REALTIME
NONPHOTOREALISTIC RENDERING Softwarepraktikum
Computergraphik Saoud Asla:
Ang. Informatik Student Betreuerin: Dr. Susanne Kr๖mker 


What this is about ? The project is an implementation in
C++ using OpenGL in Qt application of a nonphotorealistic rendering technique that automatically
and in realtime performance delivers a stylized abstraction of a photograph. Looking at the image as a
height field of pixel intensities, the task then is to display significant
height discontinuities and
remove all insignificant height discontinuities. Which result
in a line drawing and smoothed image. The combination of both result in a
cartoon like image. For both subtasks an
adaptive version of the Difference of Gaussian for line extraction and an
adaptive version of the bilateral flter for
smoothing are employed. Both filters are guided by the Edge Tangent flow. The
edge tangent flow is constructed first by computing the orthogonal to the
gradient vector by the Sobel operator. Subsequently, the resulting vector
field with two main weighting functions is iteratively smoothed. The first
one ensures that tangents where the gradients have a larger magnitude weigh
more, while the second ensures that tangents with similar directions have
more weight: The FlowBased Difference of
Gaussian applies one dimensional Difference of Gaussian in the gradient
direction in the first pass: The filter responses along the
edge flow are weighted in the second pass with Gaussian function:
The
FlowBased Bilateral Filter applies linear bilateral filter along the edge
directions in the first pass: and applies linear bilateral
filter along the gradient directions in the second pass:
The smoothed image is
stylized by performing a uniformsizedbin luminance quantization:
In order to allow parallel processing (to
exploit all GPUs computational units), the filters are implemented in fragment
programs using the OpenGL Shading Language (GLSL). Qt
GUI is used for the realization of graphical user interfaces. Performance: On
an intel core i3 7100u 2.4ghz with Windows 10 and an intel hd graphics 620, typical
performance for a 640 ื 360 resolution and default parameters is 30
Millisecond. Here is a typical procedure when working with the program to be tried.
In
terms of abstraction and stylization the adaptation of both filter to a
curved kernel, which follows the local edge flow. enhances the spatial coherence
of lines and also suppresses noise by the FDoG. and
helps convey clear and enhanced shape boundaries by the FBL. In terms of
execution time the curved kernel of the FDoG and
FBL filters provide linear time complexity with respect to the kernel radius.
[1] Kang H., Lee S., Chui C. K.:
Flowbased image abstraction. IEEE Transactions on Visualization and Computer
Graphics 15, 1 (2009), 6276. [2] H. Winnem๖ller, S. Olsen, and B. Gooch, RealTime
Video Abstraction, Proc. ACM SIGGRAPH 06, pp. 12211226, 2006. Contact: asla@stud.uniheidelberg.de 