Why do I have the feeling that there is a gradient when there isn’t?

I was trying to edit the following picture in GIMP when I noticed something strange.

This is the original picture:
Original picture from @On_Air_Music

And this is what it looks like when opened in GIMP (the only important thing here is that GIMP uses a somewhat light background).
enter image description here

When seeing the picture in a small thumbnail size (around 64×64) in Google Images, I saw that it was simply a red square with some text, but here in GIMP it looks like the red in the sides is darker than in the middle, like if there were a gradient from the inner to the outer. But I can confirm that the red is plain #CE0400 (206, 4, 0) apart from some places where JPEG compression turned it to weird brown. Definitely not a gradient.

Two questions:

  • Am I crazy?
  • If not crazy, why is this effect happening?


This is due two effects.

One is due tonal contrast. A brignt zone next to a flat uniform zone of color.

Take a look at this explanation: Gradient “white mark” optical illusion

The second is Persistance of vision. https://en.wikipedia.org/wiki/Persistence_of_vision

In this case, when your eyes move arround reading the text in an horizontal form, the retina reacts in that part to a brighter estimule and when you move the eye that zone nows apear a bit darker.

Think as if the signal of the retina “wares out” a bit after a moment.

Source : Link , Question Author : zdimension , Answer Author : Rafael

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