What are distance-dependent illusions?
Distance-dependent illusions look like plain patterns or noise up close, but text or a picture appears when you move away from the screen. They are also known as hybrid images. It is a single image, and only your viewing distance changes what you see.
How to try it
Open Hidden Text and try any of these:
- Hold your phone at full arm’s length, or step back two or three paces from your computer.
- Squint.
- Take off your glasses, or shrink the image on screen.
All of them make fine detail harder to see.
Why does distance change what you see?
An image can be thought of as fine changes (high spatial frequency) laid over broad light and dark (low spatial frequency). Up close, the fine pattern stands out and the broad shading is lost in the background. From farther away, your eye can no longer resolve the fine pattern, and only the broad light and dark remains. In this illusion, the text is put in the broad light-and-dark layer and the noise in the fine-pattern layer.
Connection to other illusions
Not seeing something up close but seeing it from afar feels a lot like Hidden and ambiguous images. In hidden images your interpretation switches. Here, the part of the image you can see switches.