图片压缩到一定大小

-(UIImage *)saveNewImage:(UIImage )image{
CGFloat maxFileSize = 321024;
CGFloat compression = 0.9f;

UIGraphicsBeginImageContext(CGSizeMake(320, 480));
[image drawInRect:CGRectMake(0,0,320, 480)];
UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

NSData *compressedData = UIImageJPEGRepresentation(newImage, compression);
while ([compressedData length] > maxFileSize ) {
    if (compression<=0.1) {
        compression = 0.9;
    }
    else
    {
        compression -= 0.1;
    }
    UIImage *image_m = [UIImage imageWithData: compressedData];
    compressedData = UIImageJPEGRepresentation(image_m, compression);
    
    
}
UIImage *compressedImage = [UIImage imageWithData:compressedData];
return compressedImage;

}