Image Analysis: A tool for identification and classification of feathers
from birds of prey.
Antonio Y. Solís1; José J. Chanona2*; Marcela Vergara1; María de L. Alonso1, José
Blasco3
1
Universidad Autónoma Metropolitana. Unidad Xochimilco. Calzada del Hueso No. 1100, Col.
Villa Quietud. Del. Coyoacán. México 04960, México D. F.
2
Escuela Nacional de Ciencias Biológicas. IPN. Prolongación de Carpio y Plan de Ayala s/n,
Col. Santo Tomas C.P. 11340 Delegación Miguel Hidalgo México, D.F.
3
Centro de Agroingeniería. Instituto Valenciano de Investigaciones Agrarias (IVIA), Ctra.
Moncada-Náquera km 5, 46113 Moncada (Valencia), Spain
*Corresponding author: jorge_chanona@hotmail.com
Abstract
The red tailed hawk (Buteo jamaicencis spp.) has an important role in the food webs as
predators, pest controllers of small mammals (rodents and rabbits), and thus they provide an
important balance in the ecosystem and agricultural zones. About 17 subspecies of red-tailed
hawk has been reported and its main phenotypic difference is the plumage color which varied
from white-brown to dark brown. The aim of this work was to use image analysis methodology
for categorized the types of red tailed hawk feathers based in geometric, color and texture
descriptors, as a preliminary approaching for providing criteria for the classification of the
subspecies detected in the Republic of Mexico. Around 68 feathers of red tailed hawk were
collected from 20 birds. Feathers from breast, wings and tail zones could be obtained and they
were characterized by using image analysis methodology. A rectangular image lighting system
with a digital camera was used to obtain the color images. Pre-processing consisted of crop,
grey level and binary operations. Twelve features of each feather were selected to characterize
the different kinds of feathers in the birds using a simple ANOVA for the classification. Geometric
and color parameters were efficient to classify the types of feathers in the birds by zone and
position. Breast zone provide four types of feathers (vaned 1-4) that correspond at different
heights of breast. From wings zone it was possible to separate three types of fly feathers
(primary, secondary and tertiary). Tail feathers provide only one type. Image analysis was
successful and non-invasive tool for characterization of red tailed hawk feathers. This
preliminary study provides information for describe of plumage of red tailed hawk and it could be
helpful for classification and conservation the subspecies present in México.
Key words: Buteo jamaicencis, biological control, image analysis
1. Introduction
Birds benefits growers by providing important regulating services by scavenging carcasses and
waste, by controlling population of invertebrate and vertebrate pests or by pollinating and
dispersing the seeds of plants (Sekercioglu, 2006). Species extinction is irreversibly lost,
because some provides environmental services, their disappearance promotes a disequilibrium
in the ecosystems and agricultural zones. The red tailed hawk (Buteo jamaicencis) has an
important role in the food webs as predators, pest controllers of small mammals (rodents and
rabbits), and thus they provide an important balance in the ecosystem. About 17 subspecies of
red-tailed hawk has been reported and its main phenotypic difference is the plumage color which
varied from white-brown to dark brown. The birds have several kinds of feathers but only three
are characteristic. Vaned feathers, these cover the entire body of bird and provide external
protection against agents such as rain, sun or abrasion. There are three types of flight feathers:
primary, secondary and tertiary. Flight feathers usually are covered by short vanned feathers
and tail feathers which are inserted in the last caudal vertebrae and it have functions to drive fly
(Figure 1). Plumage color on the breast of these birds has been used as a criterion to identify
the different subspecies, but this criterion tends to be subjective because it depends on visual
appreciation (Ferguson-Lees et al., 2001). An important aspect to preserve this specie could be
the characterization of subspecies trough their feathers by means of image analysis. This could
be useful as a quantitative tool to establish criteria for the classification of subspecies of redtailed hawk. The aim of this work was to use image analysis methodology for categorized the
types of red tailed hawk feathers based in geometric, color and texture descriptors, as a
preliminary approaching for providing criteria for the classification of the subspecies detected in
the Republic of Mexico.
2. Materials and methods
2.1. Collection of feathers.
We used a total of 68 breast and wing feathers pre-classified in vaned, flight (remiges) and tail
(rectrices) feathers, collected from the CIVS (Centro para la Conservación e Investigación de la
Vida Silvestre, Mexico), they were placed in paper envelopes and stored in a cool dry place for
analysis.
2.2. Image Acquisition.
An image processing methodology was used for characterized the feathers according to
reported by Arzate-Vázquez et al., (2011). A rectangular image lighting system with a CCD
digital camera (Canon EOS Kiss Digital 10 Mpx, Japan) was used to obtain the images in RGB
format. The digital camera was mounted on the inspection chamber at a distance of 60 cm from
the feathers. The lighting depends on daylight fluorescent lamps, free from outside interference.
Previously, the capture parameters were fixed in the camera, performing a calibration of the
camera using a colorimeter (Minolta Chroma Meter CR400, Osaka Light source model D65) in
accordance with those reported by Leon et al. (2006). The images were acquired using feathers
black matte background parameters held constant capture of the camera (zoom, brightness,
contrast, exposure level, resolution etc.). The images, with a size of 2456 x 2592 pixels, were
stored in JPEG format in RGB 24-bit resolution on a wooden base covered with velvet paper to
reduce glare. The images analyzed using a personal computer (Dell Precision 380) with an Intel
Pentium IV 3 GHz, 4 GB RAM, 160 GB hard drive (500 GB of storage).
2.3. Image processing.
Twelve features of each feather (area, perimeter, Feret diameter, aspect ratio, roundness, fractal
dimension of contour (FDc), entropy, energy, fractal texture (FT), and HSB color parameters)
were selected to characterized the different kinds of feathers (Figure 1). Pre-processing
consisted of crop, grey level conversion and binary operations. For processing and
segmentation of images, it were transformed to grayscale 8-bit for the extraction of texture
parameters (entropy, energy and fractal texture) and geometric (area, perimeter, Feret, DF
contour) and image format 24-bit RGB was retained for the analysis of color. In addition, for
color analysis the images feathers were separated into HSB channels and their values were
obtained. The extraction and meaning of image features have been described previously by
Haralick et al., (1973); Perea-Flores, et al. (2011) and Arzate-Vazquez et. al., (2012). All
operations in image analysis were carried out with ImageJ program v. 1.34s (National Institutes
of Health, USA). A simple ANOVA was used for statistical analysis of feathers.
Flight Feathers
Primary
Va ne d
Feathe r s
Vaned 1
Vaned 2
Vaned 3
Flight Feathers
Secondary
Vaned 4
Flight Feathers
Tertiary
Tail Feathers
Vaned Feathers
Flight Feathers
Tail Feathers
Rachis
RGB Color
Images
Hollow shaft,
Calamus
Barb
Afterfeather
Rachis
Figure 1. Red-tailed hawk (Buteo jamaicencis) and its kinds of feathers.
2.4. Entropy and Fractal Dimension texture.
From the gray-scale images, we measured the entropy of the image in the direction 0°, using the
plug-in "Texture GLCM" (Haralick, 1973) in the ImageJ program. For the calculation of the fractal
dimension was used plug-in "MapFractalCount" with the option "include subgraph" selected in
ImageJ. This plug-in is based on the Box Counting Method (MCC) proposed by Chen Wen et al.
(2003), where the image is divided into volumes (boxes) size virtual "r" while the program
performs counting the number of boxes intercepted (Nr), the algorithm is iterated by decreasing
the size of box. The fractal dimension obtained by this method is determined from the slope
obtained from least squares linear regression of logarithmic graph vs Nr. 1/r.
2.5. Color estimation.
To determine the color of the feathers in the RGB images we used the function "RGB to HSB
stack" (Sacha, 2004) of ImageJ which converts the RGB image to the parameters of the HSB
color space, then using the command "Histogram" performed the measurement of color image
which provides an average value of each parameter and histogram values (Papadakis et al.
2000). The methodology described above was used to determine the HSB values and histogram
of each feather. Finally, the H parameter is used to determine the color.
3. Results and discussion.
3.1. Geometric and texture parameters.
Table 1 shows the values of area, perimeter, Feret diameter obtained for each feathers group.
ANOVA analysis allowed finding the statistical differences between groups and subgroups of
feathers (vaned and flight). Vaned feathers increased its size since top until bottom of bird chest,
thus two different sizes could be observed, one subgroup correspond to vaned 1 and 2, while
vaned 3 and 4 can be separate into other subgroup. Small vaned (1 and 2) feathers can be
associated to feathers of top zone of bird chest, these has been reported as feathers useful for
differentiation of subspecies and functions as nuptial plumage (courtship). While the feathers
with the largest area are located mainly in the abdominal area, these corresponds to functions of
weather protection and adaptation environmental (Ferguson-Lees et al., 2001). The flight
feathers showed an increased in the size with respect to position into the wing. Feathers with
smaller sizes corresponded to tertiary (T) zone; secondary (S) feathers showed major sizes than
tertiary feathers and primary (P) feathers were largest size than other feathers. Primary feathers
must be having strength and flexibility to withstand the force of flight, for this reason these
feathers showed a largest size. Tail feathers showed similar sizes to flight feathers.
Table 1. Geometric and texture parameters of kinds of feathers (red-tailed hawk).
Area
Kinds of
feathers
2
(mm )
x10
abc
-4
Perimeter
Feret Diameter
(mm)
(mm)
Vaned 1
5182.453±1676
a
629±468
b
Vaned 2
5524.002±1404
a
1084±166
Vaned 3
7242.625±1305
b
Vaned 4
7479.765±1083
c
Flight T
6647.51±532
Flight S
7439.65±146
Flight P
8355.68±506
Tail
Aspect Ratio
Roundness
a
0.417±0.093
a
0.436±0.040
b
0.531±0.076
a
0.402±0.034
FDc
Energy
111±82
a
2.480±0.505
a
1.055±0.195
a
152±18
a
2.314±0.238
a
1.175±0.008
1340±352
a
168±14
a
1.915±0.266
b
1.178±0.036
1325±169
a
192±14
b
2.502±0.214
a
1.177±0.024
a
1010±160
a
209±25
b
3.84±0.91
a
0.27±0.06
a
1.16±0.02
a
c
1003±134
a
223±22
a
4.04±0.87
a
0.26±0.05
a
1.15±0.02
b
1065±293
a
239±21
a
4.16±0.72
a
0.25±0.06
a
1.14±0.03
7586.03±1020
1083±211
228±20
4.74±0.61
0.21±0.03
Entropy
a
0.509±0.065
a
0.451±0.065
a
0.459±0.062
a
FT
a
6.443±0.653
a
2.575±0.012
a
6.945±0.602
a
6.816±0.489
0.511±0.135
a
6.256±1.206
0.45±0.13
a
6.384±1.225
a
0.53±0.19
a
5.525±1.773
a
0.65±0.20
b
1.16±0.03
0.45±0.13
b
a
2.574±0.010
a
2.561±0.010
a
2.559±0.009
a
2.561±0.005
a
2.555±0.001
4.454±1.994
b
2.547±0.005
6.22±1.00
2.554±0.008
c
a
a
a
b
c
Same letter in the same column and subgroup indicate no significant difference (p<0.05)
AR, FDc and roundness parameters allowed to evaluate the shape of the feathers. Vaned
feathers were more irregular and compact than flight and tail feathers. In the case of vaned 1, 2,
and 4 they were not found significant differences between the shape parameters, while vaned 3
was significantly different than other vaned feathers. This difference could be due to that these
feathers are used to protect the abdominal zone, being more irregular and compact (minor AR
and roundness values). Flight and tail feathers have more elongated shape than vaned; for flight
feathers they were not found significant differences in shape parameters. Tail feathers were
more elongated than flight feathers possibly because these have functions to control and drive
the fly.
Energy, entropy and FT parameters were used for evaluated homogeneity of feathers
appearance. For groups were not found significant differences in energy and entropy
parameters. As it was expected vaned feathers showed a more irregularity than flight and tail
feathers due to color pattern of vaned feathers which have functions to camouflage and
courtship. Only FT parameter was useful to find differences between subgroups on the
homogeneity pattern of feathers. Thus vaned 1 and 2 were different with respect to vaned 3 and
4; this could be associated to different functions that have these feathers in the bird as it has
been mentioned above. In the case of flight feathers showed differences in the values of FT
parameter according to position of feathers in the wings, the irregularity was decreased from
tertiary to primary feathers; this can be due to that the feathers in the tip of wings (primary) are
more colored and homogenous than tertiary and secondary feathers. Also, tail feathers
presented a homogeneity pattern similar to flight tertiary feathers.
Vaned Feathers
3.5
7
Vaned 1
Vaned 2
Vaned 3
Vaned 4
6
1.0
Vanned 1
Vanned 2
Vanned 3
Vanned 4
3.0
Vanned 1
Vanned 2
Vanned 3
Vanned 4
0.8
2.5
5
0.6
2.0
4
1.5
2
1
0.4
%Frequency
% Frequency
% Frequency
3
1.0
0.5
0.0
0
0.0
0
0
50
100
150
0.2
20
40
200
60
80
100
0
20
40
Saturation
60
80
100
Brightness
Hue angle
Flight Feathers
3.5
10
Flight Primary
Flight Secondary
Flight Terciary
8
1.2
Flight Primary
Flight Secondary
Flight Treciary
3.0
Flight Primary
Flight Secondary
Flight Terciary
1.0
2.5
0.8
6
2.0
0.6
1.5
2
% Frequency
% Frequency
% Frequency
4
1.0
0.5
0.0
0
0
50
100
150
0
200
20
40
60
80
0.4
0.2
0.0
100
0
Saturation
Hue angle
20
40
60
80
100
Brightness
Tail Feathers
10
1.2
Tail Feathers
1.6
Tail Feathers
Tail Feathers
1.4
1.0
8
1.2
0.8
1.0
6
0.6
2
0.8
% Frequency
% Frequency
% Frequency
4
0.4
0.2
0.0
0
0
50
100
Hue angle
150
200
0.6
0.4
0.2
0.0
0
20
40
60
Saturation
80
100
0
20
40
60
80
100
Brightness
Figure 2. Histogram of HSB coordinates of feathers on the red-tailed hawk.
3.2. Color parameters.
Color histograms for H, S and B cannels showed different pattern of distribution for the three
kinds of feathers studied (Figure 2). H, S and B histograms for vaned feathers showed a major
variability than flight and tail feathers. H histogram of vaned showed the presence of red-brown
(0º-40º) and white (50º-100º) color tones; while the white tones decreased and also red-brown
tones increased for flight and tail feathers. For vaned feathers the histograms in the coordinate S
suggest that there is a difference in the saturation of the color tones for vaned 2 with respect to
vaned 1, 3 and 4. This could be related with presence of different subspecies in batch the
feathers analyzed. The histograms of S coordinate for tertiary and secondary flight feathers were
similar, while primary presented saturation towards darker tones (0º-10º). Tail showed high
saturation of red-brown tones values in the range of 40º-80º, because these feathers have a red
color more homogenous than other feathers. Brightness coordinate showed a wide distribution
in vaned feathers, while flight presented peaks around 20º, 40º and 60º; in both cases; this fact
indicates that brightness change with the changes of tone and saturation of the color pattern of
the feathers that is more heterogeneous than tail feathers. Thus this information could be useful
to classify different subspecies by using color patterns manly in the breast or vanned feathers.
4. Conclusions
Image analysis was successful and non-invasive tool for characterization of red tailed hawk
feathers. Due to the variability of colors presented in feathers vanned, these can be used for the
characterization of the subspecies. This preliminary study provides information for describe
morphology and color of plumage of red tailed hawk and it could be helpful for classification and
conservation the subspecies present in México.
5. Acknowledgements
Antonio Yoná Solís Ceja wishes to thanks CONACyT for the mixed scholarship provided. SIPIPN 20121001, CONACyT, COFAA/PIFI-IPN, Cátedra Coca-Cola Jóvenes Investigadores 2011.
Cátedra Coca-Cola-CONACyT para Jóvenes Investigadores 2011. DGVS-SEMARNAT.
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