This node does a lot of interesting things. The LAST character in the character box will ALWAYS be the luminance of the image. So if you have a blank space in the box, luminance will be represented as negative space.

Another thing you can do is play with the spacing of the characters to achieve an overlapping effect. CARFUL putting the overlap too low, it will take a lot of time to process and you essentially get back your original image.

If you use alt codes that are full colored in boxes, you can achieve a pixelation effect!

Go nuts, have fun