Squint/Spatial Illusion

To check your rendering for balance, you can squint your eyes, which helps you concentrate on shapes and lines, avoiding all the detail. Your rendering will never look complete, until you achieve balance in your composition. To show you the value of squinting, here is a squint/spatial illusion

On a close-up view, you can see on the left face, an angry man and on the right face, a woman with a neutral facial emotion. But further back, the faces change expression and even genders! if you squint, blink, or defocus, an angry man should substitute for the face of the woman, and the left angry face should not be angry anymore.

This impressive illusion created by Dr. Aude Oliva and Dr. Philippe G. Schyns, illustrates the ability of the visual system to separate information coming from different spatial frequency channels. In the right image, high Spatial Frequencies (HSF) represent a woman with a neutral facial expression, mixed with the low spatial frequency (LSF) information from the face of an angry man. On the left, the face of the angry man is represented in fine details whereas the underlying female face is made of blur only ("blobs")