Accurate color reproduction is important in many applications of 3D printing, from design prototypes to 3D color copies or portraits. Although full color is available via other technologies, multi-jet printers have greater potential for graphical 3D printing, in terms of reproducing complex appearance properties. However, to date these printers cannot produce full color, and doing so poses substantial technical challenges, from the shear amount of data to the translucency of the available color materials. In this article, we propose an error diffusion halftoning approach to achieve full color with multi-jet printers, which operates on multiple isosurfaces or layers within the object. We propose a novel traversal algorithm for voxel surfaces, which allows the transfer of existing error diffusion algorithms from 2D printing. The resulting prints faithfully reproduce colors, color gradients and fine-scale details.
3D Halftoning. @math D Halftoning has been applied to material composition using @math D error diffusion filters @cite_49 @cite_29 and @math D dispersed-dot dithering @cite_40 . For color and appearance reproduction, 3D error diffusion is not appropriate because material assignments closer to the surface will have a greater influence on the appearance of the object than material assignments deeper within the object. Thus, a 3D error diffusion filter would have to adjust its orientation during traversal to account for this and maintain a consistent orientation with respect to the surface. An isotropic filter would produce similar artifacts as are observed with isotropic filters in 2D error diffusion. In contrast, our approach of halftoning on multiple offset surfaces within the object, in addition to the surface itself, results in a halftone that inherently accounts for the geometry of the surface. The relative influence of voxels at different depths from the surface is calibrated in an offline process and built into an International Color Consortium (ICC) profile. Such an offline color calibration process would be very challenging for a 3D filter, because it would require calibrating every possible surface orientation.
@cite_40 @cite_29 @cite_49
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A dithering algorithm is presented for application to local composition control (LCC) with three-dimensional printing (3D printing) to convert continuous-tone representation of objects with LCC into discrete (pointwise) version of machine instructions. The algorithm presented effectively reduces undesirable low frequency textures of composition for individual 3D layers and also for 3D volumes. Peculiarities of the 3D printing machine, including anisotropic geometry of its picture elements (PELs) and uncertainties in droplet placement, are addressed by adapting a standard digital halftoning algorithm. Without loss of generality, our algorithm also accounts for technical limitations in the printing device, only generating lattices that can be represented within the finite memory limits of the hardware. We present a bitmap printing method and digital workflow using multi-material high resolution Additive Manufacturing (AM). Material composition is defined based on voxel resolution and used to fabricate?a design object?with locally varying material stiffness, aiming to?satisfy the design objective. In this workflow voxel resolution is set by the printer's native resolution, eliminating the need for slicing and path planning. Controlling geometry and material property variation at the resolution of the printer provides significantly greater control over structure-property-function relationships. To demonstrate the utility of the bitmap printing approach we apply it to the design of a?customized prosthetic socket. Pressure-sensing elements are concurrently fabricated with the socket, providing possibilities for evaluation of the socket's fit. The level of control demonstrated in this study?cannot be achieved using traditional CAD tools and volume-based AM workflows, implying that new CAD workflows must be developed in order to enable designers to harvest the capabilities of AM. Bitmap printing workflow enables digital fabrication in printer's native resolution.Voxel-based design and representation of objects for multi-material printing.Using 3D printed light guides, deformation of materials can be sensed. 3D halftoning is a new technique that allows the approximation of digital volumetric objects of varying material density e.g. porous media for example, by an ensemble of binary material volume elements called vels. In theory, 3D halftoning is basically an extension of the well known 2D halftoning process, as widely used in binary printing applications. In practice, however, the development of 3D halftoning algorithms is strongly related to hardware specific boundary conditions, such as particular characteristics of additive volumetric object manufacturing procedures. This paper addresses theoretical as well as practical aspects of 3D halftoning that allow the rendition of digital volumetric objects of varying density using the stereolithographic additive fabrication technique. An ultimate application of 3D halftoning is the reproduction of volumetric objects in medicine that consist of a mixture of bone, cartilage and soft-tissues, for example.