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Looking a Little Spotty

Science Snack
Looking a Little Spotty
Think you’re seeing the whole picture? Think again.
Looking a Little Spotty
Think you’re seeing the whole picture? Think again.

You’d be surprised at the small amount of information your brain needs to produce images. By digitally manipulating an image using a halftone technique, you can test how well your brain can see something where—at first glance—there appears to be nothing but spots.

Tools and Materials
  • Graphic design software that can apply a halftone filter to an image (you can try Adobe Photoshop or search for free online graphic design software or image processing apps)
  • A digital camera (your phone's camera will work, too)
  • A method of presentation such as a printer to print the image onto paper (recommended), a computer screen, or a computer projector
  1. Using a digital camera, take a picture of someone’s (or your own) face against a white or neutral background.
  2. Load the image into the graphic design software or app of your choice.
  3. Find and apply the software's halftone filter (you may need to convert your picture to grayscale first).
  4. Most programs will let you manipulate an image using halftone in a variety of ways. Try experimenting with the following variables:
    • Size of dots
    • Spacing of dots
    • Size of image
    • Angle of dots
  5. Print your halftone image (recommended) or display it using a computer screen or projector.
To Do and Notice

View the image from different distances: close up and far away. Is it easier to see what image is revealed when you are close to it or far from it? If possible, keep the identity of the image a surprise, and let participants figure it out by experimenting with his or her viewing distance.

If you are in a group, collect data on different viewers' ability to perceive the image. Consider the following:

  • At what distance can viewers perceive that the halftone image is of a face?
  • Where do they recognize whose face it is?
  • What dot size breaks the ability to recognize the original image?

What other factors affect the viewer’s ability to recognize the original image? Consider the following:

  • Are friends easier to recognize than strangers?
  • Does a plain or busy background affect how easily recognizable the image is?
  • If the subject of the photo wears glasses or a hat, does that make it easier or harder to recognize him or her in halftone?
  • Is a face photographed from the side or at an angle harder to recognize in halftone?

Try other pixelation filters, such as “pointillize” and “mosaic.” How do these filters affect a viewer’s ability to recognize the image? 

Try applying a halftone filter to images of things other than faces—does this affect a viewer’s ability to recognize the image? For example, can you tell what the image below is? (See the Resources section below for the answer.)

What’s Going On?

Halftone is a way of reproducing an image through the use of dots or spots, varying in size, shape, or spacing to generate a gradient-like effect. 

This Snack involves your brain, your eyes, and geometry. Your brain is built to recognize patterns. A pattern that looks like a face is a high priority for your brain—recognizing faces is important to our survival. The area of your brain devoted to facial recognition is known as the fusiform gyrus.

Up close, the spots are projected onto the retina, at the back of your eye. At a close distance the spots may look like, well, a bunch of spots! 

As you move farther away from the picture, the image of the face becomes smaller and you become less able to distinguish between adjacent spots. Because of your eye’s resolving power, you perceive shades of gray rather than spots and blank spaces. 

As a result, your eye–brain system is better able to recognize the smaller, slightly blurred image at a distance as being a face more easily than the up-close—but therefore larger—pixelated image.

Going Further

When television sets first came out, their resolution was terrible. Despite this, people were still amazed that they could see announcers and actors in a box in their living rooms. While the television resolution is getting better and better, we still rely on the same processing powers of our eye–brain system to perceive the images. 

Masterpieces of art often rely on our ability to resolve images with a minimal amount of information—see the work of Vincent van Gogh, Georges-Pierre Seurat, or Chuck Close for some good examples.

Your eye–brain system is always trying to recognize faces—even if there isn’t actually one there. Have you ever seen the features of a human face appear on rocks, in clouds, or on the moon? People have even seen human faces appear on Mars!


Answer: It’s a bicycle! 

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