Keywords: front-page

## Lab: Edge Detection II

[Exercises] [Workspace]

Purpose: The purpose of this lab exercise is to experiment with the Roberts, Sobel, Prewitt, and Isotropic edge detectors, and compare the results.

Activities:

1. Read the image $DIP/data/gull.kdf and display it using operators User defined and Display Image.

   1. Glyphs:Input/Output:Data Files:User defined
   2. Glyphs:Visualization:Non-Interactive Display:Display Image

2. Perform edge detection by executing four different gradient operators on the image, using the operator Gradient Operator.

   Note: The results of the gradient operators can be very high at some points, (larger than 255), so it is important to convert the input image to an appropriate pixel data type to get the proper results. After the gradient calculation, it is possible to clip the values or normalize the image.

   1. Glyphs:Image Proc:Spatial Filters:Gradient Operator
   2. Open the Gradient Operator and select the "Square Root" option (this will calculate the Euclidean Distance of the X and Y gradients).
   3. Glyphs:Data Manip:Data Conversion:Normalize

3. Display the results.

   1. Glyphs:Visualization:Non-Interactive Display:Display Image

Exercises

1. Clip the results to 255 or normalize the results to 255. Compare and comment.
2. Take the difference between the Sobel and Isotropic operators. Comment on the results. In which portions of the image should the difference between the Sobel and Isotropic results be small or large?

Khoros Workspace
Execute the visual program c9s2detect-edges.wk