Black-and-white or colour? This viral optical illusion has people amazed globally

A photo showing a group of young girls posing with a small tortoise is doing the rounds online and people are realising that what they see isn't what it is.

What appears to be a colourful image on a closer look seems otherwise.

A black-and-white photo that users can see in colour is the latest viral image on social media. The photo shows a group of young girls posing with a small tortoise.

While the entire photo is in black and white, it has coloured lines within the image. The brilliant optical illusion basically tricks the human brain into seeing a colour image, and it’s only when you look closely that you realise it.

Lionel Page, an economist at UTC Economics, shared the picture on Twitter recently and got everyone talking and discussing about why the human brain does this.

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“What you ‘see’ is what your brain predicts the reality to be, given the imperfect information it gets” he wrote online.

This is a black and white photograph. Only the lines have colour.

What you “see” is what your 🧠 predicts the reality to be, given the imperfect information it gets. pic.twitter.com/gwttlcC2Zw

— Lionel Page (@page_eco) July 27, 2019

While most couldn’t comprehend what was happening, others explained the science behind it.

My brain can’t comprehend this https://t.co/yQS4whbtSf

— Marcel Lasaj (@thewirv) August 1, 2019

I zoomed in to this picture and it is not true. It’s just like, pixelated grayscale with a bit of blurry colour added in there to fool you. https://t.co/8NoLDBoQfd

— Jokic one handed rebound cum full court assist (@colingfun) August 1, 2019

This is messing with my brain. https://t.co/Ttk1vss3Vc

— Jen at Redgate (@Jen_RedGate) July 31, 2019

Mind blown. https://t.co/4whyHdmGQP

— Tot Rockin’ Beats (@TotRockinBeats) July 31, 2019

Black-and-white or Color? https://t.co/UEly7CjtIb

— Ayan Debnath (@ayandebnath) July 31, 2019

This is amazing! https://t.co/0ijrOKDjBO

— Toby Bartlett (@tobybartlett) July 31, 2019

Whoa.. interesting.. looks color to me! https://t.co/mumSuzWfQp

— Brian Cook (@cookiestem) July 31, 2019

This is so freaky https://t.co/6DiCoR3cZc

— Luna (@Just_Luns) July 31, 2019

I can see both https://t.co/3NjH5dUsjq

— Melissa Magrath (@mommahoss) July 30, 2019

I never trusted you anyway brain. https://t.co/C4kpVyX2f3

— Shane McHale (@shanemchale) July 30, 2019

pic.twitter.com/rdhC8ewPgX

— Eh Wall (@WJadam024) July 28, 2019

pic.twitter.com/2Ck9uj6yrr

— Justin Varricchione (@Taco_Jones) July 28, 2019

pic.twitter.com/7VduDRLemr

— Haiku Jonah (@HaikuJonah) July 28, 2019

The image is 36% colored. pic.twitter.com/tjXKMoOgvN

— Roger Johansson🇸🇪🇪🇺 (@RogerAlsing) July 28, 2019

This only half works for me. The blue and green shirts come through but girl in front has a white shirt with yellow stripes, not a yellow shirt. And all the faces are grey with colored lines over them.

— Hypertorus (@Rite_Brite) July 27, 2019

This is not correct.

There is significant chroma noise in the part of the image that is intended to be black and white.

This is a result of image compression.

— Andrew Pullin (@AndrewPullin) July 27, 2019

Well, in case you are wondering what’s this all about, it’s actually an image digitally modified for a visual experiment. Øyvind Kolås, the digital media artist and software developer who developed it, described the technique as a ‘colour assimilation grid illusion’. He said the image achieves the effect by simply laying a grid of selectively coloured lines over the originally black-and-white image.

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“An over-saturated coloured grid overlaid on a grayscale image causes the grayscale cells to be perceived as having colour,” Kolås explained on his Patreon page.