Hough Transform Algorithm#

Disclaimer: this article was generated by GPT-3.5. Prompt: Write a technical-oriented article explaining the Hough transform algorithm for finding circles in a grayscale image.


Computer vision plays a vital role in a wide range of applications, including object recognition, image segmentation, and feature extraction. Circle detection is a fundamental task in computer vision, with applications in robotics, medical imaging, and industrial quality control. The Hough Transform algorithm is a powerful technique for detecting circles in grayscale images. In this article, we will delve into the intricacies of the Hough Transform algorithm and explore its workings in circle detection.

Understanding the Hough Transform#

The Hough Transform is a feature extraction technique that enables the detection of shapes, such as lines, circles, and ellipses, in digital images. Initially developed for line detection, it has been extended to handle circles as well. The core idea behind the Hough Transform lies in transforming the image space into parameter space, facilitating the detection of specific shapes based on their characteristic patterns.

Circle Detection using the Hough Transform#

Detecting circles in a grayscale image using the Hough Transform involves the following steps:

Step 1: Preprocessing Convert the input grayscale image into a binary image using appropriate thresholding techniques. This simplifies the circle detection process by reducing the complexity of the input image.

Step 2: Edge Detection Apply an edge detection algorithm, such as the Canny edge detector, to identify edges in the binary image. Edges are crucial for circle detection as they represent transitions between different intensity levels, which often correspond to the boundaries of objects, including circles.

Step 3: Hough Space Accumulation Create an accumulator array, often referred to as the Hough space, to store the voting information for potential circles. The dimensions of this accumulator array correspond to the radius and center coordinates of the circles being detected.

Step 4: Voting for every edge pixel in the binary image, compute all possible circles that could pass through that pixel. Increment the corresponding accumulator cells in the Hough space to vote for the circles that have overlapping parameters.

Step 5: Thresholding and Circle Extraction After the voting process, examine the accumulator array and identify the cells with the highest number of votes. These cells correspond to the potential circles present in the image. By setting a suitable threshold, we can filter out weaker circle candidates.

Step 6: Circle Parameter Estimation Retrieve the center coordinates and radii of the circles based on the cells with the highest votes. These parameters represent the estimated circles in the original image.

Step 7: Visualization Finally, overlay the detected circles on the original grayscale image to visualize the circle detection results.

Benefits and Limitations of the Hough Transform Algorithm#

The Hough Transform algorithm offers several advantages for circle detection:

  1. Robustness: The Hough Transform is capable of detecting circles even in the presence of noise, occlusions, and partial circles.

  2. Parameterization: The algorithm provides a parameterized representation of the detected circles, making it easier to analyze and extract relevant information.

However, the Hough Transform algorithm also has certain limitations:

  1. Computational Complexity: The Hough Transform can be computationally expensive, particularly for large images or images with high resolution. Various optimization techniques, such as the use of an accumulator matrix, can help mitigate this issue.

  2. Limited to Defined Shape: The Hough Transform assumes a predefined shape model (e.g., a circle) and may not work effectively for detecting circles with varying radii or non-circular shapes.


The Hough Transform algorithm has proven to be a valuable tool for circle detection in grayscale images. By leveraging the power of parameter space and voting, it enables the identification of circular patterns in images, opening up possibilities for numerous applications. While the algorithm has limitations, ongoing research and advancements in computer vision continue to enhance its effectiveness and broaden its scope for shape detection tasks.


  • Duda, R.O., Hart, P.E., & Stork, D.G. (2001). Pattern Classification (2nd ed.). Wiley-Interscience.

  • Ballard, D.H. (1981). Generalizing the Hough Transform to Detect Arbitrary Shapes. Pattern Recognition, 13(2), 111-122.

  • Hough transform. Retrieved June 18, 2023, from Hough transform - Wikipedia