to locate in the image the marking element that corre-
sponds to a given measurement, surrounding it with a
bounding box. This is a detection task, another prime
application for deep learning.
We have therefore modified an efficient neural ar-
chitecture dedicated to object detection in images, by
adapting it to the case of road markings and by adding
a sub-network allowing the inference of the sought in-
dicators. To carry out the training of this composite
network and the evaluation of its predictions, a large
quantity of images was collected and annotated by an
operator in a semi-supervised fashion. We show the
promising results obtained by this novel method.
The rest of the paper is organized as follows. In
sec. 2, we propose a brief review of existing related
works. Then, we describe in sec. 3 how we collected
the data needed to train and evaluate our method.
Sec. 4 is dedicated to methodological aspects related
to the annotation of markings, the architecture of the
proposed deep learning model and its training. Ex-
perimental results are presented in sec. 5, and sec. 6
concludes the paper.
2 RELATED WORK
In this paper, we aim at evaluating the visual qual-
ity of the markings, with characteristics that can
be related to the performance of both human vi-
sion and automated vehicle (AV) systems, in day-
light. It was shown that the contrast between mark-
ing and surrounding road surface is a good candidate
for this (Carlson and Poorsartep, 2017) and there-
fore it is one of our parameters of interest. We
moreover consider the percentage of residual marking
(PRM), which also conditions the visibility of mark-
ings. Even if the latter is defined in several coun-
tries, like UK (CS 126, 2022), Korea (Lee and Cho,
2023), Germany (Mesenberg, 2003) and France (NF
EN 1824, 2020), it often appears in the form of
a score, quantized according to wear level classes,
called cover index. Moreover, the standardized mea-
surement geometry (2.29
◦
observation angle) is too
grazing to evaluate it precisely and, to our knowledge,
there is no operational PRM measurement system, un-
til now. We propose an answer to this need, thanks
to an imaging device that acquires images at traffic
speed, under a 90
◦
angle, and to a method that esti-
mates a PRM figure, not a wear level class.
Road marking detection has been investigated for
more than 40 years with the aim of designing ADAS,
in particular lane keeping systems: a complete survey
of the topic is therefore out of the scope of this pa-
per. Note that processing methods have been devel-
oped for passive acquisition systems (supplying im-
ages) (Zhang et al., 2022) as well as for active ones
(using laser scanners or retroreflectometers) (Zhang
et al., 2019). The system we use is active, which al-
lows getting rid of illumination variations (e.g. shad-
ows) and therefore, to obtain infrastructure-intrinsic
measurements.
Earlier methods (see e.g. (Bar Hillel et al., 2014)
for a survey) used an algorithmic approach in which,
typically, putative marking elements are first extracted
from the images by global thresholding (a great clas-
sic is the Otsu method), or by local thresholding and
geometric selection (Veit et al., 2008). Then, curves
are fitted to the detections in a robust manner, for ex-
ample using the Hough transform (Em et al., 2019) or
M-estimators (Tarel et al., 2002), to model marking
lines. Although these methods have made it possible
to drive vehicles automatically for a long time, they
involve adjusting many parameters and their detec-
tion performances have now been largely surpassed
by those of deep learning methods.
Deep learning approaches, based on convolutional
neural networks (CNNs), require the annotation of a
huge number of markings on images, which can be
very time consuming. We propose automatisms, im-
plemented in an ergonomic graphical user interface,
which provide a non-negligible help to the operator.
Once the CNN has been trained from the annotated
images, it can be used to detect the road markings and
then, to model the marking lines, see e.g. (Liang et al.,
2020; Zhang et al., 2022).
All the above methods are dedicated to the detec-
tion of road markings. Among the few publications
that deal with the evaluation of road markings, we can
cite (Lee and Cho, 2023), where a Mask R-CNN (He
et al., 2017) model is applied to detect the markings
in the image. Then, Otsu thresholding is used to seg-
ment it and a quality measure, that appears to be the
complement to one of the PRM, is computed. Using
the Otsu method for segmentation seems to us some-
what incomprehensible, since Mask R-CNN is an in-
stance segmentation algorithm and, as such, already
provides a segmentation. In (Soil
´
an et al., 2022), the
intensity of laser scanning data is processed to evalu-
ate the performance of road markings and to relate it
to retroreflection (the standard measurement of mark-
ing quality of use in night conditions). The process
involves a segmentation of the markings, but no de-
tails on this step are given in the paper. We note that
both approaches include a segmentation step, which
we do not consider necessary to estimate the quality
measure of the marking from its visual appearance.
IMPROVE 2024 - 4th International Conference on Image Processing and Vision Engineering
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