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