Doxygen tutorials: basic structure

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Maksim Shabunin
2014-11-27 15:39:05 +03:00
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Load, Modify, and Save an Image {#tutorial_load_save_image}
===============================
@note
We assume that by now you know how to load an image using @ref cv::imread and to display it in a
window (using @ref cv::imshow ). Read the @ref Display_Image tutorial otherwise.
Goals
-----
In this tutorial you will learn how to:
- Load an image using @ref cv::imread
- Transform an image from BGR to Grayscale format by using @ref cv::cvtColor
- Save your transformed image in a file on disk (using @ref cv::imwrite )
Code
----
Here it is:
@code{.cpp}
#include <opencv2/opencv.hpp>
using namespace cv;
int main( int argc, char** argv )
{
char* imageName = argv[1];
Mat image;
image = imread( imageName, 1 );
if( argc != 2 || !image.data )
{
printf( " No image data \n " );
return -1;
}
Mat gray_image;
cvtColor( image, gray_image, COLOR_BGR2GRAY );
imwrite( "../../images/Gray_Image.jpg", gray_image );
namedWindow( imageName, WINDOW_AUTOSIZE );
namedWindow( "Gray image", WINDOW_AUTOSIZE );
imshow( imageName, image );
imshow( "Gray image", gray_image );
waitKey(0);
return 0;
}
@endcode
Explanation
-----------
1. We begin by loading an image using @ref cv::imread , located in the path given by *imageName*.
For this example, assume you are loading a RGB image.
2. Now we are going to convert our image from BGR to Grayscale format. OpenCV has a really nice
function to do this kind of transformations:
@code{.cpp}
cvtColor( image, gray_image, COLOR_BGR2GRAY );
@endcode
As you can see, @ref cv::cvtColor takes as arguments:
- a source image (*image*)
- a destination image (*gray_image*), in which we will save the converted image.
- an additional parameter that indicates what kind of transformation will be performed. In
this case we use **COLOR_BGR2GRAY** (because of @ref cv::imread has BGR default channel
order in case of color images).
3. So now we have our new *gray_image* and want to save it on disk (otherwise it will get lost
after the program ends). To save it, we will use a function analagous to @ref cv::imread : @ref
cv::imwrite
@code{.cpp}
imwrite( "../../images/Gray_Image.jpg", gray_image );
@endcode
Which will save our *gray_image* as *Gray_Image.jpg* in the folder *images* located two levels
up of my current location.
4. Finally, let's check out the images. We create two windows and use them to show the original
image as well as the new one:
@code{.cpp}
namedWindow( imageName, WINDOW_AUTOSIZE );
namedWindow( "Gray image", WINDOW_AUTOSIZE );
imshow( imageName, image );
imshow( "Gray image", gray_image );
@endcode
5. Add the *waitKey(0)* function call for the program to wait forever for an user key press.
Result
------
When you run your program you should get something like this:
![image](images/Load_Save_Image_Result_1.jpg)
And if you check in your folder (in my case *images*), you should have a newly .jpg file named
*Gray_Image.jpg*:
![image](images/Load_Save_Image_Result_2.jpg)
Congratulations, you are done with this tutorial!