If these colors all have the same lightness, then why does my brain tell me some are lighter than others?

My human brain has a certain sensation of how “bright” a color is. More formally there is Lightness:

Human vision has a nonlinear perceptual response to brightness: a source having a luminance only 18% of a reference luminance appears about half as bright. The perceptual response to luminance is called Lightness. It is denoted L* and is defined by the CIE as a modified cube root of luminance:

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Lab is one color model where colors with the same Lightness should appear to have the same “bright-ish-ness“. Except when i look at a color picker showing colors with the same L, they don’t appear equally “bright” to me:

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Maybe it’s limited to my brain, and other’s don’t see it, but when i look at that color swatch some i see lines separating darker areas from lighter ones:

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What accounts for this variation in Lightness?

  • is it just me?
  • is it because my monitor is not color calibrated with Photoshop’s sRGB?
  • is it a limitation of a trisimululus color representation (i.e. red+green+blue) used by LCD monitors?
  • is it a limitation of the Lab color model?
  • is it a limitation of the XYZ color model?

Why is it that colors that should have the same Lightness have different apparent brightness?

Answer

Goes back to this illusion…..

Checker shadow illusion

The squares marked A and B are the exact same shade of gray.

Surrounding values alter the human perception. One reason why a neutral grey desktop is very beneficial when doing color critical work.

I don’t know all the science behind it. I expect it would take a medical degree to fully understand.

(photo from http://web.mit.edu/persci/people/adelson/checkershadow_illusion.html)

Attribution
Source : Link , Question Author : Ian Boyd , Answer Author : Ilmari Karonen

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