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

Question

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

This is the original picture:

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

When seeing the picture in a small thumbnail size (around 64x64) 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?

Answer 1

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.

Answer 2

There are some very slight differences in the red in various places, when checking with the colour picker in Photoshop. Top right corner d00013, bottom right ce0012, bottom left ce0012, Top left d00013. Middle d00013.

To be honest the colour variation might have something to do with the image being a jpeg which looks like it has been severely compressed, with some quite horrible jpeg artefacts, especially visible around the text - like the kind of thing facebook compression does to jpegs.

So no, I don't think you are imagining it, however the differences are very slight, but the original image is low quality anyway. If you were to recreate that image from scratch, and export in a lossless format such as PNG, it wouldn't suffer from those deficiencies.

Here's one I made in GIMP, I don't have the exact same font, but you'll see the difference.

Incidentally, you can get themes for GIMP to change that light grey colour scheme. If you search on youtube, you'll find them.

Answer 3

I completely see it. Perhaps has something to do with the white in the middle, making that area seem bright, and the edges seem dark in comparison, especially if put against something not pure white.