Plant recordings with the OEOS 800 sensor
OEOS vs. Camera
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Kevin C. Bilges / Simon Kerssen / Daniel Mentrup / Tina J. Rosemann
Released
28.05.2015
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version
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date
V1
Translation Version
15.05.15 Rosemann
V2.1
Released Version
28.05.15 Rosemann / H.
Kerssen
Plant recordings with the OEOS 800 sensor (V2.1)
name
Page 1 of 16
Table of contents
1 INTRODUCTION ..................................................................................... 4
2 CONSTRUCTION OF THE SENSOR ........................................................... 5
3 POTENTIAL APPLICATIONS ................................................................... 6
4 EXPERIMENTAL SETUP ........................................................................... 7
5 MEASUREMENT RESULTS ....................................................................... 8
Advantage 1: Parallel projection ......................................................................................................8
Advantage 2: Detail depth.................................................................................................................9
Advantage 3: Background ..............................................................................................................10
Advantage 4: Lighting conditions ..................................................................................................11
Advantage 5: Measurement height ................................................................................................12
Advantage 6: Awns detection .........................................................................................................13
6 INVESTIGATION ABOUT AWN NUMBERS.............................................. 14
7 COMPARISON: OEOS VS. CAMERA ........................................................ 15
8 CONCLUSION ....................................................................................... 16
Plant recordings with the OEOS 800 sensor (V2.1)
Page 2 of 16
List of figures
Figure 1: Principle description ...................................................................................................... 4
Figure 2: Construction of OEOS 800 ............................................................................................ 5
Figure 3: Unmatched raw data ..................................................................................................... 5
Figure 4: Usage of Height-Algorithm (1)....................................................................................... 6
Figure 5: Usage of Height-Algorithm (2)....................................................................................... 6
Figure 6: Experimental setup ....................................................................................................... 7
Figure 7: Measurement 1 with OEOS 800.................................................................................... 8
Figure 8: Measurement 1 comparison photo with a camera......................................................... 8
Figure 9: Measurement 2 with OEOS 800.................................................................................... 9
Figure 10: Measurement 2 comparison photo with a camera....................................................... 9
Figure 11: Segment of the OEOS 800 measurement ................................................................... 9
Figure 12: Segment of the comparison photo .............................................................................. 9
Figure 13: Measurement 3 with OEOS 800................................................................................ 10
Figure 14: Measurement 3 comparison photo with a camera..................................................... 10
Figure 15: Measurement 4 with OEOS 800................................................................................ 11
Figure 16: Comparison photo with easy conditions .................................................................... 11
Figure 17: Comparison photo with dark conditions .................................................................... 11
Figure 18: Comparison photo with intense side lighting ............................................................. 11
Figure 19: Comparison photo with easier side lighting ............................................................... 11
Figure 20: Measurement 5 with OEOS 800................................................................................ 12
Figure 21: Measurement 5 comparison photo with a camera..................................................... 12
Figure 22: Measurement 6 with OEOS 800................................................................................ 13
Figure 23: Measurement 6 comparison photo with a camera..................................................... 13
Figure 24: Usage of the algorithm .............................................................................................. 14
Plant recordings with the OEOS 800 sensor (V2.1)
Page 3 of 16
1 Introduction
This document presents the sensor system OEOS with its advantages in comparison to a conventional camera. The sender side of the Opto Electronic Object Scanner produces parallel laser beams. If an object interrupts these beams, it is visible
on the receiver unit.
The sensor is available in several configuration levels (98 mm up to 2000 mm) with
a high resolution of 64 µm in measurement height direction.
The images in this document were recorded with an OEOS 800 system which signifies
an effective measurement height of 800 mm.
With this sensor it is now
possible to scan any object,
e.g. plants, and get a
shadow image of it. The
schematic view on the left
hand (Figure 1) illustrate it.
The plants passes the scan
field (of view) of the sensor:
At time “t1” OEOS has
nearly scanned the first
plant.
At time “t2” OEOS is just in
the middle of recording the
4th plant.
At the time “t3” all plants
are scanned.
Figure 1: Principle description
Plant recordings with the OEOS 800 sensor (V2.1)
Page 4 of 16
2 Construction of the sensor
The OEOS 800 system works with nine modules (with each one 98 mm) which are
cascaded to a measurement height of 800 mm (view Figure 2).
Figure 3 displays the individual shifted recordings. But for the most applications you
need raw data where the plant is already matched to a clone of the real plant. Therefore, there is an algorithm which matches the overlapping edges of the individual
recordings. This algorithm is named “Matching-Algorithm”.
Figure 2: Construction of OEOS 800
Plant recordings with the OEOS 800 sensor (V2.1)
Figure 3: Unmatched raw data
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3 Potential applications
There are many fields of applications for the OEOS sensor. The sensor may be used
in with different applications, both in- and outdoor (greenhouse, field robot).
Consequently one of them (the sensor or the object you want to scan) has to be
stationary. If the sensor is fixed, the object or plant has to move through it, for
example by a conveyer belt. Otherwise if the object or plant is stationary, you have
to pass the sensor by the plants. Therefor you need a carrier platform or another
portal.
In the application field of plant phenotyping (no matter if in- or outdoor) you can
monitor growth process by gauging the same plants regularly (daily). Therefore before planting, the ground section can be preparing differently. Alternatively if you are
using different fertilizers while the plants are growing, you can manage and control
the growth in an efficient way.
With other algorithms it is feasible to ascertain information like plant height, leaf
count, plant density or ear/leaf length. Figure 4 and Figure 5 demonstrate the result
of a Height-Algorithm.
Figure 4: Usage of Height-Algorithm (1)
Plant recordings with the OEOS 800 sensor (V2.1)
Figure 5: Usage of Height-Algorithm (2)
Page 6 of 16
4 Experimental setup
For the following plant measurements the OEOS 800 system is mounted on a conveyer belt (Figure 6). For this purpose the velocity of the conveyer belt and the scan
rate of the sensor were constant. Furthermore the system is linked to a computer via
an Ethernet interface which receives and saves the measured raw data. Afterwards
the Matching-Algorithm matches the records of the single modules to a coherent
picture.
Figure 6: Experimental setup
Additionally to all measurements by the OEOS sensor a conventional camera took a
comparison photograph of the measurement objects.
Moreover all measurements that are shown in this document and some more are
available on our website under http://www.iotec-gmbh.de/EN/oeos.html.
Plant recordings with the OEOS 800 sensor (V2.1)
Page 7 of 16
5 Measurement results
Advantage 1: Parallel projection
Figure 7 and Figure 8 show crops stuck into a Styrofoam plate.
One advantage of the OEOS sensor is the horizontal line array of the laser beams.
Therefore you get a parallel projection of the measured objects over the complete
measurement height. As a result you get a distortion-free shadow image of the objects.
Whereas a conventional camera has a focus point and the emerging image is defined
by the opening angle of the camera lens. The photo is taken from the middle height
of the plant. So as you can see in Figure 8 an angled view cannot be avoided on the
Styrofoam.
Figure 7: Measurement 1 with OEOS 800
Figure 8: Measurement 1 comparison photo with a camera
Plant recordings with the OEOS 800 sensor (V2.1)
Page 8 of 16
Advantage 2: Detail depth
The following plant has many tiny hairs on the surface. This measurement 2 clarifies
how the sensor has the ability to make very fine structures visible.
Figure 9 and Figure 10 show the whole plant.
Figure 11 and Figure 12 show a detailed view of the pictures above.
In Figure 12 as you can see, the fine bright-colored hairs are only visible when the
background offers a good contrast to the object. The OEOS sensor does not have this
restriction.
Figure 9: Measurement 2 with OEOS 800
Figure 10: Measurement 2 comparison
photo with a camera
Figure 11: Segment of the OEOS 800 measurement
Figure 12: Segment of the comparison photo
Plant recordings with the OEOS 800 sensor (V2.1)
Page 9 of 16
Advantage 3: Background
Another advantage of the sensor system is the fact that only the object which passes
through is imaged. On the other hand a photo taken by a camera, especially outdoor
may have difficult backgrounds which complicate the digital image processing when
extracting the different measurement objects from the background. For the OEOS
sensor the background is not importance.
As proof the measurement of the OEOS sensor in Figure 13 shows a perfect shadow
image of a root.
In Figure 14 the fine structures of the root are obscured because of the non-linear
background.
Figure 13: Measurement 3 with OEOS 800
Plant recordings with the OEOS 800 sensor (V2.1)
Figure 14: Measurement 3 comparison
photo with a camera
Page 10 of 16
Advantage 4: Lighting conditions
For taking a shadow image with the OEOS sensor you don‘t have to bring the measurement object into a special lighting (compare Figure 16 to Figure 19). The receiver
unit is equipped with band-pass filters which filter out all wavelengths except those
of the sender unit (Figure 15).
The plant which was scanned is a conifer. All fine needles of the plants are made
visible by the OEOS sensor and a density estimation of the vegetation growth can be
calculated of the shadow image by an algorithm.
Figure 15: Measurement 4 with OEOS 800
Figure 16: Comparison
photo with easy conditions
Figure 17: Comparison
photo with dark conditions
Figure 18: Comparison
photo with intense
side lighting
Figure 19: Comparison
photo with easier
side lighting
Plant recordings with the OEOS 800 sensor (V2.1)
Page 11 of 16
Advantage 5: Measurement height
The OEOS system can be cascaded to any length in measurement height direction.
Standard configurations are between 98 mm and 2000 mm. Larger systems are realizable as an oversize product, therefor contact us.
Independent of the size, color or shape (Figure 21) the OEOS sensor creates an optimal shadow image of the passing objects (Figure 20).
Figure 20: Measurement 5 with OEOS 800
Plant recordings with the OEOS 800 sensor (V2.1)
Figure 21: Measurement 5 comparison
photo with a camera
Page 12 of 16
Advantage 6: Awns detection
Because of the high resolution of the OEOS system it is possible to detect fine structures like awns (Figure 22 and Figure 23).
These can be counted by algorithms and for example perform a non-destructive estimation about the crop forecasting.
Such algorithm will be presented in the following chapter.
Figure 22: Measurement 6 with OEOS 800
Plant recordings with the OEOS 800 sensor (V2.1)
Figure 23: Measurement 6 comparison
photo with a camera
Page 13 of 16
6 Investigation about awn numbers
The following points explain the first steps for detecting awns. The following algorithm
was used for calculating the count of the (visible) awns:
•
•
•
•
•
•
A complete ear was isolated from a shadow image (Figure 24-1)
The isolated image is processed by erosion for deleting the awns. (Figure 242)
The result is expanded (pixel were added to the outlines of the object). (Figure
24-3)
A difference image is generated, which is formed by subtracting Figure 24-3
from Figure 24-1. Thus, an image that contains only the awns arises. With the
removal of the expanded image (Figure 24-3) of the original image it is ensure
that possible ears areas that were lost in the erosion process, are recovered
(Figure 24-4).
Following functions like correction, expansion, addition and skeleton are used.
(Figure 24-9)
The count of the awns could now determine by automatically recognizing the
beginnings of the awns which are colored in red in Figure 24-10
….
Figure 24: Usage of the algorithm
Plant recordings with the OEOS 800 sensor (V2.1)
Page 14 of 16
7 Comparison: OEOS vs. Camera
In the following table a comparison between OEOS sensor and a conventional camera
is listed. The table is based on the advantages referred to chapter 5 Measurement
results.
Table 1: Comparison OEOS vs. Camera
OEOS
camera
Optics method
Parallel projection,
distortion-free measurement
over the whole measuring
range
Detail depth
64 µm resolution,
Varying,
fine, sharp-edged structures depending on the quality of
visible over the whole meas- the camera aperture
uring range
Influence of the
background
No influence,
only the by passing objects
are recognized
Wide influence,
there is always an random
background around the object which you want to take
a picture of
Influence of lighting conditions
No influence,
band-pass filters only
passes a special range of
wavelengths
Wide influence,
depending on different lighting conditions, the image
processing can get very
complex
Measurement
height
Any, without losses in
detail depth,
typical measurement height
between 98 mm and
2000 mm
Any, with losses in detail
depth,
the higher the object, the
greater the distance from
the camera
Awns detection
Easily possible,
by applying an algorithm to
the raw image data
Limited possible,
depending on photograph
quality. It is possible, but
you always need a complex
image processing to extract
the awns
Plant recordings with the OEOS 800 sensor (V2.1)
Image built-up over one
focus point,
distortion photograph, limited on one focus level
Page 15 of 16
8 Conclusion
With the use of this OEOS sensor system there is no need of complicated image
processing to knock out the background of a photo. Additionally the image information is saved binary (black/white picture). This is a huge simplification for later
image analyzing over algorithms.
Because of the parallel projection you get a distortion-free measurement over the
whole range. The sensor has the ability to take a maximum of 4000 (nearly continuous) exposures per second, to create a shadow image. Therefor between the exposures only a fixed death time of 20 µs are needed. This is not even 10 % of the whole
measurement time. Additionally the light-sensitive elements are not successive sampled like with other light grids. There is a permanent lighting of the elements in the
receiver unit with a continuous synchronous exposure.
The result of the high sampling rate (4000 Hz) and resolution (64 µm in measurement
height direction) is that smallest structures like awns or tiny hairs on the surface of
plants become visible regardless of the weather (outdoor) or other lighting conditions
(in- or outdoor).The resolution in movement direction depends on the velocity of the
passing object for example a velocity close to 1 km/h (0.62 miles/h) also leads to a
resolution close to 64 µm.
With this sensor system it is possible to scan plants in constant intervals for tracing
the growth process.
As described beforehand the OEOS sensor is indeed not a camera, but the shadow
imaging has distinct advantages. If the sensor is operated in combination with a
camera, the advantage of both systems are given.
In the field of plant phenotyping the OEOS sensor may be a perfect assistant. Phenotyping becomes more and more automated, objective and reproducible. Therefor
the evaluation gets easier and the results even more precisely.
Moreover you are able to connect other sensors to this sensor system and let them
work as a unit. For example, if you attach a start and stop trigger to a conveyer belt,
it will automatically (by triggering of a passing object) start and stop the measurement. In addition it is possible to connect your own sensors to this sensor system.
Plant recordings with the OEOS 800 sensor (V2.1)
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