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.. _Load_Save_Image:
Load, Modify, and Save an Image
*******************************
.. note::
We assume that by now you know how to load an image using :readwriteimagevideo:`imread <imread>` and to display it in a window (using :user_interface:`imshow <imshow>`). Read the :ref:`Display_Image` tutorial otherwise.
Goals
======
In this tutorial you will learn how to:
.. container:: enumeratevisibleitemswithsquare
* Load an image using :readwriteimagevideo:`imread <imread>`
* Transform an image from BGR to Grayscale format by using :miscellaneous_transformations:`cvtColor <cvtcolor>`
* Save your transformed image in a file on disk (using :readwriteimagevideo:`imwrite <imwrite>`)
Code
======
Here it is:
.. code-block:: cpp
:linenos:
#include <cv.h>
#include <highgui.h>
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, CV_BGR2GRAY );
imwrite( "../../images/Gray_Image.jpg", gray_image );
namedWindow( imageName, CV_WINDOW_AUTOSIZE );
namedWindow( "Gray image", CV_WINDOW_AUTOSIZE );
imshow( imageName, image );
imshow( "Gray image", gray_image );
waitKey(0);
return 0;
}
Explanation
============
#. We begin by loading an image using :readwriteimagevideo:`imread <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, CV_BGR2GRAY );
As you can see, :miscellaneous_transformations:`cvtColor <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 **CV_BGR2GRAY** (because of :readwriteimagevideo:`imread <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 :readwriteimagevideo:`imread <imread>`: :readwriteimagevideo:`imwrite <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, CV_WINDOW_AUTOSIZE );
namedWindow( "Gray image", CV_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!
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