When it comes to 3D printing, besides speed, color is the next biggest impediment to widespread use among many areas of manufacturing and prototyping. Although there has been rapid advancements made within the area of colorizing 3D prints using a variety of new techniques, there is still a general lack of consistent methods of doing so.
While it is currently impossible to print anything in high definition full color with FDM/FFF techniques, there has been some progress made in the colorization of 3D prints, thanks to Mcor Technologies who uses a method of inkjet printing and cutting of typical office paper, as well as other companies like Stratasys who are using inkjet technology to print photosensitive resins, millions of voxels at a time. While these methods of printing in color certainly provide much needed progress, they both have their downfalls as well.
With all this said, today, new research has been revealed in a paper titled ‘Pushing the Limits of 3-D Color Printing: Error Diffusion with Translucent Materials,’ where Alan Brunton and colleagues at the Fraunhofer Institute for Computer Graphics Research in Germany, outlined an algorithmic process of producing highly defined and accurate colored 3D prints which have an incredibly life-like look to them.
“In this paper, we leverage the knowledge of decades of research in color imaging, color management and 2D color printing, to maximize the quality and exploit the full capabilities of high- resolution multi-material 3D printers–and push their limits towards realism,” wrote the researchers.
They focus on inkjet voxelized 3D printing. For those unfamiliar with the term ‘voxel’, it’s basically a three dimensional pixel which would be represented by a single inkjet droplet. What makes full color 3D printing so incredibly tough in the accurate portrayal of an object, is that in a single 3D print which measures just one cubic centimeter, there are approximately 18 million droplets of resin present. That’s an incredibly large number of voxels to algorithmically control, hence most colorized inkjet 3D prints are not the best when it comes it color accuracy.
What the researchers have done here though, is take things a step further by controlling voxel color very precisely, as well as accounting for the translucency of the resins. This is required because most of the resins currently available have some degree of translucency to them. This means that when they are printed, the colors from within the object also play an important role in how the object is seen from the surface. In the paper, they propose a geometry-adaptive error diffusion halftoning algorithm which includes the following technical contributions:
- “A traversal algorithm for voxel representations of surfaces, which maps 2D anisotropic error diffusion filters onto a surface in a consistently oriented way and requires only local information to do so.”
- “A layered halftoning algorithm, which combines the traversal algorithm with an arbitrary 2D error diffusion algorithm, and can adapt to the translucency of the materials or increase the color gamut by varying the number of layers”
Basically what they’ve done is create algorithms which are able to direct a 3D printer (in this case a Stratasys Objet 500 Connex 3 machine) to control the color and material of each individual voxel using a layered halftoning method. Halftoning, for those unfamiliar with the term, is the use of dots to simulate continuous tone across an object.
As you may be aware, the Objet 500 machine only supports the mixing of 3 main colors and then a support materials. The researchers, however, decided to dye the support resin yellow, adding an additional color to their palette. As you can see from some of the images provided within the paper, their technique worked remarkably well. Even more incredible is the fact that they believe the method will only improve over time. They write:
“The introduction of more opaque color materials will allow our algorithms to print with larger color gamuts using fewer layers, resulting in a performance boost. Better exploiting parallelism in our computations is a key direction for future work as printer resolutions and build volumes increase. As the number of printing materials increase, it will be important to consider printer models in characterizing the printers and computing profiles.”
It will be interesting to see if this research in anyway is used by Stratasys or any other major 3D printer manufacturer to improve the consistency and results of their inkjet machines.