Image Processing using LabVIEW. By, Sandip Nair sandipnair.hpage.com

Transcription

1 Image Processing using LabVIEW By, Sandip Nair sandipnair.hpage.com

2 What is image? An image is two dimensional function, f(x,y), where x and y are spatial coordinates, and the amplitude, f at any pair of coordinates (x,y) is called the intensity or grey level of the image at that point. I = [f{x,y}] where x = row index, y = column index f{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 bit image where 0 = black, 255 = white colored images are multi plane image

3 Image representation Note: - Image representation is not same as the conventional coordinate system representation because an image is considered as a matrix and the matrix starts from the left top corner of the table as shown above

4 Digital image representation

5 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 Blue HSL = Hue Saturation Luminance

6 Colored image representation

7 Image processing using Labview Image processing in Labview is done in IMAQ vision toolkit and IMAQ vision builder Imaq vision uses additional window for image instead of the front panel Front panel does not offer any control or indicator for image

8 Labview basic image vi definition Image create: - allocates a memory location for an image Image dispose: - de-allocates the memory of an image before the program stops Image winddraw: - used for displaying image in Image winddraw: - used for displaying image in image window

9 Image acquisition from webcam go to in block diagram vision and motion>vision express>vision acquisition vi select the integrated webcam from the list of drivers shown as shown in the next slide and follow the steps after following the steps a vi gets created in the block diagram

10

11 Image processing It is the manipulation done in an image when the output is an image The following images gives an example of image processing

12 Image analysis It is the manipulation done in an image when the output is not an image It is the extraction of meaningful information from an image Example: - Face recognition, bar code reading, object detection etc

13 Machine vision Machine vision is termed for image processing and image analysis Image processing and analysis done for high level application which come close to human vision capabilities of recognition

14 IMAQ vision assistant environment

15 IMAQ vision assistant environment Image processing and analysis is done in the same window The environment is divided into 3 sections: - 1) Acquire images 2) Browse images 3) Process images

16 IMAQ vision assistant environment 1) Acquire images: - Used to acquire images from the imaging device connected with the system. Can acquire single image or continuous images

17 IMAQ vision assistant environment 2) Browse images: - Used to display a collection of images in memory in either full size or thumbnail

18 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 down menu of the window. During manual processing a script is generated which can be stored and can be used to process other images automatically. The script can be converted to equivalent vi from Tools>create labview vi. Thus vision assistant is useful to generate labview code without labview programming knowledge.

19 IMAQ vision assistant environment

20 Image acquisition CCD cameras occupy the biggest area in the camera market The sensor will have the same matrix similar to the image matrix sensor data has to be collected -> data transferred over cable or other media serially -> rearranged to display it on the monitor

21 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 capacitor The values are shifted from one cell to another till it reaches the output

22 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 I PH I PH = S ᴓ e where I PH = photo detector current S = light sensitivity ᴓ e = light radiation power

23 CCD transfer mechanism