Intenational Jounal of Electonics and Electical Engeeg ol. 1, No. 1, Mach 013 Bilateal Filte Based Selective Unshap Maskg Usg Intensity and/o Satuation Components Noiaki Suetake, Yohei Kuamoto, and Eii Ucho Yamaguchi Univesity/Gaduate School of Science and Engeeg, Yamaguchi 753-850, Japan Email: {nsuetake, s10vc, ucho}@yamaguchi-u.ac.p Kazuhio Tokunaga Fuzzy Logic Systems Institute, Fukuoka 80-0067, Japan Email: tokunaga@flsi.o.p, Sadanoi Hiose Yamaguchi Univesity/Faculty of Science, Yamaguchi 753-851, Japan Email: n046de@yamaguchi-u.ac.p Abstact Conventionally, ode to shapen and enhance blued digital images, unshap maskg (UM) has been used widely. Howeve, ove-enhancement is geneated fequently edge pats of the image and the atifacts such as aggy and halo ae sometimes seen the esultant image. To cope with the poblem, the selective UM methods wee poposed so fa. Howeve, they wee not always effective fo the ealization of the atifact suppession and image shapeng at the same time. In this pape, we popose new selective UM methods which employ the bilateal filte and Laplacian of tensity and/o satuation components of image. In the methods, the occuence of aggy and halo is suppessed by weakeng the shapeng effect especially at the edge pats of obects the image, and the image is well shapened totally. Though the expeiments usg some images, the effectiveness of the poposed methods is illustated. Index Tems image shapeng, unshap maskg, selective unshap maskg, bilateal filte I. INTRODUCTION In ode to shapen and enhance the blued images, unshap maskg (UM), which the high fequency components of the image ae calculated, weighted and added to the image, has been used widely because its calculation pocedue is vey simple and can poduce good esults [1]. Howeve, UM sometimes geneates atifacts such as aggy and halo at the edge pats of the obects the esultant image as shown Fig.1. This is deived fom unifom addition of the weighted high fequency components even to the pats of the edges. To cope with this poblem, the selective UM methods have been poposed so fa []--[4]. In this selective UM, the amounts of the high fequency components, which ae added to the image, ae adusted based on the local image featues. Howeve, even the selective UM methods, thee wee some cases whee the atifacts wee geneated Manuscipt eceived Januay 5, 013; evised Mach 3, 013. the images o the shapeng effect was vey weak, that is, the image was not well shapened and enhanced. Figue 1. Example of atifact. oigal image, image obtaed by UM. In this pape, we popose new selective UM methods, which use atios of the local vaiances of the oigal put image and the edge-peseved smoothed image obtaed by the bilateal filte ode to contol shapeng effect, and uses high fequency components of the tensity and/o the satuation of the image to enhance the textue pats well. In these methods, the occuence of aggy and halo is suppessed by weakeng the shapeng effect especially at the edge pats of obects the image, and detail and textue pats of the image ae well shapened and enhanced totally. In this study, the expeiments usg some images ae executed ode to veify the effectiveness of the poposed methods. II. PROPOSED METHOD The poposed methods ae ealized by usg the edgepesevg image smoothg and the image shapeng techniques. In this section, techniques used hee, that is, the bilateal filte and the conventional UMs ae descibed at fist. Then details of the poposed methods ae given. A. Bilateal Filte A numbe of edge-pesevg smoothg filtes have been poposed so fa. In this study, the bilateal filte (BF) 013 Engeeg and Technology Publishg doi: 10.170/ieee.1.1.10-14 10
Intenational Jounal of Electonics and Electical Engeeg ol. 1, No. 1, Mach 013 which is most typical edge-pesevg smoothg filte [5] is employed. Let be component (tensity) of put image HS colo space. Then the output image bf by BF is given as follows:. bf 1 l m w ( 1 l m w ( (, (1) whee is a positive constant to deteme the size of the neighbog pixels of ( used to obta the bf (. w 1 can be expessed by the poduct of the spatial weightg function w x and the photometic one w d as follows: w1 ( wx ( l, m) wd ( i l,. () In geneal, w x is given as the followg Gaussian function which does not depend on the coodate ( : ( l, m) exp( ( l m )), (3) w x whee is a positive constant. w d is given as: wd ( exp[ ( ) ], (4) whee is a positive constant. w d has small value the case whee the diffeence between ( and its neighbog pixel (i+l, +m) is lage. It has the effect of edge-pesevg B. Unshap Maskg UM is a method to enhance high fequency components of an image. It maly enhances edge pats of the obects the image, and the esultg edge enhanced image gives shapened impession to obseves. In nomal UM, the high fequency components of the tensity of the put image ae extacted and weighed. Then, the image shapeng is achieved by addg them to the image. The shapened image um obtaed by UM is calculated as follows:, (5) un whee is a positive constant to adust the stength of the shapeng effect. stands fo the output of the high-pass filteg of the put image. In many cases, 4-neighbo Laplacian filte is employed as the high-pass filte UM. 4-neighbo Laplacian filte used hee is given as follows: 4 ( i 1, ( i 1, 1) 1). (6) Figue. Pocessg flows of the poposed methods. Futhemoe, as the method which consides not only the high fequency component of the tensity but also that of the satuation the shapeng of the image tensity, UM usg spatially adaptive satuation feedback (UMS)[6] has been poposed by B.A. Thomas et al. In UMS, the detail and textue pats of the image ae well enhanced compaison with nomal UM. The output image ums of UMS is obtaed as follows: ums S S, (7) whee S ( is S component (satuation) of the pixel ( of the put image HS colo space, and is S also a positive constant to adust the stength of the shapeng effect. In Eq.(7), is a coelation coefficient the pixel ( between the tensity and satuation components ode to hamonize signs of tensity and satuation components, and is calculated by: l m l m ( ( S (, S ( l m (8) (, (9) S( S( S(, (10) whee and S ae local aveages of ( and S (, espectively. In the poposed method, we patially use the pocedue of UMS the shapeng pocess. C. Algoithm of the Poposed Methods In the poposed methods, fistly, an edge-peseved smoothed image bf is obtaed by the bilateal filte. Then, the image um, ums, o m,ax is obtaed by UM pocessg descibed below. Fally, the output image po1, po o po3 is obtaed as the weighted sum of the put image and um, ums o max. The weight fo each pixel is decided by usg the atio of the local vaiances of and bf. Fig. shows the pocessg flows of the poposed methods. The concete pocedues of the poposed methods ae descibed usg some equations as follows. An output image po1 of the poposed methods is obtaed as follows: w( (1 w( ) ), (11) po1 um 0 w( v bf / v ) v 0, othewise, (1) x x 1, x ) (13) 1 othewise, whee w( is a weight fo the pixel (, and v ( stands fo a local vaiance of pixel values of at the coodate (. The local egion suoundg ( of size ( is a positive odd tege, and is lage than 11
Intenational Jounal of Electonics and Electical Engeeg ol. 1, No. 1, Mach 013 o equal to 3) is consideed, and the vaiance of pixels values the egion is calculated. v bf ( is the local vaiance of bf at the coodate (. (c) (d) (e) Figue 3. Test images. image 1, image, (c) image 3, (d) image 4, (e) image 5. (c) (d) (e) Figue 4. Weights calculated each image. these values ae nomalized a ange [0,1] to show as gay-scale images. image 1, image, (c) image 3, (d) image 4, (e) image 5. The local vaiance is elated to whethe the edge is cluded the local egion o not. In the case whee the local egion cludes the edges of the subects, both v ( and v bf ( tend to be lage values. Theefoe the atio v bf ( /v ( becomes nea to 1. Contastively, v bf tends to be nealy 0 when the local egion cludes only plane egion, and the atio v bf ( /v ( becomes nea to 0 this occasion. At the pixels located nea to o on the edge, the shapeng effect should be weakened ode to suppess the occuence of atifacts. On the othe hand, othe egions cludg plane and detailed patten egions should be shapened and enhanced effectively. Eq.(11) executes the switched pocessg mentioned above without any paamete. The ange of w( becomes [0, 1] afte the calculation of. An output image po of the poposed methods is obtaed as follows: w( (1 w( ) ). (14) po ums In the output image po, it is expected that the enhancement effect especially the detail and textue pats of the obects is well ealized compag with the output image po1. Moeove, an output image po3 of the poposed methods is obtaed as follows: w( (1 w( ) ), (15) po3 max S S, max S S othewise. (16) In the output image po3, it is expected that the oveenhancement is suppessed by adoptg a maximum opeato the UM pocess compaison with the output image po. III. EXPERIMENTAL RESULTS In ode to veify the effectiveness of the poposed methods, the image shapeng/enhancement expeiments usg five test images ae achieved. The test images used hee ae shown Fig. 3. Fig. 4 shows the weights calculated fo the test images the poposed methods. In Fig. 4, weight values ae nomalized a ange [0, 1] and ae shown as the gayscale images. As shown Fig. 4, weights become lage at edges of the obects, and as a consequence, the shapeng effect of the poposed methods is weakened at the edge pat of the obects. In the expeiments, UMS and the poposed methods (Po1, Po and Po3) ae employed. In Figs. 5 and 6, esultant images of the shapeng only fo images 1 and 4 ae shown as examples. These esultant images ae patially enlaged ode to effectively show the shapeng effect of each method and to save the space. Fig. 5 shows a pat of the test image 1. And Figs. 5, (c), (d) and (d) show the pats of the esultant images obtaed by UMS, Po1, Po and Po3, espectively. In the visual evaluation, to discuss the shapeng effect efficiently, it is taken notice the head pat of a bid. Fom Fig. 5, it is obseved that the aggy and halo ae seen at the obect the images obtaed by UMS. On the othe hand, it can be seen that the aggy and halo does not exist the image obtaed by the poposed methods as shown Figs. 5(c), (d) and (e). Moeove, fom Figs. 5(d) and (e), it can be said that detailed pats ae well shapened by Po and Po3. 1
Intenational Jounal of Electonics and Electical Engeeg ol. 1, No. 1, Mach 013 Figue 5. Expeimental esults fo the test image 1. patially enlaged images ae shown to save the space and to illustate effectively the diffeences among methods. oigal put image, ums, (c) po1, (d)po, (e) po3. Figs. 6,, (c), (d) and (e) show the pats of the oigal and shapened esultant images fo the test image 4 the simila manne to Figs. 5,, (c), (d) and (e). In UMS, the esultant image is unnatual due to oveenhancement as shown Fig. 6. In Po1, it can be said that the shapeng effect is not enough at detailed pats as shown Figue 6(c). On the othe hand, it can be seen that edges and detailed pats of the images obtaed by Po and Po3 give us the natual impession like those of the oigal image, and ae well shapened and enhanced, as shown Fig. 6. Then, ode to show the effectiveness of the poposed methods quantitatively, the shapeng esults ae evaluated by usg Scheffe's paied compaison test. In the paied compaison test, two stimuli ae picked up fom vaious stimuli and ae evaluated. Concetely, two images aanged ight and left ae compaed and scoed by the examee. In the scog, if the ight image is udged as bette than the left image then a positive value is given. Othewise, a negative value is given. Afte the evaluations fo all combations, esults ae numeically epesented by usg the yadstick method, and it becomes possible to show which images is bette fo examees. In this study, the evaluation was achieved by 5 examees, and scog by each examee was done by givg one of [-1, 0, 1]. Paamete values of each method wee decided by each examee fo each image. And the evaluation and scog wee achieved by payg attention to the followg two pots: 1) whethe a detailed pat is clea o not, and ) whethe thee is unnatual shape/colo (aggy/halo) the edge o not. Tables I and II show the numeical esults of the paied compaison test. Fom Tables I and II, it is undestood that the poposed methods Po and Po3 ae supeio to the othe methods totally. I. CONCLUSIONS In this pape, new selective UM methods, which use atios of the local vaiances of the oigal put image and the edge-peseved smoothed image obtaed by the bilateal filte ode to contol shapeng effect, wee poposed. TABLE I. QUANTITATIE EALUATION BY PAIRED COMPARISON METHOD IN THE IEWPOINT OF SHARPENING Images Oigal UMS Po1 Po Po3 Image -0.80 0.46-0.0 0.3 0.04 Image -0.48 0.48-0.0-0.06-0.14 Image 3-0.76 0.34 0.08 0. 0.1 Image 4-0.68 0.3-0.36 0.46 0.6 Image 5-0.68 0.5-0.8 0.4 0.0 Aveage -0.68 0.4-0.01 0.4 0.01 (c) (d) TABLE II. QUANTITATIE EALUATION BY PAIRED COMPARISON METHOD IN THE IEWPOINT OF IMPROEMENT OF JAGGY/HALO Images Oigal UMS Po1 Po Po3 Image 0.10-0.38-0.10 0.18 0.0 Image 0.60-0.66 0.18-0. 0.10 (e) Figue 6. Expeimental esults fo the test image 4. patially enlaged images ae shown the simila manne to figue 5. oigal put image, ums, (c) po1, (d)po, (e) po3. Image 3 0. -0.16 0.30 0.0-0.16 Image 4 0.6-0.66 0.30-0.16-0.10 Image 5 0.48-0.40-0.06-0.04 0.0 Aveage 0.40-0.45 0.1-0.09 0.01 13
Intenational Jounal of Electonics and Electical Engeeg ol. 1, No. 1, Mach 013 In these methods, it was confimed that the occuence of aggies and halos was suppessed especially at the edge pats of subects and the image was well shapened totally. Futhemoe, the expeiments usg some images wee achieved. In the expeiments, the esultg images wee evaluated by a paied compaison test, and effectiveness of the poposed methods was veified. Futue woks ae to establish the auto-tung method of the paametes, and to save the calculation costs to ealize the eal time pocessg. REFERENCES [1] A. K. Ja, Fundamentals of Digital Image Pocessg, Pentice- Hall, Englewood Cliffs, NJ, 1989. [] A. Polesel, G. Rampon and.j. Mathews, Image enhancement via adaptive unshap maskg,'' IEEE Tan. on Image Pocessg, vol.9, pp.505-510, Ma. 000. [3] G. Tanaka, N. Suetake, and E. Ucho, An edge pesevg filtebased selective unshap maskg fo noisy images,'' Poc. 3d Int. Technical Conf. on Cicuits/Systems, Computes and Communications, pp.469-47, 008. [4] R. C. Bilcu and M. ehvilae, Constaed unshap maskg fo image enhancement,'' In A. Elmoataz, O. Lezoay, F. Nouboud and D. Mammass (Eds.), Image and Signal Pocessg, LNCS 5099, Spge, pp.10-19, 008. [5] C. Tomasi and R. Manduch Bilateal filteg fo gay and colo images,'' Poc. 1998 IEEE Int. Conf. Compute ision, pp.839-846, 1998. [6] B. A. Thomas, et. al., Colo image enhancement usg spatially adaptive satuation feedback,'' Poc. IEEE Int. Conf. Image Pocessg, vol.3, pp.30-33, 1997. Eii Ucho eceived the Ph.D. degee systems engeeg 1988 fom Hioshima Univesity, Japan. He is cuently a pofesso of the Gaduate School of Science and Engeeg at Yamaguchi Univesity, Japan. He is also a chaiman of the boad of diectos at the Fuzzy Logic Systems Institute (FLSI), Japan. He was a isitg Scientist at the Aachen Institute of Technology (RWTH), Gemany, 1994, and at the Univesity of Bistol, UK, 1996. His eseach teests clude adaptive system modelg, telligent signal, and image pocessg, and human ba based fomation pocessg system. He is an Honoay Membe of the Ukaian Academy of Sciences sce 00. Noiaki Suetake eceived the B.E., M.E. and Ph.D. degees fom Kyushu Institute of Technology, Japan, 199, 1994 and 000, espectively. He is cuently with the Gaduate School of Science and Engeeg, Yamaguchi Univesity, Japan, whee he is an associate pofesso. His eseach teests clude digital signal pocessg, image pocessg, and telligent systems. He is a membe of IEEE, OSA, and d IEICE. Kazuhio Tokunaga eceived the B.E., M.E. and Ph.D. degees fom Kyushu Institute of Technology, Japan, 001, 003, and 006, espectively. He is cuently with the Fuzzy Logic Systems Institute, Japan, whee he is a eseach scientist. His eseach teests clude neual netwoks and patten ecognition. He is a membe of JNNS. Yohei Kuamoto eceived the B.S. degee fom Yamaguchi Univesity, Japan, 01. He is cuently with the Gaduate School of Science and Engeeg at Yamaguchi Univesity, Japan, whee he is a gaduate student. He is teested signal and image pocessg. Sadanoi Hiose is cuently with the Faculty of Science at Yamaguchi Univesity, Japan, whee he is an undegaduate student. He is teested signal and image pocessg. 14