Swift 在CALayer中添加并居中图像

我想把图像放在CALayer的中心。甚至图像大小也必须相应地修改，并且图像的颜色也应该着色。问题是我无法设置图像大小，甚至无法添加颜色

    //premium gradient
    let premiumViewLayer=CALayer()
    premiumViewLayer.bounds=CGRect(x:0, y:0, width:(getGradientWidth()), height:(LKView.bounds.height))
    premiumViewLayer.backgroundColor = UIColor.clear.cgColor

    let premiumimageViewLayer=CALayer()
    premiumimageViewLayer.frame = SSView.frame
    premiumimageViewLayer.contents=UIImage(named: "premium")?.cgImage
    premiumimageViewLayer.contentsGravity = kCAGravityCenter

    premiumViewLayer.addSublayer(premiumimageViewLayer)

我想实现以下目标：

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试试这一款，它能用：：

  let premiumViewLayer=CALayer()
    premiumViewLayer.frame = CGRect(origin: CGPoint.zero, size: imgView.frame.size)//CGRect(x:0, y:0, width:375, height:333.5)
    premiumViewLayer.backgroundColor = UIColor(white: 1.0, alpha: 0.5).cgColor
    premiumViewLayer.contents=UIImage(named: "premium")?.cgImage
    premiumViewLayer.contentsGravity = kCAGravityCenter
    view(on which on want to add this layer).layer.addSublayer(premiumViewLayer)

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锁的图像与图层相比太大了。你能告诉我图像的大小吗。。。或者根据您的要求选择图像大小a/c，例如2x或3x2x是图像的大小。图像太大。