Neon Color Spreading and Watercolor illusion

Neon color spreading (also referred to as neon-like color spreading) is an optical illusion characterized by fluid borders between the edges of a colored object and the background in the presence of black lines. The illusion was first documented in 1971 and was eventually rediscovered in 1975 by Van Tuijl.

"Neon" references a neon tube and the bright colors that appear within one. "Color spreading" references how the colors seem to spread out from the center of the colored portion of the object.

Neon color spreading is similar to the watercolor illusion, though the two are not to be confused with one another as they are produced in different ways.
(Wikipedia)


 

Neon Color Spreading

The neon-like glow of a color that escapes the boundaries of a real figure and spreads to where there is no color.
The exact causes of the neon color spreading illusion are not known. It seems to occur most often when black lines are substituted with colored lines on a white background.
The brightness conditions under which the color spreading figures are viewed change the perceived intensity of the effect. Under bright lighting the effect will be inhibited and under dim lighting the effect will be enhanced. (Wikipedia)

Neon Color Spreading

Neon Color Spreading

An example of neon color spreading.

Neon Color Spreading

Neon Color Spreading

An example of a circle created by color spreading.


A blue inner circle appears within the black contours. In the actual image this area is white, which is made evident if the image is magnified.

  

Neon Color Spreading


 

Neon Color Spreading

Neon Color Spreading

Color effects: Another aspect of neon color spreading that can affect the magnitude of the illusion are the colors used within the illusion. Different colors tend to cause a less or more intense illusion. Changing the color of the background can also enhance or inhibit the effect. If contrasting colors are used, such as a yellow background with blue and black lines, the effect will be enhanced. If similar colors are used, the effect will be inhibited.
Blue and red versus green and yellow: Long and short wavelength light, where the human eye is less sensitive to spatial detail, seem to enhance the effect. This means that if the illusion is created with red or blue lines, black lines, and a white background, the effect will be more intense.[1] This is particularly notable when the colors are more saturated. In contrast to this, green and yellow tend to suppress the effect of neon color spreading when used in the same way. (Wikipedia)

Ehrenstein figures

Neon Color Spreading

Ehrenstein figures are a good way of easily making persistent color spreading effects. They are good for showing both the neon color spreading illusion and illusory contours. They are also good for showing examples of differences in hue between inner and outer lines and how they affect the neon color spreading illusion. (Wikipedia)


 



Watercolor illusion

Watercolor illusion

Watercolor illusion

The watercolor illusion is a phenomenon that can be observed when a figure is defined by a contour consisting of a pair of parallel lines on white background: a dark line, and a lighter colored line on the inside. The interior of the figure then appears slightly tinted with the hue of the lighter colored line. Simply put, the watercolor effect is perceived when a dark contour is flanked by a lighter contour. Under these conditions, the lighter color will assimilate over the entire enclosed area.

Watercolor illusion

Watercolor illusion

This shape's yellow and blue border create the illusion of the object being pale yellow rather than white.



Additional images of Watercolor illusion:
http://opticalillusions4kids.blogspot.com/2007/06/watercolor-optical-illusion.html  
http://www-cvrl.ucsd.edu/gallery/Watercolor-illusion.htm  
http://www.psy.ritsumei.ac.jp/~akitaoka/watercolorillusionsamples.jpg  
http://scienceblogs.com/


 

The watercolor illusion, also referred to as the water-color effect, is an optical illusion in which a white area takes on a pale tint of a thin, bright, intensely colored polygon surrounding it if the coloured polygon is itself surrounded by a thin, darker border (Figures 1 and 2). The inner and outer borders of watercolor illusion objects often are of complimentary colours (Figure 2). The watercolor illusion is best when the inner and outer contours have chromaticities in opposite directions in color space. The most common complimentary pair is orange and purple. The watercolor illusion is dependent on the combination of luminance and color contrast of the contour lines in order to have the color spreading effect occur. (Wikipedia)

Watercolor illusion

Watercolor illusion

Figure 1: The vertical gratings are black and white with a thin line of red along each black bar. The horizontal gratings are black and white with a thin line of green along each black bar. The illusion is that the red and green appear to speed over the black and white regions of the vertical and horizontal gratings respectively. (Wikipedia)

Watercolor illusion

Watercolor illusion

Figure 2: Purple undulated contours adjacent to orange ones are perceived as two unknown shapes evenly colored by a light veil of orange tint spreading from the orange contours (coloration effect). The two shapes show a strong figure-ground segregation and a solid figural appearance comparable to a bas-relief illuminated from the top and to rounded surfaces segregated in depth and extending out from the flat surface (figural effect). On the contrary, the complementary regions appear as empty spaces with the appearance of holes. (Wikipedia)

 

The Watercolor Effect

Watercolor effect, in which the lighter of two colors seems to spread.

The Watercolor Effect

Figure 3: The map of the Mediterranean Sea emerges at once when the tint that at first seems to cover the sea (top) spreads to the land area.

One of our early experiments with illusory color illustrates how important color can be in delineating the extent and shape of a figure. Under certain conditions, color changes in response to the surrounding color; it can become more different (called contrast) or more similar (called assimilation). The spreading of similar color has been described only over rather narrow areas, in agreement with the finding that most connections among visual neurons in the brain are relatively short range. We were therefore surprised to find that when an uncolored area is enclosed by two differently colored boundary contours— with the inner contour lighter than the outer contour—tint emanates from the inner contour, spreading across the entire area, even over rather long distances [see Figure 3].

Because the color resembles a faint veil such as that seen in watercolor painting, we call this illusion the watercolor effect.

We found that the spreading requires the two contours to be contiguous so that the darker color can act as a barrier, confining the spreading of the lighter color to the inside while preventing it from spreading to the outside. The figure defined by the illusory watercolor appears dense and slightly elevated. When the colors of the double contour are reversed, the same region appears a cold white and slightly recessed.

The watercolor effect defines what becomes figure and what becomes ground even more powerfully than the properties discovered by the Gestalt psychologists at the turn of the 20th century, such as proximity, smooth continuation, closure, symmetry, and so on. The side of the double contour that has the lighter color fills in with watercolor and is perceived as figure, whereas the side that has the darker color is perceived as ground. This asymmetry thus helps to counteract ambiguity. The phenomenon is reminiscent of the notion of Edgar Rubin, one of the pioneers of figure-ground research, that the border belongs to the figure, not the ground.

A possible neural explanation for the watercolor illusion is that the combination of a lighter contour flanked by a darker contour (on an even lighter background) stimulates neurons that respond only to a contour that is lighter on the inside than the outside or to a contour that is darker on the inside than the outside, but not to both. Border ownership most likely is encoded at early stages of processing in the visual cortex, such as in brain areas V1 and V2. In experiments with monkeys, neurophysiologists have found that approximately half the neurons in the visual cortex respond to the direction of contrast (whether it gets lighter or darker) and therefore could delineate the border. These same neurons have a role in depth perception that might contribute to figure-ground segregation.

Our investigations showed that wiggly lines produce stronger watercolor spreading than straight ones do, probably because the undulating borders engage more neurons responsive to orientation. The color signaled by these uneven edges must be propagated across regions of cortex that serve large areas of the visual field, continuing the spread of color until border-sensitive cells on the other side of the enclosed area provide a barrier to the flow. Color and form are thus bound together inextricably in the brain and perception at this level of cortical analysis.

 

 

 

The Noguchi-Takashima effect (the sumi painting effect)

The regions surrounded by light borders appear to be lighter than they are while those surrounded by dark borders appear to be darker than they are.


The Watercolor Effect
The Watercolor Effect