gistfile1.m

CGSize imageSize = image.size;
    CGSize targetSize = CGSizeMake(36.0, 36.0);
    CGFloat scaleFactor = 1.0;
    CGFloat scaledWidth = imageSize.width;
    CGFloat scaledHeight = imageSize.height;
    CGPoint scaledOrigin = CGPointMake(0.0,0.0);
    CGFloat widthFactor = targetSize.width / imageSize.width;
    CGFloat heightFactor = targetSize.height / imageSize.height;
    // only scale if larger than target
    if ((image.size.width > targetSize.width) || (image.size.height > targetSize.height)) {
        // compute scaling
        
        if (widthFactor < heightFactor) 
            scaleFactor = widthFactor; // scale to fit height
        else
            scaleFactor = heightFactor; // scale to fit width
        scaledWidth  = imageSize.width * scaleFactor;
        scaledHeight = imageSize.height * scaleFactor;        
    }
    
    // center the image
    if (targetSize.height > scaledHeight)
    {
        scaledOrigin.y = (targetSize.height - scaledHeight) * 0.5; 
    }
    if (targetSize.width > scaledWidth)
    {
        scaledOrigin.x = (targetSize.width - scaledWidth) * 0.5;
    }