This is my first post and I decided to post about my recent obsession towards Computer Vision. I am still a noob working my way out. Most of the time I take my vision for granted, it amazes me how one needs to understand mathematical concepts to work with computer vision which is not as intuitive as that of my vision.
I have always skipped learning python and am not a great fan of script style programming languages. I worked with opencv (c++) and I found that I need to type in huge number of lines and I needed manage memory. The fact that computer vision is mind bending and writing housekeeping codes in c++ is like adding salt to the wound.
OpenCV comes with python interface(duh!). I gave python a try. I was cursing myself for not having learnt it. No need of memory management, no need of typecasting variables *bliss*.
I would recommend you to learn python from this book from Swaroop. It is neat and simple.
Now coming back to business, I have included the program for tracking a blue coloured object below. The program follows these steps for tracking the blue coloured object
- Find the approximate HSV colour range of the object of interest using gimp or ms paint.
- Block the pixels which are not falling in the range and shoot up the pixel values to 255 which are in the range, so that we get a binary image.
- Calculate the centroid of the blob formed in the binary image using image moments.
- Track the motion of the centroid and draw a line trailing its path.
I have used the logic from Aishack and there is detailed explanation there.
(Please make sure that the indentation is correct, in case you copy the program, gist is sometimes buggy 
)
[gist id="4379792" file="colortrack.py"]
<pre>from cv import * #bad practice, its just that am bit lazy
def GetThresholdedImage(img):
#returns thresholded image of the blue bottle
imgHSV = CreateImage(GetSize(img), 8, 3)
#converts a BGR image to HSV
CvtColor(img, imgHSV, CV_BGR2HSV)
imgThreshed = CreateImage(GetSize(img), 8, 1)
#InRangeS takes source, lowerbound color, upperbound color and destination
#It converts the pixel values lying within the range to 255 and stores it in
#the destination
InRangeS(imgHSV, (100, 94, 84), (109, 171, 143), imgThreshed)
return imgThreshed
def main():
color_tracker_window = "output"
thresh_window = "thresh"
capture = CaptureFromCAM(-1)
NamedWindow( color_tracker_window, 1 )
NamedWindow( thresh_window, 1 )
imgScrible = None
posX = 0
posY = 0
while True:
frame = QueryFrame(capture)
Smooth(frame, frame, CV_BLUR, 3)
if(imgScrible is None):
imgScrible = CreateImage(GetSize(frame), 8, 3)
imgBlueThresh = GetThresholdedImage(frame)
mat = GetMat(imgBlueThresh)
#Calculating the moments
moments = Moments(mat, 0)
area = GetCentralMoment(moments, 0, 0)
moment10 = GetSpatialMoment(moments, 1, 0)
moment01 = GetSpatialMoment(moments, 0,1)
#lastX and lastY stores the previous positions
lastX = posX
lastY = posY
#Finding a big enough blob
if(area > 100000):
global posX
global posY
#Calculating the coordinate postition of the centroid
posX = int(moment10 / area)
posY = int(moment01 / area)
print 'x: ' + str(posX) + ' y: ' + str(posY) + ' area: ' + str(area)
#drawing lines to track the movement of the blob
if(lastX > 0 and lastY > 0 and posX > 0 and posY > 0):
Line(imgScrible, (posX, posY), (lastX, lastY), Scalar(0, 255, 255), 5)
#Adds the three layers and stores it in the frame
#frame -> it has the camera stream
#imgScrible -> it has the line tracking the movement of the blob
Add(frame, imgScrible, frame)
ShowImage(thresh_window, imgBlueThresh)
ShowImage(color_tracker_window, frame)
c = WaitKey(10)
if(c!=-1):
break
return;
if __name__ == "__main__":
main()
There are a few bugs in the program, the execution freezes once the object of interest is out of the frame and some warnings due to sloppy handling of global variables. ( Need to get my python right, learning! The problem is that there is no static variables in python, need to find a workaround)
Note that softwares like Gimp and MS paint uses Hue(H) value ranging from 0-360 degrees and 0-100% for Saturation(S) and Value(V). But OpenCV uses 0-180 degs for Hue and 0-255 for Saturation and Value. So you need convert to OpenCV’s HSV convention.
Next post I will correct those bugs!
, which inserted the code into if block.
