上传图片的正确方式：上传图片到服务器一般是将图片NSData上传到服务器，服务器返回一个图片NSString地址，之后再将NSString的路径转为url并通过url请求去更新图片（图片此时更新的便是NSString）
上传的图片一般压缩方式是：
NSData *eachImgData = UIImageJPEGRepresentation(image, 0.5);
但，你可能会发现这样设置之后，上传还是比较慢，即使是把压缩比例设置为0.1 结果还是一样。
不过，如果你去查看上传之后的图片，就可以发现问题所在：
首先，你也许会看到图片大小 大概为200-300KB 为何这么小了 还是上传比较慢，或者加载比较慢，这是因为你忽略了一个图片分辨率的压缩过程，所以此时你要压缩的不只是图片大小，还是图片分辨率
然后，附上图片分辨率压缩代码：
//等比例压缩
+ (UIImage *) imageCompressForSize:(UIImage *)sourceImage targetSize:(CGSize)size {
UIImage *newImage = nil;
CGSize imageSize = sourceImage.size;
CGFloat width = imageSize.width;
CGFloat height = imageSize.height;
CGFloat targetWidth = size.width;
CGFloat targetHeight = size.height;
CGFloat scaleFactor = 0.0;
CGFloat scaledWidth = targetWidth;
CGFloat scaledHeight = targetHeight;
CGPoint thumbnailPoint = CGPointMake(0.0, 0.0);
if(CGSizeEqualToSize(imageSize, size) == NO){
CGFloat widthFactor = targetWidth / width;
CGFloat heightFactor = targetHeight / height;
if(widthFactor > heightFactor){
scaleFactor = widthFactor;
}
else{
scaleFactor = heightFactor;
}
scaledWidth = width * scaleFactor;
scaledHeight = height * scaleFactor;
if(widthFactor > heightFactor){
thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
}else if(widthFactor < heightFactor){
thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
}
}
UIGraphicsBeginImageContext(size);
CGRect thumbnailRect = CGRectZero;
thumbnailRect.origin = thumbnailPoint;
thumbnailRect.size.width = scaledWidth;
thumbnailRect.size.height = scaledHeight;
[sourceImage drawInRect:thumbnailRect];
newImage = UIGraphicsGetImageFromCurrentImageContext();
if(newImage == nil){
NSLog(@"scale image fail");
}
UIGraphicsEndImageContext();
return newImage;
}
这样双重压缩，完美解决图片压缩问题。