.. _Load_Save_Image: Load, Modify, and Save an Image ******************************* .. note:: We assume that by now you know how to load an image using :readwriteimage:`imread ` and to display it in a window (using :user_interface:`imshow `). Read the :ref:`Display_Image` tutorial otherwise. Goals ====== In this tutorial you will learn how to: .. container:: enumeratevisibleitemswithsquare * Load an image using :readwriteimage:`imread ` * Transform an image from BGR to Grayscale format by using :miscellaneous_transformations:`cvtColor ` * Save your transformed image in a file on disk (using :readwriteimage:`imwrite `) Code ====== Here it is: .. code-block:: cpp :linenos: #include 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; } Explanation ============ #. We begin by loading an image using :readwriteimage:`imread `, located in the path given by *imageName*. For this example, assume you are loading a RGB image. #. 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-block:: cpp cvtColor( image, gray_image, COLOR_BGR2GRAY ); As you can see, :miscellaneous_transformations:`cvtColor ` takes as arguments: .. container:: enumeratevisibleitemswithsquare * 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 :readwriteimage:`imread ` has BGR default channel order in case of color images). #. 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 :readwriteimage:`imread `: :readwriteimage:`imwrite ` .. code-block:: cpp imwrite( "../../images/Gray_Image.jpg", gray_image ); Which will save our *gray_image* as *Gray_Image.jpg* in the folder *images* located two levels up of my current location. #. 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-block:: cpp namedWindow( imageName, WINDOW_AUTOSIZE ); namedWindow( "Gray image", WINDOW_AUTOSIZE ); imshow( imageName, image ); imshow( "Gray image", gray_image ); #. 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 :alt: Load Save Image Result 1 :align: center 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 :alt: Load Save Image Result 2 :align: center Congratulations, you are done with this tutorial!