Multiple Color Detection in Real-Time using Python-OpenCV

For a robot to visualize the environment, along with the object detection, detection of its color in real-time is also very important.

Why this is important? : Some Real-world Applications

• In self-driving car, to detect the traffic signals.
• Multiple color detection is used in some industrial robots, to performing pick-and-place task in separating different colored objects.

This is an implementation of detecting multiple colors (here, only red, green and blue colors have been considered) in real-time using Python programming language.
Python Libraries Used:

• NumPy
• OpenCV-Python

Work Flow Description:

Step 1: Input: Capture video through webcam.
Step 2: Read the video stream in image frames.
Step 3: Convert the imageFrame in BGR(RGB color space represented as three matrices of red, green and blue with integer values from 0 to 255) to HSV(hue-saturation-value) color space. Hue describes a color in terms of saturation, represents the amount of gray color in that color and value describes the brightness or intensity of the color. This can be represented as three matrices in the range of 0-179, 0-255 and 0-255 respectively.
Step 4: Define the range of each color and create the corresponding mask.
Step 5: Morphological Transform: Dilation, to remove noises from the images.
Step 6: bitwise_and between the image frame and mask is performed to specifically detect that particular color and discrad others.
Step 7: Create contour for the individual colors to display the detected colored region distinguishly.
Step 8: Output: Detection of the colors in real-time.

Below is the implementation.

# Python code for Multiple Color Detection


import numpy as np
import cv2


# Capturing video through webcam
webcam = cv2.VideoCapture(0)

# Start a while loop
while(1):

    # Reading the video from the
    # webcam in image frames
    _, imageFrame = webcam.read()

    # Convert the imageFrame in
    # BGR(RGB color space) to
    # HSV(hue-saturation-value)
    # color space
    hsvFrame = cv2.cvtColor(imageFrame, cv2.COLOR_BGR2HSV)

    # Set range for red color and
    # define mask
    red_lower = np.array([136, 87, 111], np.uint8)
    red_upper = np.array([180, 255, 255], np.uint8)
    red_mask = cv2.inRange(hsvFrame, red_lower, red_upper)

    # Set range for green color and
    # define mask
    green_lower = np.array([25, 52, 72], np.uint8)
    green_upper = np.array([102, 255, 255], np.uint8)
    green_mask = cv2.inRange(hsvFrame, green_lower, green_upper)

    # Set range for blue color and
    # define mask
    blue_lower = np.array([94, 80, 2], np.uint8)
    blue_upper = np.array([120, 255, 255], np.uint8)
    blue_mask = cv2.inRange(hsvFrame, blue_lower, blue_upper)

    # Morphological Transform, Dilation
    # for each color and bitwise_and operator
    # between imageFrame and mask determines
    # to detect only that particular color
    kernel = np.ones((5, 5), "uint8")

    # For red color
    red_mask = cv2.dilate(red_mask, kernel)
    res_red = cv2.bitwise_and(imageFrame, imageFrame,
                              mask = red_mask)

    # For green color
    green_mask = cv2.dilate(green_mask, kernel)
    res_green = cv2.bitwise_and(imageFrame, imageFrame,
                                mask = green_mask)

    # For blue color
    blue_mask = cv2.dilate(blue_mask, kernel)
    res_blue = cv2.bitwise_and(imageFrame, imageFrame,
                               mask = blue_mask)

    # Creating contour to track red color
    contours, hierarchy = cv2.findContours(red_mask,
                                           cv2.RETR_TREE,
                                           cv2.CHAIN_APPROX_SIMPLE)

    for pic, contour in enumerate(contours):
        area = cv2.contourArea(contour)
        if(area > 300):
            x, y, w, h = cv2.boundingRect(contour)
            imageFrame = cv2.rectangle(imageFrame, (x, y),
                                       (x + w, y + h),
                                       (0, 0, 255), 2)

            cv2.putText(imageFrame, "Red Colour", (x, y),
                        cv2.FONT_HERSHEY_SIMPLEX, 1.0,
                        (0, 0, 255))

    # Creating contour to track green color
    contours, hierarchy = cv2.findContours(green_mask,
                                           cv2.RETR_TREE,
                                           cv2.CHAIN_APPROX_SIMPLE)

    for pic, contour in enumerate(contours):
        area = cv2.contourArea(contour)
        if(area > 300):
            x, y, w, h = cv2.boundingRect(contour)
            imageFrame = cv2.rectangle(imageFrame, (x, y),
                                       (x + w, y + h),
                                       (0, 255, 0), 2)

            cv2.putText(imageFrame, "Green Colour", (x, y),
                        cv2.FONT_HERSHEY_SIMPLEX,
                        1.0, (0, 255, 0))

    # Creating contour to track blue color
    contours, hierarchy = cv2.findContours(blue_mask,
                                           cv2.RETR_TREE,
                                           cv2.CHAIN_APPROX_SIMPLE)
    for pic, contour in enumerate(contours):
        area = cv2.contourArea(contour)
        if(area > 300):
            x, y, w, h = cv2.boundingRect(contour)
            imageFrame = cv2.rectangle(imageFrame, (x, y),
                                       (x + w, y + h),
                                       (255, 0, 0), 2)

            cv2.putText(imageFrame, "Blue Colour", (x, y),
                        cv2.FONT_HERSHEY_SIMPLEX,
                        1.0, (255, 0, 0))

    # Program Termination
    cv2.imshow("Multiple Color Detection in Real-TIme", imageFrame)
    if cv2.waitKey(10) & 0xFF == ord('q'):
        cap.release()
        cv2.destroyAllWindows()
        break

Output: