self.cgImage!;
        
        let width = cgImage.width
        let height = cgImage.height
        
        let colorSpace = CGColorSpaceCreateDeviceRGB()
        let bytesPerPixel:Int = 4
        let bytesPerRow = bytesPerPixel * width
        let bitsPerComponent = 8
        let bitmapInfo: UInt32 = CGImageAlphaInfo.premultipliedLast.rawValue | CGBitmapInfo.byteOrder32Big.rawValue
        
        guard let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo),
            let ptr = context.data?.assumingMemoryBound(to: UInt8.self) else {
                return self
        }
        
        context.draw(self.cgImage!, in: CGRect(x: 0, y: 0, width: width, height: height))
        
        var minX = width
        var minY = height
        var maxX: Int = 0
        var maxY: Int = 0
        
        for x in 1 ..< width {
            for y in 1 ..< height {
                
                let i = bytesPerRow * Int(y) + bytesPerPixel * Int(x)
                let a = CGFloat(ptr[i + 3]) / 255.0
                
                if(a>0) {
                    if (x < minX) { minX = x };
                    if (x > maxX) { maxX = x };
                    if (y < minY) { minY = y};
                    if (y > maxY) { maxY = y};
                }
            }
        }
        
        let rect = CGRect(x: CGFloat(minX),y: CGFloat(minY), width: CGFloat(maxX-minX), height: CGFloat(maxY-minY))
        let imageScale:CGFloat = self.scale
        let croppedImage =  self.cgImage!.cropping(to: rect)!
        let ret = UIImage(cgImage: croppedImage, scale: imageScale, orientation: self.imageOrientation)
        
        return ret;
    }
}

Answer 1

在这一行中检查 alpha 分量是否 > 零可能还不够:

if(a>0) {
    if (x < minX) { minX = x }
    if (x > maxX) { maxX = x }
    if (y < minY) { minY = y }
    if (y > maxY) { maxY = y }
}

也许您可以提高阈值:if(a > 0.5) 或什至更高。 if (a == 1) 将是限制，它会保证完全没有透明度。

如果您希望 imageCroppedBg 具有与 imgWithClearBackgroung 相同的大小，则设置包含 UIImageView 的内容模式 imgWithClearBackgroung 到 .scaleAspectFit:

let imageCroppedBg = imgWithClearBackgroung.cropAlpha()
imageView.image = imageCroppedBg
imageView.contentMode = .scaleAspectFit

有关内容模式的更多信息，请查看 here .

附言:在 Swift 中，; 不需要放在行尾。