Logic behind centering the image in the thumbnail


In the method -(void)setThumbDataFromImage:(UIImage *)image we set the dimensions and coordinate for projRect thumbnail.
I got the width and height computation wherein we multiply the origImageSize with scaling factor/ratio.
But then we use the following to give the thumbnail a position—

projectRect.origin.x= (newRect.size.width- projectRect.size.width)/2;
projectRect.origin.y= (newRect.size.height- projectRect.size.height)/2;

This i fail to understand. I cannot wrap my head around it. :confused:
Is this part of the centering process. I mean, are we using a mathematical relation here to position the thumbnail or is it some random calculation i.e could have been anything… Am i missing some fundamental behind these two lines of code?? :confused: :confused: