Twelve color features were extracted from the bean
images. Table 1 lists descriptive statistics of the bean
color features computed from images. They are seed
color components (whole seed and spot seed), in the
RGB model (which stands for Red, Green and Blue
channels) and HSI model (that stands for Hue, Saturation
and Intensity channels, measured as mean grey
levels). Twelve of the color feature values were plotted
against bean varieties (Fig. 4). As can be seen in this
figure, it is clear that less overlapping features are more
efficient in separating the bean varieties. There were
complex relationships between bean varieties and color
features. It was difficult to develop a simple model,
like a linear model to predict bean varieties on these
color features. Therefore all the 12 variables of seed
color and spot information were inserted in the model
of the MLP-ANN to identify the 10 varieties. The neural
networks, with four layers, were trained and selected
using two different data subsets (training and validation
sets, respectively) and were then tested, with the
experimental data not used in the two previous steps.
Several neural networks were trained and the network
which gave the minimum mean square error (MSE) of
the validation subset was chosen (Table 2). The two
hidden layers of the selected network had different
numbers of neurons, being 20 and 10, respectively.