th 174 - Detecting Two Colors with `Cv2.Inrange` in Python-OpenCV

Detecting Two Colors with `Cv2.Inrange` in Python-OpenCV

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Are you familiar with the wonders of computer vision? If so, you must have heard of Python-OpenCV. This powerful library offers a wide range of image processing capabilities that can help detect objects, track motions, and much more. However, if you want to detect specific colors in an image, you must learn how to use the `Cv2.Inrange` method.

This article will guide you through the basics of detecting two colors using `Cv2.Inrange` in Python-OpenCV. You will discover how to set the lower and upper bounds of the color range you want to detect and use masks to isolate the desired colors. Furthermore, you will learn how to display the results of your color detection algorithm in real-time, allowing you to fine-tune your parameters until you achieve the desired outcome.

If you are a developer, researcher, or hobbyist interested in computer vision algorithms, this article is for you. By providing step-by-step instructions and sample code, you will gain a better understanding of how `Cv2.Inrange` works and how to apply it to your projects. Don’t miss out on the opportunity to level up your image processing skills and read the full article now!

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“How To Detect Two Different Colors Using `Cv2.Inrange` In Python-Opencv?” ~ bbaz


In this digital age, image processing has become a vital element of various industries such as medical imaging, surveillance, and robotics. Python-OpenCV is one of the most popular libraries used by developers and researchers for image processing tasks. This library provides functions to perform various image processing tasks, including color detection. In this article, we will discuss how to detect two colors with `Cv2.Inrange` in Python-OpenCV.

What is `Cv2.Inrange`?

`Cv2.Inrange` is a function provided by the Python-OpenCV library that is used to extract pixels from an image within a specific range of color values. This function takes two arguments: the input image and the color range in the form of lower and upper bounds. The resulting binary image shows only the pixels that fall within the specified color range.

Detecting Two Colors with `Cv2.Inrange`

Detecting two colors with `Cv2.Inrange` involves specifying the ranges for both colors separately and then merging the resulting binary images. The following code segment demonstrates detecting red and blue colors in an image:

    import numpy as np    import cv2    image = cv2.imread(sample.jpg)        # define red color range    lower_red = np.array([0, 0, 180])    upper_red = np.array([50, 50, 255])        # define blue color range    lower_blue = np.array([180, 0, 0])    upper_blue = np.array([255, 50, 50])        # detect red color    red_mask = cv2.inRange(image, lower_red, upper_red)        # detect blue color    blue_mask = cv2.inRange(image, lower_blue, upper_blue)        # combine masks    final_mask = red_mask + blue_mask        # apply mask on original image to see the results    result = cv2.bitwise_and(image, image, mask=final_mask)    # display output    cv2.imshow(Result, result)    cv2.waitKey(0)    cv2.destroyAllWindows()

Explanation of the Code Segment

The code segment starts by importing the necessary libraries and loading the input image. The color ranges for red and blue colors are defined using arrays of lower and upper bounds of BGR values. The `cv2.Inrange` function is called twice with these ranges to extract the pixels that lie within the specified ranges. Both binary images are then combined into a single final mask by adding them together. The final mask is applied to the original image using the `cv2.bitwise_and` function to obtain the result. The output is displayed using the `cv2.imshow` function.

Performance Comparison

We have compared the performance of detecting two colors with `Cv2.Inrange` against two other commonly used methods:

Method Pros Cons
Masking Using NumPy Faster than `Cv2.Inrange` Not suitable for complex color ranges
Color Filtering Using HSV Robust to changes in lighting conditions Requires color conversion to HSV
`Cv2.Inrange` Simple and easy to use Not very robust to changes in lighting conditions

Based on the above comparison, we can conclude that `Cv2.Inrange` is a simple and effective method for detecting two colors in an image. However, it might not be the best method in all situations and other methods such as masking using NumPy or color filtering using HSV might be more suitable depending on the specific requirements of the task at hand.

Limitations of `Cv2.Inrange`

The main limitation of `Cv2.Inrange` is its sensitivity to changes in lighting conditions. This method relies on a fixed color range and any changes in lighting conditions can affect the accuracy of the results. Additionally, detecting more than two colors with `Cv2.Inrange` can become increasingly complex and can require specifying multiple ranges and combining them accordingly.

Applications of Detecting Two Colors

Detecting two colors in an image can have various applications in several fields such as:

  • Traffic light detection and recognition
  • Sports analytics to track players and teams based on their jersey colors
  • Robotics to distinguish between different objects based on their colors
  • Medical imaging to identify tissues based on their color properties


Python-OpenCV provides a simple and effective method for detecting two colors in an image using `Cv2.Inrange`. This method can have various applications in different fields and can be combined with other image processing techniques to solve complex tasks. However, this method has its limitations and might not be the best choice in all situations. Ultimately, the choice of method depends on the specific requirements of the task at hand and the tradeoffs between accuracy and complexity.

Thank you for reading our article on detecting two colors with `Cv2.Inrange` in Python-OpenCV. We hope that the information we provided has been useful to you, and that you are now able to apply what you have learned in your own projects.

As we mentioned in the article, detecting colors is a common task in computer vision applications, and it can be done in many ways. However, using `Cv2.Inrange` offers a simple and efficient solution when dealing with color ranges. By specifying the lower and upper bounds of the colors you want to detect, this function returns a binary image where the pixels that fit the criteria are set to 1 (white), while the others are set to 0 (black).

We encourage you to experiment with this function and try different color combinations, thresholds, and processing techniques. Remember that OpenCV provides a wide range of tools for image processing and analysis, and it is up to you to choose the most suitable approach for your specific problem. If you have any questions or comments, feel free to leave them below. We would love to hear from you.

Once again, thank you for your interest in our article. We hope to see you again soon for more exciting topics related to computer vision and image processing.

People often ask various questions about detecting two colors with `Cv2.Inrange` in Python-OpenCV. Here are some of the most common questions and their answers:

  1. What is `Cv2.Inrange`?

    `Cv2.Inrange` is a function in the OpenCV library in Python that takes an input image, a lower bound, and an upper bound as arguments, and returns a binary mask indicating which pixels in the input image fall within the specified range.

  2. How can `Cv2.Inrange` be used to detect two colors?

    To detect two colors using `Cv2.Inrange`, two separate calls to the function can be made, each with a different color range. The resulting binary masks from both calls can then be combined using bitwise operations to create a final mask that indicates where both colors are present in the input image.

  3. What are lower and upper bounds?

    In the context of `Cv2.Inrange`, lower and upper bounds refer to the minimum and maximum values of each color channel (e.g., red, green, blue) that are considered to be within the range of interest. For example, to detect pixels that are red or yellow, the lower and upper bounds for the red channel would be set to different values, while the green and blue channels would be ignored.

  4. How can I choose the correct lower and upper bounds for my application?

    The optimal color ranges depend on the specific colors and lighting conditions in your application. Experimentation and trial-and-error may be necessary to find the best values. Alternatively, you may be able to use color segmentation techniques based on color histograms or machine learning algorithms to automatically determine the ranges.

  5. Are there any limitations to using `Cv2.Inrange` for color detection?

    `Cv2.Inrange` can be limited by its sensitivity to lighting conditions, shadows, and reflections. Additionally, it may not be effective for detecting colors that are very similar to each other or for complex scenes with many different colors.