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Eurographics Italian Chapter Conference (2006)G. Gallo and S. Battiato and F. Stanco (Editors)

A Survey of Digital Mosaic Techniques

S. Battiato, G. i Blasi, G.!. Farinella, G. Galloiparti"ento di !ate"atica ed Infor"atica

#ni$ersit% di Catania$ia &. oria, 6 ' *2 Catania (Ital+)

e"ail-attiato, gdilasi, gfarinella, gallo/d"i.unict.it

Abstract

Art often provides valuable hints for technological innovations especially in the field of Image Processing andComputer Graphics. In this paper we survey in an unified framework several methods to transform a raster inputimage into good quality mosaics. The common and different ideas among the methods are reported anddescribed. inally we try to address the evaluation problem of an !P" algorithm.

Categories and Su1ect escriptors (according to &C! CCS) . 3&rts and hu"anities4 &rchitecture, Fine&rts

1. Introduction

5esearch in the field of Co"puter Graphics hastraditionall+ een do"inated + atte"pts to achie$ephotorealis" "odeling ph+sical pheno"ena such as lightreflection and refraction to produce scenes lit, ostensil+,in a natural "anner.

7$er the past decade the de$elop"ent of no$elrendering st+les outside the ounds of photorealis" has

gathered "o"entu" the so called non8photorealisticrendering or 9:5. 9:5 has een successfull+ applied +scientific $isuali;ation researchers to i"pro$e the clarit+and a"ple) e>ploded diagra"s in"aintenance "anuals and false color satellite i"ager+ aret?o co""on e>a"ples of such $isuali;ations.

Se$eral 9:5 technia"ple the creation of Aancient "osaics of

artistic

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S. Battiato G. i Blasi G.!. Farinella G. Gallo H & Sur$e+ of igital !osaic =echnitre"e $ariailit+ of the @aeerliKs techniel neighorhood. !oreo$er the+ descrie a"ethod to speed up the "o$ing process.

2.# $austino and $igueiredo!s i%"rove%ent

5ecentl+, Faustino and Figueiredo 3FF04 presented atechniagonal lattice of the i"age, ut the+ find the seeds ofthe first Joronoi diagra" + sa"pling the i"ageadapti$el+ using a

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S. Battiato G. i Blasi G.!. Farinella G. Gallo H & Sur$e+ of igital !osaic =echniagonal grids)adapted to place tiles in cur$ing sis isad1usted locall+ to follo? a chosen direction field (co"ingfro" the edge features). Co"puting the CJ is "adepossile + le$eraging the ;8uffer algorith" a$ailale in

"an+ graphics cards. =he @ausnerKs algorith" can eoutlined as follo?s

S=list of random points on the input image

while (!converged)

for each p in S, place a square

pyramid with apex at p

rotate each pyramid about the z axis

to align it the the direction field

render the pyramid with an orthogonal

projection onto the xy plane,

producing a Voronoi diagram

compute the centroid of each Voronoi

region

move each p to the centroid of its

region

end while

#.2 Traditional %osaics by 'lber and (olberg

& $er+ ad$anced approach to the rendering oftraditional "osaics is presented in 3E04. =his techni and the le$el line "atri>. place the tile.

In particular point . can e descried as follo?s

?hile there are chains of pi>els not +et processed in

the le$el line "atri>a. select a chain. starting fro" an aritrar+ pi>el on it Afollo? the

chainc. place ne? tiles at regular distances along the

path (the orientation of the tiles is assigned usingthe gradient infor"ation fro" "atri>).

#.). *ender+ots

5ecentl+ a no$el techni

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S. Battiato G. i Blasi G.!. Farinella G. Gallo H & Sur$e+ of igital !osaic =echnielated portraits to stud+ hu"an perception and theauto"atic pattern recognition issues. For e>a"ple he usedthe" as a de"onstration of the "ini"al condition torecogni;e a face. =he i"age in Figure a is 1ust a $er+ lo?resolution rendering (22 pi>els) of a gra+ i"age ofMincoln. Each pi>el is seen as a Atile. =his i"age ofMincoln needs to e $ie?ed at a distance to see the face.=he fact that MincolnKs face is so ?ell no?n "aes itsrecognition easier.

In *D6 Sal$ador ali 390*4 co"pleted the paintingin Figure titled AGala conte"plating the !editerraneanSea, ?hich at 0 "eters eco"es the portrait of &raha"Mincoln (@o"age to 5otho). 9ote that MincolnKs face is"ade up + pictures ?ith full tonal ranges perhaps theearliest e>a"ple of this techniel ca"e fro" an artist to+ing ?ith &doe:hotoshopN 3&do064 and the earliest e>a"ple of a

photographic co"puter "osaic is the i"age created +a$e !cOean for JertigoHC co"ics in * (see Figured).

Co"puter replicated i"ages "ade fro" tiled digitalphotographic pictures is recent ecause it reture, shape and color.Sil$ers ?as co""issioned + the #S Mirar+ of Congressto create the portrait of Mincoln in Figure e using archi$edphotos of the &"erican Ci$il ar.

=he Eurographics &ssociation 2006.

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S. Battiato G. i Blasi G.!. Farinella G. Gallo H & Sur$e+ of igital !osaic =echnitended+ Olein et al. OGFC02to $ideos otaining a $ideo "osaicand recentl+ i Blasi and :etralia 3:04 presented anapproach to speed up the search process ased on the&ntipole strateg+ 3CF:P04.

-. ,uzzle I%age Mosaics

:u;;le I"age !osaic is inspired + Giuseppe&rci"oldo 3Str4, a 5enaissance Italian painter in$entorof a for" of painting called the co"posite head ?herefaces are painted not in flesh, ut ?ith rendered clu"ps of$egetales and other "aterials slightl+ defor"ed to etter"atch the hu"an features.

-.1. i% and ,ellacini!s a""roach

Oi" and :ellacini 3O:024 introduce a "osaicingtechni

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S. Battiato G. i Blasi G.!. Farinella G. Gallo H & Sur$e+ of igital !osaic =echnia"plethe photo"osaic algorith" created + Sil$er 3S@D4 istoda+ used + 5una?a+ =echnolog+ 35un064 (Sil$ersKco"pan+) to produce photo"osaic i"ages as logos andillustrations for indi$iduals, corporations and pulications,!agic !osaics (3!ag064) produces pu;;le i"age "osaicposters and anners using a "odified $ersion of the

soft?are proposed + i Blasi et al. 3G:04 and thesoft?are proposed + i Blasi and Gallo 3G04 hasrecei$ed interest fro" "an+ artists, co"panies and Fine&rts &cade"ies.

. Conclusions $uture (or3s

In this paper, ?e sur$e+ed se$eral approaches to non8photorealistic rendering of digital i"ages. In particular ?epresented so"e "ethods to create "osaic effects.

=here are se$eral ?a+s to i"pro$e the aesthetic of theresults and se$eral ideas started fro" these ?ors. Inparticular*. for ancient "osaics

a. a different strateg+ for choosing, in case of tileo$erlapping, ?hich tile has to e cut heuristic

rules or, perhaps, rando"i;ed choices couldproduce different outco"es

. generali;ation of the A"osaicistsK heuristic toother ind of pri"iti$e ased non photorealistici"age processing see"s possile and citing direction of research.

*eferences

3&do064 &doe :hotoshop. httpHH???.adoe.co", 20063&rc064 &rcSoft :hoto!ontage.

httpHH???.arcsoft.co", 20063BFG064Battiato S., i Blasi G., Farinella G.!., Gallo

G., A !ovel Technique for 0pus 3ermiculatum2osaic "endering. =o appear in SCG2006,anuar+ 2006

3BlaL4 Blae S., httpHH???.arcodeart.co"H, *L3CF:P04 Cantone C., Ferro &., :ul$irenti &., 5eforgiato

5ecupero ., Shasha .,Antipole Tree inde&ingto support range search and 4*nearest neighborsearch in metric spaces. IEEEH=OE, Jolu"e

*D, Issue , pp. 80, 2003CloD04 Close C., httpHH???.chucclose.coe.uh.eduH,

*D03G04 i Blasi G., Gallo G., Artificial 2osaics. =he

Jisual Co"puter, Jolu"e 2*, Issue 6, pp. D8L, 200

3G:04 i Blasi G., Gallo G., :etralia !., :u;;le I"age!osaic. In :roceedings of I&S=EHJII:200,Septe"er 200

3@9024oashi ., @aga =., ohan @., 9ishita =., &!ethod for Creating !osaic I"ages #singJoronoi iagra"s. In :roceedings ofEurographics2002, Septe"er 2002

=he Eurographics &ssociation 2006.

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S. Battiato G. i Blasi G.!. Farinella G. Gallo H & Sur$e+ of igital !osaic =echni