This is an old technique that uses the “color assimilation” effect to colorize pictures. This perceptual effect, also known by scientists as the Von Bezold spreading effect, occurs when our visual system transfers perceived colors to their adjacent areas.
Is the first photo of a variety of pumpkins in color?
I am currently working on new “neon color spreading” effects. Have a look at the pictures below… Though you perceive fluorescent grinning skulls, the vertical white stripes don’t contain any color at all, they are uniformly white! The trick lies on the fact that some black lines have very thin color edges. This illusory shading effect is also known as “subjective transparency” or “Tron effect”.
The neon color effect was first observed by D. Varin in 1971. The human ability to perceive a neon effect may be a remnant of the development of our power of sight under water at extreme depths, where light is very poor.
My Op Art Skulls are available as prints and t-shirts from my online store.