Category: optical illusion

See “true cyan”!

February 10, 2022 • 2:00 pm

This video supposedly enables you to see a color that apparently can’t be reproduced on the screen: “true cyan“, a color between green and blue.   Turn on the sound, put your face about a foot from the screen, and then fix your gaze on the white dot in the center for the duration of the soundtrack. When the music ends, close your eyes, and with luck you’ll have an afterimage of the “true cyan” color. It is a lovely blue.

This source gives a bit more information:

True cyan illusion

Even though the human eye is incredibly sophisticated, there are times when you can trick your brain into seeing things that completely bizarre. For example, we know that there are three primary colours – red, yellow and blue – and all other colours are formed by mixing them. There are still shades of colour that often occur naturally and are difficult to produce on electronic screens.

What if we tell you there’s a colour known as true cyan, which is a greenish-blue pigment and is difficult to capture on television and is often diluted to a lesser form?

An optical illusion posted on social media has left netizens amazed as they could see the dazzling green-blue pigment.

TikTok user Kate Bacon posted a video telling people that would show them a colour that they’ve probably never seen before. She said, “It’s called true cyan, and most TVs and monitors aren’t capable of producing this pigment.”

Viewers are shown a red circle with a white dot against a blue background. Kate says that you need to stare at the white dot for at least 30 seconds, but the longer the better. Afterwards, if you close your eyes really tightly, you should see a ‘glowing orb’ in the colour of true cyan.

A similar video available on Youtube instructs the viewer to stare at the white dot in the centre of the red circle as the camera slowly pans out. By the time the video ends, the viewer will be able to see the true cyan colour appear like a halo around the red circle.

A mirage of Chicago

April 13, 2020 • 12:45 pm

Reader Edward sent this breathtaking photo of a mirage of the Chicago Skyline, just featured as the Earth Science Photo of the Day.  It was taken in 2008 from the Indiana Dunes, a state park 37 miles from the city, and a place from which the city isn’t visible.  It is in fact an inferior mirage, formed only under special atmospheric conditions (see also here). Those distant “puddles of water” that you see far away on a hot highway, for instance, are inferior mirages of the sky. Read more at the first link, including details about the equipment and how the photo was taken.

Optical illusion: the Troxler effect

April 10, 2018 • 2:30 pm

Have a look at the video below, which demonstrates “the Troxler effect” or “Troxler fading”, a phenomenon that occurs when you try to stop the involuntary movements of your eye (“scanning”):

As we focus on a certain point in our perception field, that point becomes the main object of our visual system. When a blurry stimulus appears in a region of the visual field further from the point we are fixating, and we keep our eyes still, that stimulus will disappear even though it is still there. The phenomenon is known as Troxler’s fading. It occurs because even if our eyes move a little when we are fixating a point, away from that point, in the perception field, the movements aren’t large enough to observe other elements. The neurons remain focused on the main object and our visual system doesn’t involve new ones for the other elements.

Here’s an example from Wikipedia:

In this example, the spots in the “lilac chaser” illusion fade away after several seconds when the black cross is stared at long enough. This leaves a grey background and the cross. Some viewers may notice that the moving space has faded into a moving blue-green spot, possibly with a short trail following it. Furthermore, moving one’s eyes away from the image after a period of time may result in a brief, strong afterimage of a circle of green spots.

And here’s the most obvious picture to use to demonstrate the effect: a Cheshire cat!

INSTRUCTIONS. Keep very still and keep your gaze focused on the central black cross. Do not strain your eyes, but try not to let your gaze wander from the cross.

You can read more on the Troxler Effect here, including this:

The Troxler Effect is named after Swiss physician and philosopher Ignaz Paul Vital Troxler (1780-1866). In 1804, Troxler made the discovery that rigidly fixating one’s gaze on some element in the visual field can cause surrounding stationary images to seem to slowly disappear or fade. They are replaced with an experience, the nature of which is determined by the background that the object is on. This is known as filling-in.

The Troxler effect illustrates the importance of saccades, the involuntary movements of the eye which occur even while one’s gaze is apparently settled. If we could perfectly fixate on some point in our visual field by suppressing saccadic movement, a static scene would slowly fade from view after a few seconds due to the local neural adaptation of the rods, cones and ganglion cells in the retina. In brief, any constant light stimulus will cause an individual neuron to become desensitized to that stimulus, and hence reduce the strength of its signal to the brain.

When we attempt to fix our gaze on an object, the eye undergoes extremely rapid and relatively large-scale sudden movements called microsaccades, in contrast to saccadic drifts or small oscillations. Microsaccades cause the pattern of activity which forms the retinal image to shift across hundreds of photoreceptors at a time, providing a constant “refreshing” of the image (Martinez-Conde 2010).

 

Still more on the color illusion

February 18, 2018 • 7:45 am

Well, a reader showed in an email that that the hearts in the illusion below really were very slightly different colors due to the compression algorithms used in making the image. (However, those slight differences do not account for the striking perceptual effect).  The reader who demonstrated this anomaly won an autographed book from Matthew.

HOWEVER, reader Mel made his own illusion, so we know that here the colors of the squares really are identical. His notes:

To demonstrate the phenomenon a bit more cleanly I constructed the following image using a spreadsheet. I used very small cells (0.3 cm x 0.3 cm) and filled them with various colors and then took a screenshot. The image still shows the illusion and only three colors were used in constructing the image (magenta, orange, blue-green).

And another demonstration using magic markers. I think the efficacy of the lines in fooling viewers about the color has been shown. We’ll now leave this illusion behind and move on.

Yesterday’s optical illusion: the hearts are the same color!

February 17, 2018 • 7:15 am

On yesterday’s Hili Dialogue, I posted this tweet, an optical illusion provided by Matthew:

The hearts are said to be the same color, with the illusion of their being different colors due to the different-colored stripes running through them. The was lots of argument among the readers, and, as far as I can remember, no consensus.

I put this question to Matthew (why do you readers make me do these things?), and he responded by checking. Here’s his response and his image. The conclusion is that the hearts are both the same color: a blue-tinted green.

They are the same colour. I have been in and checked the image, see here. The left half, with the orange, is from the ‘green’ heart. The right half, with the pink, is from the ‘blue’ heart.

Another response showing the color identity:

I think this settles it: if Matthew’s satisfied, so am I. However, if you can prove to Matthew’s satisfaction that they are really of different colors, you will win an autographed copy of his latest (and terrific) book: Life’s Greatest Secret, about the cracking of the genetic code. The first one to disprove color identity of the hearts will get the book. You can email me or put your “proof” in the comments.

Matthew sets out the rules:

People need to download the original large image (attached) and then enlarge it to show they are differerent colours. They won’t be able to do it.