Abney effect: what it is and how it influences our perception of color

Our perception deceives us. Often what we think we are seeing is not what it seems, and one of the examples we have in the curious case of the Abney effect.

Discovered at the beginning of the last century, this effect occurs when, when applying white light to the same color, it is perceived with a different tone, as if it has changed hue or saturation.

Next, we’ll go into more detail about the Abney effect, who discovered it, and the physiological explanation behind such a curious phenomenon.

    What is the Abney effect?

    The Abney effect is the perceived change in tone that occurs when white light is added to a monochrome light source. In other words, it involves seeing from another shade of color to a color, with specific undertones and saturation, when more lighting is applied. The addition of white light produces, psychologically, a desaturation of the monochrome font, giving the impression that the color has changed hue and saturation, although the only thing that has happened is that it now has a higher luminance. .

    The nature of this phenomenon is purely physiological and not physical. It is counterintuitive for the human eye to perceive a tone of another color when light is added to it., Since it would make more sense to see this same color alone than brighter. For example, the color brown is actually nothing more than a dull orangey red which when white light is applied becomes that color. It gives the impression that we have a new color, or that brown has turned orange, when in fact it has always been orange.

    This phenomenon was first described in 1909 by the English chemist and physicist Sir William de Wiveleslie Abney.. He found that by applying a source of white light from the three primary colors of light, namely red, blue and green, one could induce changes in the perception of certain colors, even though they essentially remained the same nuances.

    Chromaticity diagrams

    To better understand this phenomenon, it is necessary to talk a little about a tool used in color theory. Chromaticity diagrams are two-dimensional diagrams in which colors are represented in XYZ coordinates. The X, Y, and Z values, or tri-stimulus values, are simply used as values ​​to create new colors from primary colors in the same way the RGB model is used.

    In this type of diagram, two aspects of colors are represented: hue and saturation. Hue is the color itself or chromaticity, represented in the near which is the color of pure green, red or blue when we speak of light colors. Saturation is the degree of intensity of the color, ranging from the lightest to the most intense. What is not shown in these diagrams is the illumination or luminance of the color.

    Colors in chromaticity diagrams are shown in rows and columns. For example, lines can represent hue (blue, greenish blue, turquoise, green …) while columns can represent saturation, from lighter tones to more saturated tones. The Abney effect occurs when, upon applying white light in these colors, the changes are perceived as if the hues or saturations of them have changed.

    To return to the previous case, brown and reddish orange are the same color, with the same degree of hue and the same saturation, but with different degrees of illumination. In a chromaticity diagram, two colors would be the same, reddish orange. It would be when the lighting is changed, whether of greater or lesser intensity, that the perceived color would be different, with brown being the result of a reddish orange with low lighting.

    This is why chromaticity diagrams are so useful for detecting colors that, by changing only the lighting, they are perceived as new colors on a psychological level. It is thanks to these instruments and simply by focusing white light on them that we can detect the colors that our BRAIN interprets as if they were different tones.

      Physiology of the phenomenon

      According to the model of the opposite process of the visual system, three neurological channels are involved in color perception: two chromatic channels and one achromatic. The chromatic channels consist of a channel which perceives red and green (red-green channel) and a channel which perceives blue and yellow (yellow-blue channel), these being responsible for the perception of tones. themselves. The achromatic channel is responsible for luminance, seeing how close the color is to white or black.

      Hue, saturation and illumination are perceived through the combined and varied activity of these three neurological channels, which consist of axonal pathways of retinal ganglion cells. The activity of these three channels is closely related to the reaction time in color response. Some activities depend on one or the other channel, or both types are equally involved. The achromatic channel has a faster response rate than the color channels, under most conditions.

      There is a special situation where the achromatic channel emits a slower response than the color channels, and that is when white light is added to an already observed color. The achromatic channel shows a slightly shorter response time than under conditions without bright light. However, its amplitude of response will be stronger than chromatic, giving way to a false perception.

      We do not know why we can see the same color as if it were another depending on the luminance. The spectral sensitivity of the observer, the relative number of each type of cone or the age of the individual do not seem to be factors influencing the intensity of the perception of the different shades. What is clear is that the light of the environment you are in significantly influences, giving the same image a different color, as seen in illusions such as the blue or white dress.

      This would explain why color judgments vary based on differences in color environment or exposure to a given color. It could also be due to the time that the cones in the retina were stimulated, causing them, for a short period of time, not to give an adequate signal when different types of wavelengths affect them.

      Bibliographical references:

      • Pridmore, R. (2007) Effect of Purity on Hue (Abney Effect) under Various Conditions “Research and Application of Color. 32.1: 25–39.
      • W. by W. Abney. (1909) On the change of hue of the colors of the spectrum by dilution with white light. “Proceedings of the Royal Society of London. Series A, containing articles of a mathematical and physical nature. 83.560: 120-127.

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