ios – 使用CGContextClip剪切带图像的圆圈

在我的应用程序中有一个imageViewA(框架{0,0,320,200}),我想用imageViewA的中心剪切一个圆,半径= 50,并绘制到另一个imageViewB(框架{0,0,100,100});
像这样的原始图像效果：

并使用下面的代码来剪辑：

UIGraphicsBeginImageContext(self.frame.size);
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGFloat height = self.bounds.size.height;
CGContextTranslateCTM(ctx, 0.0, height);
CGContextScaleCTM(ctx, 1.0, -1.0);
CGContextAddArc(ctx, self.frame.size.width/2, self.frame.size.height/2, 50, 0, 2*M_PI, 0);
CGContextClosePath(ctx);
CGContextSaveGState(ctx);
CGContextClip(ctx);
CGContextDrawImage(ctx, CGRectMake(0,0,self.frame.size.width, self.frame.size.height), image.CGImage);
CGContextRestoreGState(ctx);
CGImageRef imageRef = CGBitmapContextCreateImage (ctx);
UIImage *newImage = [UIImage imageWithCGImage:imageRef];
NSString *headerPath = [NSString stringWithFormat:@"%@/header.png",HomeDirectory];
NSData *imageData = UIImageJPEGRepresentation(newImage, 1.0);
if([imageData writeToFile:headerPath atomically:YES]){
    imageViewB.image = [UIImage imageWithContentsOfFile:headerPath];
}

剪辑图像效果如下：

我只需要圆形视图,但剪辑效果显示imageViewB有空白区域.
如何正确剪辑此图片？
谢谢！

imageViewB.layer.cornerRadius = 50.0;
imageViewB.layer.masksToBounds = YES;