iphone关于图片的剪裁问题

创建一个UIImage：

@implementation UIImage (Crop)

- (UIImage *)crop:(CGRect)cropRect {

    cropRect = CGRectMake(cropRect.origin.x*self.scale, 
                      cropRect.origin.y*self.scale, 
                      cropRect.size.width*self.scale, 
                      cropRect.size.height*self.scale);       

    CGImageRef imageRef = CGImageCreateWithImageInRect([self CGImage], cropRect);
    UIImage *result = [UIImage imageWithCGImage:imageRef 
                                          scale:self.scale 
                                    orientation:self.imageOrientation]; 
    CGImageRelease(imageRef);
    return result;
}