13-10-2010, 03:51 PM
This article is presented by:
Deepak Malani, REC Calicut
Anant Malewar, IIT Bombay
Introduction to Video analysis
using
MATLAB
using
MATLAB
Introduction
In this section, an overview of vision controlled motion (VCM) as a system is explained.
1.1 System Description:
The system for VCM consists of:
1. Image acquisition setup: It consists of a video camera, web camera, or an analogue camera with suitable interface for connecting it to processor.
2. Processor: It consists of either a personal computer or a dedicated image processing unit.
3. Image analysis: Certain tools are used to analyze the content in the image captured and derive conclusions e.g. locating position of an object.
4. Machine control: After making the conclusion, mechanical action is to be taken e.g. Using serial or parallel port of a PC to control left and right motors of a robot to direct it towards the ball
Pictorially, the system can be represented as:
1. Image capturing can be done using video camera available in various resolutions e.g. 640 x 480 pixels. There are two types of cameras generally available: Digital cameras (CCD – charge coupled device and CMOS sensor based) and analogue cameras. Digital cameras generally have a direct interface with computer (USB port), but analogue cameras require suitable grabbing card or TV tuner card for interfacing with PC.
Power requirements: CCD cameras give high quality, low-noise images. It generates an analog signal and uses analog to digital converter (ADC) and thus consumes high power.
CMOS cameras have lesser sensitivity resulting in poor image quality but consume lesser power resulting in more battery life.
2. Image analysis consists of extracting useful information from the captured images. We first decide the characteristics of the object to look for, in the image. This characteristic of the object must be as robust as possible. Generally, for the purpose of tracking or identifying the object we utilize:
i. Color
ii. Intensity
iii. Texture or pattern
Image Acquisition
Device
e.g. CCD camera
Image Processor
e.g. PC, DSP
Image Analysis Tool
e.g. MATLAB
Machine Control
e.g. Using parallel port to control left and right motors
3 © Nex Robotics Pvt. Ltd. http://www.nex-roboticsworkshop.html
iv. Edges – circular, straight, vertical stripes
v. Structure – Arrangement of objects in a specific manner
Quantitative/ Statistical analysis of image:
i. Center of gravity - point where the desired pixels can be balanced
ii. Pixel count – a high pixel count indicates presence of object
iii. Blob – an area of connected pixels
3. Machine control consists of controlling a robot based on the conclusion derived from image analysis.
Once the image acquisition setup is ready, the captured images need to be stored in suitable format to process them. Generally, a raw image is stored as a matrix of color intensities.
MATLAB provides a very easy platform for image acquisition and processing. Even serial and parallel ports can be directly accessed using MATLAB. It serves as a handy tool for beginner level VCM. It provides a powerful built-in library of many useful functions for image processing.
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