Color Styling Tools

Creative tools are proposed that allow color stylists to take advantage of their training in the art and design fields. A simple reflection model is employed that has the minimum number of free parameters required to design solid and metallic color finishes from conceptualization to fabrication. The parameters correspond to color specification terms familiar to designers such as face color, flop color, travel, and gloss. We demonstrate how the reflection model can also be used to develop effective interfaces for color stylists. We create a virtual mood board that allows direct selection of the reflection model parameters from pictures. We also develop an image based BRDF tweaker for adjusting color appearance directly on a 3D object. Introduction Industrial designers, interior designers, and architects all make extensive use of exemplars when they choose colors for a new product. They collect material samples from suppliers, they select illustrations from fashion magazines, and they take pictures of objects with interesting surface finishes. These exemplars are organized and displayed on “mood boards” (see Figure 1) that allow the designer to compare the colors and make final selections. The designer uses the mood board as a reference point when communicating their intentions to others and applying the design. Traditional hue, saturation, and brightness (HSB) color organization systems are used, after the fact, to provide a name and a specification for the final color. The existing computer graphic tools for color simulation and selection do not readily facilitate the color design process used in these traditional design fields. Computer graphic reflection models have been developed with the goal of accurately portraying subtle color appearance effects. These models have grown increasingly complex, and they include physical parameters for which aesthetic designers have no intuition. Numerous computer graphic HSB color systems have been proposed, but they are not able by themselves to convey the spatial aspects that separate one color appearance from another. In addition, in the traditional design process, exemplars and sketches are used more often than HSB color systems to ideate color. In this paper we propose a set of computer graphic tools to facilitate color design in the traditional aesthetic design fields. We employ a reflection model that covers the widest range of color appearances encountered by designers including solid colors, metallic colors, and the glossiness of these colors. The reflection model is constructed to have the minimum number of free parameters and to select these parameters so that they correspond to color specification terms familiar to designers such as face color, flop color, travel, and gloss. The model is defined in a way that allows it to be used as a manufacturing specification for the final color. Figure 1. Designers often use mood boards to propose the selection of colors and materials. They might start out collecting images from fashion magazines or other visually appealing artifacts like dried leaves or butterfly wings that can be pinned onto a mood board. As the designer’s vision develops, they rearrange and refine the images on the board. Finally, the designer uses the mood board when discussing their concepts with others and as a reference when implementing the design. The art director of a style and fashion magazine was invited to participate in the user study. She proposed “Orange Ball of Paris” that appeals to a young and fashionable audience. We also demonstrate how the reflection model can be used to develop effective interfaces for color designers. We create a virtual mood board that allows direct selection of the reflection model parameters from pictures. We also describe a novel color design interface for tweaking color and appearance directly on a 3D surface. Relevant work There is a variety of background work in providing artistic and design oriented controls over computer graphic reflection models. Design galleries presents renderings with variations of computer graphic parameters as a interface for tweaking scene parameters in [11]. Ngan [12] created image driven navigation systems for specifying the parameters to various BRDF models. Pellacini created a psychophysically-based BRDF model that aided the specification of gloss parameters in [13]. Kautz [8] allows an artist to create a bitmap texture that represents the shape and color of a reflectance distribution. Khan introduced a system for doing image space material editing in [9]. This paper focused on the rendering system that could apply new material designs to existing images. An intuitive and artistic interface for painting BRDFs was presented in [3]. The interface provides the ability to create a BRDF by positioning and manipulating highlights on a spherical canvas. A mapping between painted highlights and specular lobes was created for an extended Ward model. This software is constrained to a point light source and a spherical canvas. Sloan [19] developed a novel technique for capturing 3D non-photorealistic shading models from 2D artwork. The interface has a tool for selecting a region of a 2D source image to approximate an illuminated sphere that is later used to render 3D models. This allows for unconstrained lighting and shape, but does not pull pure BRDF information. The information collected convolves lighting with the BRDF, similar to a prefiltered environment map. Outside of our own work, there has been a variety of research on realistic rendering of optical phenomena relevant to the design of automotive paints. Rendering of interference and wave based optical phenomena was covered in [4, 7, 20]. Image based measurement techniques was applied to automotive paints in [6, 16]. Face/flop/travel/gloss reflection model This section describes the reflection model. First, the variables of the reflection model are defined, along with how they control the physical appearance of the resulting material. Since these variables cannot be directly related to graphics rendering, they are linked to a parametric representation that has been previously tied to a realtime rendering engine [17]. This reflection model is connected to the physical world through measurement tools and rapid color prototyping systems. Face/flop/travel/gloss form We describe a reflection model that has the following parameters: face, flop, travel, and gloss. Figure 2 gives a visualization of how the parameters of this reflection model correlate to the shape of the BRDF. “Face” is the color at 15◦ off specular angle and is represented as a Lab tristimulus value. This angle establishes the directionally diffuse color while avoiding the specular highlight resulting from the first surface coatings. “Flop” is the color at far from specular and is represented as a Lab tristimulus value. The particular angle that flop is associated with is the variable travel. Travel represents how color changes with viewing direction. This is intended to be the color of the diffuse portion of the material at as close to a specular angle as possible. If the face and flop colors are identical, the color is a solid color and therefore travel does not alter the appearance of the material. Figure 2. A diagram illustrating how the four components of the metallic reflection model relate to the shape of the BRDF lobe. The incoming light L is at 45◦ from the surface normal N. The specular reflection direction is