A Template Matching and Ellipse Modeling Approach to Detecting Lane Markers - Advanced Concepts for Intelligent Vision Systems - page 181

Template

Connected
components
labeling

Threshold
coefficients > High

Keep large
regions

Create binary
mask

Residual Label
Growing

Connected
components
labeling “ lblLow”

Threshold
coefficients > Low

Residual
Labeled Regions

Color channel

Fig. 3. Flowchart illustrating template matching procedure

(a) Labeled re-
gion.

(b) Binary (c) After bit-

wise AND op-
eration.

(d) Residual
label regions. mask.

Fig. 4. Steps involved in the Residual Label Growing

the coecients map. The resultant binary image undergoes connected compo-
nents labeling as a way to ignore small regions while keeping large connected
regions. These remaining labels will serve as a binary mask. Another application
of connected components labeling is used to create a separate labeled region
called “lblLow” from the coecients map thresholded by τ Low . Finally, Residual
Label Growing (RLG) is used to find residual labeled regions which will be sent
for morphological processing.
The Residual Label Growing process can be explained by referring to
Fig. 4. A labeled region containing lane markers and a stray object are shown
in Fig. 4a. Each color in Fig. 4a represents a different label with black being the
background. A bitwise AND operation is performed between the labeled region
and the binary to mask in Fig. 4b to produce residual labels as shown in Fig.
4c. Consequently, the entire regions corresponding to the residual labels are ex-
tracted and serve as the desired output as shown in Fig. 4d. The RLG process
uses a hysteresis approach to segment lane markers by utilizing a high and low
threshold on the coecients map. It is evident by comparing Fig. 4a and 4d that
the stray object shown in cyan has been eliminated while the lane markers are
untouched. With a mask created using an appropriate τ High threshold, similar
stray objects can be ignored. This is a key feature of the RLG.
The template matching procedure for the Y channel with a normal lane marker
template is illustrated in Fig. 3. To detect the other markers on the road that