Volume Hatching for Illustrative Visualization

Moritz Gerl
Volume Hatching for Illustrative Visualization
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Information

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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BibTeX

@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.",
  month =      nov,
  address =    "Favoritenstrasse 9-11/E193-02, A-1040 Vienna, Austria",
  school =     "Institute of Computer Graphics and Algorithms, Vienna
               University of Technology ",
  URL =        "https://www.cg.tuwien.ac.at/research/publications/2006/gerl-2006-vhi/",
}