Trick Your Brain: Turn Black and White Photo Into Colour

A few days ago I came across a video of an illusion where I saw color in a black and white photo. This fascinated me so much that I dug into it further. After the necessary research, I understand the effect of this illusion and I did the trick myself. I would like to share this knowledge with you!

Let's start with the illusion in question:

If you stay fixed on the red dot and do not scan the image, you will eventually see color in the black and white photo! You keep seeing this until you deviate from the tip or blink once. But how is this possible? You'll see that in the next steps!

Of course I also made a version for this Instructable:

Supplies

Colorful image
Computer with image editing software

Step 1: Find a Good Image

To start, you need a good image with lots of color. These can be different colors but 1 or 2 predominant colors will also work fine. I chose an image with different bright colors, mainly to distinguish which colors this illusion works best with.

I put a red dot in the middle of the image. This point is for you to focus on. For this I have used Paint3D but this can of course be done with almost any image editing software.

Step 2: Create a "negative" of the Image.

The illusion is based on chromatic adaptation. Chromatic adaptation is the human visual system’s ability to adjust to changes in illumination in order to preserve the appearance of object colors. It is responsible for the stable appearance of object colors despite the wide variation of light which might be reflected from an object and observed by our eyes. This Wikipedia page explains it very well. This process is so powerful that it can actually be used to trick your brain into adding color to a black-and-white image. By first looking at the negative of the original image for a few seconds and then immediately after the black and white version, the chromatic adaptation process ensures that your brain shows your colors!

Invert the colors of the image with an image editing program. Here is explained how you can do this with Photoshop, but of course there are also several programs for this.

Open Photoshop, and load in the image that you want to invert.
In the menu bar at the top, click on "Image". In the drop-down menu, hover your mouse over "Adjustments" to create a new sub-menu.
From the "Adjustments" sub-menu, select "Invert". Your photo will immediately become inverted.

Step 3: The Black and White Image

Finally, we need a black and white or gray scale version of the image to use after the inverted version. I also used Photoshop for this. Open the original image, go to image, then adjustments and select desaturate.

Step 4: Ready for the Illusion

Now look for a few seconds at the dot on the image with the inverted colors. Immediately afterwards, look at the dot in the grayscale image. This can be done by opening the images in quick succession, but it works much better if you put them one after the other in a video. The less your attention moves away from the image, the better this illusion works!

The trick will work far better if you’re watching the video at full screen, but if you managed it, you’ll notice that as long as you don’t scan the image, the black-and-white photograph looks as if it’s in color. The image itself is 100% grayscale!