ios 截图原图、压缩图

注意：获取原图的时候，需要考虑图片的scale，否则截取的图片不对。

/// 获得某个范围内的屏幕图像 -- 原图需要考虑scale
+ (UIImage *)imageFromView:(UIView *)view atFrame:(CGRect)rect {
    /// 不是高清的
//    UIGraphicsBeginImageContextWithOptions(view.frame.size, NO, 1.0);
    /// 高清的
    UIGraphicsBeginImageContextWithOptions(view.frame.size, NO, 0.0);
    [view.layer renderInContext:UIGraphicsGetCurrentContext()];
    
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    // 原图的话需要考虑 scale ---- 这样就ok了，原图，并且图片正常
    CGRect myImageRect = CGRectMake(rect.origin.x*image.scale, rect.origin.y*image.scale, rect.size.width*image.scale, rect.size.height*image.scale);
    // 不是原图，不用考虑
//    CGRect myImageRect = rect;

    CGImageRef imageRef = image.CGImage;
    CGImageRef subImageRef = CGImageCreateWithImageInRect(imageRef,myImageRect );
    
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextDrawImage(context, myImageRect, subImageRef);
    UIImage* smallImage = [UIImage imageWithCGImage:subImageRef];
    CGImageRelease(subImageRef);
    UIGraphicsEndImageContext();
    
    return smallImage;
}