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Commit 4e514645 authored by even's avatar even
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Article: intro revisited

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......@@ -37,7 +37,7 @@ blurred segments of fixed width in gray-level images was already introduced.
It is based on a first rough detection in a local area
of the image either defined by the user in supervised context or blindly
explored in automatic mode. The goal is to disclose the presence of an edge.
Therefore, a simple test as the gradient maximal value is performed.
Therefore a simple test as the gradient maximal value is performed.
In case of success, refinement steps are run through an exploration of
the image in the direction of the detected edge.
......@@ -48,25 +48,23 @@ untill a correct candidate with an acceptable gradient orientation is found.
Only the gradient information is processed as it provides a good information
on the image dynamics, and hence the presence of edges.
Trials to also use the intensity signal were made through costly correlation
techniques, but they were mostly successful for detecting objects with
stable appearance such as metallic pipes \cite{AubryAl17}.
techniques, but they were mostly successful for detecting shapes with a
stable appearance such as metallic tubular objects \cite{AubryAl17}.
Despite of good performances obtained compared to other methods from the
literature, several drawbacks remain.
First, the blurred segment width is not measured, but initially set by the
user to meet the application requirements, so that no quality information
can be derived from the computed segment.
Moreover, the blurred segment hull is left free to shift sidewards, or worst,
to rotate around a thin edge in the image, and the produced orientation
value can be largely biased.
Despite of good performances achieved, several drawbacks remain.
First, the blurred segment width is not measured but initially set by the
user according to the application requirements. The produced information
on the edge quality is rather poor, and especially when the edge is thin,
the risk to incorporate outlier points is quite high, thus producing a
biased estimation of the edge orientation.
Then, two refinement steps are systematically run to cope with most of the
tested data, although this is useless when the first detection is successfull.
Beyond, there is no guarantee that this could treat all kinds of data.
The search direction is fixed by the support vector of the blurred segment
detected at the former step, and because the set of vectors in a bounded
discrete space is finite, there is necessarily a limit on this direction
accuracy.
Then, two refinement steps are systematically run.
On one hand, this is useless when the first detection is successfull.
On the other hand, there is no guarantee that this approach is able to
process larger images.
The search direction relies on the support vector of the blurred segment
detected at the former step, and the numerization rounding fixes a limit
on this estimated orientation accuracy.
It results that more steps would inevitably be necessary to process higher
resolution images.
......@@ -83,10 +81,10 @@ As a side effect, these two major evolutions also led to a noticeable
improvement of the time performance of the detector.
In the next section, the main theoretical notions this work relies on are
introduced, with a specific focus on the new concept of adaptive directional
scanner.
Then the new detector workflow and its integration into both supervised and
unsupervised contexts are presented and discussed in \RefSec{sec:method}.
introduced.
Then the new detector workflow, the adaptive directional scanner, the control
of the assigned with and their integration into both supervised
and unsupervised contexts are presented and discussed in \RefSec{sec:method}.
Experiments led to assess the expected increase of performance are decribed
in \RefSec{sec:expe}.
Finally achieved results are summarized in \RefSec{sec:conclusion},
......
......@@ -267,7 +267,7 @@ This distinction is illustrated on \RefFig{fig:edgeDir}.
Another option, called multi-detection allows the detection of all the
segments crossed by the input stroke $AB$.
The multi-detection algorithm is displayed below.
The multi-detection algorithm (Algorithm 1) is displayed below.
\input{Fig_method/algoMulti}
......@@ -282,6 +282,7 @@ detected blurred segments $\mathcal{B}_j''$ at the end of each successful
detection;
iii) points marked as occupied are rejected when selecting candidates for the
blurred segment extension in the fine tracking step.
Multiple detections of the same edge are thus avoided.
In edge selection mode (\RefFig{fig:edgeDir} b), the multi-detection
algorithm is executed twice.
......@@ -341,7 +342,8 @@ segment.
\subsection{Automatic blurred segment detection}
An unsupervised mode is also proposed to automatically detect all the
straight edges in the image. A stroke that crosses the whole image, is
straight edges in the image. The principle of this automatic detection
is described in Algorithm 2. A stroke that crosses the whole image, is
swept in both direction, vertical then horizontal, from the center to
the borders. At each position, the multi-detection algorithm is run
to collect all the segments found under the stroke.
......
......@@ -67,7 +67,7 @@ DS = \left\{ S_i = \mathcal{D} \cap \mathcal{N}_i \cap \mathcal{I}
\end{array} \right. \right\}
%S_i = \mathcal{D} \cap \mathcal{N}_i, \mathcal{N}_i \perp \mathcal{D}
\end{equation}
In this expression, the clause
In this definition, the clause
$\delta(\mathcal{N}_i) = - \delta^{-1}(\mathcal{D})$
expresses the othogonality constraint between the scan lines $\mathcal{N}_i$
and the scan strip $\mathcal{D}$.
......@@ -79,7 +79,7 @@ The scans $S_i$ are developed on each side of a start scan $S_0$,
and ordered by their distance to the start line $\mathcal{N}_0$ with
a positive (resp. negative) sign if they are on the left (resp. right)
side of $\mathcal{N}_0$ (\RefFig{fig:ds}).
The directional scan is iterately processed from the start scan to both ends.
The directional scan is iterately parsed from the start scan to both ends.
At each iteration $i$, the scans $S_i$ and $S_{-i}$ are successively processed.
\begin{figure}[h]
......@@ -111,9 +111,11 @@ At each iteration $i$, the scans $S_i$ and $S_{-i}$ are successively processed.
\put(-60,30){$\mathcal{N}_8$}
\put(-169,8){$\mathcal{N}_{-5}$}
\end{picture}
\caption{A directional scan: the start scan $S_0$ in blue, odd scans in
green, even scans in red, scan lines bounds $\mathcal{N}_i$ in
plain lines and scan strip bounds $\mathcal{D}$ in dotted lines.}
\caption{A directional scan.
The start scan $S_0$ is drawn in blue, odd scans in green,
even scans in red, the bounds of scan lines $\mathcal{N}_i$
with plain lines and the bounds of scan strip $\mathcal{D}$
with dotted lines.}
\label{fig:ds}
\end{figure}
......
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