将图片重新绘制

- (UIImage *)resetImage:(UIImage *)sourceImage withSize:(CGSize)size withRect:(CGRect)newImageRect

{

    UIGraphicsBeginImageContext(size); //size 为CGSize类型，即你所需要的图片尺寸

    [sourceImage drawInRect:newImageRect]; //newImageRect指定了图片绘制区域

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    

    return newImage;

}