Sobel algorithm

The Sobel algorithm is a simple, effective way to find the edges in an image. It works by measuring how quickly pixel brightness changes.

Here is the concise, step-by-step process:

1. Grayscale: The algorithm first converts the color image to grayscale, as it only needs to track brightness (intensity), not color.

2. Scan for Gradients: It uses two 3x3 “kernels” (small matrices) to scan every pixel.

   • $G_x$ Kernel: This kernel detects changes in brightness horizontally (finding vertical edges).

   • $G_y$ Kernel: This kernel detects changes in brightness vertically (finding horizontal edges).

3. Combine Results: For each pixel, the algorithm combines the horizontal ($G_x$) and vertical ($G_y$) scores using a formula (like $G=\sqrt{G_x^2+G_y^2}$) to calculate the pixel’s total “edge strength.”

4. Create Edge Map: This process creates a new image where the brightness of each pixel corresponds to its “edge strength.” Bright white pixels mean a strong edge was found, while black pixels mean the area was flat.

In short, the algorithm finds edges by scanning the image for sharp changes in brightness, both horizontally and vertically, and then combines those findings into a final edge map.