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The aim of this work is to bring the cultural heritage of two-dimensional art
closer to being accessible by blind and visually impaired people.
We present a computer-assisted workflow for the creation
of tactile representations of paintings, suitable to be used as
a learning tool in the context of guided tours in museums or galleries.
Starting from a high-resolution scan of the painting,
the image is simplified into the most important structures.
For this work, we decided to manually trace selected boundaries
using a standard graphics tablet, which is a very natural way
of extracting the desired lines and gives superior quality.
The resulting edge-image automatically vectorized and augmented
with different line types and fill patterns
can be printed on swell-paper and used as tactile diagrams.
While giving a good overview of the individual structures and
the overall composition, the medium is essentially two-dimensional.
The human visual sense has the unique ability to infer
the third dimension from various visual queues in the painting.
In order to add this information to the tactile paintings
we developed layered depth diagrams, composed from several
laser-cut sheets, glued on top of each other.
We implemented an annotation-based user-interface that enables
an artist to quickly augment these missing depth relations.
The edge-image is loaded and the segmented areas are automatically detected.
Drawing an arrow establishes an "in front of" relation,
and drawing a line a "same height" relation.
After a short computation, absolute heigth values are computed
and displayed as a height map.
If an area is not yet connected, it is displayed in a special color.
Annotations can be interactively added and changed,
until all depth relations are as desired.
Here we see a simulation of the resulting Layered Depth Diagram.
Giving discrete depth values is often not enough.
For example, the arm of Madonna cannot have a constant depth,
neither behind nor in front of little Jesus.
Instead it should start at the dress layer at the shoulder
and bend gradually forward in order to touch little Jesus' belly.
The artist can mark a part of the region as bend-area,
where depth values are gradually interpolated.
In addition, discontinuities on top of bend-areas can occur,
for example at the edge of Madonna's sleeve.
In order to ensure a smooth interpolation even accross
discontinuity borders, a special border-type is available.
Here is the resulting depth map of the whole painting.
In order to get the shapes for production, the depth map
is automatically sliced into layers of constant thickness,
while correctly handling all bend-areas.
Fill-layers are introduced, to shape the layers on top of it.
Each shape is laser-cut, and finally hand-assembled on top of each other.
Our blind test persons quickly got the overall composition of the painting.
Compared to conventional two-dimensional touch-tools, they were able
to feel the outlines of the different structures much more easily,
were not confused by crossing lines since these occur at different heights,
and found it very useful to get an impression of the depth relations in the image.
In order to further include texture and surface information in
the tactile painting, we extended our technique into Textured Reliefs.
We developed an interactive 3D Preview that allows
to inspect and adjust the resulting tactile painting.
Local texture information is extracted from the original painting
using a configurable, edge-preserving, zero-mean filter-bank,
and is added to the height field from the layered depth diagram.
Many parameters allow an optimal configuration of the filter bank,
which can be changed and visualized in real-time.
Important features like faces are modeled in external programs,
and imported as correction layers.
These highly detailed Textured Reliefs
are produced using CNC-milling machines.
Using our integrated CAM-module, the machine codes can be directly created.
It takes several hours until the fine tools carve out all the details.
A negative cast is created, in which several copies
can be molded in a durable and dirt-repellant material.
Currently several textured reliefs of famous paintings
are presented at Kunsthistorisches Museum in Vienna.
In contrast to pure verbal description, blind visitors report
a clearer perception of the composition, and that our
tactile paintings open them “a new dimension” of perceiving images,
especially, to get a three-dimensional impression.