What Is the Color Afterimage Illusion? | Why a Black-and-White Image Looks Colored, and How to Make One
Stare at a color-inverted image for a while, then switch to a black-and-white version, and the photo that should be grayscale appears to have color. This guide explains why this “negative afterimage” happens, tips for seeing it clearly, and how to make the illusion from your own photos.
What is the color afterimage illusion (negative afterimage)?
The color afterimage illusion is what happens when, after looking at a color for a while, you look at a white surface or a black-and-white image and see the opposite of the color you were looking at. Because what appears is the opposite color rather than the original one, it is technically called a “negative afterimage”.
A well-known example shows a green pig and a pink frog. Stare at the mark in the center for a few tens of seconds, then switch to the black-and-white image, and the pig looks pink and the frog green even though the image has no color. The color isn't really there; a change happening in your eyes makes it look that way.
- You see the opposite color: staring at green brings up pink, staring at blue brings up yellow
- It lasts a few seconds: blinking or moving your eyes makes it fade quickly
- It varies from person to person: how well you see it depends on screen brightness, tiredness and how long you stared
A famous piece using the same principle has you stare at a flag with inverted colors and then look at white paper, where a flag in its real colors appears. Whether it is a flag or a photo, the mechanism is exactly the same.
Why you see color in a black-and-white image
The human retina has three kinds of cone cells that sense color. They respond most strongly to long wavelengths (reddish light), medium wavelengths (greenish light) and short wavelengths (bluish light), and the differing balance of these three responses is what we perceive as color.
- 1
Looking at one color tires the cells responsible for it
As you stare at a green area, the response of the cells that react strongly to green gradually drops. This is called adaptation: the process of getting used to a strong stimulus.
- 2
When it switches to black and white, they respond with the balance still off
A black-and-white image contains all wavelengths evenly, but because only the green-side sensitivity has dropped, the response on the red and pink side comes out relatively stronger.
- 3
The opposite color appears
As a result, the opposite color appears to sit on the black-and-white surface. The parts that were green in the inverted image look pink because the original color from before inversion is coming back.
In other words, staring at a color-inverted image is a way of burning the original colors in as an afterimage. The inverted image is made of the complementary colors of the original photo, so when that afterimage overlaps the black-and-white image, colors close to the original photo emerge.
How to try the afterimage illusion in your browser
There is nothing to install and no sign-up. All image conversion happens inside your browser, so your photos are never sent to a server.
- 1
Choose the staring time
Choose from 10, 20, 30 or 45 seconds. 20 seconds is about right to start with; for a stronger effect, use 30 seconds or more.
- 2
Press start and look only at the center mark
When the color-inverted image appears, keep your eyes on the ✕ in the center. Looking around the whole image blurs the afterimage.
- 3
Keep looking after it turns black and white
When the countdown ends, the image switches to black and white automatically. Don't move your eyes; keep staring for a few seconds and the colors will rise up.
- 4
Compare with the original color image
Switch to the color image to check whether the colors you saw were close to the real ones. If they roughly match, it worked.
- 5
Go full screen and repeat
The effect is easily affected by surrounding brightness, so full-screen mode makes it more consistent. You can also switch and restart with the space key or a click.
Making the illusion from your own photos
You can make the illusion not only from the sample image but from your own photos and illustrations. Besides choosing a file, you can swap the image by drag and drop.
- 1
Load an image
Choose an image from “Try your own image”. Large photos are scaled down to 1200 pixels on the long side before processing, so smartphone photos work as they are.
- 2
Adjust the color strength
This sets how vivid the inverted image is. Turn it up for photos with pale colors, and keep it modest for photos that are already highly saturated.
- 3
Pick a staring time and try it
The best length differs by photo. If 20 seconds is weak, extend it to 30 or 45 seconds and compare.
- 4
Save the inverted image and share it
“Save inverted image” exports it as a PNG. As material for a class or a stream, showing it together with the black-and-white version makes the reaction easy to see.
Photos that work well have something in common. What matters is not the amount of fine detail but how much clear area of color there is.
- Colors split into areas: things with large areas of color, such as sky, grass, fruit or sports uniforms
- High saturation: vivid colors produce a stronger afterimage than dull ones
- A large subject: something small in the frame is too fine to make out even in the afterimage
- Medium contrast: pure black and pure white areas don't take on afterimage color easily
Checks when you can't see the color
When you can't see any color at all, the cause is almost always how you are looking or which image you chose. Checking in the order below narrows it down quickly.
| Symptom | Likely cause | What to do |
|---|---|---|
| No color at all | Your eyes are moving | Look only at the center mark, and don't move your eyes for a few seconds after the switch |
| It appears for a moment and vanishes | That is normal | Afterimages fade within seconds. When it fades, use “Again” to burn it in again |
| The colors are faint | The staring time is too short | Extend it from 20 seconds to 30 or 45, and raise the color strength |
| The image is too bright to keep looking at | The color strength is too high | Lower the strength or turn down the screen brightness |
| It's hard to see with photos | The color areas are small and complex | Switch to a photo with large color areas, or get a feel for it with the sample |
| The surroundings are too bright | Outside light | Go full screen and dim the room lights a little |
How it looks also varies between people. The same image produces different strengths for different people, so finding it hard to see does not mean your eyesight is poor. If an image that looks similar comes from the screen itself, the fix is different. How to tell them apart is covered in telling screen image retention from burn-in.
Enjoying it without straining your eyes
The afterimage illusion is a phenomenon you cause by deliberately staring at strong colors. By its nature it puts some strain on your eyes, so please follow these points.
- Don't repeat it many times in a row; rest your eyes each time, for example by looking into the distance
- Don't turn the screen brightness up too high. If it feels glaring, lower the color strength
- When your eyes are tired or before bed, keep to the short 10- or 20-second settings
- Stop immediately if you feel a headache or nausea. If you are sensitive to flashing light, don't push yourself to try it
FAQ
- Why does a black-and-white image look colored?
- When you keep looking at a color-inverted image, the sensitivity of the cone cells that respond to those colors drops temporarily. Looking at a black-and-white image in that state, the side whose sensitivity hasn't dropped responds relatively more strongly, and the opposite of the color you were looking at, which is the original color before inversion, appears. The image itself has no color; it is a phenomenon happening in your eyes.
- How long does the afterimage last?
- It is clearly visible for a few seconds, then gradually fades away. The longer you stared, the stronger and longer-lasting the afterimage, but blinking and moving your eyes break it up easily. When it disappears, staring at the inverted image again brings it back in the same way.
- Can I make the illusion from my own photo?
- Yes. When you load an image, an inverted image in complementary colors and a black-and-white image are prepared automatically. Photos with large, vivid areas of color such as sky or grass work best, and for photos with dull colors, raising the color strength slider makes the effect easier to see. Processing is done entirely in your browser and the image is never sent to a server.
- Is it bad for my eyes?
- For a short time, it is the same temporary response as the afterimage you get after looking at a bright light. It does involve staring at strong colors, though, so don't repeat it many times in a row, and rest your eyes each time. Lowering the screen brightness and shortening the staring time also help. Stop if you feel a headache or nausea.
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