How to Resize image before downloading it to iphone

I am downloading images from server and saving them locally in my iphone,But sometimes the image is too large.for ex (2500*3200). i want to reduce the size to 300*500 before downloading that into iphone.how can i do this .Please help me in this .THANKS IN ADVANCE

+(void)DownloadImage:(NSString*)ImagePath{

    if ([ImagePath isEqualToString:@""])
        return;

    NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:[IMAGEURL stringByAppendingPathComponent:Im开发者_如何学GoagePath]]];

    NSString *docDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    [data writeToFile:[docDir stringByAppendingPathComponent:ImagePath] atomically:YES];        

}

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If you don't have option to scale it down on the server (which would be better).

then look at this: Any code/library to scale down an UIImage?

which should enable you to download the image, then scale it down, then save it to the phone etc.