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Taddeüs Kroes
uva
Commits
1d7e5c00
Commit
1d7e5c00
authored
Oct 09, 2011
by
Sander Mathijs van Veen
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ImProc: Added machine specs and reformatted paragraphs.
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improc/ass3/report/report.tex
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1d7e5c00
...
...
@@ -147,13 +147,15 @@ So, using the HSV color model does improve the results.
\subsection
{
Finding Waldo
}
The assignment is to find Waldo (
\emph
{
waldo.tiff
}
) in a large image containing
Waldo and many other characters (
\emph
{
waldo
\_
env.tiff
}
) using Histogram Backprojection.
Waldo and many other characters (
\emph
{
waldo
\_
env.tiff
}
) using Histogram
Backprojection.
The idea of Histogram Backprojection is explained in the paper by Swain and Ballard,
so we will not explain it here. The algorithm as described in the paper is as follows:
The idea of Histogram Backprojection is explained in the paper by Swain and
Ballard, so we will not explain it here. The algorithm as described in the
paper is as follows:
Given histograms
$
M
$
(model, Waldo) and
$
I
$
(environment), create the back
projection
$
b
$
in the following steps:
Given histograms
$
M
$
(model, Waldo) and
$
I
$
(environment), create the back
projection
$
b
$
in the following steps:
\begin{enumerate}
\item
for each histogram bin
$
j
$
do
$
R
_
j :
=
frac
{
M
_
j
}{
I
_
j
}$
...
...
@@ -183,46 +185,49 @@ the following result:
\subsection
{
Basic algorithm
}
The algorithm is implemented in the function
\texttt
{
hbp
}
:
First,
$
M
$
and
$
I
$
are created using
\texttt
{
colHist
}
.
$
R
$
is then created by
division (step 1). Afterwards, the back projection is created using the loop in step 2.
Finally,
a convolution function is used to soften the back projection. To create the
convolution, we have used the function
\texttt
{
scipy.ndimage.correlate
}
with a
circular
weight mask.
The algorithm is implemented in the function
\texttt
{
hbp
}
:
First,
$
M
$
and
$
I
$
are created using
\texttt
{
colHist
}
.
$
R
$
is then created by division (step 1).
Afterwards, the back projection is created using the loop in step 2. Finally,
a convolution function is used to soften the back projection. To create the
convolution, we have used the function
\texttt
{
scipy.ndimage.correlate
}
with a
circular
weight mask.
The following result is generated with 64 bins in each color dimension and a
convolution
radius of 15 pixels:
The following result is generated with 64 bins in each color dimension and a
convolution
radius of 15 pixels:
\begin{figure}
[H]
\hspace
{
-4cm
}
\includegraphics
[width=20cm]
{
found
_
waldo.png
}
\caption
{
\emph
{
found
\_
waldo.tiff
}
: Back projection of Waldo in the larger
image, the
red spot is Waldo's location.
}
\caption
{
\emph
{
found
\_
waldo.tiff
}
: Back projection of Waldo in the larger
image, the
red spot is Waldo's location.
}
\end{figure}
This result is created in roughly 27 seconds on a laptop from 2009.
This result is created in roughly 27 seconds on a laptop from 2009, with an
Intel dual core and 4 GB RAM.
\subsection
{
Experimental cluster detection using K-means
}
In addition to the assignment, we thought it would be interesting to be able to draw a
rectangle around possible occurences of Waldo in the image. Therefore, we created the
function
\texttt
{
find
\_
peaks
}
, which returns a number of possible locations averages.
To do this, we eliminate all pixels in the back projection which are below a certain
threshold (which is given as e number from 0 to 1, and then multiplied by the maximum
value in the projection). This leaves us with a number of pixels clusters, of which we
can calculate the centers using K-means
algorithm
\footnote
{
\url
{
http://en.wikipedia.org/wiki/K-means
\_
clustering
}}
(function
\texttt
{
scipy.cluster.vq.kmeans
}
). To find the initial estimators, we find all pixels
that are further away from all other estimators than the diagonal of the model image
(
\emph
{
waldo.png
}
). Around each center pixel, a rectangle with the size of the model
image is drawn over the larger image. With 32 bins in each color dimension, a threshold
of 0.25 and a convolution radius of 10 pixels, the result is as follows:
In addition to the assignment, we thought it would be interesting to be able to
draw a rectangle around possible occurences of Waldo in the image. Therefore,
we created the function
\texttt
{
find
\_
peaks
}
, which returns a number of
possible locations averages. To do this, we eliminate all pixels in the back
projection which are below a certain threshold (which is given as e number from
0 to 1, and then multiplied by the maximum value in the projection). This
leaves us with a number of pixels clusters, of which we can calculate the
centers using K-means
algorithm
\footnote
{
\url
{
http://en.wikipedia.org/wiki/K-means
\_
clustering
}}
(function
\texttt
{
scipy.cluster.vq.kmeans
}
). To find the initial estimators, we
find all pixels that are further away from all other estimators than the
diagonal of the model image (
\emph
{
waldo.png
}
). Around each center pixel, a
rectangle with the size of the model image is drawn over the larger image. With
32 bins in each color dimension, a threshold of 0.25 and a convolution radius
of 10 pixels, the result is as follows:
\begin{figure}
[H]
\hspace
{
-4cm
}
\includegraphics
[width=20cm]
{
k-means.png
}
\caption
{
\emph
{
k-means.png
}
: Multiple possible locations using a low
threshold
and convolution radius.
}
\caption
{
\emph
{
k-means.png
}
: Multiple possible locations using a low
threshold
and convolution radius.
}
\end{figure}
\end{document}
...
...
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