•
The proposal of a weight-per-pixel metric for the
estimation of weight ratios of each type of kernels;
•
The design of a complete system which integrates
these approaches to produce high-precision rice quality
evaluation results automatically.
The rest of the paper is organized as follows: Section II
reviews existing methods for rice classification and defect
detection. Section III introduces the details of the proposed
system and methods. Experimental evaluation is presented in
Section IV, and Section Vgives the conclusions.
II. RELATED WORK
During the last decades, various approaches for automatic
rice classification and quality analysis have been proposed.
Rice classification:
Most work adopts the following route:
extracting features with image processing algorithms and then
classifying the rice based on these features. Kuo et al. [4]
classified 30 varieties rice grains using image processing and
sparse-representation-based classification (SRC). Kambo and
Yerpude [5] distinguished the variety of Basmati Rice Grain
using K-NN and Principal Component Analysis (PCA), after
preprocessing the images with smoothing and segmentation
techniques. To improve the classification accuracy, Rad
et al. [6] presented a rice classification algorithm with
optimal morphological features and back propagation neural
network-based (BPNN). Here, 18 morphological features
were extracted, and 6 features were selected. Silva and
Sonnadara [7] combined neural network (NN) with PCA
to classify the rice seed varieties. 34 features were extracted
by some pre-processing operations before PCA was applied to
perform dimensionality reduction, and one individual neural
network was created for each feature set.
With the widespread application of deep learning and their
excellent performance in image tasks, more and more rice
classification work starts to adopt deep neural networks. Lin et
al. [8] proposed a model using convolutional neural networks
(CNN) for rice kernel classification which reached a 99.52
%
accuracy. However, they found the accuracy of classification
is closely related to the preprocessing effect of the image,
which was done with image enhancement operations, such
as re-scaling, mean subtraction, and feature standardization.
Qiu et al. [9] presented a hyperspectral-CNN based rice
variety classification algorithm. The rice image captured from
the hyperspectral system was pre-processed with a wavelet
transform and image segmentation process. 100-3000 rice
samples were used to build KNN, SVM, and CNN models.
They found CNN outperformed SVM and KNN. Similar
to this work, Chatnuntawech et al. [10] provided a rice
classification algrithom for identification with the synergy
between hyperspectral imaging and deep CNN. They found
that the classification effect has been significantly improved
with the deepening of the number of neural network layers.
Patel proposed two methods for rice types classification. One
used CNN with segmented rice images as input. Another used
a pretrained VGG-16 model and transfer learning to achieve a
better result. Kiratiratanapruk et al. [3] applied deep learning
to detect and identify rice disease in images. They conducted
experiments with 4 models namely Faster R-CNN [11],
RetinaNet [12], YOLOv3 [13] and Mask RCNN [14].
Rice quality analysis:
Different solutions have been
applied on rice grain analysis. These approaches can broadly
be classified into geometric, statistical, and machine learning.
Geometric approaches consider morphological features as
key factors to analysis. Ajay et al. [2] used shape descriptors
and geometric features to determine quantity of broken
kernels among milled rice samples. Asif et al. [15] used
morphological features to determine the quality of five
types of rice grains after a grain classification. Mahale and
Korde [16] applied image processing techniques to grade
and evaluate rice grains based on grain size and shape, such
as length, width and their ratio. In contrast, Ali et al. [17]
proposed an low cost solution for rice quality analysis based
on more features. They computed the average length, average
width, the area and number of small rice grains, medium rice
grains and broken rice grains to analysis rice quality.
Statistical approaches primarily focus on summarizing data
and making inferences according to the population. Mahajan
and Kaur [18] proposed a method of quality analysis for three
types of Indian Basmati rice grains including normal grains,
long grains and small grains. They applied morphological
closing and opening operations and top-hat transformation
to calculate the length of the major and minor axes of rice.
The rice was graded by analyzing histograms.
With the successful application of machine learning and
its excellent performance, Agustin and Oh [19] proposed an
automatic quality evaluation framework for milled rice kernels,
in which a probabilistic neural network (PNN) classifier is
used to detect defective rice including head rice, broken, and
brewer kernels. At the same time, a linear regression model
was developed for estimating individual kernel weight with
a given blob area. [20] applied neural network and image
processing approach for rice grain identification and grading
on three varieties of Indian rice. Rice images, obtained from
a flatbed scanner, were pre-processed with several image
smoothing operations. The length, width, and perimeter of
the rice grains were extracted and input neural network to do
classification. It was able to accurately classify rice into sound,
cracked, chalky, broken and damaged kernels. Ngampak and
Piamsa-Nga [21] proposed a method for finely classifying
broken rice into small broken, broken, big broken and head
rice. They used Least-Square Support Vector Machine (LS-
SVM) with Radius Basis Function (RBF) kernel as their
classifier. Kaur et al. [22] divided rice kernels into four
grades using Multi-Class SVM. They categorized rice into
head rice, broken rice and brewers according to the kernel
shape, length and chalkiness.
While there are many different methods for detecting rice
with different defects, none of them have classified rice with
dual properties.
III. METHOD
In this section, the rice kernel quality evaluation problem
will be formulated first. Then the hardware setup for rice