GENERAL
The main goal of the work is to implement a widely used
classification method and test it with fairly simple data. The work is
carried out with Matlab software. In this work, the data consist of
images of fruits.
FILES
As the main purpose of the work is not to learn how to use Matlab but
to get more familiar with pattern recognition methods, some of the
Matlab code is provided. Your task is to code the recognizer.
Data
The profile images of the fruits are available
here. The images are
of varying size and shape and the fruits are pictured in different
angles and positions.
You can have a look on some of the fruit images at here.
Matlab functions
You can perform the feature extraction with the following functions:
cent2, pca2, and plen2. The first function calculates the
center of mass for a two dimensional image. The second function
returns principal components of the image. The third function
calculates the lengths from a given point to the boundaries of the
image. The first length is calculated in the direction of the first
base vector. The vector base is given as an argument of the
function. The change in the directions of the following lengths is a
constant also given as an argument.
You can get the functions from here: cent2.m, pca2.m, and plen2.m.
EXERCISES
Feature selection
You can use the lengths from an inside point to the boundaries of the
image as features.
Normalization methods
If you calculate the lengths from the mass center
of the image you can avoid the effects of translation. In order
to get features insensitive to rotational variations, calculate the
lengths in the directions defined by the principal component axes of the
image and sort them in increasing order. These features will be
invariant to the size variations if the feature vectors are scaled so that
sum of the features is a constant. What is a sufficient number of
features?
Recognition methods
Implement one of the following recognition methods: 1) the k Nearest
Neighbors (knn) classifier, 2) Learning Vector Quantization (LVQ) classifier, 3)
Bayesian classifier, or 4) Multi-layer perceptron (MLP). In the first two cases,
use Euclidean metric. Experiment with different values of k and
prototype set sizes. Use linearly decaying learning coefficient for
LVQ. In case of Bayesian classifier, assume that the probability
distributions are Gaussian. In case MLP, use functions from Matlab
Neural Network Toolbox, keep the size of the network reasonable, and
start experimenting by using default settings.
Divide the samples into two set and use one set for training and the other one for testing the recognition system.
Reporting
In the report, give a brief description of the recognition method
applied, justify all the selection you have made, and give the
recognition results of the best recognizer (calculate the total error
rate and occurrences of all error types). Also, include your Matlab
code with comments.