Скачать или смотреть How to Calculate the Perimeter of a Binary Image Using OpenCV 4.2 in C+ +

Learn how to accurately compute the perimeter of a white blob in a binary image using OpenCV 4.2. This step-by-step guide provides clear instructions and practical coding examples.
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Understanding the Problem

Calculating the perimeter of a white blob in a binary image can be quite a task, especially when transitioning between different versions of libraries, like OpenCV. In this particular case, we are dealing with OpenCV 4.2, which has deprecated some functions that were previously available in earlier versions. A common issue arises when trying to pass images in a different format, leading to confusion for those who are new to the OpenCV framework.

If you find yourself facing similar challenges, you're not alone! In this guide, we'll break down how to compute the perimeter of a single white blob within a 512x512 binary image using the recent functionality of OpenCV 4.2.

Problem Summary

You currently have a code snippet that works in OpenCV 3 but runs into issues when upgraded to OpenCV 4.2. Specifically, the use of IplImage is deprecated, and passing a Mat object directly to the cvFindContours function does not function as expected. Let's explore how to resolve this issue with a new approach.

The Solution

Step 1: Set Up Your Function

To start, you need to define a function that accepts a pointer to your binary image along with its dimensions. Here’s how you can do that:

[[See Video to Reveal this Text or Code Snippet]]

In the code excerpt above, we first create a Mat object from the input image pointer. We also define a 3x3 structuring element used during the erosion step.

Step 2: Process the Image

Next, you'll apply the erosion on the original binary image, and then invert the result:

[[See Video to Reveal this Text or Code Snippet]]

After applying erosion, we invert the image to obtain the edges of the blob effectively.

Step 3: Find Contours

With the processed edge image ready, it’s time to find the contours of the blob. OpenCV provides the findContours function which is much more user-friendly in version 4.2:

[[See Video to Reveal this Text or Code Snippet]]

We will retrieve only the external contour of the blob.

Step 4: Calculate the Perimeter

Finally, the contours obtained will be used to calculate the perimeter of the blob using the following logic:

[[See Video to Reveal this Text or Code Snippet]]

This section of the code efficiently sums the distances based on whether the points are aligned vertically or horizontally and adjusts for corners.

Conclusion

Calculating the perimeter of a binary image in OpenCV can initially seem daunting, particularly when updating to newer library versions. However, by leveraging updated functions and clear logical structuring of your code, like with the findContours and processing steps mentioned above, you will be able to accomplish your goal effectively.

Feel free to experiment with the provided code and tailor it according to your particular requirements! Happy coding!