Computer aided clothing pattern design with 3D editing and pattern alteration

w e s i Clothing computer aided design Cross parameterization Mesh editing/deformation Pattern alteration proposed to speed up the clothing design process. A series of new techniques from cross parameterization, geometrical and physical integrated deformation, to novel editing methods are proposed. First, a cross parameterization technique is employed to map clothing pattern pieces on a model surface. The pattern can be precisely positioned to form the initial shapewith low distortion. Next, a new deformationmethod called hybrid pop-up is proposed to approximate the virtual try-on shape. This method is an integration of geometrical reconstruction and physical based simulation. In addition, user interactive operations are introduced for style editing and pattern alteration in both 2D and 3D manners. The standard rules regulating pattern editing in the fashion industry can be incorporated in the system, so that the resulting clothing patterns are suitable for everyday production. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction The research in clothing computer aided design (CAD) has flourished since the pioneer work of the MIRALab led by Prof. Magnenat-Thalmann in the late 80s. In the past two decades, computer graphics community has made significant contributions to this area, covering all aspects of clothing design, from design au- tomation, interactive editing, virtual try-on, pattern generation to custom-design clothing. 1.1. Related work of clothing CAD The first research problem that needs to be solved for any clothing CAD systems is to accurately display a design. Most researchers follow two main approaches to visualize garment models. One approach represents garments as 2D patterns, which are placed around a human model and then assembled virtually to form 3D garments. This can be named as a 2D-to-3D approach. Fuhrmann [1] used developable surfaces, like cylinders or cones, to position clothing patterns around the virtual human, and then applied the physically based approach for an automated drape simulation. McCartney et al. [2] represented a garment as a collection of panels offset from the body surface, and constructed ∗ Corresponding author. Tel.: +852 27664442; fax: +852 27731432. E-mail address: Tracy.Mok@inet.polyu.edu.hk (P.Y. Mok). the garment around a static human model. Volino et al. [3] provided an interactive design environment to edit patterns in 2D and immediately visualized the garment draping results in 3D. Meng et al. [4] used physical-based real-time simulation to visualize design effects by virtually sewing up complex garment patterns on human models. An online made-to-measure system was presented by Cordier et al. [5], allowing shoppers to virtually try on garments on the web. Another approach uses parameterized surfaces and curves to model garments in 3D space directly. Kim et al. [6,7] drew grids on the mannequin and then scanned this information to construct a 3D garment surface. Liu et al. [8] adopted Bezier’s parametric surface to represent a 3D garment surface. Wang et al. [9] proposed a 3D garment design system involving the participation of customers for mass personalization, and they employed style surface and curves to represent garments. Other researchers used approximate surface and offset surface techniques, for example, Turquin et al. [10] and Decaudin et al. [11] sketched garment contours directly onto 3D human models and then generated 3D garments using a predefined distance field around the human model. Wang et al. [12] suggested a system to construct garments around a human model directly in 3D space by stroke input. Luo and Yuen [13] represented patterns as loop of curves, so that the pattern sizes would change in accordance with the size of the human models used. Such a predefined relationship between clothing and body embeds the ‘fit’ in garment modelling. All of Computer-Aided Desig Contents lists available a Computer-A journal homepage: www Computer aided clothing pattern design Yuwei Meng a,b, P.Y. Mok b,∗, Xiaogang Jin a a State Key Lab of CAD&CG, Zhejiang University, Hangzhou, China b Institute of Textile & Clothing, The Hong Kong Polytechnic University, Hong Kong a r t i c l e i n f o Article history: Received 25 July 2011 Accepted 15 March 2012 Keywords: a b s t r a c t The traditional apparel prod involves trial-and-error. In repeated cycles of sample pr itself is time-consuming, co a novel computer aided des 0010-4485/$ – see front matter© 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.cad.2012.03.006 n 44 (2012) 721–734 t SciVerse ScienceDirect ided Design .elsevier.com/locate/cad ith 3D editing and pattern alteration uct development process is a typical iterative ‘optimization’ process that order to confirm the design and achieve a satisfactory fit, a number of paration, trial fitting and pattern alteration must be conducted. The process tly, and dependent on the designer’s skills and experience. In this paper, gn (CAD) solution for virtual try-on, fitting evaluation and style editing is e 722 Y. Meng et al. / Computer-Aid these are pure geometrical methods. In other words, the designs are freeform designs. Apart from visualizing a clothing design on the computer, it is also important to allow designers to edit the design and check the clothing fit. In 2D-to-3D based clothing CAD applications, design editing and alterations are carried out on 2D patterns and then followed by a drape simulation to examine the results. In applications that follow the second approach of modelling garments directly in 3D space, the design editing can be done by deforming the 3D garments. However, a process must be provided to project the 3D design into 2D space, so as to obtain the pattern pieces. The typical approach is by flattening the designed 3D surfaces to 2D planes. Azariadis and Aspragathos [14] proposed two optimization methods for flattening 3D surfaces: One without taking into consideration of the geodesic curvature constraints of the surface isoparametric curves, and the other method uses the constraints to control the local accuracy of the derived planar patterns. Kim and Kang [15] proposed a projection algorithm to flatten surface models by strain minimization and introducing darts automatically. The pattern flatteningmethods employed play a crucial part in 3D garment design, since they determine the quality of the final manufactured garments. It is important to note that flattening a freeform design has to involve some kinds of deformation. In addition, alterations in design very often start from editing the human models, because the ‘fit’ – gap between the clothing model and the human model – is predefined in the 3D garment modelling. If a design is changed, it needs to do the 3D garment modelling anew. In summary, the 3D-to-2D approach suffers from thedrawbacks of either limited style variation or impractical shape of the flattened patterns for apparel manufacturing applications. In 2D- to-3D approach, physical based systems are often used to simulate realistic clothing drape and even catwalk animation. However, the computational intensive nature of physical-based simulation forces researchers to trade accuracy for speed by using simplified models in the simulations. The simulated results may be good for virtual characters or film animation, but it cannot reach the required accuracy in clothing production. 1.2. Traditional fitting process for pattern optimization The traditional clothing product development is an iterative effort for fit and design optimization, involving stages like design, sample preparation, fit evaluation, and pattern alterations. In the industry, clothing patterns are often constructed in 2D by pattern experts through manipulating a set of basic blocks, or altering from the patterns of similar style. A sample garment is then prepared and put on a mannequin or a live model to evaluate the fit achieved. In the fitting process, pattern experts visually examine the sample by looking at where wrinkles are created, so as to estimate the spatial relationship between the sample and the body, namely the clothing gap. Necessary corrections are marked with pens and pins on the sample, and the 2D patterns are altered accordingly. Another sample garment would then be made. The process is repeated for a number of cycles until a satisfactory fit is achieved (see [16] for detailed guideline on trial fitting process). It is important to note that although the clothing gap is critical for fit evaluation, the traditional sample fitting process is not able to visualize the gap in any form. With reference to fit evaluation, both geometrical and physical based CAD approaches have limitations. In geometrical based CAD systems, the clothing eases for every design/style are predefined; but this concept is obviously very different from the traditional practice of the industry described above, where 2D patterns are altered to fit the customer’s body shape. The concept of predefined d Design 44 (2012) 721–734 easemaybepossible only for staple itemswhere style change is not frequent, like shirts or trousers. However, for fashionable items, the predefined ease concept is not practical because apparel products have diverse fit designs and people also have varied preferences on fit [17]. In physical-based systems, drape simulation could not provide accurate clothing gap for fit evaluation, but can simulate the clothing stretch and strain. These simulated stretch and strain could only give designers limited insight on the fit achieved or the ways for fit improvement. In addition, all clothing design and alterations are done on 2D patterns in physical-based CAD system, thus another simulation must be launched to examine the effect of any alterations made. All in all, true computer-aided ‘design’ is still absent, because synchronized 2D and 3Ddesign editing are not possible during the fit evaluation. In this paper, a method is proposed to establish the spatial relationship among 2D patterns, 3D garment and the human model. The main advantage of such association is that any pattern alterations, either in 2Dor 3D, can be reflected on thehumanmodel for fit improvement and style editing. 1.3. Research concept and system overview In this paper, a novel three-phase framework is proposed to enable virtual try-on simulation and fit evaluation. In contrast to the typical approach of 2D-to-3D CAD systems, where 2D pat- terns pieces are pulled towards the human model for virtual sewing simulation, the proposed method adopts a rather differ- ent approach. In the proposed method, 2D pattern pieces are first precisely mapped onto the human model surface by a cross- parameterization process. Next, a hybrid position update method integrating both geometrical reconstruction and physical simula- tion is developed. By this method, the garment pops up from the body surface, based on a few defined contact points, to restore its original size. After the pop-up process, a gap is formed between the clothing and the body that approximates the clothing gap in pat- tern design, which is fundamentally important for fit evaluation. Since a relationship between the clothing and the body has been defined, pattern editing for fit improvement or design amendment could later be facilitated. Finally, a systematic multi-view editing tool is suggested for synchronized 2D and 3D style editing and pat- tern alteration. A brief outline of the proposed three-phasemethod is given in Fig. 1. Each phase of the method will be discussed in separated Sections 2–4. Phase three of style editing and pattern al- terations is a large topic in clothing development, involving many steps and operations. In view of the substantial contents involved, Section 4 only briefly explains the underlying concept, and a more detailed discussion of the topic is given in [18]. Section 5 provides experimental results. The main contributions of this paper are summarized as follows: • A new mesh-to-mesh cross parameterization method is sug- gested for positioning the pattern pieces onto the humanmodel that precisely preserves the pattern shapes of the final gar- ments. The virtual try-on is achieved automatically. • A novel hybrid method combining physical-based simulation and geometrical reconstruction is proposed to deform the garment from initial form to the ‘desired’ shape, i.e., to resume its original size. The hybrid schema enables the local coordinate technique to be used not only for single closedmesh deformation, but also for openmesh surface reconstruction. • A unique pattern alteration method is proposed for garment editing in both 2D and 3D manners, and such idea has never been reported in the literature before. The method uses fashion design rules to control the style editing and pattern alteration, making it suitable for practical implementation of fashion product development. e technique was first proposed by Maillot et al. [19], who obtained the planar development of a 3D surface by solving a global opti- mization problem. Sheffer and Hart [20] described a faster tech- nique to lower the visual distortions. Haker et al. [21] suggested a spherical texture domain for seamless mapping of closed surfaces. Sander et al. [22] and Levy et al. [23] subdivided the surface into multiple small patches and texturemapped the patches separately. In summary, interactive texture mapping methods strive to mini- mize the distortion in the mapping process according to different distortion metrics. To establish spatial relationship between clothing pattern and human model, a new surface parameterization technique is re- quired because clothing patterns of different designs vary largely in geometrical shapes, for instance, darts and inside darts may be involved. In this paper, a duplex mapping scheme is proposed, involving the following three steps: (1) Feature definition: spec- ify the corresponding feature points on both the human mesh model and the pattern mesh; (2) Mesh segmentation and region mapping: triangulate 2D patterns based on defined feature points to obtain ancillary patterns, and segment the human body mesh accordingly to match with the ancillary patterns; and (3) Cross- parameterization: embed each patch on the body mesh surface to points on both the clothing patterns and the human model. Figs. 2 and 3 show the human model feature points FH and the clothing pattern feature points FP , respectively. The definition of body feature points is available in most pattern-making literature [24] or body measurement standards [25]. Huang [17] described detail methods to define feature points on a mesh model automatically. In every pattern piece, the corner points, also called grade points, are important features. If any of the grade points do not correspond to the predefined body features FH (for example, pink circle points in Fig. 3), the system calculates their relative positions on the model surface based on known feature points (black square points) by proportion. The system defines the relative position of a pink circle point on the shortest path between two known feature points, FH . The shortest path calculation will be explained in later Section 3.2. In addition to obtaining the feature point positions automatically by proportion, a user interface is also provided for users to define the features manually. 2.2. Mesh segmentation and region mapping After inputting the clothing pattern M and the corresponding feature points FP , the system adds additional auxiliary points to the feature curves of the pattern pieces, as shown in Fig. 4. This is Y. Meng et al. / Computer-Aid Fig. 1. Syste 2. Pattern-to-model cross parameterization Clothing try-on demands a rigid correspondence between the clothing feature points and the human model feature points. The proposed computer aided design system starts by first establishing a spatial relationship between the 2D clothing patterns and the human model by a surface parameterization process. Surface parameterization consists of generating a planar pa- rameterization for a 3D mesh surface. Parameterization has var- ious applications in science and engineering, including scattered data fitting, re-parameterization of spline surfaces, and repair of CAD models. Texture mapping is an important application of parameterization that commonly used to increase the visual complexity of computer generated images while maintaining sim- plicity in the underlying geometric models. Texture mapping algo- rithms provide parameterization by using an embedding function and barycentric coordinates for each pair ofmesh triangles that de- fine a piecewise-affine mapping. An interactive texture mapping the corresponding clothing pattern mesh to generate parameteri- zation coordinates. d Design 44 (2012) 721–734 723 m overview. 2.1. Nomenclature and feature definitions A list of symbols used in cross parameterization process is provided below: FH : feature points of the human model FP : feature points of the clothing pattern M: Mesh of 2D patterns M ′: Mesh of ancillary 2D patterns generated based on FP M∗: 3D configuration of the patternM , i.e., the mapping result Pi: patch of the human model Ti: triangle inM T ′i : triangle inM ′ (pk, pl): vertex in Pi (v′k, v ′ l ): vertex in T ′ i (vk, vl): vertex in Ti The planar patterns M and triangulated human model are inputs to the process. The process starts from defining the feature done to ensure satisfactory triangulation results in the later step. The positions of these auxiliary points are computed as average e Fig. 3. The corresponding feature points on a front and a back pattern pieces, FP . splitting between two defined feature points. Each boundary curve is divided into ⌈li/κ⌉ segments, where κ is the length of the shortest boundary curve, li is the length of the current boundary curve, and ⌈•⌉means a round up operation. Constrained Delaunay triangulation is then carried out on all pattern pieces by using predefined feature points and the auxiliary points as the vertices. This will obtain a set of ancillary pattern pieces, M ′, which are the simplified forms of the pattern pieces, M . Fig. 6(b) shows an example of ancillary patternsM ′, the front piece. After triangulating the clothing pattern M , the human mesh model is segmented based on the ancillary pattern M ′ by an approximated shortest path method, as shown in Fig. 6(e). Traditional Dijkstra shortest path connects two specific vertices on to iteratively subdivide the impact triangle edges and construct new weighted graphs, so that the path is closer to the ideal one could by iterations. However, such method costs a considerable amount of memory space and it is rather time consuming. In this paper, a simple shortest path method is developed to segment the human model mesh, see Fig. 5. It uses pre-computation rather than an iterative schema. In the graph construction stage, the set of impact edges are subdivided according to the edge length of the corresponding triangle T ′i on the ancillary pattern M ′. Given a defined length, each edge is inserted with several intermediate points and the number of points inserted is proportional to the length of the triangle edge, as shown in Fig. 5. Thus, a long edge is divided into more segments compared with a short edge. Fig. 2. Feature points on human model, FH . 724 Y. Meng et al. / Computer-Aid a mesh with edges, which is not the exact shortest path on a mesh surface. A known method to improve the Dijkstra shortest path is d Design 44 (2012) 721–734 Another method was also suggested to calculate the shortest path in [26]. It partitioned the mesh into valid sub-regions after e r After the mesh segmentation process, a bijective mapping is constructed between the pattern and the corresponding region of the human model. Each triangle T ′i on the ancillary patterns M ′ is then matche