Performance issues when trimming UIImage (CoreGraphics, iOS)

The main idea of ​​what we are trying to do is that we have a large UIImage and we want to cut it into several parts. The user of the function can pass in the number of rows and the number of columns, and the image will be cropped accordingly (i.e. 3 rows and 3 columns cut the image into 9 parts). The problem is that we are having performance issues when trying to accomplish this using CoreGraphics. The largest grid we need is 5x5, and it takes a few seconds to complete the operation (which registers as a timeout for the user). This, of course, is far from optimal.

My colleague and I spent quite a lot of time on this, and unsuccessfully searched the Internet for answers. None of us have experience with Core Graphics, so I hope that the code will have some kind of stupid error that will help fix our problems. He left you SO users to help us figure it out!

We used the tutorial at http://www.hive05.com/2008/11/crop-an-image-using-the-iphone-sdk/ to update our code.

Function below:

-(void) getImagesFromImage:(UIImage*)image withRow:(NSInteger)rows withColumn:(NSInteger)columns
{
    CGSize imageSize = image.size;
    CGFloat xPos = 0.0;
    CGFloat yPos = 0.0;
    CGFloat width = imageSize.width / columns;
    CGFloat height = imageSize.height / rows;

    int imageCounter = 0;

    //create a context to do our clipping in
    UIGraphicsBeginImageContext(CGSizeMake(width, height));
    CGContextRef currentContext = UIGraphicsGetCurrentContext();

    CGRect clippedRect = CGRectMake(0, 0, width, height);
    CGContextClipToRect(currentContext, clippedRect);

    for(int i = 0; i < rows; i++)
    {
        xPos = 0.0;
        for(int j = 0; j < columns; j++)
        {
            //create a rect with the size we want to crop the image to
            //the X and Y here are zero so we start at the beginning of our
            //newly created context
            CGRect rect = CGRectMake(xPos, yPos, width, height);

            //create a rect equivalent to the full size of the image
            //offset the rect by the X and Y we want to start the crop
            //from in order to cut off anything before them
            CGRect drawRect = CGRectMake(rect.origin.x * -1,
                                     rect.origin.y * -1,
                                     image.size.width,
                                     image.size.height);

            //draw the image to our clipped context using our offset rect
            CGContextDrawImage(currentContext, drawRect, image.CGImage);

            //pull the image from our cropped context
            UIImage* croppedImg = UIGraphicsGetImageFromCurrentImageContext();


            //PuzzlePiece is a UIView subclass
            PuzzlePiece* newPP = [[PuzzlePiece alloc] initWithImageAndFrameAndID:croppedImg :rect :imageCounter];
            [slicedImages addObject:newPP];

            imageCounter++;
            xPos += (width);
        }
        yPos += (height);
    }
    //pop the context to get back to the default
    UIGraphicsEndImageContext();
}

ANY advice is highly appreciated!