別紙41 信果程博士(英文))Date of submission (month day, yea"Ja1川ary 7小,2022

Deparιmenl ofColnputer science ofSludCΠ11D NⅡmber

D131304

En ineerinSupeτⅥSors

Kowa Koida

ShigekiNakauchi
APP11Canl's nameTama Kanematsu

Abstract (Doct0わ
Title ofThesis

Arox

C010r appeal'ance of extl'eme fine stimuli: e仟ect ofoptical and neul'al factols

80o wmds

The c010rs of fine details are essentialin our ]ives. For example, fabrics are made of
Various c010red threads, and facial emotions are expressed by faint c010rs of the cheeksand ]ips. The in)portance of fine c010r details has increased in the era of hiσh・resolution
displays.1t is known that a surrounding area inauences the c010r appearance of a center
area, and the innuence becomes critical for detailed images,1t is also known that theOptical aYtifacts of the hulnan eye, such as blUγΥing and chr0111atic aberYations, degrade
丘ne details and the c010rs of images. These neural and optical effects are integrated via
the visual system and form our perception. Thus, it is important to differentiate theseeffects to understand how our co]OY vision w'OYks.

This thesis focuses on the Monnier・sheve11il]usion, which induces a sio'nificant c010r shift

Of a center st11nulus accord]ng to t、No surrounding, spatia11y alternating colnplelnentary

C010rs. The i11Usion is evident for s・cone c010rs (blue‑ye110w pairs) but not for L/M・cone
C010rs (red・牙reen pairs) for unknown reasons.1t is thought that the effect works better
f0王' S・cone c010rs because the i11Usion is due to a synergistic e任ect of assilni]ation n'om
the proximal c010rs and contrast fron〕 the distanuy surrounding c010YS, and kn0工刃nSpatlal representatlon of c010rs ln the early vlsual system ls con)paYable foY both s、coneand L/M、cone c010rs except for its spatial resolution. Here,1 report a ne、N spatia] context

Of the Monnier・sheve11i11Usion, in which a thin gray line (test ]ine) aanked with whiteIines (contour) appears reddish when surrounded by a uniform cyan. psych010gicalexperiments and simulations excluded the possibility of the i11Usion being induced byOptica] aYtifacts, Experiment 2 Showed that a chromatic (as opposed to an achromatic)
Contour n〕odified c010r shifts, indicating linear summation of the c010r induction effect,CI〕roma of the contour, and chroma of the test.1n Experiment 3,1 investigated the effect
Ofline widths ofthe iⅡUsion and found that maxilnuln effects for the L/M・cone c010rs were0.9 and l.9 min of visua] angle f01' the contour and the test line. These widths
Corresponded to the width of a sin套le phot01'eceptor and were eight times thinner thanOptimal widths for the s・cone c0101'S. obseYved differences of the optimal widths between
two c010rs could l'eaect the known diffeYence in spatial property between two c010rs

Experiment 4 examined the effect ofluminance contrast of the contour and found that ablac]く Contour instead of a wh北e one diminished the i11Usory e仔ect, indicating theilnportance ofthe white contour, and simple spatial organization along the chromatic axis
failed to explain the i11Usion
Simulation of the chromatic shift due to optica] artifacts predicted u〕e large
Chromatic shi丘 at the retina; however, perceived c010r closely matched the actual
Chromaticity of the stin〕uli. This indicates that the human c010r systen〕 seems to provide
Veridical perceptlon of c010r using solne type of con〕pensation, which could be attalned

through contrast enhancelnent froln distant surroundings. This colnpensation works wel]for simple unifonn back旦rounds, but patterned backgrounds, such as our stimU11 0f
aanking white contours and the original Monnier・sheve11 i11Usion, induce

anUnexpectedly large c010r shift because the aankin今 White contours break the balance
between the proxjmal assimilation and distant contrast effects. This interpretation

Suggests the MonnieY・sheve11i11Usion is the side effect of removing chrolnatic shifts by
the optical artifacts. This thesis describes the c010r appearances of 丘ne stimuli and theeffect of the complex spatial context. The neura11nechanisms and models revealed here
are usefulfor modern high・definition image・engineering appHcations