Predicting ball movement from live sports using Open-CV Python & Kalman filter

Today, I’m going to discuss another Computer Vision installment. I’ll use Open CV & Kalman filter to predict a live ball movement of Cricket, one of the most popular sports in the Indian sub-continent, along with the UK & Australia. But before we start a deep dive, why don’t we first watch the demo?

Isn’t it exciting? Let’s explore it in detail.

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Architecture:

Let us understand the flow of events –

The above diagram shows that the application, which uses Open CV, analyzes individual frames. It detects the cricket ball & finally, it tracks every movement by analyzing each frame & then it predicts (pink line) based on the supplied data points.

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Python Packages:

Following are the python packages that are necessary to develop this brilliant use case –

pip install opencv-python
pip install numpy
pip install cvzone

CODE:

Let us now understand the code. For this use case, we will only discuss three python scripts. However, we need more than these three. However, we have already discussed them in some of the early posts. Hence, we will skip them here.

• clsPredictBodyLine.py (The main class that will handle the prediction of Cricket balls in the real-time video feed.)

Please find the key snippet from the above script –

kf = clsKalmanFilter()

The application is instantiating the modified Kalman filter.

myColorFinder = ColorFinder(False)

This command has more purpose than creating a proper mask in debug mode if you want to isolate the color of any object you want to track. To debug this property, one needs to set the flag to True. And you will see the following screen. Click the next video to get the process to generate the accurate HSV.

In the end, you will get a similar entry to the below one –

And you can see the entry that is available in the config for the following parameter –

'HSV': {'hmin': 173, 'smin':177, 'vmin':57, 'hmax':178, 'smax':255, 'vmax':255},

The next important block is –

def predStream(self, img, hsvVals, FrNo):
    try:
        pT1 = self.pT1
        pT2 = self.pT2
        pT3 = self.pT3
        pT4 = self.pT4

The four points mentioned above will help us determine the best region for the ball, forcing the batsman to play the shots & a 90% chance of getting caught behind.

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The snippets below will apply the mask & identify the contour of the objects which the program intends to track. In this case, we are talking about the pink cricket ball.

#Find the color ball
imgColor, mask = myColorFinder.update(img, hsvVals)

#Find location of the red_ball
imgContours, contours = cvzone.findContours(img, mask, minArea=500)

if contours:
    posListX.append(contours[0]['center'][0])
    posListY.append(contours[0]['center'][1])

The next key snippets are as follows –

if posListX:
    # Find the Coefficients
    A, B, C = np.polyfit(posListX, posListY, 2)

    for i, (posX, posY) in enumerate(zip(posListX, posListY)):
        pos = (posX, posY)
        cv2.circle(imgContours, pos, 10, (0,255,0), cv2.FILLED)

        # Using Karman Filter Prediction
        predicted = kf.predict(posX, posY)
        cv2.circle(imgContours, (predicted[0], predicted[1]), 12, (255,0,255), cv2.FILLED)

        ballDetectFlag = True
        if ballDetectFlag:
            print('Balls Detected!')

        if i == 0:
            cv2.line(imgContours, pos, pos, (0,255,0), 5)
            cv2.line(imgContours, predicted, predicted, (255,0,255), 5)
        else:
            predictedM = kf.predict(posListX[i-1], posListY[i-1])

            cv2.line(imgContours, pos, (posListX[i-1], posListY[i-1]), (0,255,0), 5)
            cv2.line(imgContours, predicted, predictedM, (255,0,255), 5)

The above lines will track the original & predicted lines & then it will plot on top of the frame in real time.

The next line will be as follows –

if len(posListX) < 10:

    # Calculation for best place to ball
    a1 = A
    b1 = B
    c1 = C - pT1

    X1 = int((- b1 - math.sqrt(b1**2 - (4*a1*c1)))/(2*a1))
    prediction1 = pT2 < X1 < pT3

    a2 = A
    b2 = B
    c2 = C - pT4

    X2 = int((- b2 - math.sqrt(b2**2 - (4*a2*c2)))/(2*a2))
    prediction2 = pT2 < X2 < pT3

    prediction = prediction1 | prediction2

if prediction:
    print('Good Length Ball!')
    sMsg = "Good Length Ball - (" + str(FrNo) + ")"
    cvzone.putTextRect(imgContours, sMsg, (50,150), scale=5, thickness=5, colorR=(0,200,0), offset=20)
else:
    print('Loose Ball!')
    sMsg = "Loose Ball - (" + str(FrNo) + ")"
    cvzone.putTextRect(imgContours, sMsg, (50,150), scale=5, thickness=5, colorR=(0,0,200), offset=20)

• predictBodyLine.py (The main python script that will invoke the class to predict Cricket balls in the real-time video feed.)

Here is the final key snippet –

# Passing source data csv file
x1 = pbdl.clsPredictBodyLine()

# Execute all the pass
r1 = x1.processVideo(debugInd, var)

if (r1 == 0):
    print('Successfully predicted body-line deliveries!')
else:
    print('Failed to predict body-line deliveries!')

The above lines will first instantiate the main class & then invoke it.

You can find it here if you want to know more about the Kalman filter.

So, finally, we’ve done it.

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FOLDER STRUCTURE:

You will get the complete codebase in the following GitHub link.

I’ll bring some more exciting topics in the coming days from the Python verse. Please share & subscribe to my post & let me know your feedback.

Till then, Happy Avenging! 🙂

Note: All the data & scenarios posted here are representational data & scenarios & available over the internet & for educational purposes only. Some of the images (except my photo) we’ve used are available over the net. We don’t claim ownership of these images. There is always room for improvement & especially in the prediction quality.