調整UIImage Size，方便縮圖使用。
呼叫：
UIImage* image =[self imageWithImageSimple:image scaledToSize:CGSizeMake(512.0, 512.0)];//縮小至512X512
函式：
//照片縮小 image,最大寬高
- (UIImage*)imageWithImageSimple:(UIImage*)image scaledToSize:(CGSize)newSize
{
float width,height;
if (image.size.width<newSize.width && image.size.height<newSize.height){
//如果已經小於newSize則不縮小
width=image.size.width;
height=image.size.height;
}else if (image.size.height >= (newSize.height/newSize.width)*image.size.width){
width=image.size.width/image.size.height*newSize.height;
height=newSize.height;
}else{
height=image.size.height/image.size.width*newSize.height;
width=newSize.width;
}
newSize.width=width;
newSize.height=height;
// Create a graphics image context
UIGraphicsBeginImageContext(newSize);
// Tell the old image to draw in this new context, with the desired
// new size
[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
// Get the new image from the context
UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
// End the context
UIGraphicsEndImageContext();
// Return the new image.
return newImage;
}
