The Bezold-Brucke effect can be generalized as a change in the perception of hue as the intensity of light changes. As we move towards high intensities (intensity increases), the spectral colors tend to shift more towards Blue or Yellow shades. However, at the lower intensities, Red or Green shades of the color dominates. This effect/shift was named after the two discoverers Wilhelm von Bezold and M.E. Brücke.
The shift in the hue of the colors that occur as the intensity of the corresponding energy change is materially increased, except in some cases like the change for certain invariable hues (approximating the psychologically primary hues). Both Bezold & Brücke worked on this Bezold-Brucke effect and gave important contributions in the field of optical illusions.
INTRODUCTION – BEZOLD-BRUCKE EFFECT
It is very much clear from the above observation that a change may occur to the perception of colors under the effect of an increased or decreased amount of light intensities. The apparent brightness of the hues changes as the number of illumination changes.
When there are increasing intensities, the wavelengths below 500 nm shift more towards the Blue end, and when the wavelength is above 500 nm, the hues shift more toward the Yellow end. This means that the Reds become Yellower with increasing brightness. Light may change in the perceived hue as its brightness changes, despite the fact that it retains a constant spectral composition.
In particular, we can say that at high-intensity, a long-wavelength red light appears to be somewhat tinged with yellow, while in the case of short-wavelength violet light, the violet becomes bluer. This phenomenon is stated as the Bezold-Brücke hue shift.
The shift in the hue is also accompanied by the changes in the perceived saturation. As the brightness of the color stimuli increases, their color strength also increases to a maximum point and then decreases again; in such a way that it is still wavelength specific. This can, to an extent, be considered as an inverse of the Helmholtz-Kohlrausch effect. In the case of the Helmholtz Kohlrausch effect, the partially desaturated stimulus is seen to be brighter than fully saturated or achromatic stimulus.
It has been argued that the Bezold-Brücke shift does not serve for the surface mode color. This point was not based on the psychophysical data but was based on the comparison of the ‘Munsell chart’ and ‘The Natural Color System codes’ for the pigment samples seen against their spectral measurements. It was also argued that the shift is so clearly visible and easily understood in the normal natural environment that it could be widely recognized by various artists.
Even if this effect made a slight difference; that too only in the artificial conditions of the aperture color, these conditions are hardly negligible or unimportant. These are widely present in Cathode Ray Tube (CRT) displays and other machines that use user interfaces. But the main importance of these effects lies in what they show about the processing of the color information. In a particular model, it is stated that shifts in the hue and saturation are considered to be the result of non-linear responses from six classes of the cone cells’ opponents in the retina of the human eye.
The procedure has been in specific terms applied to the shifts in the hue and also to the saturation shifts. There are some Color naming functions that provide the most necessary data which quantify the Bezold-Brücke shift. For each wavelength at the higher light emission, the lower light emission wavelength can easily be found which draws the same frequencies of color responses. In such cases, the contrast effect does not arise because the stimuli are viewed in isolation. The ability of the color naming procedure to obtain some unique hues from the same informant is also considered important.
Color-naming has been used to examine color appearance in the case of dichromats (a state where we have two types of functioning color receptors, called cone cells which are present in the eyes). Their color naming functions are highly peculiar and do not allow themselves to direct the calculation of the Bezold-Brücke shift through a simple cross luminance comparison method.
LIMITATIONS – BEZOLD-BRUCKE EFFECT
Very often, these color choices and their combinations are used to describe how sometimes the stimuli differ to such an extent between the high and the low luminance, that for many of the high luminance stimulus, it becomes difficult to find a lower Luminant match anywhere on the spectrum. The main problem is that for dichromats (two-color receptors), the color terms Red and Green are no longer the opponent hues; they may even serve as the descriptions of the light intensities.
In the case of a deuteranopic subject (a kind of color blindness), green responses decrease greatly with the increasing amount of light. This is because of their abnormal spectral efficiency functions; for such kind of observers, it is easy to get confused between the hue and intensity dimensions when they learn all about what colors are.
A protanope (a person having defective cones for a long wavelength of light) lacks the appropriate pigments or cones. Because of that, the lights that a normal observer would see effortlessly as a red light will also turn out to be quite dim for them. An option here can be to step up from the actual terms that are used and look upon some possible interstimulus similarities that could be abstracted from them.