压缩图片

- (UIImage*)scaleFromImage:(UIImage*)image scaledToSize:(CGSize)newSize
{
 CGSize imageSize = image.size;
 CGFloat width = imageSize.width;
 CGFloat height = imageSize.height;
     
 if (width <= newSize.width && height <= newSize.height){
  return image;
 }
     
 if (width == 0 || height == 0){
  return image;
 }
     
 CGFloat widthFactor = newSize.width / width;
 CGFloat heightFactor = newSize.height / height;
 CGFloat scaleFactor = (widthFactor<heightFactor?widthFactor:heightFactor);
     
 CGFloat scaledWidth = width * scaleFactor;
 CGFloat scaledHeight = height * scaleFactor;
 CGSize targetSize = CGSizeMake(scaledWidth,scaledHeight);
     
    UIGraphicsBeginImageContext(targetSize);
    [image drawInRect:CGRectMake(0,0,scaledWidth,scaledHeight)];
    UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}