.. literalinclude:: ../../../../samples/cpp/tutorial_code/introduction/display_image/display_image.cpp
:language: cpp
:tab-width: 4
- :lines: 1-4
+ :lines: 1-6
We also include the *iostream* to facilitate console line output and input. To avoid data structure and function name conflicts with other libraries, OpenCV has its own namespace: *cv*. To avoid the need appending prior each of these the *cv::* keyword you can import the namespace in the whole file by using the lines:
.. literalinclude:: ../../../../samples/cpp/tutorial_code/introduction/display_image/display_image.cpp
:language: cpp
:tab-width: 4
- :lines: 6-7
+ :lines: 8-9
-This is true for the STL library too (used for console I/O). Now, let's analyze the *main* function. We start up assuring that we acquire a valid image name argument from the command line.
+This is true for the STL library too (used for console I/O). Now, let's analyze the *main* function. We start up assuring that we acquire a valid image name argument from the command line. Otherwise take a picture by default: "HappyFish.jpg".
.. literalinclude:: ../../../../samples/cpp/tutorial_code/introduction/display_image/display_image.cpp
:language: cpp
:tab-width: 4
- :lines: 11-15
+ :lines: 13-17
Then create a *Mat* object that will store the data of the loaded image.
.. literalinclude:: ../../../../samples/cpp/tutorial_code/introduction/display_image/display_image.cpp
:language: cpp
:tab-width: 4
- :lines: 17
+ :lines: 19
Now we call the :imread:`imread <>` function which loads the image name specified by the first argument (*argv[1]*). The second argument specifies the format in what we want the image. This may be:
.. literalinclude:: ../../../../samples/cpp/tutorial_code/introduction/display_image/display_image.cpp
:language: cpp
:tab-width: 4
- :lines: 18
+ :lines: 20
.. note::
.. literalinclude:: ../../../../samples/cpp/tutorial_code/introduction/display_image/display_image.cpp
:language: cpp
- :lines: 26
+ :lines: 28
:tab-width: 4
Finally, to update the content of the OpenCV window with a new image use the :imshow:`imshow <>` function. Specify the OpenCV window name to update and the image to use during this operation:
.. literalinclude:: ../../../../samples/cpp/tutorial_code/introduction/display_image/display_image.cpp
:language: cpp
- :lines: 27
+ :lines: 29
:tab-width: 4
Because we want our window to be displayed until the user presses a key (otherwise the program would end far too quickly), we use the :wait_key:`waitKey <>` function whose only parameter is just how long should it wait for a user input (measured in milliseconds). Zero means to wait forever.
.. literalinclude:: ../../../../samples/cpp/tutorial_code/introduction/display_image/display_image.cpp
:language: cpp
- :lines: 29
+ :lines: 31
:tab-width: 4
Result
#include <opencv2/core/core.hpp>
#include <opencv2/imgcodecs.hpp>
#include <opencv2/highgui/highgui.hpp>
+
#include <iostream>
+#include <string>
using namespace cv;
using namespace std;
int main( int argc, char** argv )
{
- if( argc != 2)
+ string imageName("../data/HappyFish.jpg"); // by default
+ if( argc > 1)
{
- cout <<" Usage: display_image ImageToLoadAndDisplay" << endl;
- return -1;
+ imageName = argv[1];
}
Mat image;
- image = imread(argv[1], IMREAD_COLOR); // Read the file
+ image = imread(imageName.c_str(), IMREAD_COLOR); // Read the file
if( image.empty() ) // Check for invalid input
{