Volume Hatching for Illustrative Visualization

Moritz Gerl
Volume Hatching for Illustrative Visualization
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Abstract

The evolution of drawing reaches back to the origin of human cultural history. Over 20.000 years ago prehistoric men started to picture their environment in petroglyphs. From these caveman paintings to mythological depictions of the ancient Egyptians, from medieval illuminated manuscripts to Leonardo Da Vinci’s anatomical studies in the Renaissance, drawings served the purpose of transforming information into a visually perceptible form. Maybe it is this historical tradition that gives drawings the character of being perceived as beautiful by a widespread public. Maybe it is the abstract nature of drawings that lets them be an art form commonly chosen for illustration. Often the first type of imagery we deal with in our lifetime are hand-drawn images in children’s books. So we literally grow up with drawings as a familiar medium for depiction. This could also be a cause for the high acceptance drawings usually meet. Drawings are commonly used in a scientific and educational context to convey complex information in a comprehensible and effective manner. Illustration demands abstraction for focusing attention on important features by avoiding irrelevant detail. Abstraction is a characteristic inherent in drawing, as a drawing always abstracts real world. Therefore drawings serve the purpose of illustration very well. In addition to that, the expressiveness and attraction of drawings bestow them the property of communicating information in a way mostly felt as enjoyable. Specific applications of volume visualization require exactly these visual properties. Therefore increasing effort has been spent on developing and applying illustrative or non-photorealistic rendering methods for volume visualization in recent years. This is the field of study this thesis is devoted to. The described capabilities of drawing make it the art form we chose to mimic for the non-photorealistic volume rendering approach developed in this thesis. A common shading technique in drawings is hatching. Hatching is also standard practice in schematic hand-drawn illustrations as known from textbooks. We implemented a system capable of generating hatching drawings from volume datasets. The basic idea was to exploit illustrative and aesthetic excellence of hatching drawings for the creation of expressive representations of volumetric data. The drawing in Figure 1 gives an example of an illustration where hatching has been used for shading. This figure shall demonstrate that hatching is a technique capable of conveying spatial properties of the depicted object in an abstract and expressive way. It is an artwork of Vesalius’ De humani corporis fabrica, a textbook of human anatomy from the Renaissance. We propose some possible fields of application to further explain the motivation to engage in generating hatching drawings from three-dimensional data. The majority of these data are generated in medical scanning devices, and medicine offers numerous possibilities for employing volume hatching. One possible medical application would be to illustrate upcoming surgeries to patients. Explaining a surgery with the help of a volume hatching rendering is perhaps more comprehensible for a layman than with tomography slices. It also could be more readily accepted by patients as a realistic rendering, due to the visually pleasing nature of hand drawings and the distaste of some people on viewing inner body parts realistically. Another potential field of application for volume hatching is the automated generation of educational illustrations. Figures in scientific textbooks, for instance in medicine or botany, which shall convey important structural features by a schematic representation of objects, are often drawn by hand. The preferred drawing medium here is pen-and-ink, and a reduced drawing technique is used where shading is realized with a sparse and even hatching. Volume hatching can be employed for creating images resembling such illustrations from volumetric data. On the one hand, this offers the possibility for automated generation of still images for text- or schoolbooks. On the other hand, interactive illustrations could be applied in teaching, since they provide exploration and examining possibilities while depicting the objects in a familiar illustrative style. This thesis is organized as follows. First, we give an overview about research done in fields related to this thesis in Chapter 2. In Chapter 3 we present the algorithms we developed for rendering hatching drawings from volume data. This includes the creation of contour drawings, curvature estimation and generation of hatching strokes. We continue with shortly outlining the concept of implementing these algorithms in Chapter 4. In Chapter 5 we present and discuss result images, revealing advantages and limitations of our approach. We summarize the content of this thesis in Chapter 6. Finally, we draw a conclusion on the results of this thesis and propose ideas for further enhancing our work in Chapter 7.

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@mastersthesis{gerl-2006-vhi,
  title =      "Volume Hatching for Illustrative Visualization",
  author =     "Moritz Gerl",
  year =       "2006",
  abstract =   "The evolution of drawing reaches back to the origin of human
               cultural history. Over 20.000 years ago prehistoric men
               started to picture their environment in petroglyphs. From
               these caveman paintings to mythological depictions of the
               ancient Egyptians, from medieval illuminated manuscripts to
               Leonardo Da Vinci’s anatomical studies in the
               Renaissance, drawings served the purpose of transforming
               information into a visually perceptible form. Maybe it is
               this historical tradition that gives drawings the character
               of being perceived as beautiful by a widespread public.
               Maybe it is the abstract nature of drawings that lets them
               be an art form commonly chosen for illustration. Often the
               first type of imagery we deal with in our lifetime are
               hand-drawn images in children’s books. So we
               literally grow up with drawings as a familiar medium for
               depiction. This could also be a cause for the high
               acceptance drawings usually meet. Drawings are commonly used
               in a scientific and educational context to convey complex
               information in a comprehensible and effective manner.
               Illustration demands abstraction for focusing attention on
               important features by avoiding irrelevant detail.
               Abstraction is a characteristic inherent in drawing, as a
               drawing always abstracts real world. Therefore drawings
               serve the purpose of illustration very well. In addition to
               that, the expressiveness and attraction of drawings bestow
               them the property of communicating information in a way
               mostly felt as enjoyable. Specific applications of volume
               visualization require exactly these visual properties.
               Therefore increasing effort has been spent on developing and
               applying illustrative or non-photorealistic rendering
               methods for volume visualization in recent years. This is
               the field of study this thesis is devoted to. The described
               capabilities of drawing make it the art form we chose to
               mimic for the non-photorealistic volume rendering approach
               developed in this thesis. A common shading technique in
               drawings is hatching. Hatching is also standard practice in
               schematic hand-drawn illustrations as known from textbooks.
               We implemented a system capable of generating hatching
               drawings from volume datasets. The basic idea was to exploit
               illustrative and aesthetic excellence of hatching drawings
               for the creation of expressive representations of volumetric
               data. The drawing in Figure 1 gives an example of an
               illustration where hatching has been used for shading. This
               figure shall demonstrate that hatching is a technique
               capable of conveying spatial properties of the depicted
               object in an abstract and expressive way. It is an artwork
               of Vesalius’ De humani corporis fabrica, a textbook
               of human anatomy from the Renaissance. We propose some
               possible fields of application to further explain the
               motivation to engage in generating hatching drawings from
               three-dimensional data. The majority of these data are
               generated in medical scanning devices, and medicine offers
               numerous possibilities for employing volume hatching. One
               possible medical application would be to illustrate upcoming
               surgeries to patients. Explaining a surgery with the help of
               a volume hatching rendering is perhaps more comprehensible
               for a layman than with tomography slices. It also could be
               more readily accepted by patients as a realistic rendering,
               due to the visually pleasing nature of hand drawings and the
               distaste of some people on viewing inner body parts
               realistically. Another potential field of application for
               volume hatching is the automated generation of educational
               illustrations. Figures in scientific textbooks, for instance
               in medicine or botany, which shall convey important
               structural features by a schematic representation of
               objects, are often drawn by hand. The preferred drawing
               medium here is pen-and-ink, and a reduced drawing technique
               is used where shading is realized with a sparse and even
               hatching. Volume hatching can be employed for creating
               images resembling such illustrations from volumetric data.
               On the one hand, this offers the possibility for automated
               generation of still images for text- or schoolbooks. On the
               other hand, interactive illustrations could be applied in
               teaching, since they provide exploration and examining
               possibilities while depicting the objects in a familiar
               illustrative style. This thesis is organized as follows.
               First, we give an overview about research done in fields
               related to this thesis in Chapter 2. In Chapter 3 we present
               the algorithms we developed for rendering hatching drawings
               from volume data. This includes the creation of contour
               drawings, curvature estimation and generation of hatching
               strokes. We continue with shortly outlining the concept of
               implementing these algorithms in Chapter 4. In Chapter 5 we
               present and discuss result images, revealing advantages and
               limitations of our approach. We summarize the content of
               this thesis in Chapter 6. Finally, we draw a conclusion on
               the results of this thesis and propose ideas for further
               enhancing our work in Chapter 7.",
  address =    "Favoritenstrasse 9-11/186, A-1040 Vienna, Austria",
  school =     "Institute of Computer Graphics and Algorithms, Vienna
               University of Technology",
  month =      nov,
  URL =        "http://www.cg.tuwien.ac.at/research/publications/2006/gerl-2006-vhi/",
}