Huang, Zhehao

Zaidi, Qasim

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Color	transparency	from	motions	of	backgrounds	and	overlays	Zhehao	Huang	&	Qasim	Zaidi	Graduate	Center	for	Vision	Research,	State	University	of	New	York	Motion	in	specific	configurations	is	sufficient	to	create	impressions	of	moving	transparent	layers	and	of	movement	behind	holes.		By	translating	one	of	6	spectrally	selective	transparent	circular	filters	on	backgrounds	selected	from	280	spectrally	selective	surface	reflectances,	we	created	vivid	percepts	of	moving	transparency.		Using	the	same	filters	and	reflectances,	by	moving	the	background	alone	inside	a	static	circular	segment,	we	created	a	vivid	percept	of	a	transparent	hole.		When	the	hole	with	internal	motion	is	moved	in	a	manner	similar	to	the	filter,	the	percept	is	of	a	moving	filter,	despite	T-junctions	instead	of	transparency	consistent	X-junctions,	revealing	the	powerful	role	of	motion	cues.	Using	matches	with	adjustable	spectral	reflectance	on	achromatic	backgrounds	(Fig	1),	we	quantified	the	perceived	colors	of	the	overlays	in	all	three	conditions.	We	repeated	all	three	measurements	with	the	surround	of	the	filter	and	hole	turned	to	black.		In	that	case	the	filter	configuration	looked	like	a	moving	spotlight	on	a	stationary	background	and	the	hole	as	flow	illuminated	by	a	stationary	spotlight.		 Khang	and	Zaidi	(2004)	matched	moving	filters	and	spotlights.	To	estimate	the	color	of	the	spotlight	with	spectrum	𝐸" 𝜆 ,	they	proposed	a	luminance	weighted	grey-world	model	based	on	calculating	𝜌% 𝐸" 	(𝑘 = 3)		the	absorptions	of	three	cone	types	with	spectral	sensitivity	𝑅% 𝜆 :	𝜌% 𝐸" = 𝑉+,+ 𝐸" 𝜆 𝑆+ 𝜆 𝑅% 𝜆 𝑑𝜆.	Where	the	cone	catch	for	each	pixel	𝑥	with	object	reflectance	𝑆+ 𝜆 	is	weighted	by	its	luminance	raised	to	a	power	𝑉+,	(n=0	means	no	weighting,	and	the	larger	the	n	the	higher	the	weight	of	the	brightest	objects).		This	model	predicted	that	the	average	color	of	the	background	would	bias	the	spotlight	color	estimate,	and	provided	a	good	fit	to	the	empirical	matches	biased	from	veridical	on	different	sets	of	colored	backgrounds.		To	estimate	the	color	of	the	filter	with	spectrum	𝐸" 𝜆 	relative	to	the	color	of	the	illuminant	on	the	visible	surround,	the	model	assumed	that	each	of	the	two	illuminants	was	estimated	separately	with	the	weighted	grey-world	model,	and	the	relative	filter	color	was	estimated	by	the	ratio	of	the	three	weighted	cone	absorptions.		This	approximate	heuristic	was	justified	by	the	empirical	fact	that	filters	in	general	change	cone	absorptions	from	all	background	objects	by	one	multiplicative	constant	per	cone	type,	and	this	ratio	provides	a	good	estimate	of	the	multiplier.		This	model	provided	a	satisfactory	fit	to	the	empirical	filter	matches,	which	were	generally	close	to	veridical	when	the	background	illuminant	was	equal	energy	white.		Here	we	test	if	the	model	for	the	moving	filter	also	explains	the	case	of	the	stationary	and	moving	hole	configurations.		 Using	the	same	filter	and	object	spectra,	but	with	a	distinctly	shaped	background	element,	we	also	quantified	the	perceived	colors	of	overlaid	elements	in	all	six	conditions,	by	matching	the	colors	seen	behind	the	test	filter	with	an	adjustable	reflectance	seen	behind	a	neutral	density	filter	on	the	same	background	(Fig	2).		This	is	a	more	stringent	test	of	color	scission.		Once	the	spotlight	color	or	relative	filter	color	is	estimated	using	the	heuristic	model,	the	same	empirical	fact	justifies	a	model	where	the	cone	catches	from	the	matched	reflectance	under	the	neutral	density	filter,	multiplied	by	the	estimated	cone	catches	for	the	spotlight	or	filter,	should	be	equal	to	cone	catches	from	the	target	element.		Here	we	use	this	test	to	compare	the	extent	of	color	scission	in	the	filter	conditions	versus	the	hole	conditions.	Reference	Khang,	B.	G.,	&	Zaidi,	Q.	(2004).	Illuminant	color	perception	of	spectrally	filtered	spotlights.	Journal	of	Vision,	4(9),	2-2.	Figure	1	Figure	2	

Color transparency from motions of backgrounds and overlays

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1146&amp;context=modvis

Color transparency from motions of backgrounds and overlays

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