按尺寸質量調整任何影象大小

- (UIImage *)drawImageBySize:(CGSize)size quality:(CGInterpolationQuality)quality
{
    UIGraphicsBeginImageContextWithOptions(size, NO, 0.0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetInterpolationQuality(context, quality);
    [self drawInRect: CGRectMake (0, 0, size.width, size.height)];
    UIImage *resizedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return resizedImage;
}