Remapping¶

Goal¶

In this tutorial you will learn how to:

Use the OpenCV function 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

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as:

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where

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is the remapped image,

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the source image and

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is the mapping function that operates on

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.
Let’s think in a quick example. Imagine that we have an image

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and, say, we want to do a remap such that:

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What would happen? It is easily seen that the image would flip in the

System Message: WARNING/2 (x)

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direction. For instance, consider the input image:

observe how the red circle changes positions with respect to x (considering

System Message: WARNING/2 (x)

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the horizontal direction):
In OpenCV, the function 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

 #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:

Mat src, dst;
Mat map_x, map_y;
char* remap_window = "Remap demo";
int ind = 0;

Load an image:
```
src = imread( argv[1], 1 );
```

Create the destination image and the two mapping matrices (for x and y )

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

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:
```
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. 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
  
  System Message: WARNING/2 (h(i,j))
  latex exited with error: [stderr] [stdout] This is pdfTeX, Version 3.1415926-1.40.10 (TeX Live 2009/Debian) entering extended mode (./math.tex LaTeX2e <2009/09/24> Babel <v3.8l> and hyphenation patterns for english, usenglishmax, dumylang, noh yphenation, loaded. (/usr/share/texmf-texlive/tex/latex/base/article.cls Document Class: article 2007/10/19 v1.4h Standard LaTeX document class (/usr/share/texmf-texlive/tex/latex/base/size12.clo)) (/usr/share/texmf-texlive/tex/latex/base/inputenc.sty (/usr/share/texmf-texlive/tex/latex/ucs/utf8x.def)) (/usr/share/texmf-texlive/tex/latex/ucs/ucs.sty (/usr/share/texmf-texlive/tex/latex/ucs/data/uni-global.def)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsmath.sty For additional information on amsmath, use the `?’ option. (/usr/share/texmf-texlive/tex/latex/amsmath/amstext.sty (/usr/share/texmf-texlive/tex/latex/amsmath/amsgen.sty)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsbsy.sty) (/usr/share/texmf-texlive/tex/latex/amsmath/amsopn.sty)) (/usr/share/texmf-texlive/tex/latex/amscls/amsthm.sty) (/usr/share/texmf-texlive/tex/latex/amsfonts/amssymb.sty (/usr/share/texmf-texlive/tex/latex/amsfonts/amsfonts.sty)) (/usr/share/texmf-texlive/tex/latex/tools/bm.sty) (/usr/share/texmf-texlive/tex/latex/euler/euler.sty Package: `euler’ v2.5 <1995/03/05> (FJ and FMi) ) (/usr/share/texmf-texlive/tex/latex/graphics/color.sty (/etc/texmf/tex/latex/config/color.cfg) (/usr/share/texmf-texlive/tex/latex/graphics/dvips.def) (/usr/share/texmf-texlive/tex/latex/graphics/dvipsnam.def)) ! LaTeX Error: File `bbm.sty’ not found. Type X to quit or <RETURN> to proceed, or enter new name. (Default extension: sty) Enter file name: ! Emergency stop. <read *> l.11 ...ackage{amsmath}\usepackage{bbm}\usepackage {colortbl}^^M No pages of output. Transcript written on math.log.
- 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:
1. Reduce the picture to half its size and will display it in the middle:
  
  System Message: WARNING/2 (h(i,j) = ( 2*i - src.cols/2 + 0.5, 2*j - src.rows/2 + 0.5))
  
  latex exited with error: [stderr] [stdout] This is pdfTeX, Version 3.1415926-1.40.10 (TeX Live 2009/Debian) entering extended mode (./math.tex LaTeX2e <2009/09/24> Babel <v3.8l> and hyphenation patterns for english, usenglishmax, dumylang, noh yphenation, loaded. (/usr/share/texmf-texlive/tex/latex/base/article.cls Document Class: article 2007/10/19 v1.4h Standard LaTeX document class (/usr/share/texmf-texlive/tex/latex/base/size12.clo)) (/usr/share/texmf-texlive/tex/latex/base/inputenc.sty (/usr/share/texmf-texlive/tex/latex/ucs/utf8x.def)) (/usr/share/texmf-texlive/tex/latex/ucs/ucs.sty (/usr/share/texmf-texlive/tex/latex/ucs/data/uni-global.def)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsmath.sty For additional information on amsmath, use the `?’ option. (/usr/share/texmf-texlive/tex/latex/amsmath/amstext.sty (/usr/share/texmf-texlive/tex/latex/amsmath/amsgen.sty)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsbsy.sty) (/usr/share/texmf-texlive/tex/latex/amsmath/amsopn.sty)) (/usr/share/texmf-texlive/tex/latex/amscls/amsthm.sty) (/usr/share/texmf-texlive/tex/latex/amsfonts/amssymb.sty (/usr/share/texmf-texlive/tex/latex/amsfonts/amsfonts.sty)) (/usr/share/texmf-texlive/tex/latex/tools/bm.sty) (/usr/share/texmf-texlive/tex/latex/euler/euler.sty Package: `euler’ v2.5 <1995/03/05> (FJ and FMi) ) (/usr/share/texmf-texlive/tex/latex/graphics/color.sty (/etc/texmf/tex/latex/config/color.cfg) (/usr/share/texmf-texlive/tex/latex/graphics/dvips.def) (/usr/share/texmf-texlive/tex/latex/graphics/dvipsnam.def)) ! LaTeX Error: File `bbm.sty’ not found. Type X to quit or <RETURN> to proceed, or enter new name. (Default extension: sty) Enter file name: ! Emergency stop. <read *> l.11 ...ackage{amsmath}\usepackage{bbm}\usepackage {colortbl}^^M No pages of output. Transcript written on math.log.
  
  for all pairs
  
  System Message: WARNING/2 ((i,j))
  
  latex exited with error: [stderr] [stdout] This is pdfTeX, Version 3.1415926-1.40.10 (TeX Live 2009/Debian) entering extended mode (./math.tex LaTeX2e <2009/09/24> Babel <v3.8l> and hyphenation patterns for english, usenglishmax, dumylang, noh yphenation, loaded. (/usr/share/texmf-texlive/tex/latex/base/article.cls Document Class: article 2007/10/19 v1.4h Standard LaTeX document class (/usr/share/texmf-texlive/tex/latex/base/size12.clo)) (/usr/share/texmf-texlive/tex/latex/base/inputenc.sty (/usr/share/texmf-texlive/tex/latex/ucs/utf8x.def)) (/usr/share/texmf-texlive/tex/latex/ucs/ucs.sty (/usr/share/texmf-texlive/tex/latex/ucs/data/uni-global.def)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsmath.sty For additional information on amsmath, use the `?’ option. (/usr/share/texmf-texlive/tex/latex/amsmath/amstext.sty (/usr/share/texmf-texlive/tex/latex/amsmath/amsgen.sty)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsbsy.sty) (/usr/share/texmf-texlive/tex/latex/amsmath/amsopn.sty)) (/usr/share/texmf-texlive/tex/latex/amscls/amsthm.sty) (/usr/share/texmf-texlive/tex/latex/amsfonts/amssymb.sty (/usr/share/texmf-texlive/tex/latex/amsfonts/amsfonts.sty)) (/usr/share/texmf-texlive/tex/latex/tools/bm.sty) (/usr/share/texmf-texlive/tex/latex/euler/euler.sty Package: `euler’ v2.5 <1995/03/05> (FJ and FMi) ) (/usr/share/texmf-texlive/tex/latex/graphics/color.sty (/etc/texmf/tex/latex/config/color.cfg) (/usr/share/texmf-texlive/tex/latex/graphics/dvips.def) (/usr/share/texmf-texlive/tex/latex/graphics/dvipsnam.def)) ! LaTeX Error: File `bbm.sty’ not found. Type X to quit or <RETURN> to proceed, or enter new name. (Default extension: sty) Enter file name: ! Emergency stop. <read *> l.11 ...ackage{amsmath}\usepackage{bbm}\usepackage {colortbl}^^M No pages of output. Transcript written on math.log.
  
  such that:
  
  System Message: WARNING/2 (\dfrac{src.cols}{4}<i<\dfrac{3 \cdot src.cols}{4})
  
  latex exited with error: [stderr] [stdout] This is pdfTeX, Version 3.1415926-1.40.10 (TeX Live 2009/Debian) entering extended mode (./math.tex LaTeX2e <2009/09/24> Babel <v3.8l> and hyphenation patterns for english, usenglishmax, dumylang, noh yphenation, loaded. (/usr/share/texmf-texlive/tex/latex/base/article.cls Document Class: article 2007/10/19 v1.4h Standard LaTeX document class (/usr/share/texmf-texlive/tex/latex/base/size12.clo)) (/usr/share/texmf-texlive/tex/latex/base/inputenc.sty (/usr/share/texmf-texlive/tex/latex/ucs/utf8x.def)) (/usr/share/texmf-texlive/tex/latex/ucs/ucs.sty (/usr/share/texmf-texlive/tex/latex/ucs/data/uni-global.def)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsmath.sty For additional information on amsmath, use the `?’ option. (/usr/share/texmf-texlive/tex/latex/amsmath/amstext.sty (/usr/share/texmf-texlive/tex/latex/amsmath/amsgen.sty)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsbsy.sty) (/usr/share/texmf-texlive/tex/latex/amsmath/amsopn.sty)) (/usr/share/texmf-texlive/tex/latex/amscls/amsthm.sty) (/usr/share/texmf-texlive/tex/latex/amsfonts/amssymb.sty (/usr/share/texmf-texlive/tex/latex/amsfonts/amsfonts.sty)) (/usr/share/texmf-texlive/tex/latex/tools/bm.sty) (/usr/share/texmf-texlive/tex/latex/euler/euler.sty Package: `euler’ v2.5 <1995/03/05> (FJ and FMi) ) (/usr/share/texmf-texlive/tex/latex/graphics/color.sty (/etc/texmf/tex/latex/config/color.cfg) (/usr/share/texmf-texlive/tex/latex/graphics/dvips.def) (/usr/share/texmf-texlive/tex/latex/graphics/dvipsnam.def)) ! LaTeX Error: File `bbm.sty’ not found. Type X to quit or <RETURN> to proceed, or enter new name. (Default extension: sty) Enter file name: ! Emergency stop. <read *> l.11 ...ackage{amsmath}\usepackage{bbm}\usepackage {colortbl}^^M No pages of output. Transcript written on math.log.
  
  and
  
  System Message: WARNING/2 (\dfrac{src.rows}{4}<j<\dfrac{3 \cdot src.rows}{4})
  
  latex exited with error: [stderr] [stdout] This is pdfTeX, Version 3.1415926-1.40.10 (TeX Live 2009/Debian) entering extended mode (./math.tex LaTeX2e <2009/09/24> Babel <v3.8l> and hyphenation patterns for english, usenglishmax, dumylang, noh yphenation, loaded. (/usr/share/texmf-texlive/tex/latex/base/article.cls Document Class: article 2007/10/19 v1.4h Standard LaTeX document class (/usr/share/texmf-texlive/tex/latex/base/size12.clo)) (/usr/share/texmf-texlive/tex/latex/base/inputenc.sty (/usr/share/texmf-texlive/tex/latex/ucs/utf8x.def)) (/usr/share/texmf-texlive/tex/latex/ucs/ucs.sty (/usr/share/texmf-texlive/tex/latex/ucs/data/uni-global.def)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsmath.sty For additional information on amsmath, use the `?’ option. (/usr/share/texmf-texlive/tex/latex/amsmath/amstext.sty (/usr/share/texmf-texlive/tex/latex/amsmath/amsgen.sty)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsbsy.sty) (/usr/share/texmf-texlive/tex/latex/amsmath/amsopn.sty)) (/usr/share/texmf-texlive/tex/latex/amscls/amsthm.sty) (/usr/share/texmf-texlive/tex/latex/amsfonts/amssymb.sty (/usr/share/texmf-texlive/tex/latex/amsfonts/amsfonts.sty)) (/usr/share/texmf-texlive/tex/latex/tools/bm.sty) (/usr/share/texmf-texlive/tex/latex/euler/euler.sty Package: `euler’ v2.5 <1995/03/05> (FJ and FMi) ) (/usr/share/texmf-texlive/tex/latex/graphics/color.sty (/etc/texmf/tex/latex/config/color.cfg) (/usr/share/texmf-texlive/tex/latex/graphics/dvips.def) (/usr/share/texmf-texlive/tex/latex/graphics/dvipsnam.def)) ! LaTeX Error: File `bbm.sty’ not found. Type X to quit or <RETURN> to proceed, or enter new name. (Default extension: sty) Enter file name: ! Emergency stop. <read *> l.11 ...ackage{amsmath}\usepackage{bbm}\usepackage {colortbl}^^M No pages of output. Transcript written on math.log.
2. Turn the image upside down:
  
  System Message: WARNING/2 (h( i, j ) = (i, src.rows - j))
  
  latex exited with error: [stderr] [stdout] This is pdfTeX, Version 3.1415926-1.40.10 (TeX Live 2009/Debian) entering extended mode (./math.tex LaTeX2e <2009/09/24> Babel <v3.8l> and hyphenation patterns for english, usenglishmax, dumylang, noh yphenation, loaded. (/usr/share/texmf-texlive/tex/latex/base/article.cls Document Class: article 2007/10/19 v1.4h Standard LaTeX document class (/usr/share/texmf-texlive/tex/latex/base/size12.clo)) (/usr/share/texmf-texlive/tex/latex/base/inputenc.sty (/usr/share/texmf-texlive/tex/latex/ucs/utf8x.def)) (/usr/share/texmf-texlive/tex/latex/ucs/ucs.sty (/usr/share/texmf-texlive/tex/latex/ucs/data/uni-global.def)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsmath.sty For additional information on amsmath, use the `?’ option. (/usr/share/texmf-texlive/tex/latex/amsmath/amstext.sty (/usr/share/texmf-texlive/tex/latex/amsmath/amsgen.sty)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsbsy.sty) (/usr/share/texmf-texlive/tex/latex/amsmath/amsopn.sty)) (/usr/share/texmf-texlive/tex/latex/amscls/amsthm.sty) (/usr/share/texmf-texlive/tex/latex/amsfonts/amssymb.sty (/usr/share/texmf-texlive/tex/latex/amsfonts/amsfonts.sty)) (/usr/share/texmf-texlive/tex/latex/tools/bm.sty) (/usr/share/texmf-texlive/tex/latex/euler/euler.sty Package: `euler’ v2.5 <1995/03/05> (FJ and FMi) ) (/usr/share/texmf-texlive/tex/latex/graphics/color.sty (/etc/texmf/tex/latex/config/color.cfg) (/usr/share/texmf-texlive/tex/latex/graphics/dvips.def) (/usr/share/texmf-texlive/tex/latex/graphics/dvipsnam.def)) ! LaTeX Error: File `bbm.sty’ not found. Type X to quit or <RETURN> to proceed, or enter new name. (Default extension: sty) Enter file name: ! Emergency stop. <read *> l.11 ...ackage{amsmath}\usepackage{bbm}\usepackage {colortbl}^^M No pages of output. Transcript written on math.log.
3. Reflect the image from left to right:
  
  System Message: WARNING/2 (h(i,j) = ( src.cols - i, j ))
  
  latex exited with error: [stderr] [stdout] This is pdfTeX, Version 3.1415926-1.40.10 (TeX Live 2009/Debian) entering extended mode (./math.tex LaTeX2e <2009/09/24> Babel <v3.8l> and hyphenation patterns for english, usenglishmax, dumylang, noh yphenation, loaded. (/usr/share/texmf-texlive/tex/latex/base/article.cls Document Class: article 2007/10/19 v1.4h Standard LaTeX document class (/usr/share/texmf-texlive/tex/latex/base/size12.clo)) (/usr/share/texmf-texlive/tex/latex/base/inputenc.sty (/usr/share/texmf-texlive/tex/latex/ucs/utf8x.def)) (/usr/share/texmf-texlive/tex/latex/ucs/ucs.sty (/usr/share/texmf-texlive/tex/latex/ucs/data/uni-global.def)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsmath.sty For additional information on amsmath, use the `?’ option. (/usr/share/texmf-texlive/tex/latex/amsmath/amstext.sty (/usr/share/texmf-texlive/tex/latex/amsmath/amsgen.sty)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsbsy.sty) (/usr/share/texmf-texlive/tex/latex/amsmath/amsopn.sty)) (/usr/share/texmf-texlive/tex/latex/amscls/amsthm.sty) (/usr/share/texmf-texlive/tex/latex/amsfonts/amssymb.sty (/usr/share/texmf-texlive/tex/latex/amsfonts/amsfonts.sty)) (/usr/share/texmf-texlive/tex/latex/tools/bm.sty) (/usr/share/texmf-texlive/tex/latex/euler/euler.sty Package: `euler’ v2.5 <1995/03/05> (FJ and FMi) ) (/usr/share/texmf-texlive/tex/latex/graphics/color.sty (/etc/texmf/tex/latex/config/color.cfg) (/usr/share/texmf-texlive/tex/latex/graphics/dvips.def) (/usr/share/texmf-texlive/tex/latex/graphics/dvipsnam.def)) ! LaTeX Error: File `bbm.sty’ not found. Type X to quit or <RETURN> to proceed, or enter new name. (Default extension: sty) Enter file name: ! Emergency stop. <read *> l.11 ...ackage{amsmath}\usepackage{bbm}\usepackage {colortbl}^^M No pages of output. Transcript written on math.log.
4. Combination of b and c:
  
  System Message: WARNING/2 (h(i,j) = ( src.cols - i, src.rows - j ))
  
  latex exited with error: [stderr] [stdout] This is pdfTeX, Version 3.1415926-1.40.10 (TeX Live 2009/Debian) entering extended mode (./math.tex LaTeX2e <2009/09/24> Babel <v3.8l> and hyphenation patterns for english, usenglishmax, dumylang, noh yphenation, loaded. (/usr/share/texmf-texlive/tex/latex/base/article.cls Document Class: article 2007/10/19 v1.4h Standard LaTeX document class (/usr/share/texmf-texlive/tex/latex/base/size12.clo)) (/usr/share/texmf-texlive/tex/latex/base/inputenc.sty (/usr/share/texmf-texlive/tex/latex/ucs/utf8x.def)) (/usr/share/texmf-texlive/tex/latex/ucs/ucs.sty (/usr/share/texmf-texlive/tex/latex/ucs/data/uni-global.def)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsmath.sty For additional information on amsmath, use the `?’ option. (/usr/share/texmf-texlive/tex/latex/amsmath/amstext.sty (/usr/share/texmf-texlive/tex/latex/amsmath/amsgen.sty)) (/usr/share/texmf-texlive/tex/latex/amsmath/amsbsy.sty) (/usr/share/texmf-texlive/tex/latex/amsmath/amsopn.sty)) (/usr/share/texmf-texlive/tex/latex/amscls/amsthm.sty) (/usr/share/texmf-texlive/tex/latex/amsfonts/amssymb.sty (/usr/share/texmf-texlive/tex/latex/amsfonts/amsfonts.sty)) (/usr/share/texmf-texlive/tex/latex/tools/bm.sty) (/usr/share/texmf-texlive/tex/latex/euler/euler.sty Package: `euler’ v2.5 <1995/03/05> (FJ and FMi) ) (/usr/share/texmf-texlive/tex/latex/graphics/color.sty (/etc/texmf/tex/latex/config/color.cfg) (/usr/share/texmf-texlive/tex/latex/graphics/dvips.def) (/usr/share/texmf-texlive/tex/latex/graphics/dvipsnam.def)) ! LaTeX Error: File `bbm.sty’ not found. Type X to quit or <RETURN> to proceed, or enter new name. (Default extension: sty) Enter file name: ! Emergency stop. <read *> l.11 ...ackage{amsmath}\usepackage{bbm}\usepackage {colortbl}^^M No pages of output. Transcript written on math.log.

This is expressed in the following snippet. Here, map_x represents the first coordinate of h(i,j) and map_y the second coordinate.

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:
This is the result of reducing it to half the size and centering it:
Turning it upside down:
Reflecting it in the x direction:
Reflecting it in both directions:

Remapping¶

Goal¶

Theory¶

What is remapping?¶

Code¶

Explanation¶

Result¶

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Remapping¶

Goal¶

Theory¶

What is remapping?¶

Code¶

Explanation¶

Result¶

Help and Feedback

Table Of Contents

Previous topic

Next topic

This Page

Quick search

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