HighGui

Highgui is a module in OpenCV that provides a lightweight, platform-independent interface for basic graphical user interaction and simple image/video I/O. It enables loading images from disk, displaying them in windows, and handling user input, making it a convenient tool for quick visualization and debugging. Core functions include imread, imwrite, imshow, waitKey, and destroyAllWindows, as well as window management APIs such as namedWindow, resizeWindow, moveWindow, and destroyWindow. The API also supports simple GUI controls like trackbars with createTrackbar and related functions, and a mouse callback via setMouseCallback.

Implementation and backends: Highgui relies on platform-specific GUI backends (for example Win32 on Windows, Cocoa on macOS, X11/GTK+ on Linux, or Qt) and selects between them at build time. This design allows the same API to work across operating systems while providing native windowing and input handling.

Relation to OpenCV structure and limitations: Highgui is intended for quick visualization and basic interaction rather than full-featured GUI development. For more advanced video capture and I/O, OpenCV uses the videoio module for camera input and video operations, while highgui remains the minimal front end for display and simple controls.

Usage and scope: Typical use cases include displaying intermediate results during image processing, obtaining simple user input through key presses or trackbars, and debugging algorithms. Because it depends on a graphical display environment, code that uses highgui may not run in headless environments and requires appropriate GUI support on the target system.