mirror of
https://github.com/opencv/opencv.git
synced 2024-12-22 14:47:59 +08:00
be63ce723f
updated links in cheatsheet renamed directory for Mat tutorial changed links from willow docs to opencv.itseez.com, from Trac to current Redmine
315 lines
8.7 KiB
ReStructuredText
315 lines
8.7 KiB
ReStructuredText
.. _remap:
|
|
|
|
Remapping
|
|
*********
|
|
|
|
Goal
|
|
====
|
|
|
|
In this tutorial you will learn how to:
|
|
|
|
a. Use the OpenCV function :remap:`remap <>` to implement simple remapping routines.
|
|
|
|
Theory
|
|
======
|
|
|
|
What is remapping?
|
|
------------------
|
|
|
|
* It is the process of taking pixels from one place in the image and locating them in another position in a new image.
|
|
|
|
* To accomplish the mapping process, it might be necessary to do some interpolation for non-integer pixel locations, since there will not always be a one-to-one-pixel correspondence between source and destination images.
|
|
|
|
* We can express the remap for every pixel location :math:`(x,y)` as:
|
|
|
|
.. math::
|
|
|
|
g(x,y) = f ( h(x,y) )
|
|
|
|
where :math:`g()` is the remapped image, :math:`f()` the source image and :math:`h(x,y)` is the mapping function that operates on :math:`(x,y)`.
|
|
|
|
* Let's think in a quick example. Imagine that we have an image :math:`I` and, say, we want to do a remap such that:
|
|
|
|
.. math::
|
|
|
|
h(x,y) = (I.cols - x, y )
|
|
|
|
What would happen? It is easily seen that the image would flip in the :math:`x` direction. For instance, consider the input image:
|
|
|
|
.. image:: images/Remap_Tutorial_Theory_0.jpg
|
|
:alt: Original test image
|
|
:width: 120pt
|
|
:align: center
|
|
|
|
observe how the red circle changes positions with respect to x (considering :math:`x` the horizontal direction):
|
|
|
|
.. image:: images/Remap_Tutorial_Theory_1.jpg
|
|
:alt: Original test image
|
|
:width: 120pt
|
|
:align: center
|
|
|
|
* In OpenCV, the function :remap:`remap <>` offers a simple remapping implementation.
|
|
|
|
Code
|
|
====
|
|
|
|
#. **What does this program do?**
|
|
|
|
* Loads an image
|
|
* Each second, apply 1 of 4 different remapping processes to the image and display them indefinitely in a window.
|
|
* Wait for the user to exit the program
|
|
|
|
#. The tutorial code's is shown lines below. You can also download it from `here <http://code.opencv.org/svn/opencv/trunk/opencv/samples/cpp/tutorial_code/ImgTrans/Remap_Demo.cpp>`_
|
|
|
|
.. code-block:: cpp
|
|
|
|
#include "opencv2/highgui/highgui.hpp"
|
|
#include "opencv2/imgproc/imgproc.hpp"
|
|
#include <iostream>
|
|
#include <stdio.h>
|
|
|
|
using namespace cv;
|
|
|
|
/// Global variables
|
|
Mat src, dst;
|
|
Mat map_x, map_y;
|
|
char* remap_window = "Remap demo";
|
|
int ind = 0;
|
|
|
|
/// Function Headers
|
|
void update_map( void );
|
|
|
|
/**
|
|
* @function main
|
|
*/
|
|
int main( int argc, char** argv )
|
|
{
|
|
/// Load the image
|
|
src = imread( argv[1], 1 );
|
|
|
|
/// Create dst, map_x and map_y with the same size as src:
|
|
dst.create( src.size(), src.type() );
|
|
map_x.create( src.size(), CV_32FC1 );
|
|
map_y.create( src.size(), CV_32FC1 );
|
|
|
|
/// Create window
|
|
namedWindow( remap_window, CV_WINDOW_AUTOSIZE );
|
|
|
|
/// Loop
|
|
while( true )
|
|
{
|
|
/// Each 1 sec. Press ESC to exit the program
|
|
int c = waitKey( 1000 );
|
|
|
|
if( (char)c == 27 )
|
|
{ break; }
|
|
|
|
/// Update map_x & map_y. Then apply remap
|
|
update_map();
|
|
remap( src, dst, map_x, map_y, CV_INTER_LINEAR, BORDER_CONSTANT, Scalar(0,0, 0) );
|
|
|
|
/// Display results
|
|
imshow( remap_window, dst );
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* @function update_map
|
|
* @brief Fill the map_x and map_y matrices with 4 types of mappings
|
|
*/
|
|
void update_map( void )
|
|
{
|
|
ind = ind%4;
|
|
|
|
for( int j = 0; j < src.rows; j++ )
|
|
{ for( int i = 0; i < src.cols; i++ )
|
|
{
|
|
switch( ind )
|
|
{
|
|
case 0:
|
|
if( i > src.cols*0.25 && i < src.cols*0.75 && j > src.rows*0.25 && j < src.rows*0.75 )
|
|
{
|
|
map_x.at<float>(j,i) = 2*( i - src.cols*0.25 ) + 0.5 ;
|
|
map_y.at<float>(j,i) = 2*( j - src.rows*0.25 ) + 0.5 ;
|
|
}
|
|
else
|
|
{ map_x.at<float>(j,i) = 0 ;
|
|
map_y.at<float>(j,i) = 0 ;
|
|
}
|
|
break;
|
|
case 1:
|
|
map_x.at<float>(j,i) = i ;
|
|
map_y.at<float>(j,i) = src.rows - j ;
|
|
break;
|
|
case 2:
|
|
map_x.at<float>(j,i) = src.cols - i ;
|
|
map_y.at<float>(j,i) = j ;
|
|
break;
|
|
case 3:
|
|
map_x.at<float>(j,i) = src.cols - i ;
|
|
map_y.at<float>(j,i) = src.rows - j ;
|
|
break;
|
|
} // end of switch
|
|
}
|
|
}
|
|
ind++;
|
|
}
|
|
|
|
Explanation
|
|
===========
|
|
|
|
#. Create some variables we will use:
|
|
|
|
.. code-block:: cpp
|
|
|
|
Mat src, dst;
|
|
Mat map_x, map_y;
|
|
char* remap_window = "Remap demo";
|
|
int ind = 0;
|
|
|
|
#. Load an image:
|
|
|
|
.. code-block:: cpp
|
|
|
|
src = imread( argv[1], 1 );
|
|
|
|
#. Create the destination image and the two mapping matrices (for x and y )
|
|
|
|
.. code-block:: cpp
|
|
|
|
dst.create( src.size(), src.type() );
|
|
map_x.create( src.size(), CV_32FC1 );
|
|
map_y.create( src.size(), CV_32FC1 );
|
|
|
|
#. Create a window to display results
|
|
|
|
.. code-block:: cpp
|
|
|
|
namedWindow( remap_window, CV_WINDOW_AUTOSIZE );
|
|
|
|
#. Establish a loop. Each 1000 ms we update our mapping matrices (*mat_x* and *mat_y*) and apply them to our source image:
|
|
|
|
.. code-block:: cpp
|
|
|
|
while( true )
|
|
{
|
|
/// Each 1 sec. Press ESC to exit the program
|
|
int c = waitKey( 1000 );
|
|
|
|
if( (char)c == 27 )
|
|
{ break; }
|
|
|
|
/// Update map_x & map_y. Then apply remap
|
|
update_map();
|
|
remap( src, dst, map_x, map_y, CV_INTER_LINEAR, BORDER_CONSTANT, Scalar(0,0, 0) );
|
|
|
|
/// Display results
|
|
imshow( remap_window, dst );
|
|
}
|
|
|
|
The function that applies the remapping is :remap:`remap <>`. We give the following arguments:
|
|
|
|
* **src**: Source image
|
|
* **dst**: Destination image of same size as *src*
|
|
* **map_x**: The mapping function in the x direction. It is equivalent to the first component of :math:`h(i,j)`
|
|
* **map_y**: Same as above, but in y direction. Note that *map_y* and *map_x* are both of the same size as *src*
|
|
* **CV_INTER_LINEAR**: The type of interpolation to use for non-integer pixels. This is by default.
|
|
* **BORDER_CONSTANT**: Default
|
|
|
|
How do we update our mapping matrices *mat_x* and *mat_y*? Go on reading:
|
|
|
|
#. **Updating the mapping matrices:** We are going to perform 4 different mappings:
|
|
|
|
a. Reduce the picture to half its size and will display it in the middle:
|
|
|
|
.. math::
|
|
|
|
h(i,j) = ( 2*i - src.cols/2 + 0.5, 2*j - src.rows/2 + 0.5)
|
|
|
|
for all pairs :math:`(i,j)` such that: :math:`\dfrac{src.cols}{4}<i<\dfrac{3 \cdot src.cols}{4}` and :math:`\dfrac{src.rows}{4}<j<\dfrac{3 \cdot src.rows}{4}`
|
|
|
|
b. Turn the image upside down: :math:`h( i, j ) = (i, src.rows - j)`
|
|
|
|
c. Reflect the image from left to right: :math:`h(i,j) = ( src.cols - i, j )`
|
|
|
|
d. Combination of b and c: :math:`h(i,j) = ( src.cols - i, src.rows - j )`
|
|
|
|
This is expressed in the following snippet. Here, *map_x* represents the first coordinate of *h(i,j)* and *map_y* the second coordinate.
|
|
|
|
.. code-block:: cpp
|
|
|
|
for( int j = 0; j < src.rows; j++ )
|
|
{ for( int i = 0; i < src.cols; i++ )
|
|
{
|
|
switch( ind )
|
|
{
|
|
case 0:
|
|
if( i > src.cols*0.25 && i < src.cols*0.75 && j > src.rows*0.25 && j < src.rows*0.75 )
|
|
{
|
|
map_x.at<float>(j,i) = 2*( i - src.cols*0.25 ) + 0.5 ;
|
|
map_y.at<float>(j,i) = 2*( j - src.rows*0.25 ) + 0.5 ;
|
|
}
|
|
else
|
|
{ map_x.at<float>(j,i) = 0 ;
|
|
map_y.at<float>(j,i) = 0 ;
|
|
}
|
|
break;
|
|
case 1:
|
|
map_x.at<float>(j,i) = i ;
|
|
map_y.at<float>(j,i) = src.rows - j ;
|
|
break;
|
|
case 2:
|
|
map_x.at<float>(j,i) = src.cols - i ;
|
|
map_y.at<float>(j,i) = j ;
|
|
break;
|
|
case 3:
|
|
map_x.at<float>(j,i) = src.cols - i ;
|
|
map_y.at<float>(j,i) = src.rows - j ;
|
|
break;
|
|
} // end of switch
|
|
}
|
|
}
|
|
ind++;
|
|
}
|
|
|
|
|
|
Result
|
|
======
|
|
|
|
#. After compiling the code above, you can execute it giving as argument an image path. For instance, by using the following image:
|
|
|
|
.. image:: images/Remap_Tutorial_Original_Image.jpg
|
|
:alt: Original test image
|
|
:width: 250pt
|
|
:align: center
|
|
|
|
#. This is the result of reducing it to half the size and centering it:
|
|
|
|
.. image:: images/Remap_Tutorial_Result_0.jpg
|
|
:alt: Result 0 for remapping
|
|
:width: 250pt
|
|
:align: center
|
|
|
|
#. Turning it upside down:
|
|
|
|
.. image:: images/Remap_Tutorial_Result_1.jpg
|
|
:alt: Result 0 for remapping
|
|
:width: 250pt
|
|
:align: center
|
|
|
|
#. Reflecting it in the x direction:
|
|
|
|
.. image:: images/Remap_Tutorial_Result_2.jpg
|
|
:alt: Result 0 for remapping
|
|
:width: 250pt
|
|
:align: center
|
|
|
|
#. Reflecting it in both directions:
|
|
|
|
.. image:: images/Remap_Tutorial_Result_3.jpg
|
|
:alt: Result 0 for remapping
|
|
:width: 250pt
|
|
:align: center
|
|
|