The Verriest Lecture: Visual properties of metameric blacks beyond cone vision Françoise Viénot, Hans Brettel To cite this version: Françoise Viénot, Hans Brettel. The Verriest Lecture: Visual properties of metameric blacks beyond cone vision. Journal of the Optical Society of America. A Optics, Image Science, and Vision, Optical Society of America, 2014, 31, 10.1364/JOSAA.31.000A38. hal-01565638 HAL Id: hal-01565638 https://hal.archives-ouvertes.fr/hal-01565638 Submitted on 11 Aug 2017 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Visual properties of metameric blacks beyond cone vision Françoise ViénotViénot,,,,111,*1,*,*,* Hans BrettelBrettel,,,,222 1Centre de Recherche sur la Conservation des Collections, Muséum National d’Histoire Naturelle, 36 rue Geoffroy Saint- Hilaire, F-75005 Paris, France 2CNRS LTCI, Telecom ParisTech, 46 rue Barrault, F-75013 Paris, France *Corresponding author: [email protected] Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc. ID XXXXX); published Month X, XXXX The generic framework of metamerism implies that the number of sensors is smaller than the dimension of the stimulus. The metameric black paradigm was introduced by Wyszecki [Farbe, 222,2 39 (1953)] and developed by Cohen and Kappauf [Am. J. Psychol. 959595,95 537 (1982)]. Within a multi-receptor and multi-primary scheme, we investigate how far the choice of illumination can isolate a photo-receptor response. The spectral profiles of the fundamental metamers that correspond to a collection of (x, y) values over the chromaticity diagram is shown. When the luminance is set at a fixed value, the relative excitation of the melanopsin cells and of the rods elicited by the fundamental metamers varies over the chromaticity diagram. The range of excitation of the melanopsin cells and of the rods that could be achieved at a given chromaticity, by manipulating the metameric black content, is examined. When only the melanopsin excitation is manipulated, the range of melanopsin excitation that can be achieved is rather limited. On the chromaticity diagram, the largest range of variation of the rods and the melanopsin cells excitation is obtained for (x, y) chromaticity coordinates near (1/3, 1/3). Extension of Cohen’s procedure to rod and cone metamers is proposed. The higher the number of spectral bands, the wider the choice of metameric lights. © 2012 Optical Society of America OCIS codes: (330.1715) Color, rendering and metamerism; (330.1720) Color vision; (330.4595) Optical effects on vision. 1.1.1. CONTEXT AND INTRODUCTION The visual sensitivity range of ipRGCs partly covers the rod intensity response range and parallels the cone response range Metamerism is fundamental to colour science. It refers to the [4]. Isolating responses of one or another type of photoreceptor phenomenon by which stimuli appear identical in colour but requires specific paradigms. The time taken to reach peak in have different spectral power distributions. The term the ERG from the responses of the ipRGCs significantly differs “metamer” (“Metamere Farben”), transposed from chemistry from that of rods and cones [5]. Nevertheless, due to overlap of science into the colour field by Ostwald [1], is most often spectral sensitivity for cones, rods and melanopsin cells, employed within the context of trichromacy. The definition assessing the relative contribution of the receptor types to given by Kaiser and Boynton [2] “Two stimuli, which are image and non-image visual functions is difficult. physically different but visually indistinguishable, are called The three-dimensionality of colour stimuli has often been metamers” is not only valid when cone vision is operative but is questioned at photoreceptor level. Considering that rods and/or also applicable to other sets of visual receptors. The generic melanopsin cells are responsive, the visual response is no framework of metamerism implies that the number of sensors longer three-dimensional [6,7,8]. It is four- or five-dimensional. is smaller than the dimension of the stimulus. Thus any colour Trichromacy no longer holds in colour matching at low stimulus function projects into the sensor space in a well- luminance levels or in the peripheral visual field when rods are defined response but the reverse projection is loosely defined. liable to be active [9,10,11,12]. Following the recent discovery of Metamers are usually defined with respect to cones whereas the melanopsin photopigment, it was proposed that metamers they may excite differently other photoreceptors that are could successfully be used to stimulate ipRGCs independently present in the retina. Rods convey the night-time image of cone mechanisms using a silent-substitution technique with information. A few retinal ganglion cells contain a four-primary stimulation [13]. At high photopic levels, above photosensitive pigment named melanopsin. The so-called rod saturation, detection threshold measurements deviate "intrinsically photosensitive retinal ganglion cells" (ipRGC) from trichromatic theory. Explaining peripheral sensitivity in project to the pretectum and convey information that is not threshold measurements and sensitivity to rapid flickering devoted to image formation but signal light for unconscious lights requires absorptions in four, not three, photopigment visual function such as the pupillary reflex and photo- classes. The most likely hypothesis is that melanopsin entrainment of the circadian rhythm [3,4]. In addition to being absorption influences sensitivity [14]. Considering that the intrinsically photosensitive, giant melanopsin ganglion cells perceived brightness of light sources is not always predicted by are strongly activated by rods and cones and project to the their respective luminance, Brown et al. [15], using four lateral geniculate nucleus [4]. primary stimuli silent for cones, above rod saturation, and a two-interval alternative forced-choice procedure, provided with the maximum saturation method, one primary colour evidence that healthy human subjects perceive greater should be added to the monochromatic light to successfully brightness as melanopsin excitation increases. match the additive mixture of the other two primaries. Since in The metameric black paradigm was introduced by Wyszecki colorimetry, stimuli obey the rules of linear algebra, in 1953 [16]. It hypothesizes that any stimulus can be subtracting one mixture from the other yields a null stimulus, decomposed into a fundamental metamer and a metameric i.e. a stimulus that evokes no cone response. Following such black. In 1982, Cohen initiated a series of articles to describe construction, Wyszecki proposed an independent set within all potential metamers as vectors [17,18]. His mathematical which each metameric black contains only four reflectance method has been applied to predicting the illuminant- values different from zero at the position of the experimental independent properties of reflectance functions [19], to spectral primaries, the fourth one, being always equal to 1.0, studying the structure and reducing the dimensionality of varying its position in the spectrum from one metameric black colour space [20,21,22,23], to founding theories of colour to the other [27]. In the wake of this experimental example, constancy [24], to reducing the number of channels in multi- Wyszecki determined further metameric blacks by producing spectral imaging [25], and to estimating the spectral linear combinations of the original set. Wyszecki’s first sensitivities of colour camera sensors [26]. proposal was restricted to the division of any stimulus into two The metameric black paradigm gains advantage as soon as unique components, the fundamental metamer and the receptors other than cones are sensitive to visible light. In a residual, i.e. a metameric black. Practically, Wyszecki proposed previous paper, we exploited Cohen’s method in the case of a method for the realization of a large number of metameric multi-band illumination obtained with independent colour colours, which was based on a precalculated set of linearly LEDs. Here, within the same multi-receptor and multi- independent metameric blacks. primary scheme, we investigate how far the choice of illumination can isolate one or another receptor response. BBB.B. Generating metamers from metameric blacks: the CoCohenhen 2. METAMERIC BLACKS and Kappauf procedure As Cohen commented, “Wyszecki did not isolate even a A. Wyszecki’s view single fundamental” [18]. Nevertheless, he did compute We know that, even though metameric colour stimuli have “residuals” by taking the difference between an initial stimulus different spectral power distributions, they excite the three and its matching stimulus. families of cones identically. They have identical tristimulus Cohen and Kappauf, in 1982 [17], presented a procedure for values such as L10 , M10 , S10 , referring to the long-wave accomplishing the decomposition of any stimulus into the sensitive, middle-wave sensitive and short-wave sensitive cone fundamental