While OpenCV was designed for use in full-scale applications and can be used within functionally rich UI frameworks (such as Qt*, WinForms*, or Cocoa*) or without any UI at all, sometimes there it is required to try functionality quickly and visualize the results. More...

Collaboration diagram for High-level GUI:

Modules
	OpenGL support

	Qt New Functions
	![image](pics/qtgui.png)

	WinRT support
	This figure explains new functionality implemented with WinRT GUI.

	C API

Typedefs
typedef void(*	cv::ButtonCallback) (int state, void *userdata)
	Callback function for a button created by cv::createButton. More...

typedef void(*	cv::MouseCallback) (int event, int x, int y, int flags, void *userdata)
	Callback function for mouse events. More...

typedef void(*	cv::OpenGlDrawCallback) (void *userdata)
	Callback function defined to be called every frame. More...

typedef void(*	cv::TrackbarCallback) (int pos, void *userdata)
	Callback function for Trackbar see cv::createTrackbar. More...

Enumerations
enum	cv::MouseEventFlags { cv::EVENT_FLAG_LBUTTON = 1, cv::EVENT_FLAG_RBUTTON = 2, cv::EVENT_FLAG_MBUTTON = 4, cv::EVENT_FLAG_CTRLKEY = 8, cv::EVENT_FLAG_SHIFTKEY = 16, cv::EVENT_FLAG_ALTKEY = 32 }
	Mouse Event Flags see cv::MouseCallback. More...

enum	cv::MouseEventTypes { cv::EVENT_MOUSEMOVE = 0, cv::EVENT_LBUTTONDOWN = 1, cv::EVENT_RBUTTONDOWN = 2, cv::EVENT_MBUTTONDOWN = 3, cv::EVENT_LBUTTONUP = 4, cv::EVENT_RBUTTONUP = 5, cv::EVENT_MBUTTONUP = 6, cv::EVENT_LBUTTONDBLCLK = 7, cv::EVENT_RBUTTONDBLCLK = 8, cv::EVENT_MBUTTONDBLCLK = 9, cv::EVENT_MOUSEWHEEL = 10, cv::EVENT_MOUSEHWHEEL = 11 }
	Mouse Events see cv::MouseCallback. More...

enum	cv::QtButtonTypes { cv::QT_PUSH_BUTTON = 0, cv::QT_CHECKBOX = 1, cv::QT_RADIOBOX = 2, cv::QT_NEW_BUTTONBAR = 1024 }
	Qt "button" type. More...

enum	cv::QtFontStyles { cv::QT_STYLE_NORMAL = 0, cv::QT_STYLE_ITALIC = 1, cv::QT_STYLE_OBLIQUE = 2 }
	Qt font style. More...

enum	cv::QtFontWeights { cv::QT_FONT_LIGHT = 25, cv::QT_FONT_NORMAL = 50, cv::QT_FONT_DEMIBOLD = 63, cv::QT_FONT_BOLD = 75, cv::QT_FONT_BLACK = 87 }
	Qt font weight. More...

enum	cv::WindowFlags { cv::WINDOW_NORMAL = 0x00000000, cv::WINDOW_AUTOSIZE = 0x00000001, cv::WINDOW_OPENGL = 0x00001000, cv::WINDOW_FULLSCREEN = 1, cv::WINDOW_FREERATIO = 0x00000100, cv::WINDOW_KEEPRATIO = 0x00000000, cv::WINDOW_GUI_EXPANDED =0x00000000, cv::WINDOW_GUI_NORMAL = 0x00000010 }
	Flags for cv::namedWindow. More...

enum	cv::WindowPropertyFlags { cv::WND_PROP_FULLSCREEN = 0, cv::WND_PROP_AUTOSIZE = 1, cv::WND_PROP_ASPECT_RATIO = 2, cv::WND_PROP_OPENGL = 3, cv::WND_PROP_VISIBLE = 4 }
	Flags for cv::setWindowProperty / cv::getWindowProperty. More...

Functions
int	cv::createTrackbar (const String &trackbarname, const String &winname, int value, int count, TrackbarCallback onChange=0, void userdata=0)
	Creates a trackbar and attaches it to the specified window. More...

void	cv::destroyAllWindows ()
	Destroys all of the HighGUI windows. More...

void	cv::destroyWindow (const String &winname)
	Destroys the specified window. More...

int	cv::getMouseWheelDelta (int flags)
	Gets the mouse-wheel motion delta, when handling mouse-wheel events cv::EVENT_MOUSEWHEEL and cv::EVENT_MOUSEHWHEEL. More...

int	cv::getTrackbarPos (const String &trackbarname, const String &winname)
	Returns the trackbar position. More...

double	cv::getWindowProperty (const String &winname, int prop_id)
	Provides parameters of a window. More...

void	cv::imshow (const String &winname, InputArray mat)
	Displays an image in the specified window. More...

void	cv::moveWindow (const String &winname, int x, int y)
	Moves window to the specified position. More...

void	cv::namedWindow (const String &winname, int flags=WINDOW_AUTOSIZE)
	Creates a window. More...

void	cv::resizeWindow (const String &winname, int width, int height)
	Resizes window to the specified size. More...

void	cv::setMouseCallback (const String &winname, MouseCallback onMouse, void *userdata=0)
	Sets mouse handler for the specified window. More...

void	cv::setTrackbarMax (const String &trackbarname, const String &winname, int maxval)
	Sets the trackbar maximum position. More...

void	cv::setTrackbarMin (const String &trackbarname, const String &winname, int minval)
	Sets the trackbar minimum position. More...

void	cv::setTrackbarPos (const String &trackbarname, const String &winname, int pos)
	Sets the trackbar position. More...

void	cv::setWindowProperty (const String &winname, int prop_id, double prop_value)
	Changes parameters of a window dynamically. More...

void	cv::setWindowTitle (const String &winname, const String &title)
	Updates window title. More...

int	cv::startWindowThread ()

int	cv::waitKey (int delay=0)
	Waits for a pressed key. More...

int	cv::waitKeyEx (int delay=0)
	Similar to waitKey, but returns full key code. More...

Detailed Description

While OpenCV was designed for use in full-scale applications and can be used within functionally rich UI frameworks (such as Qt*, WinForms*, or Cocoa*) or without any UI at all, sometimes there it is required to try functionality quickly and visualize the results.

This is what the HighGUI module has been designed for.

It provides easy interface to:

Create and manipulate windows that can display images and "remember" their content (no need to handle repaint events from OS).
Add trackbars to the windows, handle simple mouse events as well as keyboard commands.

Typedef Documentation

typedef void(* cv::ButtonCallback) (int state, void *userdata)

#include <highgui/include/opencv2/highgui.hpp>

Callback function for a button created by cv::createButton.

Parameters

state	current state of the button. It could be -1 for a push button, 0 or 1 for a check/radio box button.
userdata	The optional parameter.

typedef void(* cv::MouseCallback) (int event, int x, int y, int flags, void *userdata)

#include <highgui/include/opencv2/highgui.hpp>

Callback function for mouse events.

see cv::setMouseCallback

Parameters

event	one of the cv::MouseEventTypes constants.
x	The x-coordinate of the mouse event.
y	The y-coordinate of the mouse event.
flags	one of the cv::MouseEventFlags constants.
userdata	The optional parameter.

typedef void(* cv::OpenGlDrawCallback) (void *userdata)

#include <highgui/include/opencv2/highgui.hpp>

Callback function defined to be called every frame.

See cv::setOpenGlDrawCallback

Parameters

userdata The optional parameter.

typedef void(* cv::TrackbarCallback) (int pos, void *userdata)

#include <highgui/include/opencv2/highgui.hpp>

Callback function for Trackbar see cv::createTrackbar.

Parameters

pos	current position of the specified trackbar.
userdata	The optional parameter.

Enumeration Type Documentation

enum cv::MouseEventFlags

#include <highgui/include/opencv2/highgui.hpp>

Mouse Event Flags see cv::MouseCallback.

Enumerator
EVENT_FLAG_LBUTTON	indicates that the left mouse button is down.
EVENT_FLAG_RBUTTON	indicates that the right mouse button is down.
EVENT_FLAG_MBUTTON	indicates that the middle mouse button is down.
EVENT_FLAG_CTRLKEY	indicates that CTRL Key is pressed.
EVENT_FLAG_SHIFTKEY	indicates that SHIFT Key is pressed.
EVENT_FLAG_ALTKEY	indicates that ALT Key is pressed.

enum cv::MouseEventTypes

#include <highgui/include/opencv2/highgui.hpp>

Mouse Events see cv::MouseCallback.

Enumerator
EVENT_MOUSEMOVE	indicates that the mouse pointer has moved over the window.
EVENT_LBUTTONDOWN	indicates that the left mouse button is pressed.
EVENT_RBUTTONDOWN	indicates that the right mouse button is pressed.
EVENT_MBUTTONDOWN	indicates that the middle mouse button is pressed.
EVENT_LBUTTONUP	indicates that left mouse button is released.
EVENT_RBUTTONUP	indicates that right mouse button is released.
EVENT_MBUTTONUP	indicates that middle mouse button is released.
EVENT_LBUTTONDBLCLK	indicates that left mouse button is double clicked.
EVENT_RBUTTONDBLCLK	indicates that right mouse button is double clicked.
EVENT_MBUTTONDBLCLK	indicates that middle mouse button is double clicked.
EVENT_MOUSEWHEEL	positive and negative values mean forward and backward scrolling, respectively.
EVENT_MOUSEHWHEEL	positive and negative values mean right and left scrolling, respectively.

enum cv::QtButtonTypes

#include <highgui/include/opencv2/highgui.hpp>

Qt "button" type.

Enumerator
QT_PUSH_BUTTON	Push button.
QT_CHECKBOX	Checkbox button.
QT_RADIOBOX	Radiobox button.
QT_NEW_BUTTONBAR	Button should create a new buttonbar.

enum cv::QtFontStyles

#include <highgui/include/opencv2/highgui.hpp>

Qt font style.

Enumerator
QT_STYLE_NORMAL	Normal font.
QT_STYLE_ITALIC	Italic font.
QT_STYLE_OBLIQUE	Oblique font.

enum cv::QtFontWeights

#include <highgui/include/opencv2/highgui.hpp>

Qt font weight.

Enumerator
QT_FONT_LIGHT	Weight of 25.
QT_FONT_NORMAL	Weight of 50.
QT_FONT_DEMIBOLD	Weight of 63.
QT_FONT_BOLD	Weight of 75.
QT_FONT_BLACK	Weight of 87.

enum cv::WindowFlags

#include <highgui/include/opencv2/highgui.hpp>

Flags for cv::namedWindow.

Enumerator
WINDOW_NORMAL	the user can resize the window (no constraint) / also use to switch a fullscreen window to a normal size.
WINDOW_AUTOSIZE	the user cannot resize the window, the size is constrainted by the image displayed.
WINDOW_OPENGL	window with opengl support.
WINDOW_FULLSCREEN	change the window to fullscreen.
WINDOW_FREERATIO	the image expends as much as it can (no ratio constraint).
WINDOW_KEEPRATIO	the ratio of the image is respected.
WINDOW_GUI_EXPANDED	status bar and tool bar
WINDOW_GUI_NORMAL	old fashious way

enum cv::WindowPropertyFlags

#include <highgui/include/opencv2/highgui.hpp>

Flags for cv::setWindowProperty / cv::getWindowProperty.

Enumerator
WND_PROP_FULLSCREEN	fullscreen property (can be WINDOW_NORMAL or WINDOW_FULLSCREEN).
WND_PROP_AUTOSIZE	autosize property (can be WINDOW_NORMAL or WINDOW_AUTOSIZE).
WND_PROP_ASPECT_RATIO	window's aspect ration (can be set to WINDOW_FREERATIO or WINDOW_KEEPRATIO).
WND_PROP_OPENGL	opengl support.
WND_PROP_VISIBLE	checks whether the window exists and is visible

Function Documentation

int cv::createTrackbar	(	const String &	trackbarname,
		const String &	winname,
		int *	value,
		int	count,
		TrackbarCallback	onChange = `0`,
		void *	userdata = `0`
	)

#include <highgui/include/opencv2/highgui.hpp>

Creates a trackbar and attaches it to the specified window.

The function createTrackbar creates a trackbar (a slider or range control) with the specified name and range, assigns a variable value to be a position synchronized with the trackbar and specifies the callback function onChange to be called on the trackbar position change. The created trackbar is displayed in the specified window winname.

Note

[Qt Backend Only] winname can be empty (or NULL) if the trackbar should be attached to the control panel.

Clicking the label of each trackbar enables editing the trackbar values manually.

Parameters

trackbarname	Name of the created trackbar.
winname	Name of the window that will be used as a parent of the created trackbar.
value	Optional pointer to an integer variable whose value reflects the position of the slider. Upon creation, the slider position is defined by this variable.
count	Maximal position of the slider. The minimal position is always 0.
onChange	Pointer to the function to be called every time the slider changes position. This function should be prototyped as void Foo(int,void*); , where the first parameter is the trackbar position and the second parameter is the user data (see the next parameter). If the callback is the NULL pointer, no callbacks are called, but only value is updated.
userdata	User data that is passed as is to the callback. It can be used to handle trackbar events without using global variables.

Examples:: contours2.cpp, demhist.cpp, distrans.cpp, edge.cpp, ffilldemo.cpp, fitellipse.cpp, laplace.cpp, morphology2.cpp, and pca.cpp.

void cv::destroyAllWindows ( )

#include <highgui/include/opencv2/highgui.hpp>

Destroys all of the HighGUI windows.

The function destroyAllWindows destroys all of the opened HighGUI windows.

void cv::destroyWindow ( const String & winname )

#include <highgui/include/opencv2/highgui.hpp>

Destroys the specified window.

The function destroyWindow destroys the window with the given name.

Parameters

winname Name of the window to be destroyed.

Examples:: ffilldemo.cpp, and grabcut.cpp.

int cv::getMouseWheelDelta ( int flags )

#include <highgui/include/opencv2/highgui.hpp>

Gets the mouse-wheel motion delta, when handling mouse-wheel events cv::EVENT_MOUSEWHEEL and cv::EVENT_MOUSEHWHEEL.

For regular mice with a scroll-wheel, delta will be a multiple of 120. The value 120 corresponds to a one notch rotation of the wheel or the threshold for action to be taken and one such action should occur for each delta. Some high-precision mice with higher-resolution freely-rotating wheels may generate smaller values.

For cv::EVENT_MOUSEWHEEL positive and negative values mean forward and backward scrolling, respectively. For cv::EVENT_MOUSEHWHEEL, where available, positive and negative values mean right and left scrolling, respectively.

With the C API, the macro CV_GET_WHEEL_DELTA(flags) can be used alternatively.

Note

Mouse-wheel events are currently supported only on Windows.

Parameters

flags The mouse callback flags parameter.

int cv::getTrackbarPos	(	const String &	trackbarname,
		const String &	winname
	)

#include <highgui/include/opencv2/highgui.hpp>

Returns the trackbar position.

The function returns the current position of the specified trackbar.

Note

[Qt Backend Only] winname can be empty (or NULL) if the trackbar is attached to the control panel.

Parameters

trackbarname	Name of the trackbar.
winname	Name of the window that is the parent of the trackbar.

double cv::getWindowProperty	(	const String &	winname,
		int	prop_id
	)

#include <highgui/include/opencv2/highgui.hpp>

Provides parameters of a window.

The function getWindowProperty returns properties of a window.

Parameters

winname	Name of the window.
prop_id	Window property to retrieve. The following operation flags are available: (cv::WindowPropertyFlags)

See also: setWindowProperty

void cv::imshow	(	const String &	winname,
		InputArray	mat
	)

#include <highgui/include/opencv2/highgui.hpp>

Displays an image in the specified window.

The function imshow displays an image in the specified window. If the window was created with the cv::WINDOW_AUTOSIZE flag, the image is shown with its original size, however it is still limited by the screen resolution. Otherwise, the image is scaled to fit the window. The function may scale the image, depending on its depth:

If the image is 8-bit unsigned, it is displayed as is.
If the image is 16-bit unsigned or 32-bit integer, the pixels are divided by 256. That is, the value range [0,255*256] is mapped to [0,255].
If the image is 32-bit floating-point, the pixel values are multiplied by 255. That is, the value range [0,1] is mapped to [0,255].

If window was created with OpenGL support, cv::imshow also support ogl::Buffer , ogl::Texture2D and cuda::GpuMat as input.

If the window was not created before this function, it is assumed creating a window with cv::WINDOW_AUTOSIZE.

If you need to show an image that is bigger than the screen resolution, you will need to call namedWindow("", WINDOW_NORMAL) before the imshow.

Note: This function should be followed by cv::waitKey function which displays the image for specified milliseconds. Otherwise, it won't display the image. For example, waitKey(0) will display the window infinitely until any keypress (it is suitable for image display). waitKey(25) will display a frame for 25 ms, after which display will be automatically closed. (If you put it in a loop to read videos, it will display the video frame-by-frame)

[Windows Backend Only] Pressing Ctrl+C will copy the image to the clipboard.

[Windows Backend Only] Pressing Ctrl+S will show a dialog to save the image.

Parameters

winname	Name of the window.
mat	Image to be shown.

Examples:: contours2.cpp, convexhull.cpp, demhist.cpp, distrans.cpp, edge.cpp, ffilldemo.cpp, fitellipse.cpp, grabcut.cpp, houghcircles.cpp, houghlines.cpp, kmeans.cpp, laplace.cpp, lsd_lines.cpp, minarea.cpp, morphology2.cpp, pca.cpp, polar_transforms.cpp, segment_objects.cpp, and watershed.cpp.

void cv::moveWindow	(	const String &	winname,
		int	x,
		int	y
	)

#include <highgui/include/opencv2/highgui.hpp>

Moves window to the specified position.

Parameters

winname	Name of the window.
x	The new x-coordinate of the window.
y	The new y-coordinate of the window.

Examples:: polar_transforms.cpp.

void cv::namedWindow	(	const String &	winname,
		int	flags = `WINDOW_AUTOSIZE`
	)

#include <highgui/include/opencv2/highgui.hpp>

Creates a window.

The function namedWindow creates a window that can be used as a placeholder for images and trackbars. Created windows are referred to by their names.

If a window with the same name already exists, the function does nothing.

You can call cv::destroyWindow or cv::destroyAllWindows to close the window and de-allocate any associated memory usage. For a simple program, you do not really have to call these functions because all the resources and windows of the application are closed automatically by the operating system upon exit.

Note

Qt backend supports additional flags:

WINDOW_NORMAL or WINDOW_AUTOSIZE: WINDOW_NORMAL enables you to resize the window, whereas WINDOW_AUTOSIZE adjusts automatically the window size to fit the displayed image (see imshow ), and you cannot change the window size manually.
WINDOW_FREERATIO or WINDOW_KEEPRATIO: WINDOW_FREERATIO adjusts the image with no respect to its ratio, whereas WINDOW_KEEPRATIO keeps the image ratio.
WINDOW_GUI_NORMAL or WINDOW_GUI_EXPANDED: WINDOW_GUI_NORMAL is the old way to draw the window without statusbar and toolbar, whereas WINDOW_GUI_EXPANDED is a new enhanced GUI. By default, flags == WINDOW_AUTOSIZE | WINDOW_KEEPRATIO | WINDOW_GUI_EXPANDED

Parameters

winname	Name of the window in the window caption that may be used as a window identifier.
flags	Flags of the window. The supported flags are: (cv::WindowFlags)

Examples:: contours2.cpp, demhist.cpp, distrans.cpp, edge.cpp, ffilldemo.cpp, fitellipse.cpp, grabcut.cpp, laplace.cpp, morphology2.cpp, pca.cpp, polar_transforms.cpp, segment_objects.cpp, and watershed.cpp.

void cv::resizeWindow	(	const String &	winname,
		int	width,
		int	height
	)

#include <highgui/include/opencv2/highgui.hpp>

Resizes window to the specified size.

Note

The specified window size is for the image area. Toolbars are not counted.
Only windows created without cv::WINDOW_AUTOSIZE flag can be resized.

Parameters

winname	Window name.
width	The new window width.
height	The new window height.

void cv::setMouseCallback	(	const String &	winname,
		MouseCallback	onMouse,
		void *	userdata = `0`
	)

#include <highgui/include/opencv2/highgui.hpp>

Sets mouse handler for the specified window.

Parameters

winname	Name of the window.
onMouse	Mouse callback. See OpenCV samples, such as https://github.com/opencv/opencv/tree/master/samples/cpp/ffilldemo.cpp, on how to specify and use the callback.
userdata	The optional parameter passed to the callback.

Examples:: ffilldemo.cpp, grabcut.cpp, and watershed.cpp.

void cv::setTrackbarMax	(	const String &	trackbarname,
		const String &	winname,
		int	maxval
	)

#include <highgui/include/opencv2/highgui.hpp>

Sets the trackbar maximum position.

The function sets the maximum position of the specified trackbar in the specified window.

Note

[Qt Backend Only] winname can be empty (or NULL) if the trackbar is attached to the control panel.

Parameters

trackbarname	Name of the trackbar.
winname	Name of the window that is the parent of trackbar.
maxval	New maximum position.

void cv::setTrackbarMin	(	const String &	trackbarname,
		const String &	winname,
		int	minval
	)

#include <highgui/include/opencv2/highgui.hpp>

Sets the trackbar minimum position.

The function sets the minimum position of the specified trackbar in the specified window.

Note

[Qt Backend Only] winname can be empty (or NULL) if the trackbar is attached to the control panel.

Parameters

trackbarname	Name of the trackbar.
winname	Name of the window that is the parent of trackbar.
minval	New maximum position.

void cv::setTrackbarPos	(	const String &	trackbarname,
		const String &	winname,
		int	pos
	)

#include <highgui/include/opencv2/highgui.hpp>

Sets the trackbar position.

The function sets the position of the specified trackbar in the specified window.

Note

[Qt Backend Only] winname can be empty (or NULL) if the trackbar is attached to the control panel.

Parameters

trackbarname	Name of the trackbar.
winname	Name of the window that is the parent of trackbar.
pos	New position.

void cv::setWindowProperty	(	const String &	winname,
		int	prop_id,
		double	prop_value
	)

#include <highgui/include/opencv2/highgui.hpp>

Changes parameters of a window dynamically.

The function setWindowProperty enables changing properties of a window.

Parameters

winname	Name of the window.
prop_id	Window property to edit. The supported operation flags are: (cv::WindowPropertyFlags)
prop_value	New value of the window property. The supported flags are: (cv::WindowFlags)

void cv::setWindowTitle	(	const String &	winname,
		const String &	title
	)

#include <highgui/include/opencv2/highgui.hpp>

Updates window title.

Parameters

winname	Name of the window.
title	New title.

int cv::startWindowThread ( )

#include <highgui/include/opencv2/highgui.hpp>

int cv::waitKey ( int delay = 0 )

#include <highgui/include/opencv2/highgui.hpp>

Waits for a pressed key.

The function waitKey waits for a key event infinitely (when \(\texttt{delay}\leq 0\) ) or for delay milliseconds, when it is positive. Since the OS has a minimum time between switching threads, the function will not wait exactly delay ms, it will wait at least delay ms, depending on what else is running on your computer at that time. It returns the code of the pressed key or -1 if no key was pressed before the specified time had elapsed.

Note

This function is the only method in HighGUI that can fetch and handle events, so it needs to be called periodically for normal event processing unless HighGUI is used within an environment that takes care of event processing.

Note

The function only works if there is at least one HighGUI window created and the window is active. If there are several HighGUI windows, any of them can be active.

Parameters

delay Delay in milliseconds. 0 is the special value that means "forever".

Examples:: contours2.cpp, convexhull.cpp, demhist.cpp, distrans.cpp, edge.cpp, ffilldemo.cpp, fitellipse.cpp, grabcut.cpp, houghcircles.cpp, houghlines.cpp, kmeans.cpp, laplace.cpp, lsd_lines.cpp, minarea.cpp, morphology2.cpp, pca.cpp, polar_transforms.cpp, segment_objects.cpp, and watershed.cpp.

int cv::waitKeyEx ( int delay = 0 )

#include <highgui/include/opencv2/highgui.hpp>

Similar to waitKey, but returns full key code.

Note

Key code is implementation specific and depends on used backend: QT/GTK/Win32/etc

Modules

Typedefs

Enumerations

Functions

Detailed Description

Typedef Documentation

Enumeration Type Documentation

Function Documentation