Image Processing using LabVIEW

By,Sandip Nair

sandipnair06@yahoomail.comsandipnair.hpage.com

What is image?

• An image is two dimensional function, f(x,y),where x and y are spatial coordinates, and theamplitude, f at any pair of coordinates (x,y) is calledthe intensity or grey level of the image at that point.• I = [f{x,y}]

where x = row index, y = column indexwhere x = row index, y = column indexf{x,y} is the pixel value at (x,y) location in image

• for binary image f(x, y) = 0/1 where 0 = black, 1 =white• for gray scale image f(x, y) = 0 to 255 for 8 bitimage where 0 = black, 255 = white• colored images are multi plane image

Image representation

Note: - Image representation is not same as theconventional coordinate system representation becausean image is considered as a matrix and the matrix startsfrom the left top corner of the table as shown above

Digital image representation

Colored image representation

• Colored image is defined by equation I = [s={x, y, n}]where n is the plane counter

• Colored image can be of the following types: -RGB = Red Green BlueHSL = Hue Saturation Luminance

Colored image representation

Image processing using Labview

• Image processing in Labview is done in IMAQ visiontoolkit and IMAQ vision builder• Imaq vision uses additional window for image insteadof the front panel• Front panel does not offer any control or indicator for• Front panel does not offer any control or indicator forimage

Labview basic image vi definition

Image create: - allocates a memory location foran imageImage dispose: - de-allocates the memory of animage before the program stops

Image windDraw: - used for displaying image inImage windDraw: - used for displaying image inimage window

Image acquisition from webcam

• go to in block diagramvision and motion>vision express>vision acquisition vi• select the integrated webcam from the list of driversshown as shown in the next slide and follow the steps• after following the steps a vi gets created in the block• after following the steps a vi gets created in the blockdiagram

Image processing

• It is the manipulation done in an image when the outputis an image• The following images gives an example of imageprocessing

Image analysis

• It is the manipulation done in an image when the outputis not an image• It is the extraction of meaningful information from animage• Example: - Face recognition, bar code reading, object• Example: - Face recognition, bar code reading, objectdetection etc

Machine vision

• Machine vision is termed for image processing andimage analysis• Image processing and analysis done for high levelapplication which come close to human visionapplication which come close to human visioncapabilities of recognition

IMAQ vision assistant environment

IMAQ vision assistant environment

• Image processing and analysis is done in the samewindow• The environment is divided into 3 sections: -

1) Acquire images2) Browse images2) Browse images3) Process images

IMAQ vision assistant environment1) Acquire images: -

Used to acquire images from the imaging deviceconnected with the system. Can acquire single imageor continuous images

IMAQ vision assistant environment2) Browse images: -Used to display a collection of images in memory in either full size or thumbnail

IMAQ vision assistant environment

3) Process image: -Used to process the selected image. Process function can

be accessed from the left column or from the top downmenu of the window. During manual processing a script isgenerated which can be stored and can be used to processother images automatically.other images automatically.

The script can be converted to equivalent vi fromTools>create labview vi. Thus vision assistant is useful togenerate labview code without labview programmingknowledge.

IMAQ vision assistant environment

Image acquisition

• CCD cameras occupy the biggest area in the cameramarket• The sensor will have the same matrix similar to theimage matrix• sensor data has to be collected -> data transferred over• sensor data has to be collected -> data transferred overcable or other media serially -> rearranged to display it onthe monitor

Charged coupled device (CCD) camera

• CCDs consists of a number of photodiodes one for each pixel• Each photo detector is connected with mos capacitor• Every time the photo detector acquires a brightness value, it is stored in the capacitorit is stored in the capacitor• The values are shifted from one cell to another till it reaches the output

Principle functionality of CCD

• Mos capacitor stores the charge Q generated by the corresponding detector for a certain time• The charge Q depends on the photo detector current IPH• IPH = S ᴓe • IPH = S ᴓe where IPH = photo detector current

S = light sensitivityᴓe = light radiation power

CCD transfer mechanism