UIImage裁剪出透明像素 [英] UIImage Crop Out Transparent Pixels

问题描述

在使用swift 4从UIImage裁剪透明像素之后，我需要帮助来创建完美的清晰图像.

我要创建具有去除透明色的图像，因此我使用了下面的代码.但它会模糊带有小的小方块的图像矩形出现.

I want to create image with remove transparent color, So for that i have used below code. But it blur image with small small square rectangles appears.

使用以下代码

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;
    }
}

推荐答案

在此行中检查alpha分量是否正好> 0可能不够:

Checking that the alpha component is just > zero maybe not enough in this line:

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

也许您可以将阈值设置得更高: if(a> 0.5)甚至更高. if(a == 1)是限制，它将保证根本不透明.

Maybe you could make the threshold higher : if(a > 0.5) or even higher. if (a == 1) would be the limit and it would guarantee that there is no transparency at all.

如果您想让 imageCroppedBg 的大小与 imgWithClearBackgroung 的大小相同，请设置 UIImageView 的内容模式，其中 imgWithClearBackgroung 到 .scaleAspectFit :

If you'd like to have the imageCroppedBg with the same size of imgWithClearBackgroung, then set the content mode of the UIImageView containing imgWithClearBackgroung to .scaleAspectFit:

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

有关内容模式的更多信息，请在此处a>.

For more on content modes, have a look here.

附言:在Swift中，行末尾不需要; .

P.S: In Swift the ; is not necessary at the end of the line.

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